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  EVOLUTION

  ITS NATURE, ITS EVIDENCES, AND ITS
  RELATION TO RELIGIOUS THOUGHT


  BY
  JOSEPH LE CONTE

  AUTHOR OF “RELIGION AND SCIENCE,” ETC.
  AND PROFESSOR OF GEOLOGY AND NATURAL HISTORY IN THE
  UNIVERSITY OF CALIFORNIA

  _SECOND EDITION, REVISED_

  NEW YORK:
  D. APPLETON AND COMPANY,
  72 FIFTH AVENUE.
  1897.




  COPYRIGHT, 1888, 1891,
  BY D. APPLETON AND COMPANY.




PREFACE TO THE SECOND EDITION.


The three years which have elapsed since the publication of the first
edition of this work have been years of great activity of thought on
many of the subjects treated therein. Some changes and additions seemed
therefore imperatively called for.

For example: There has sprung up recently among the foremost writers on
evolution a warm discussion on the _factors_ of evolution, their number
and relative importance. I have therefore added a chapter (Chap. III,
Part II) on this subject--not, indeed, to discuss it fully (for this
would be impossible in the limits of a chapter), but to put the mind of
the reader in position to understand it and to judge for himself.

Again: Every reader of the first edition must have remarked that there
are many fundamental religious questions which I have not touched at
all in Part III. I had avoided these because my own mind was not yet
fully clear. I regarded what I then wrote as only a little leaven
in a very large lump. I was willing to wait and let it work. In the
mean time it has worked in my own mind, and I hope in the minds of
others. I have therefore added two chapters to this part. In one I
simply carry out to their logical consequences the doctrine of the
Divine Immanency. This brings up the questions of _First and Second
Causes_; of _General and Special Providence_; of the _Natural and the
Supernatural_; of _Mind vs. Mechanics in Nature_, etc., and shows the
necessary changes of view which are enforced by the theory of evolution.

In the other I take up very briefly “_The Relation of Evolution to the
Doctrine of the Christ_.” In the discussion of this I restrain myself
strictly within the limits of the subject as stated above.

The only other important changes are in Chapter IV, Part III, “_On the
Relation of Man to Nature_.” As I regard this as the most important
chapter in the whole book, I have endeavored still further to enforce
my view of the origin of man’s spirit, and especially to make it
clearer by means of several additional illustrations.

          JOSEPH LE CONTE.

  BERKELEY, CAL., _July 1, 1891_.




PREFACE TO THE FIRST EDITION.


The subject of the following work may be expressed in three questions:
What is evolution? Is it true? What then? Surely, there are no
questions of the day more burning than these. Much has been written
on each of them, addressed to different classes of minds: some to
the scientific, some to the popular, and some to the religious and
theological; but nothing has yet appeared which covers the whole ground
and connects the different parts together. Much, very much has been
written, especially on the nature and the evidences of evolution, but
the literature is so voluminous, much of it so fragmentary, and most
of it so technical, that even very intelligent persons have still very
vague ideas on the subject. I have attempted to give (1) a very concise
account of what we mean by evolution, (2) an outline of the evidences
of its truth drawn from many different sources, and (3) its relation to
fundamental religious beliefs. I have determined, above all, to make
a book so small that it may be read through without much expense of
time and patience. But the subject is so large that in order to do so
it was necessary to sacrifice all but what was most essential, and to
forego all redundancy (the bane of so-called popular science) even at
the risk of baldness and obscurity. Nevertheless, I hope that the first
and second parts will be found not only interesting to the intelligent
general reader, but even profitable to the special biologist. I have
tried to make these parts as untechnical as possible, but I hope not
on that account the less scientific. For I am among these who think
that it is not necessary to be superficial in order to be popular--that
science may be adapted to the intelligent popular mind without ceasing
to be science.

The third part seems to me still more important just now. There is
a deep and widespread belief in the popular mind, and even to some
extent in the scientific mind, that there is something exceptional in
the doctrine of evolution as regards its relation to religious thought
and moral conduct. Other scientific theories have required only some
modifications of religious conceptions, but this utterly destroys
the possibility of all religious belief by demonstrating a pure
materialism. Now this, I believe, is a complete misconception. Thinking
men are fast coming to see this; some, indeed, have mistaken the
change for a reaction against evolution. It is a reaction not against
evolution, but only against its materialistic implication. Evolution is
more and more firmly established every year. The tide of conviction is
one which knows no ebb. Some clear statement, in brief space, of its
true relation to religious thought seems, therefore, very important at
this time.

BERKELEY, CAL., _May, 1887_.




CONTENTS.


  PART I.

  _WHAT IS EVOLUTION?_


  CHAPTER I.

  ITS SCOPE AND DEFINITION.

  PAGE

  _A type of evolution_--Development of an egg                         3

  _Universality of evolution_--Pervades all nature and concerns
      all departments of thought--One half of all science--
      Illustrated (1) by human body, (2) by solar system, (3) by
      society, (4) by earth, (5) by organic kingdom--The term
      evolution usually, but not rightly, confined to this last        3

  _Definition of evolution_--_I. Progressive change_--Shown in
      the animal body, or the _Ontogenic_ series--In the animal
      scale, or the _Taxonomic_ series--In the geological, or
      _Phylogenic_ series--The three series similar, though not
      identical                                                        8

  _II. Change according to certain laws_--Three laws of succession
      of organic forms                                                11

  (_a_) _Law of differentiation_--Early forms are generalized;
      afterwards separated into specialized forms--Illustrated
      by fishes, by birds--Whole process of differentiation
      illustrated by growth and branching of a tree                   11

  (_b_) _Law of progress of the whole_--Mistake of confounding
      evolution with upward progress--How far true, and how far
      false--Illustrated by branching tree--Examples of this
      mistake in the popular mind--In the scientific mind             13

  (_c_) _Law of cyclical movement_--Shown in geological history--
      Age of mollusks, fishes, reptiles, mammals, man--Illustrated
      again by a branching tree--Increasing complexity as well as
      height--Illustrated by diagram                                  16

  _The above three laws are laws of evolution_--_Differentiation_
      --Shown in the development of an egg, the type of evolution     19

  _Progress of the whole_--Not progress of all parts--Shown in
      the development of an egg                                       22

  _Cyclical movement_--Less fundamental than other two--Shown in
      Ontogeny of body, of mind--Increasing complexity--Necessity
      of continued advance--Otherwise deterioration--All these
      laws shown in progress of society---Differentiation shown--
      Progress of the whole but not of all parts shown--Cyclical
      movement shown--In social evolution, however, there is
      another element, viz., conscious voluntary progress---This
      kind of evolution contrasted with the other                     22

  _III. Change by means of resident forces_--This is the point of
      dispute--Sense in which we use term resident forces--Does
      not touch question of origin of natural forces                  27

  _The two views of the origin of organic forms briefly contrasted_
      --As to whether natural or supernatural--As to variability,
      definite or indefinite--As to change from one species to
      another by transmutation or substitution--As to universality
      of law of continuity                                            29


  CHAPTER II.

  THE RELATION OF LOUIS AGASSIZ TO THE THEORY OF EVOLUTION.

  General misunderstanding on this subject--Necessary to give
      sketch of history of the idea--Greeks, Lucretius, Swedenborg,
      and Kant--First scientific presentation by Lamarck--General
      character of Lamarck’s views--Failed, and rightly so--Next,
      Chambers’s “Vestiges of Creation”--Its general character--
      Failed, and rightly so--Some think this unfortunate--Why
      not so--An obstacle must be removed and a basis laid            32

  _The obstacle removed_--Old views in regard to forces--
      Correlation of forces established--But vital force considered
      exception--Therefore living forms also supposed exception
      to mode of origin of other forms--Then vital forces also
      correlated--Therefore, _a priori_ probable that living forms
      also correlated with other forms as to mode of origin--Thus
      obstacle removed                                                35

  _The basis laid_--Agassiz laid inductive _basis_ of evolution,
      although he refused to build--He established the laws of
      evolution and perfected the method of comparison--Importance
      of method discussed--The method of _notation_--The method
      of experiment--The difficulty of applying these to life
      phenomena--Method of comparison shown--(1) In Taxonomic
      series--(2) In Ontogenic series--(3) In Phylogenic series
      --Cuvier the great worker by comparison in the Taxonomic
      series--Agassiz in the Ontogenic and Phylogenic--Agassiz
      also established the three laws of evolution given in previous
      chapter--Thus he laid foundation--Why he did not build--
      Supposed identity of evolution and materialism--The obstacle
      being removed and the basis laid, when evolution again brought
      forward it was universally accepted, because the world was
      prepared--Place of Agassiz and Darwin compared--Formal
      science _vs._ physical science--Illustrated by relation of
      Kepler to Newton--Relation of Agassiz to time cosmos similar
      to that of Kepler to space cosmos--So Darwin to Newton--
      Some reflections on the above--Gravitation is the law of
      space cosmos--Evolution of time cosmos--Of the divine
      spheral music gravitation is the chordal harmony and evolution
      the melody                                                      37


  PART II.

  _EVIDENCES OF THE TRUTH OF EVOLUTION._


  CHAPTER I.

  GENERAL EVIDENCES OF EVOLUTION AS A UNIVERSAL LAW.

  _Evolution is continuity, causal relation, gradual becoming_
      --Increasing acceptance of this idea--First accepted
      for inorganic forms, mountains, continents and seas, rocks
      and soils, earth as a whole, heavenly bodies--Therefore
      acknowledged for all inorganics--Influence of geology in
      bringing about this change--Organic forms: acknowledged
      for individuals, true for classes, orders, families, genera
      --Races and varieties also formed gradually--Artificial
      species formed gradually--Examples of gradual changes in wild
      species--Hyatt’s researches--Other examples--Summing up
      of general evidence--Sufficient ground for induction--
      But evolution is not only inductively probable but certain,
      axiomatic--It is the law of causation applied to forms, and
      therefore a necessary truth                                     53


  CHAPTER II.

  SPECIAL PROOFS OF EVOLUTION.

  _Introductory._

  _Special proofs necessary_--Evolution, though certain, is not
      yet accepted by the popular mind--Different departments from
      which proofs are drawn                                          67

  _Origin of new organic forms; the old view briefly stated_--
      Necessary to give a brief statement of theories--Old view--
      Permanency of specific types--Supernatural origin of species
      --Centers of creation--Explanation of facts of geographical
      distribution--Of geological distribution--Modification of
      extreme view--Variability, but within limits--Illustrated       68

  _The new view briefly stated_--Indefinite variability of organic
      forms--Effect of environment on rigid forms--On plastic
      forms--Taxonomic groups represent degrees of kinship            72

  _Factors of evolution_--(1) Physical environment--(2) Use
      and disuse of organs--(3) Natural selection--(4) Sexual
      selection--(5) Physiological selection--Its necessity shown
      --Its operation explained--Compared with natural selection
      --Cause of variation unknown--Explanation of this is the
      next great step in the theory of evolution                      73


  CHAPTER III.

  THE GRADES OF THE FACTORS OF EVOLUTION AND THE ORDER OF THEIR
      APPEARANCE.

  _Factors of evolution restated; their grades and the order of
      their introduction shown_--Lamarckian factors, first
      in order because they precede sexual reproduction--(1)
      Environment--(2) Use and disuse--With sexual reproduction
      selective factors introduced--(3) Natural selection--(4)
      Physiological selection--(5) Sexual selection--With man
      was introduced (6) the rational factor--In this process
      two striking stages--viz., the introduction of sex and the
      introduction of reason--Effect of each to hasten the steps of
      evolution--The last by far the greater change                   81

  _Contrast between organic and human evolution_--(1) The
      meaning of term _fittest_ in each--(2) Destiny of the
      weak and helpless in each--(3) The nature of evolutionary
      transformation in each--(4) The law of strait and narrow way
      applied in each--(5) Human evolution is a different kind and
      on a higher plane                                               88

  _Application to some questions of the day._

  I. Neo-Darwinists, their position explained--Reasons for
      dissenting--(_a_) Lamarckian factors preceded all others--
      (_b_) Though now subordinate, they still underlie and condition
      all other factors--(_c_) Shown by comparison of phylogeny
      with ontogeny                                                   92

  II. Human progress not identical with organic evolution--Mistake
      of the materialists--But neither is it wholly different, as
      some suppose                                                    96

  III. Neo-Darwinism is fatal to hopes of human progress--Reason
      may use freely Lamarckian factors, but can not use natural
      selection in the same way as Nature does                        97


  CHAPTER IV.

  SPECIAL PROOFS FROM THE GENERAL LAWS OF ANIMAL STRUCTURE, OR
      COMPARISON IN THE TAXONOMIC SERIES.

  _General Principles._

  _Analogy and homology_--Defined and illustrated by examples--
      Wings and limbs--Lungs, gradual formation of, traced in the
      Taxonomic series--Traced in the Ontogenic series--Examples
      of homology in plants: tuber, cactus-leaf, acacia-leaf--
      Definitions repeated and further explained--Common origin is
      the only explanation of homology                                99

  _Primary divisions of the animal kingdom_--True ground of such
      divisions is ability to trace homology--We take examples
      only from vertebrata and articulata--Compare to styles of
      architecture--To machines--To branching stem                   107


  CHAPTER V.

  PROOFS FROM HOMOLOGIES OF THE VERTEBRATE SKELETON.

  _Common general plan_--In several respects--Strongly suggestive of
      common origin--Details of structure demonstrative of the same  111

  _Special homology of vertebrate limbs_                             113

  _Fore-limbs_--Comparison of fore-limbs of mammals, birds,
      reptiles, and fishes, part for part--Gradual changes in
      collar-bone and coracoid--In position of elbow--In bones
      of forearm--In position of wrist--In the tread--The term
      manus--Number of toes--Modifications for flight in various
      animals--For swimming in whales and fishes                     113

  _Hind-limbs_--Comparison of hind-limbs of several mammals--
      Position of knee--Of heel--Plantigrade and digitigrade
      --Degrees of the latter--Number of toes--General law in
      regard to number of similar parts--Order of toe-dropping in
      artiodactyles--In perissodactyles                              121

  _Genesis of the horse_--Changes in foot-structure--Same true
      of other parts of skeleton--Only natural explanation is
      derivation--Nature compared with man in mode of working--
      Angels--Griffins--Centaurs--Muscular and nervous systems
      --Visceral organs                                              126


  CHAPTER VI.

  HOMOLOGIES OF THE ARTICULATE SKELETON.

  _Illustrations from this type_--Plan of structure entirely
      different--General plan of structure explained and
      modifications shown--Shrimp--Modification of segments and
      of appendages for various purposes: swimming, walking, eating,
      sense--Illustrated by other crustaceans--By myriapods--
      By marine worms--Crabs--Embryonic development of crabs--
      insects--Modification of segments and appendages--Mouth
      parts of insects                                               132

  _Illustration of the law of differentiation_--Cells--Segments
      --Individuals--Homologies in other departments of animals,
      but these are less familiar--Between primary groups, homology
      untraceable in adult forms--But these also probably connected
      by common origin--Different views as to origin of vertebrates  144


  CHAPTER VII.

  PROOFS FROM EMBRYOLOGY, OR COMPARISON IN THE ONTOGENIC SERIES.

  _Resemblance of the three series_--Frog, in Ontogeny passes
      through main stages of Taxonomy and Phylogeny--Resemblance
      only general--Many steps dropped out in Ontogeny               148

  (1) _Ontogeny of tailless amphibians_--The frog: fish stage,
      perennibranch stage, caducibranch stage, aneural stage--Same
      stages in Phylogeny                                            150

  (2) _Aortic arches_--Those of lizard described--Origin from
      gill-arches of fish--Change from one to the other in Ontogeny
      of a frog--Same changes in Phylogeny of lizard--Embryonic
      condition of mammalian heart and vessels--Gradual change and
      final condition in birds--In mammals--Gradual decrease in
      number of aortic arches as we go up the vertebrate scale--
      Cogency of the argument from aortic arches                     151

  (3) _Vertebrate brain_--Fish brain--Brain of reptiles, birds,
      mammals, man compared--Human brain passes through similar
      stages--Changes in complexity of structure in Taxonomy--
      Same changes in Ontogeny of mammals--Same in Phylogeny of
      reptiles, birds, mammals                                       162

  _Cephalization_--Explanation of, in body, in mind                  171

  (4) _Fish-tails_--Homocercal and heterocercal--Vertebrated
      and non-vertebrated--Order of change in Ontogeny--Same
      in Phylogeny--Similar changes in birds’ tails in Ontogeny
      and Phylogeny--In other tailless animals--Examples from
      articulates, insects, crustaceans, etc.                        172

  _Illustration of the differentiation of the whole animal kingdom_
      --Development of eggs of all kinds of animals--This a type
      of changes in Phylogeny--Why Ontogeny repeats Phylogeny--
      Law of acceleration                                            176

  _Proofs from rudimentary and useless organs_--Examples from
      whale: Teeth--Limbs--Hair--Olfactive organs--Examples
      from man: muscles, cæcal appendage--Significance of useless
      organs                                                         179


  CHAPTER VIII.

  PROOFS FROM GEOGRAPHICAL DISTRIBUTION OF ORGANISMS.

  _Geographical faunas and floras_--Conditions which limit           183

  _Temperature-regions_--Illustrated by plants--In latitude and
      in elevation--Same in animal species                           184

  _More perfect definition of regions_--Range of different
      Taxonomic groups--Gradual shadings on borders of range--
      Shadings out of individuals in number and vigor, but not in
      specific character--As if centers of origin--Effect of east
      and west barriers--Temperature regions repeated south of the
      equator, but not species--As if centers of origin              186

  _Continental faunas and floras_--Temperature zones continuous,
      but not species--Reason: ocean barriers--As if centers
      of origin--Polar regions: one. Why--Temperate zone--
      Different species in different continents--Species of United
      States and of Europe almost wholly different--As if origin
      local--Exceptions--(1) Introduced species--(2) Hardy or
      else wide-migrating species--(3) Alpine species--Tropical
      zone of two continents still more different--Same true of
      south temperate zone                                           188

  _Subdivisions of continental faunas and floras_--Illustrated by
      fauna and flora of United States                               191

  _Special Cases_--Australia--Madagascar--Galapagos--River
      mussels                                                        192

  _Marine species_--Same principles applicable--Therefore organic
      forms grouped in regions, sub-regions, provinces, etc.--
      Primary regions according to Wallace--According to Allen       192

  _Theory of the origin of geographical diversity_--Specific
      centers of creation--Objections to. The element of time left
      out--Progressive change in unlimited time, or evolution the
      only rational explanation--This connects with geographical
      changes in geological times, especially the Glacial epoch--
      Geographical diversity in other times                          193

  _Most probable view of the general process_--Last great period
      of change was the Glacial epoch--This, therefore, is the key
      to geographical distribution--Condition of things during the
      Glacial epoch---In America--Changes in temperature--In
      physical geography and in species--In Europe--Application
      of principles                                                  196

  (1) _Australia_--Characteristics of its fauna--Explanation
      of--Isolation very early--Position of marsupials and
      monotremes in the Taxonomic scale--Australia isolated before
      the Tertiary--Effect of competition on evolution               200

  (2) _Africa_--African region defined--Two groups of its
      mammals, indigenes, and invaders--Effect of the invasion       204

  (3) _Madagascar_--Characteristics of its fauna--Relation
      to African indigenes--Separated before the invasion--
      Significance of its lemurs                                     205

  (4) _Island life_--Two kinds of islands--Defined and
      illustrated by examples--(_a_) _Continental islands_--
      General character of fauna--Illustrated by Madagascar,
      New Zealand, British Islands, coast-islands of California
      --Characteristics of the faunas of these explained--(b)
      _Oceanic Islands_--Defined--Characteristics of faunas and
      their origin                                                   207

  (5) _Alpine species_--Characteristics of and their origin
      explained--Migrations of Arctic species during Glacial times,
      and their isolation on mountains                               215

  _Objection_--Mode of change of species on borders of ranges--
      Examples--Sweet-gum--Sequoia                                   217

  _Answer_--Distribution of these forms in time, and their
      migrations--They are remnants--Intermediate forms are extinct  219


  CHAPTER IX.

  PROOFS FROM VARIATION OF ORGANIC FORMS, ARTIFICIAL AND NATURAL.

  _Limitation of the use of experiment in morphology_--Unconscious
      experiments in breeding, and their results--Principles
      involved--Inheritance, immediate and ancestral--Effect of
      true breeding long continued--Method of selection illustrated
      by diagram--Formation of a race--Process the same in nature
      --Show selective effect of physical environment--Of organic
      environment--Of migrations--Of unlimited time--Other
      factors of change, and their effects shown in nature and in
      domestication--Differences between artificial and natural
      species                                                        222

  _First difference, reversion_--The tendency to reversion
      described--The reason explained--Illustrated by the case of
      the pointer                                                    229

  _Second difference, intermediate forms_--Reason is, these are
      eliminated in nature                                           232

  _Third difference, cross-fertility_--Natural species are usually
      cross-sterile--Degrees of cross-sterility--Two bases of
      species, morphological and physiological--Two kinds of
      isolation, sexual repugnance and cross-sterility--Latter most
      essential--Illustrated by plants and hermaphrodite animals--
      Former only higher animals--Natural laws interfered with by
      domestication--Illustrated by plants and animals               232

  _Law of cross-breeding_--Effect of close breeding--Of crossing
      varieties to a limit--The law investigated--Reproduction in
      lowest organisms--Fission--Gemmation--Internal gemmation
      --Sex introduced--Effect of, is funding of differences in
      offspring and tendency to variation--Sexual and non-sexual
      reproduction compared--Separation of sex elements--
      Of sex-individuals--Introduction of sex-attraction--
      Funding of greater differences in offspring--Crossing of
      varieties--Diagram illustrating effect in vigor--Effect
      also in plasticity--Application of these principles--
      Necessity of sexual isolation to produce species--Origin of
      cross-sterility and thus of species by Dr. Romanes’s idea--
      Why artificial varieties are cross-fertile--Geographical
      species sometimes cross-fertile--Application of principles--
      Absence of intermediate links in natural species explained--
      Under what conditions such are found--Further explanation of
      this point--Illustrated by a growing tree                      236

  _Objection answered_--Intermediate links ought to be found fossil
      --Answer (1) Imperfection of record. (2) The term species
      indefinite. (3) Transitions between all other taxonomic groups
      abundant. (4) Between species, also, both living and fossil
      --Of fossil, Planorbis of Steinheim--Other examples--(5)
      Why transition-forms are rare--Answer--Changes in every
      department of nature are paroxysmal--Illustrated--So the
      steps of evolution paroxysmal--Critical periods in evolution
      --Causes of rapid advance--Apparent discontinuity between
      species--(1) changes paroxysmal--(2) Brooks’s idea--Male
      sex is the progressive element--Illustrated by society--
      Effect of prosperous times--Mrs. Treat’s experiments--Hard
      times produce excess of males, and therefore tend to diversity
      --Summary                                                      248

  _Objection_--Egyptian drawings and mummy plants, show no change
      --Answer (1) Time too short. (2) We are now in time of slow
      change. (3) All species don’t change, most become extinct. (4)
      Evolution is probably slower now than formerly--Reasons for
      so thinking--Organic evolution approaching completion--
      Other supposed objections                                      265

  _Origin of beauty_--Explanation of, in higher animals--In
      flowering plants--But in many cases we can’t explain           269

  _Incipient organs_--Difficulty of explaining--But these are
      not objections to the _fact_ of evolution, but only to the
      sufficiency of the present _theories_ of evolution. Therefore,
      all discussion concerns special theories. The fact of evolution
      is certain                                                     270


  PART III.

  _THE RELATION OF EVOLUTION TO RELIGIOUS THOUGHT._


  CHAPTER I.

  INTRODUCTORY.

  _Evolution if true affects every department of thought_--What
      will be its effect on religious beliefs?--Objection that
      truth-seeker has nothing to do with effects--Answered          275

  _Relation of the true and the good_                                277

  _Relation of philosophy to life_--The three necessary elements
      of a rational philosophy--Application to the case in hand--
      And the subject of Part III justified--Exaggerated fears--
      Different forms of the conflict of science and religion--(1)
      Heliocentric theory--First effect and final result--(2) Law
      of gravitation--Effect and result--(3) Antiquity of the
      earth and cosmos--Effect and result--(4) Antiquity of man
      --(5) Evolution                                                277


  CHAPTER II.

  THE RELATION OF EVOLUTION TO MATERIALISM.

  _Supposed identity_--Tendency of the age--Evolution does not
      differ in this regard from other laws of Nature--Absurdity
      of identification illustrated in many ways--(1) Effect of
      discovery of process of making--(2) Effect of new form of old
      truth--(3) Manner in which vexed questions are settled and
      rational philosophy found--Illustrated--A true philosophy
      is a reconciliation of partial views--Three possible views
      of origin of individuals and of species; two one-sided and
      partial, and the third combining, reconciling, and therefore
      rational--The only bar to speedy reconciliation is dogmatism
      --Theological and scientific--The appropriate rebuke for
      each--Therefore evolution does not differ from other laws in
      regard to its relation to materialism--Nevertheless, great
      changes in our traditional beliefs impending--Main changes
      are notions concerning God, Nature, and man, in their relations
      to one another                                                 284


  CHAPTER III.

  THE RELATION OF GOD TO NATURE.

  The issue in regard to this relation stated--The growth of the
      issue described--The old view of direct relation--The
      effect of science and the resulting view--The compromise--
      Destroyed by evolution--The issue forced--The alternative
      view--Immanence of Deity--This view explained--Objection
      of idealism--Answered--It is not subjective idealism--
      Objection of pantheism--Answer deferred--Objection that the
      view is incompatible with practical life--Answered             297


  CHAPTER IV.

  THE RELATION OF MAN TO NATURE.

  _The two extreme views in this regard_--They are views from
      different points, psychical and material--The latter very
      productive in modern times--But many fear the final effect--
      Reconciliation is possible--Scientific materialism has two
      branches--_Physiological branch_ explained--Conclusion--
      Answer--Relation of psychic to brain changes is inscrutable
      --The mystery illustrated--Outside and inside view--
      Different from other phenomena in this regard                  304

  _Evolution branch_--Close relation of man to animals--Therefore
      must extend immortal spirit to animals--to plants--to all
      existence, and thus identify immortality with conservation
      of force--Embryonic series--Where did spirit enter?--
      Evolution series--Where did spirit enter?--Answer--
      Derived from Nature--The true view of origin stated--Show
      that it is not in discord with other phenomena of evolution
      --The five planes of matter and of force--The change from
      one to another not gradual now nor in the evolution of natural
      forces--Consecutive births into higher forms--Every step
      of these changes taking place now--Relation of these facts
      to immortality--The process briefly stated--Omnipresent
      divine energy individuated to separate entity in man--Anima
      of animals is spirit in embryo--Came to birth in man--
      Illustrated in other ways--(1) By more or less completed
      water-drop--(2) By submergence and emergence--(3) By
      planet birth--(4) By physical birth--(5) By grades of
      organic individuality--(6) By the body as an instrument of
      communication between two worlds--Self-consciousness the sign
      of spirit-individuality--Any animal conscious of self would
      be immortal--Similar changes in passing from animals to man
      in all other departments of psychic activity--Objection that
      other changes of energy not permanent; answered--Our view
      of origin compared with alternative views--Plato’s view--
      Orthodox view                                                  311

  _Some general conclusions_--(1) Two series of changes,
      brain-changes and mind-changes--The initiative in animals
      --In man--(2) Justification of term “_vital principle_”
      --Becomes entity in man--(3) This view is a complete
      reconciliation of realism and nominalism--(4) No meaning in
      Nature without spirit--And no meaning in geological history
      without derivative origin of spirit--Material evolution finds
      its goal in man, psychic evolution in the divine man           327


  CHAPTER V.

  THE RELATION OF GOD TO MAN.

  _Question of revelation_--Difficulty of the subject--Operation
      of divine spirit on spirit of man more direct than on Nature
      --This is revelation--This is no violation of law, but
      operation by higher law--Term supernatural is relative--
      Illustrated--There is but one kind of revelation, and this to
      all men in different degrees--Always imperfect, and therefore
      must be tried by reason                                        331


  CHAPTER VI.

  THE OBJECTION, THAT THE ABOVE VIEW IMPLIES PANTHEISM, ANSWERED.

  _The objection stated and the general answer_--In deepest
      questions single lines of thought lead to extreme views--Must
      follow other lines--These lead to personality                  335

  (1) Exact character of relation of God and of necessary law to
      man’s freedom is inscrutable                                   338

  (2) On the inside of brain-changes we find personality--So on
      the inside of natural phenomena must also be person--In
      either case science studies the outside only--In Nature
      all is mechanics on the outside, but all is mind on the
      inside--Thought behind brain-changes compels belief in same
      behind natural phenomena--Law of infinite expansion--
      Illustrated by ideas of Space and Time--So also with idea
      of self--Infinite person inconceivable, but contrary is more
      inconceivable--Illustrated by ideas of Space and Time          338

  (3) Idea of _Causation_ and of _Force_--Derived from _within_
      --Steps of the evolution of this idea--Final result is one
      infinite personal will--Expansion of idea of causal nexus
      between phenomena to the idea of one infinite cause            342

  (4) Idea of _design_ also originates _within_--Ineradicable, but
      changes form--Expands to infinity--Same change produced by
      science in all our notions concerning God--Same in our sense
      of _mystery_--Same in our notions concerning _creation_--
      Same in our conceptions of _design_--Thus, self-consciousness
      behind brain-changes compels belief in God behind Nature--The
      closeness of connection in the one case necessitates closeness
      of connection in the other--Every material change in Nature
      caused by a mental change behind Nature                        345


  CHAPTER VII.

  SOME LOGICAL CONSEQUENCES OF THE DOCTRINE OF THE DIVINE IMMANENCY.

  Religious thought subject to the law of evolution; three main
      stages                                                         351

  I. _Conception of God_--The three stages shown--(1)
      Anthropomorphism--(2) Absentee landlordism--(3) Immanence      351

  II. _Question of First and Second Causes_--The three stages shown
      here--(1) All is First Cause but man-like--(2) Distinction
      of first and second causes introduced--(3) Identification of
      these                                                          354

  III. _General and Special Providence_--The same three stages
      shown and the same outcome--viz., identification               355

  IV. _Natural and the supernatural_--The same stages and the same
      final identification--Question of miracles                     355

  V. _Question of design or mind in Nature_--The same three stages
      and the same solution shown here--Confusion in the minds of
      modern writers                                                 357

  VI. _Question of mode of creation_--Old and new views contrasted   358


  CHAPTER VIII.

  RELATION OF EVOLUTION TO THE IDEA OF THE CHRIST.

  Comparison of organic with human evolution--The idea of the first
      is _man_, of the second is the _Christ_--Definition of the
      Christ as _ideal man_--The Christ ought to differ from us
      in a superhuman way--Shown by several illustrations--The
      Christ, as ideal man, a true object of rational worship--The
      ideal of organic evolution comes _at the end_--Ideal of human
      evolution must come _in the course_--Objection that there are
      many partial ideals answered--Relative vs. absolute moral
      ideal.                                                         360


  CHAPTER IX.

  THE RELATION OF EVOLUTION TO THE PROBLEM OF EVIL.

  The difficulty of the problem--The light on it by evolution--
      Evil must be based on the constitution of Nature and therefore
      universal--Some of its forms                                   365

  (1) _Physical evil in animal kingdom_--Condition of organic
      evolution is struggle with an apparently inimical environment
      --In its course it seems evil--Looking back from the end it
      is good.                                                       365

  (2) _Physical evil in relation to man_--Necessary condition
      of social evolution is also struggle with a seeming evil
      environment--But looking back from the end this evil is also
      seen to be good--Without it man would never have emerged from
      animality.                                                     366

  (3) _Organic evil--Disease_--This also is the necessary
      condition of acquisition of knowledge of organic Nature--In
      the course of evolution it seems evil, but from the end it is
      seen to be good--In the physical world, laws of Nature are
      beneficent in their general operation, and only evil in their
      specific operation through our ignorance.                      367

  (4) _Moral evil--Moral disease_--Difference between this
      and other forms of evil--Can this also be transmuted into
      good?--This is only the highest form of evil, and therefore
      subject to the same laws of evolution--Here also elevation
      comes only through knowledge and power, and these only through
      struggle with apparent evil--In course it seems evil,
      looking back from end it is seen to be good to the race--
      In all, therefore, the individual is sacrificed to the race,
      but impossible here--A way of escape found in the nature of
      a moral being--In this case not only final victory for the
      race, but also within the power of the individual--In this
      case success is in proportion to honest effort in right spirit
      --Roots, of evil in the necessary law of evolution--It is
      the necessary condition of all progress--Without it a moral
      being is impossible--From philosophic point of view things
      are not good and evil, but only higher and lower--All things
      good in their places--Evil is discord--Good is due relation
      --Action and reaction of higher and lower is the necessary
      condition of true virtue                                       369




PART I.

_WHAT IS EVOLUTION?_




CHAPTER I.

ITS SCOPE AND DEFINITION.


=A Type of Evolution.=--Every one is familiar with the main facts
connected with the development of an egg. We all know that it begins as
a microscopic germ-cell, then grows into an egg, then organizes into
a chick, and finally grows into a cock; and that the whole process
follows some general, well-recognized law. Now, this process is
evolution. It is more--it is _the_ type of all evolution. It is that
from which we get our idea of evolution, and without which there would
be no such word. Whenever and wherever we find a process of change
more or less resembling this, and following laws similar to those
determining the development of an egg, we call it evolution.

_Universality of Evolution._--Evolution as a _process_ is not
confined to one thing, the egg, nor as a doctrine is it confined
to one department of science--biology. The process pervades the
whole universe, and the doctrine concerns alike every department of
science--yea, every department of human thought. It is literally one
half of all science. Therefore, its truth or falseness, its acceptance
or rejection, is no trifling matter, affecting only one small corner
of the thought-realm. On the contrary, it affects profoundly the
foundations of philosophy, and therefore the whole domain of thought.
It determines the whole attitude of the mind toward Nature and God.

I have said evolution constitutes one half of all science. This may
seem to some a startling proposition. I stop to make it good.

Every system of correlated parts may be studied from two points of
view, which give rise to two departments of science, one of which--and
the greater and more complex--is evolution. The one concerns changes
within the system by action and reaction between the parts, producing
equilibrium and stability; the other concerns the progressive movement
of the system, as a whole, to higher and higher conditions--the
movement of the point of equilibrium itself, by constant slight
disturbance and readjustment of parts on a higher plane, with more
complex inter-relations. The one concerns the laws of sustentation of
the system, the other the laws of evolution. The one concerns things as
they are, the other the process by which they become so. Now, Nature
as a whole is such a system of correlated parts. Every department and
sub-department of Nature, whether it be the solar system or the earth,
or the organic kingdom, or human society, or the human body, is such a
system of correlated parts, and is therefore subject to evolution. We
can best make this thought clear by examples:

1. Take, then, the _human body_. This complex and beautiful system
of correlated and nicely-adjusted parts may be studied in a state of
maturity and equilibrium, in which all the organs and functions by
action and reaction co-operate to produce perfect stability, health,
and physical happiness. This study is physiology. Or else the same may
be studied in a state of progressive change. Now, we perceive that the
stability is never perfect--the point of equilibrium is ever moving. By
the ever-changing number and relative power of the co-operating parts
the equilibrium is ever being disturbed, only to be readjusted on a
higher plane, with still more beautiful and complex inter-relations.
This is growth, development, evolution. Its study is called embryology.
2. Take another example--_the solar system_. We may study sun, planets,
and satellites in their mutual actions and reactions, co-operating to
produce perfect equilibrium, stability, beautiful order, and musical
harmony. This is the ideal of physical astronomy as embodied in
Laplace’s “Mécanique Céleste.” Or we may study the same in its origin
and progressive change. Now, we perceive that equilibrium and stability
are never absolutely perfect, but, on the contrary, there is continual
disturbance with readjustment on a higher plane--continual introduction
of infinitesimal discord, only to enhance the grandeur and complexity
of the harmonic relations. This is the nebular hypothesis--the theory
of the development of the solar system. It is cosmogony; it is
evolution. 3. Again: _society_ may be studied in the mutual play of
all its social functions so adjusted as to produce social equilibrium,
happiness, prosperity, and good government. This is social statics.
But equilibrium and stability are never perfect. Permanent social
equilibrium would be social stagnation and decay. Therefore, we must
study society also in its onward movement--the equilibrium ever
disturbed, only to be readjusted on a higher plane with more and more
complexly inter-related parts. This is dynamics--social progress. It
is evolution. 4. Again: the _earth_, as a whole, may be studied in
its present forms, and the mutual action of all its parts--lands and
seas, mountains and valleys, rivers, gulfs, and bays, currents of air
and ocean--and the manner in which all these, by action and reaction,
co-operate to produce climates and physical conditions such as we now
find them. This is physical geography. Or, we may study the earth
in its gradual progress toward its present condition--the changes
which have taken place in all these parts, and consequent changes in
climate; in a word, the gradual process of becoming what it now is.
This is physical geology--it is evolution. 5. Lastly, we may study
the whole _organic kingdom_ in its entirety as we now find it--the
mutual relation of different classes, orders, genera, and species to
each other and to external conditions, and the action and reaction
of these in the struggle for life--the geographical distribution of
species and their relation to climate and other physical conditions,
the whole constituting a complexly adjusted and permanent equilibrium.
This is a science of great importance, but one not yet distinctly
conceived, much less named.[1] Or, we may study the same in its gradual
progressive approach, throughout all geological times, toward the
present condition of things, by continual changes in the parts, and
therefore disturbance of equilibrium and readjustment on a higher plane
with more complex inter-relations. This is development of the organic
kingdom. In the popular mind it is, _par excellence_, evolution.

We might multiply examples without limit. There are the same two
points of view on all subjects. As already said, in the one we are
concerned with things as they are; in the other, with the process
by which they became so. This “law of becoming” in all things--this
universal law of progressive inter-connected change--may be called the
law of continuity. We all recognize the universal relation of things,
gravitative or other, in space. This asserts the universal causal
relation of things in _time_. This is the universal law of evolution.

But it has so happened that in the popular mind the term evolution
is mostly confined to the development of the organic kingdom, or
the law of continuity as applied to this department of Nature. The
reason of this is that this department was the last to acknowledge
the supremacy of this law; this is the domain in which the advocates
of supernaturalism in the realm of Nature had made their last stand.
But it is wholly unphilosophical thus to limit the term. If there be
any evolution, _par excellence_, it is evolution of the individual or
embryonic development. This is the clearest, the most familiar, and
most easily understood, and therefore the type of evolution. We first
take our idea of evolution from this form, and then extend it to other
forms of continuous change following a similar law. But, since the
popular mind limits the term to development of the organic kingdom, and
since, moreover, this is now the battleground between the advocates
of continuity and discontinuity--of naturalism and supernaturalism in
the _realm of Nature_--what we shall say will have reference chiefly
to this department, though we shall illustrate freely by reference to
other forms of evolution.


DEFINITION OF EVOLUTION.

Evolution is (1) continuous _progressive change_, (2) _according to
certain laws_, (3) and by means of _resident forces_. It may doubtless
be defined in other and perhaps better terms, but this suits our
purposes best. Embryonic development is the type of evolution. It
will be admitted that this definition is completely realized in this
process. The change here is certainly continuously progressive; it is
according to certain well-ascertained laws; it is by forces (vital
forces) resident in the egg itself. Is, then, the process of change
in the organic kingdom throughout geologic times like this? Does it
correspond to the definition given above? Does IT also deserve the
name of evolution? We shall see.

I. =Progressive Change.=--Every individual animal body--say man’s--has
become what it now is by a gradual process. Commencing as a microscopic
spherule of living but apparently unorganized protoplasm, it gradually
added cell to cell, tissue to tissue, organ to organ, and function to
function; thus becoming more and more complex in the mutual action of
its correlated parts, as it passed successively through the stages of
germ, egg, embryo, and infant, to maturity. This ascending series of
genetically connected stages is called the embryonic or _Ontogenic_
series.[2]

There is another series the terms of which are coexistent, and which,
therefore, is not in any sense a genetic or development series, but
which it is important to mention, because to some degree similar to
and illustrative of the last. Commencing with the lowest unicelled
microscopic organisms, and passing up to the animal scale, _as it now
exists_, we find a series of forms similar, though not identical, with
the last. Here, again, we find cell added to cell, tissue to tissue,
organ to organ, and function to function, the animal body becoming more
and more complex in structure, in the mutual action of its correlated
parts, and the mutual action with the environment, until we reach the
highest complexity of structure and of internal and external relations
only in the highest animals. This ascending series may be called
the natural history series; or, the classification or _Taxonomic
series_.[3] The terms of this series are, of course, not genetically
connected; at least, not directly so connected. In what way they are
connected, and how the series comes to be similar to the last, we shall
see by-and-by.

Finally, there is still a third series, the grandest and most
fundamental of all, but only recently recognized, and therefore
still imperfectly known. Commencing with the earliest organisms,
the very dawn of life, in the very lowest rocks, and passing onward
and upward through Eozoic, Palæozoic, Mesozoic, Cenozoic, to the
Psychozoic or present time, we again find first the lowest forms,
and then successively forms more and more complex in structure, in
the interaction of correlated parts and in interaction with the
environment, until we reach the most complex internal and external
relations, and therefore the highest structure only in the present
time.[4] This series we will call the geological or _phylogenic_
series.[5] According to the evolution theory, the terms of _this_
series also are genetically connected. It is, therefore, an evolution
series. Furthermore, it is the most fundamental of the three series,
because it is the _cause_ of the other two. The Ontogenic series is
like it because it is a brief recapitulation, through heredity, as it
were from memory, of its main points. The Taxonomic series is like
it because the _rate_ of advance along different lines was different
in every degree, and therefore every stage of the advance is still
represented in a general way among existing forms. Some of these points
will be explained more fully in future chapters, in connection with the
evidences of the truth of evolution.

It will be admitted, then, that we find _progressive change_ in organic
forms throughout geological times. This is the first point in the
definition of evolution.

II. =Change according to Certain Laws.=--We have shown continuously
progressive change in organic forms during the whole geologic history
of the earth, similar in a general way to that observed in embryonic
development. We wish now to show that the _laws of change_ are similar
in the two cases. What, then, are the laws of succession of organic
forms in geologic times? I have been accustomed to formulate them thus:
_a._ The law of differentiation; _b._ The law of progress of the whole;
_c._ The law of cyclical movement.[6] We will take up these and explain
them successively, and then, afterward, show that they are also the
laws of embryonic development, and therefore the laws of evolution.

_a._ =Law of Differentiation.=--It is a most significant fact, to
which attention was first strongly directed by Louis Agassiz, that
the earliest representatives of any group, whether class, order, or
family, were not what we would now call typical representatives of
that group; but, on the contrary, they were, in a wonderful degree,
connecting links; that is, that along with their distinctive classic,
ordinal, or family characters they possessed also other characters
which connected them closely with other classes, orders, or families,
now widely distinct, without connecting links or intermediate forms.
For example: The earliest vertebrates were fishes, but not typical
fishes. On the contrary, they were fishes so closely connected by many
characters with amphibian reptiles, that we hardly know whether to
call some of them reptilian fishes, or fish-like reptiles. From these,
as from a common vertebrate stem, were afterward separated, by slow
changes from generation to generation, in two directions, the typical
fishes and the true reptiles. So, also, to take another example, the
first birds were far different from typical birds as we now know them.
They were, on contrary, birds so reptilian in character, that there
is still some doubt whether bird-characters or reptilian characters
predominate in the mixture, and therefore whether they ought to be
called reptilian birds or bird-like reptiles. From this common stem,
the more specialized modern reptiles branched off in one direction and
typical birds in another, and intermediate forms became extinct; until
_now_, the two classes stand widely apart, without apparent genetic
connection. This subject will be more fully treated hereafter, and
other examples given. These two will be sufficient now to make the idea
clear.

Such early forms combining the characters of two or more groups,
now widely separated, were called by Agassiz _connecting_ types,
_combining_ types, _synthetic_ types, and sometimes _prophetic_ types;
by Dana, _comprehensive_ types; and by Huxley, _generalized_ types.
They are most usually known now as _generalized_ types, and their
widely-separated outcomes _specialized_ types. Thus, in general, we may
say that the widely-separated groups of the present day, when traced
back in geological times, approach one another more and more until they
finally unite to form common stems, and these in their turn unite to
form a common trunk. From such a common trunk, by successive branching
and rebranching, each branch taking a different direction, and all
growing wider and wider apart (differentiation), have been gradually
generated all the diversified forms which we see at the present day.
The last leafy ramifications--flower-bearing and fruit-bearing--of this
tree of life, are the fauna and flora of the present epoch. The law
might be called a law of ramification, of specialization of the parts,
and diversification of the whole.

_b._ =Law of Progress of the Whole.=--Many imagine that progress is
the one law of evolution; in fact, that evolution and progress are
coextensive and convertible terms. They imagine that in evolution the
movement must be upward and onward in all parts; that degeneration
is the opposite of evolution. This is far from the truth. There
is, doubtless, in evolution, progress to higher and higher planes;
but not along every line, nor in every part; for this would be
contrary to the law of differentiation. It is only progress of the
whole organic kingdom in its entirety. We can best make this clear
by an illustration. A growing tree branches and again branches _in
all directions_, some branches going upward some sidewise, and some
downward--anywhere, everywhere, for light and air; but the whole tree
grows ever taller in its higher branches, larger in the circumference
of its outstretching arms, and more diversified in structure. Even
so the tree of life, by the law of differentiation, branches and
rebranches continually in all directions--some branches going upward
to higher planes (progress), some pushing horizontally; neither rising
nor sinking, but only going farther from the generalized origin
(specialization); some going downward (degeneration), anywhere,
everywhere, for an unoccupied place in the economy of Nature, but the
whole tree grows ever higher in its highest parts, grander in its
proportions, and more complexly diversified in its structure.

It may be well to pause here a moment to show how this mistaken
identification of evolution with progress alone, without modification
by the more fundamental laws of differentiation, has given rise to
misconceptions in the popular and even in the scientific mind. The
biologist is continually met with the question, “Do you mean to say
that any one of the invertebrates, such, for instance, as a spider,
may eventually, in the course of successive generations, become a
vertebrate, or that a dog or a monkey is on the highway to become a
man?” By no means. There is but one straight and narrow way to the
highest in evolution as in all else, and few there be that have found
it--in fact, probably two or three only at every step. The animals
mentioned above have diverged from that way. In their ancestral
history, they have missed the golden opportunity, if they ever had it.
It is easy to go on in the way they have chosen, but impossible to get
back on the ascending trunk-line. To compare again with the growing
tree, only one straight trunk-line leads upward to the terminal bud. A
branch once separated must grow its own way, if it grow at all.

Of the same nature is the mistake of some extreme evolutionists,
such as Dr. Bastian and Professor Haeckel, and of nearly all
anti-evolutionists, viz., that of imagining that the truth of
evolution and that of spontaneous generation must stand or fall
together. On the contrary, _if_ life did _once_ arise spontaneously
from any lower forces, physical or chemical, by natural process,
_the conditions necessary for so extraordinary a change could hardly
be expected to occur but once in the history of the earth_. They
are, therefore, _now_, not only unreproducible, but unimaginable.
Such golden opportunities do not recur. Evolution goes only onward.
Therefore, the impossibility of the derivation of life from non-life
_now_, is no more an argument against such a derivation _once_, than
is the hopelessness of a worm ever becoming a vertebrate _now_, an
argument against the derivative origin of vertebrates. Doubtless if
life were now extinguished from the face of the earth, it could not
again be rekindled by any natural process known to us; but the same is
probably true of every step of evolution. If any class--for example,
mammals--were now destroyed, it could not be re-formed from any other
class now living. It would be necessary to go back to the time and
conditions of the separation of this class from the reptilian stem.
Therefore, the falseness of the doctrine of abiogenesis,[7] so far from
being any argument against evolution, is exactly what a true conception
of evolution and knowledge of its laws would lead us to expect.

_c._ =Law of Cyclical Movement.=--The movement of evolution has ever
been onward and upward, it is true, but not at uniform rate in the
whole, and especially in the parts. On the contrary, it has plainly
moved in successive cycles. The tide of evolution rose ever higher and
higher, without ebb, but it nevertheless came in successive waves,
each higher than the preceding and overborne by the succeeding. These
successive cycles are the dynasties or reigns of Agassiz, and ages
of Dana; the reign of mollusks, the reign of fishes, of reptiles,
of mammals, and finally of _man_. During the early Palæozoic times
(Cambrian and Silurian) there were no vertebrates.[8] But never in
the history of the earth were mollusks of greater size, number, and
variety of form than then. They were truly the rulers of these early
seas. In the absence of competition of still higher animals, they had
things all their own way, and therefore grew into a great monopoly of
power. In the later Palæozoic (Devonian) fishes were introduced. They
increased rapidly in size, number, and variety; and being of higher
organization they quickly usurped the empire of the seas, while the
mollusca dwindled in size and importance, and sought safety in a less
conspicuous position. In the Mesozoic times, reptiles, introduced a
little earlier,[9] finding congenial conditions and an unoccupied
place above, rapidly increased in number, variety, and size, until
sea and land seem to have swarmed with them. Never before or since
have reptiles existed in such numbers, in such variety of form, or
assumed such huge proportions; nor have they ever since been so
highly organized as then. They quickly became rulers in every realm
of Nature--rulers of the sea, swimming reptiles; rulers of the land,
walking reptiles; and rulers of the air, flying reptiles. In the
unequal contest, fishes therefore sought safety in subordination.
Meanwhile mammals were introduced in the Mesozoic, but small in size,
low in type (marsupials), and by no means able to contest the empire
with the great reptiles. But in the Cenozoic (Tertiary) the conditions
apparently becoming favorable for their development, they rapidly
increased in number, size, variety, and grade of organization, and
quickly overpowered the great reptiles, which almost immediately sank
into the subordinate position in which we now find them, and thus
found comparative safety. Finally, in the Quaternary, appeared man,
contending doubtfully for a while, with the great mammals, but soon (in
Psychozoic) acquiring mastery through superior intelligence. The huge
and dangerous mammals were destroyed and are still being destroyed; the
useful animals and plants were preserved and made subservient to his
wants; and all things on the face of the earth are being readjusted to
the requirements of his rule. In all cases it will be observed that
the rulers were such because, by reason of strength, organization, and
intelligence, they were fittest to rule. There is always room at the
top. To illustrate again by a growing tree: This successive culmination
of higher and higher classes may be compared to the flowering and
fruiting of successively higher and higher branches. Each uppermost
branch, under the genial heat and light of direct sunshine, received in
abundance by reason of position, grew rapidly, flowered, and fruited;
but quickly dwindled when overshadowed by still higher branches, which,
in their turn, monopolized for a time the precious sunshine.

But observe, furthermore: when each ruling class declined in
importance, it did not perish, but continued in a subordinate position.
Thus, the whole organic kingdom became not only higher and higher in
its highest forms, but also more and more complex in its structure and
in the interaction of its correlated parts. The whole process and its
result is roughly represented in the accompanying diagram, Fig. 1, in
which A B represents the course of geological time and the curve, the
rise, culmination, and decline of successive dominant classes.

[Illustration:

  MOLLUSCS--Silurian.
  FISHES--Devon. and Carb.
  REEPTILES--Mesozoic.
  MAMMALS--Tert’y and Quat.
  MAN--Present.

FIG. 1.]


THE ABOVE THREE LAWS ARE LAWS OF EVOLUTION.

These three laws we have shown are distinctly recognizable in the
succession of organic forms in the geological history of the earth.
They are, therefore, undoubtedly the _general laws of succession_. Are
they also laws of evolution? Are they also discoverable in embryonic
development, the type of evolution? They are, as we now proceed to show:

=Differentiation.=--In reproduction the new individual appears: 1.
As a _germ_-cell--a single microscopic living cell. 2. Then, by
growth and multiplication of cells, it becomes an _egg_. This may be
characterized as an aggregate of _similar_ cells, and therefore is
not yet differentiated into tissues and organs. In other words, it
is not yet visibly organized; for organization may be defined as the
possession of different parts, performing different functions, and
all co-operating for one given end, viz., the life and well-being of
the organism. 3. Then commences the really characteristic process of
development, viz., _differentiation_ or diversification. The cells
are at first all alike in form and function, for all are globular in
form, and each performs all the functions necessary for life. From
this common point now commences development in _different directions_,
which may be compared to a branching and rebranching, with more and
more complex results, according as the animal is higher in the scale
of organization and advances toward a state of maturity. First, the
cell-aggregate (egg) separates into three distinct layers of cells,
called ecto-blast, endo-blast, and meso-blast. These by further
differentiation form the three fundamental groups of organs and
functions, viz., the _nervous system_, the _nutritive system_, and the
_blood system_: the first presiding over the exchange of _force_ or
influence, by action and reaction with the environment, and between the
different parts of the organism; the second presiding over the exchange
of _matter_ with the environment, by absorption and elimination; the
third presiding over exchanges of matter between different parts of
the organism. The first system of functions and organs may be compared
to a system of telegraphy, foreign and domestic; the second to foreign
commerce; the third to an internal carrying-trade. Following out any
one of these groups in higher animals, say the nervous system, it
quickly differentiates again into two sub-systems, viz., cerebro-spinal
and ganglionic, each having its own distinctive functions, which we
can not stop to explain. Then the cerebro-spinal again differentiates
into voluntary and reflex systems. All of these have meanwhile
separated into sensory and motor centers and fibers. Then, taking
only the sensory fibers, these again are differentiated into five
special senses, each having a wholly different function. Then, finally,
taking any one of these, say the _sense of touch_ or feeling, this
again is differentiated into many kinds of fibers, each responding to
a different impression, some to heat, others to cold, still others
to pressure, etc. We have taken the nervous system; but the same
differentiation and redifferentiation takes place in all other systems,
and is carried to higher and higher points according to the position in
the scale of the animal which is to be formed.

Or, to vary the mode of presentation a little, the cells of the
original aggregate, commencing all alike, immediately begin to take on
different forms, in order to perform different functions. Some cells
take on a certain form and aggregate themselves to form a peculiar
tissue which we call muscle, and which does nothing else, can do
nothing else, than contract under stimulus. Another group of cells
take on another peculiar form and aggregate themselves to form another
and very different tissue, viz., nervous tissue, which does nothing
and can do nothing but carry influence back and forth between the
great external world and the little world of consciousness within.
Still another group of cells take still another form and aggregate
to form still another tissue, viz., the _epithelial_, whose only
function is to absorb nutritive and eliminate waste matters. Thus, by
differentiation of form and limitation of function, or division of
labor, the different parts of the organism are bound more and more
closely together by mutual dependence, and the whole becomes more and
more distinctly individuated, and separation of parts becomes more and
more a mutilation, and finally becomes impossible without death. This
process, as already said, reaches its highest point only in the later
stages of development of the highest animals.

=Progress.=--The _law of progress_ is, of course, admitted to be a
law of ontogeny; but observe here, also, it is true only of the whole
and not necessarily of all the parts, _except from the point of view
of the whole_. Thus, for example, starting all from a common form or
generalized type, some cells _advance_ to the dignity of brain-cells,
whose function is somehow connected with the generation or at least
the manifestation of thought, will, and emotion; other cells _descend_
to the position of kidney-cells, whose sole function is the excretion
of urine. But here, also, the highest cells are successively higher,
and the whole aggregate is successively nobler and more complex. It
is again a branching and rebranching, in every direction, some going
upward, some downward, some horizontally, anywhere, everywhere, to
increase the complexity of relations internal and external, and
therefore to elevate the plane of the whole.

=Cyclical Movement.=--Lastly, the law of cyclical movement is also a
law of ontogeny and therefore of evolution. This law, however, is less
fundamental than the other two, and is, therefore, less conspicuous in
the ontogenic than in the phylogenic series. It is conspicuous only in
the later stages of ontogeny, and in other higher kinds of evolution,
such as social evolution. For example, in the ontogenic development of
the body and mind from childhood to manhood we have plainly successive
culminations and declines of higher and higher functions. In bodily
development we have culminating first the _nutritive_ functions, then
the _reproductive_ and _muscular_, and last the _cerebral_. In mental
development we have culmination first of the receptive and retentive
faculties in childhood, then of imaginative and æsthetic faculties
in youth and young manhood; then of the reflective and elaborative
faculties--the faculties of productive work in mature manhood; and,
finally, the moral and religious sentiments in old age. The first
gathers and stores materials; the second vivifies and makes them
plastic building materials; the third uses them in actual constructive
work--in building the temple of science and philosophy; and the fourth
dedicates that temple only to noblest purposes.

Observe here, also, that when each group of faculties culminates and
declines, it does not perish, but only becomes subordinate to the next
higher dominant group, and the whole psychical organism becomes not
only higher and higher in its highest parts, but also more and more
complex in its structure and in the interaction of its correlated parts.

Observe, again, the necessity laid upon us by this law--the necessity
of continued evolution to the end. Childhood, beautiful childhood,
can not remain--it must quickly pass. If, with the decline of its
characteristic faculties, the next higher group characteristic of youth
do not increase and become dominant, then the glory of life is already
past and deterioration begins. Have we not all seen sad examples of
this? Youth, glorious youth, must also pass. If the next higher group
of reflective and elaborative faculties do not arise and dominate, then
progressive deterioration of character commences here--thenceforward
the whole nature becomes coarse, as we so often see in young men,
or else shrivels and withers, as we so often see in young women.
Finally, manhood, strong and self-relying manhood, must also pass. If
the moral and religious sentiments have not been slowly growing and
gathering strength all along, and do not now assert their dominance
over the whole man, then commences the final and saddest decline of
all, and old age becomes the pitiable thing we so often see it. But,
if the evolution have been normal throughout; if the highest moral and
religious nature have been gathering strength through all, and now
dominates all, then the psychic evolution rises to the end--then the
course of life is like a wave rising and cresting only at the moment
of its dissolution, or, like the course of the sun, if not brightest
at least most glorious in its setting. And thus--may we not hope?--the
glories of the close of a well-spent life become the pledge and
harbinger of an eternal to-morrow?

We have thus far illustrated the three laws of succession of organic
forms by ontogeny, because this is the type of evolution; but they
may be illustrated also by other forms of evolution. Next to the
development of the individual, undoubtedly the _progress of society_
furnishes the best illustration of these laws.

Commencing with a condition in which each individual performs all
necessary social functions, but very imperfectly; in which each
individual is his own shoemaker and tailor, and house-builder and
farmer, and therefore all persons are socially alike; as society
advances, the constituent members begin to diverge, some taking on
one social function and some another, until in the highest stages of
social organization this diversification or division and subdivision
of labor reaches its highest point, and each member of the aggregate
can do perfectly but one thing. Thus, the social organism becomes
more and more strongly bound together by mutual dependence, and
separation becomes mutilation. I do not mean to say that this extreme
is desirable, but only that an approach to this is _a_ natural law of
social development. _Is not this the law of differentiation?_

So also _progress_ is here, as in other forms of evolution--a _progress
of the whole_, but not necessarily of every part. Some members of
the social aggregate advance _upward_ to the dignity of statesmen,
philosophers, and poets; some advance _downward_ to the position
of scavengers and sewer-cleansers.[10] But the highest members are
progressively higher, and the whole aggregate is progressively grander
and more complex in structure and functions.

So, again, the _law of cyclical movement_ is equally conspicuous here.
Society everywhere advances, not uniformly, but by successive waves,
each higher than the last; each urged by a new and higher social
force, and embodying a new and higher phase of civilization. Again:
as each phase declines, its characteristic social force is not lost,
but becomes incorporated into the next higher phase as a subordinate
principle, and thus the social organism as a whole becomes not only
higher and higher, but also more and more complex in the mutual
relations of its interacting social forces.

Let us not be misunderstood, however. There is undoubtedly in social
evolution something more and higher than we have described, but which
does not concern us here, except to guard against misconstruction.
There is in society a _voluntary progress_ wholly different from the
evolution we have been describing. In _true_ or material evolution
natural law works for the betterment of the whole utterly regardless
of the elevation of the individual, and the individual contributes to
the advance of the whole quite unconsciously while striving only for
his own betterment. This unconscious evolution by natural law inherited
from the animal kingdom is conspicuous enough in society, especially in
its early stages, but we would make a great mistake if we imagined, as
some do, that this is all. Besides the unconscious evolution by natural
laws, _inherited from below_, there is a higher evolution, _inherited
from above_, indissolubly connected with man’s spiritual nature--a
conscious, voluntary striving of the best members of the social
aggregate for the betterment of the whole--a conscious, voluntary
striving both of the individual and of society toward a recognized
_ideal_. In the one kind of evolution the fittest are those most in
harmony with the environment, and which therefore always survive; in
the other, the fittest are those most in harmony with the ideal, and
which often do not survive. The laws of this free voluntary progress
are little understood. They are of supreme importance, but do not
specially concern us here. We will speak of it again in another chapter.

The three laws above mentioned might be illustrated equally well by all
other forms of evolution. We have selected only those which are most
familiar. They may, therefore, be truly called the laws of evolution.
We have shown that they are the laws of succession of organic forms.

=III. Change by Means of Resident Forces.=--Thus far in our argument
I suppose that most well-informed men will raise no objection. It
will be admitted, I think, even by those most bitterly opposed to
the theory of evolution, that there has been throughout the whole
geological history of the earth an onward movement of the organic
kingdom to higher and higher levels. It will be admitted, also, that
there is a grand and most significant resemblance between the course
of development of the organic kingdom and the course of embryonic
development--between the laws of succession of organic forms and the
laws of ontogenic evolution. But there is another essential element in
ontogenic evolution. It is that the _forces_ or causes of evolution
are _natural_; that they reside in the thing developing and in the
reacting environment. This we know is true of embryonic development; is
it true also of the geologic succession of organic forms? It is true of
ontogeny; is it true also of phylogeny? If not, then only by a metaphor
can we call the process of change in the organic kingdom throughout
geological history an evolution. This is the point of discussion, and
not only of discussion, but, alas! of heated and even angry dispute.
The field of discussion is thus narrowed to this third point only.

Before stating the two opposite views of the cause of evolution, it
is necessary to remind the reader that when the evolutionist speaks
of the forces that determine progressive changes in organic forms
as _resident_ or _inherent_, all that he means, or ought to mean,
is that they are resident in the same sense as all natural forces
are resident; in the same sense that the vital forces of the embryo
are resident in the embryo, or that the forces of the development of
the solar system according to the nebular or any other cosmogonic
hypotheses are resident in that system. In other words, they mean only
that they are _natural_, not supernatural. This does not, of course,
touch that deeper, that deepest of all questions, viz., the essential
_nature and origin of natural forces_; how far they are independent
and self-existent, and how far they are only modes of divine energy.
This is a question of philosophy, not of science. This question is
briefly discussed in another place (Part III, Chap. III); it does not
immediately concern us here.

=The Two Views briefly Contrasted.=--As already stated, all will admit
a grand resemblance between the stages of embryonic development and
those of the development of the organic kingdom. This was first brought
out clearly by Louis Agassiz, and is, in fact, the greatest result
of his life-work. All admit, also, that the embryonic development is
a natural process. Is the development of the organic kingdom also a
natural process? All biologists of the present day contend that it
is; all the old-school naturalists, with Agassiz at their head, and
all anti-evolutionists of every school, contend that it is not. We
take Agassiz as the type of this school, because he has most fully
elaborated and most distinctly formulated this view. As formulated by
him, it has stood in the minds of many as an alternative and substitute
for evolution.

According to the evolutionists, all organic forms, whether species,
genera, families, orders, classes, etc., are variable, and, if external
conditions favor, these variations accumulate in one direction and
gradually produce new forms, the intermediate links being usually
destroyed or dying out. According to Agassiz, the higher groups,
such as genera, families, orders, etc., are indeed variable by the
introduction of new species, but species are the ultimate elements of
classification, and, like the ultimate elements of chemistry, are
unchangeable; and, therefore, the speculations of the evolutionist
concerning the transmutation of species are as vain as were the
speculations of the alchemists concerning the transmutation of
metals--that the origin of man, for example, from any lower species
is as impossible as the origin of gold from any baser metal. Both
sides admit frequent change of species during geological history, but
one regards the change as a change by gradual _transmutation_ of one
species _into_ another through successive generations and by _natural_
process, the other as change by _substitution_ of one species _for_
another by direct supernatural _creative act_. Both admit the gradual
development of the organic kingdom as a whole through stages similar
to those of embryonic development; but the one regards the whole
process as natural, and therefore strictly comparable to embryonic
development, the other as requiring frequent special interference of
creative energy, and therefore comparable rather to the development
of a building under the hand and according to the preconceived plan
of an architect--a plan, in this case, conceived in eternity and
carried out consistently through infinite time. It is seen that the
essential point of difference is this: The one asserts the variability
of species (if conditions favor, and time enough is given) without
limit; the other asserts the permanency of specific forms, or their
variability only within narrow limits. The one asserts the origin
of species by “_descent with modifications_”; the other, the origin
of species by “_special act of creation_.” The one asserts the law
of continuity (i. e., that each stage is the natural outcome of the
immediately preceding stage) in this, as in every other department of
Nature; the other asserts that the law of continuity (i. e., of cause
and effect) does not hold in this department; that the links of the
chain of changes are discontinuous, the connection between them being
intellectual, not physical.

So much for sharp contrasting characterization of the two views,
necessary for clear understanding of much that follows. We will have
to give them more fully hereafter when we take up the evidences of
evolution in Part II.




CHAPTER II.

THE RELATION OF LOUIS AGASSIZ TO THE THEORY OF EVOLUTION.


In order to clear up the conception of evolution, it is necessary
to give a brief history of the idea, and especially to explain the
relation of Louis Agassiz to that theory. This is the more necessary,
because there is a deep and wide-spread misunderstanding on this
subject, and thus scant justice has been done our great naturalist,
especially by the English and Germans; and also because this relation
is an admirable illustration of an important principle in scientific
philosophy.

Like all great ideas, we find the first germs of this in Greek
philosophy, in the cosmic speculations of Thales and Pythagoras.
Next (about 100 B. C.) we find it more clearly expressed by the Roman
thinker, Lucretius, in his great philosophic poem entitled “De Rerum
Natura.” After a dormancy of nearly eighteen centuries it next emerges
with still more clearness in the theological speculations of Swedenborg
and the philosophical speculations of Kant. All these we pass over with
bare mention, because these thinkers approached the subject from the
philosophic rather than the scientific side--in the metaphysical rather
than the scientific spirit.

The first serious attempt at scientific presentation of the subject was
by the celebrated naturalist, Lamarck, in a work entitled “Philosophie
Zoölogique,” published in 1809. It is not necessary, in this rapid
sketch, to give a full account of Lamarck’s views. Suffice it to say
that the essential idea of evolution, viz., the indefinite variability
and the derivative origin of species, was insisted on with great
learning and skill, and illustrated by many examples. With Lamarck,
the factors of evolution or causes of change of organic forms were--1.
Modification of organs in function and therefore in structure, by a
changing environment--external factor; and, 2. Modification of organs
by _use_ and _disuse_--internal factor. In both cases the modifications
are inherited and increased from generation to generation, without
limit. This second factor seems to have taken, in the mind of Lamarck,
the somewhat vague and transcendental form of aspiration or upward
striving of the animal toward higher conditions. These are acknowledged
to-day as true factors of evolution, but the distinctively Darwinian
factor, viz., “divergent variation and natural selection,” was not then
thought of. The publication of Lamarck’s views produced a powerful
impression, but only for a little while. Pierced by the shafts of
ridicule shot by nimble wits of Paris, and crushed beneath the heavy
weight of the authority of Cuvier, the greatest naturalist and
comparative anatomist of that or perhaps of any time, it fell almost
still-born. I believe it was best that it should thus perish. Its birth
was premature; it was not fit to live. The world was not yet prepared
for a true scientific theory. Nevertheless, the work was not without
its effect upon some of the most advanced thinkers of that time; upon
Saint-Hilaire and Comte in France, and upon Goethe and Oken in Germany.
It was good seed sown and destined to spring up and bear fruit in
suitable environment; but not yet.

The next attempt worthy of attention in this rapid sketch is that
of Robert Chambers, in a little volume entitled “Vestiges of a
Natural History of Creation,” published in 1844. It was essentially a
reproduction of Lamarck’s views in a more popular form. It was not a
truly scientific work nor written by a scientific man. It was rather an
appeal from the too technical court of science to the supposed wider
and more unprejudiced court of popular intelligence. It was therefore
far more eloquent than accurate; far more specious than profound.
It was, indeed, full of false facts and inconsequent reasonings.
Nevertheless, it produced a very strong impression on the thinking,
popular mind. But _it_ also quickly fell, pierced by keen shafts of
ridicule, and crushed beneath the heavy weight of the authority of all
the most prominent naturalists of that time, with Agassiz at their
head. The question for the time seemed closed. I believe, again, it was
best so, for the time was not yet fully ripe.

I know full well that many think with Haeckel that biology was kept
back half a century by the baneful authority of Cuvier and Agassiz;
but I can not think so. The hypothesis was contrary to the facts
of science _as then known and understood_. It was conceived in the
spirit of baseless speculation, rather than of cautious induction; of
skillful elaboration rather than of earnest truth-seeking. Its general
acceptance would have debauched the true spirit of science. I repeat
it: the time was not yet ripe for a scientific theory. The ground
must first be cleared and a solid foundation built; an insuperable
_obstacle_ to hearty rational acceptance must first be removed, and an
inductive _basis_ must be laid.

=The Obstacle removed.=--The obstacle in the way of the acceptance
of the derivative origin of species was the then prevalent _notion
concerning the nature of life_. We must briefly sketch the change which
has taken place in the last forty years in our ideas on this subject.

Until about forty years ago, the different forces of Nature, such
as gravity, electricity, magnetism, light, heat, chemical affinity,
etc., were supposed to be entirely distinct. The realm of Nature was
divided up into a number of distinct and independent principalities,
each subject to its own sovereign force and ruled by its own petty
laws. About that time it began to be evident, and is now universally
acknowledged, that all these forces are but different _forms_ of one,
universal, omnipresent energy, and are transmutable unto one another
back and forth without loss. This is the doctrine of correlation of
forces and conservation of energy, one of the grandest ideas of modern
times. But _one_ force seemed still to be an exception. Life-force
was still believed to be a peculiar, mysterious principle or entity,
standing above other forces and subordinating them; not correlated
with, not transmutable unto, nor derivable from, other and lower
forces, and therefore in some sense supernatural. Now, if this be true
of living _forces_, it is perfectly natural, yea, almost necessary,
to believe that living _forms_ are wholly different from other forms
in their origin. New forms of dead matter may be derived, but new
living forms are _underived_. Other new forms come by natural process,
new organic forms by supernatural process. The conclusion was almost
unavoidable. But soon vital force also yielded to the general law of
correlation of natural forces. Vital forces are also transmutable into
and derivable from physical and chemical forces. Sun-force, falling on
the green leaves of plants, is absorbed and converted into vital force,
disappears as _light_ to reappear as _life_. The amount of life-force
generated is measured by the amount of light extinguished. The same
is true of animal life. As in the steam-engine the locomotive energy
is derived from the fuel consumed and measured by its amount, so in
the animal body, the animal heat and animal force are derived from and
measured by the food and tissue consumed by combustion. Thus, vital
force may be regarded as so much force withdrawn from the general fund
of chemical and physical forces, to be again refunded without loss at
death. This obstacle is, therefore, now removed. If vital force falls
in the same category as other natural forces, there is no reason why
living forms should not fall into the same category in this regard
as other natural forms. If new forms of dead matter are derived from
old forms by modification, according to _physical_ laws, there is no
reason why new living forms should not also be derived from old forms
by modification according to _physiological_ laws. Thus, at last, the
obstacle was removed--the ground was cleared.

=The Basis laid.=--But Science is not content with removal of _a
priori_ objections. She must also have positive proofs. The ground
must not only be cleared, but a true inductive basis of facts, and
especially of laws and methods, must be laid. _This was the life-work
of Agassiz._ Yes, as strange as it may seem to some, it is nevertheless
true that the whole inductive basis, upon which was afterward built
the modern theory of evolution, was laid by Agassiz, although he
himself persistently refused to build upon it any really scientific
superstructure. It is plain, then, that all attempts at building
previous to Agassiz’s work must, of necessity, have resulted in an
unsubstantial structure--an edifice built on sand, which could not
and ought not to stand. I must stop here in order to explain somewhat
fully this important point, and thus to give due credit to the work of
Agassiz.

The title of any scientist to greatness must be determined, not so much
by the multitude of new facts he has discovered as by the new laws he
has established, and especially by the new methods he has inaugurated
or perfected. Now, I think it can be shown that to Agassiz, more
than to any other man, is due the credit of having _established the
laws of succession of living forms_ in the geological history of the
earth--laws upon which must rest any true theory of evolution. Also,
that to him, more than to any other man, is due the credit of having
_perfected the method_ (method of comparison) by the use of which alone
biological science has advanced so rapidly in modern times. This is
high praise. I wish to justify it. I begin with the method.

Scientific methods bear the same relation to _intellectual progress_
that tools, instruments, machines, mechanical contrivances of
all sorts, bear to _material progress_. They are intellectual
_contrivances_--indirect ways of accomplishing results far too hard
for bare-handed, unaided intellectual strength. As the civilized man
has little or no advantage over the savage in bare-handed strength of
muscle, and the enormous superiority of the latter in accomplishing
material results is due wholly to the use of mechanical contrivances
or machines; even so, in the higher sphere of intellect, the scientist
makes no pretension to the possession of greater unaided intellectual
strength than belongs to the uncultured man, or even perhaps to the
savage. The amazing intellectual results achieved by science are due
wholly to the use of intellectual contrivances or scientific methods.
As in the lower sphere of material progress the greatest benefactors of
the race are the inventors or perfecters of new mechanical contrivances
or _machines_, so also in the higher sphere of intellectual progress
the greatest benefactors of the race are the inventors or perfecters of
new intellectual contrivances or _methods of research_.

To illustrate the power of methods, and the necessity of their use,
take the case of the _method of notation_, so characteristic of
mathematics, and take it even in its simplest and most familiar form:
Nine numeral figures, having each a value of its own, and another
dependent upon its position; a few letters, _a_ and _b_, and _x_ and
_y_, connected by symbols, + and-and =: that is all. And yet, by the
use of this simple contrivance, the dullest school-boy accomplishes
intellectual results which would defy the utmost efforts of the
unaided strength of the greatest genius. And this is only the simplest
tool-form of this method. Think of the results accomplished by the use
of the more complex machinery of the higher mathematics!

Take next the method of experiment so characteristic of physics and
chemistry. The phenomena of the external world are far too complex and
far too much affected by disturbing forces and modifying conditions to
be understood at once by bare, unaided intellectual insight. They must
first be simplified. The physicist, therefore, contrives artificial
phenomena under ideal conditions. He removes one complicating condition
after another, one disturbing cause and then another, watching
meanwhile the result, until finally the necessary condition and the
true cause are discovered. On this method rests the whole fabric of the
physical and chemical sciences.

But when we rise still higher, viz., into the plane of life, the
phenomena of Nature become still more complex and difficult to
understand directly; and yet just here, where we are the most powerless
without some method, our method of experiment almost wholly _fails
us_. The phenomena of life are not only far more complex than those
of dead matter, but the conditions of life are so nicely adjusted,
the equilibrium of forces so delicately balanced, that, when we
attempt to introduce our clumsy hands in the way of experiment, we
are in danger of overthrowing the equilibrium, of destroying the
conditions of the experiment, viz., life; and then the whole problem
falls immediately into the domain of chemistry. What shall we do?
In this dilemma we find that Nature herself has already prepared
for us, ready to hand, an elaborate series of simplified conditions
equivalent to experiments. The phenomena of life are, indeed, far too
complex to be at once understood--the problem of life too hard to be
solved--in the higher animals; but, as we go down the animal scale,
complicating conditions are removed one by one, the phenomena of life
become simpler and simpler, until in the lowest microscopic cell or
spherule of living protoplasm we finally reach the simplest possible
expression of life. The equation of life is reduced to its simplest
terms, and now, if ever, we begin to understand the true value of the
unknown quantity. This is the natural history series, or _Taxonomic_
series, already spoken of on page 10. Again, Nature has prepared, and
is now preparing daily before our eyes, another series of gradually
simplified conditions. Commencing with the mature condition of one of
the higher animals--for example, man--and going backward along the
line of individual history through the stages of infant embryo, egg
and germ, we find again the phenomena of life becoming simpler and
simpler, until we again reach the simplest conceivable condition in
the single microscopic cell or spherule of living protoplasm. This, as
already explained, is the embryonic or _Ontogenic_ series. Again, that
there be no excuse for man’s ignorance of the laws of life, Nature has
prepared still another series; and this the grandest of all, for it is
the cause of both the others. Commencing with the plants and animals of
the present epoch, and going back along the track of geological times,
through Cenozoic, Mesozoic, Palæozoic, Eozoic, to the very dawn of
life--the first syllable of recorded time--and we find again a series
of organic forms growing simpler and simpler, until, if we could find
the very first, we would undoubtedly again reach the simplest condition
in the lowest conceivable forms of life. This, as we have already seen,
is the geologic or evolution, or _Phylogenic_ series. We have already
explained these three series, only in this connection it suits our
purpose to take the terms backward.

Now, it is by _comparison_ of the terms of each of these series going
up and down, and watching the first appearance, the growth, and the
perfecting of tissues, organs, functions, and by the comparison of
the three series with one another term by term--I say it is wholly
by comparison of this kind that biology has in recent times become a
true inductive science. This is the “_method of comparison_.” It is
the great method of research in all those departments which can not be
readily managed by the method of experiment. It has already regenerated
biology, and is now applied with like success in sociology under the
name of _historic method_. Yes; anatomy became scientific only through
comparative anatomy, physiology through comparative physiology, and
embryology through comparative embryology. May we not add, sociology
will become truly scientific only through comparative sociology, and
psychology through comparative psychology?

Now, while it is true that this method, like all other methods, has
been used, from the earliest dawn of thought, in a loose and imperfect
way, yet it is only in very recent times that it has been organized,
systematized, perfected, as a true scientific method, as a great
instrument of research; and the prodigious recent advance of biology is
due wholly to this cause. Now, among the great leaders of this modern
movement, Agassiz undoubtedly stands in the very first rank. I must try
to make this point plain, for it is by no means generally understood.

Cuvier is acknowledged to be the great founder of comparative anatomy.
He it was that first perfected the method of comparison, but comparison
only in one series--the _Taxonomic_. Von Baer and Agassiz added to
this comparison in the ontogenic series also, and comparison of
these two series with each other, and therefore the application of
embryology to the classification of animals. If Von Baer was the
first announcer, Agassiz was the first great practical worker by this
method. Last and most important of all, in its relation to evolution,
Agassiz added _comparison in the geologic or phylogenic series_. The
one grand idea underlying Agassiz’s whole life-work was the essential
identity of the three series, and therefore the light which they must
shed on one another. The two guiding and animating principles of his
scientific work were--1. That the embryonic development of one of the
higher representatives of any group repeated in a general way the
terms of the Taxonomic series in the same group, and therefore that
embryology furnished the key to a true classification; and, 2. That the
succession of forms and structure in geological times in any group is
similar to the succession of forms and structure in the development of
the individual in the same group, and thus that embryology furnishes
also the key to geological succession. In other words, during his
whole life, Agassiz insisted that the laws of embryonic development
(ontogeny) are also the laws of geological succession (phylogeny).
Surely this is the foundation, the only solid foundation, of a true
theory of evolution. It is true that Agassiz, holding as he did the
doctrine of permanency of specific types, and therefore rejecting the
doctrine of the derivative origin of species, did not admit the causal
or natural relation of phylogenic succession to embryonic succession
and taxonomic order as we now believe it--it is true that for him the
relation between the three series was an intellectual not a physical
one--consisted in the preordained plans of the Creator, and not in
any genetic connection or inherited property; but evidently the first
and greatest step was the discovery of the relation itself, however
accounted for. The rest was sure to follow.

But more. Not only did Agassiz establish the essential identity of the
geologic and embryonic succession, the general similarity of the two
series, phylogenic and ontogenic, but he also announced and enforced
all the formal laws of geologic succession (i. e., of evolution), as
we now know them. These, as already stated and illustrated, are the
law of differentiation, the law of progress of the whole, and the law
of cyclical movement, although he did not formulate them in these
words. No true inductive evidence of evolution was possible without
the knowledge of these laws, and for this knowledge we are mainly
indebted to Agassiz. He well knew also that they were the laws of
embryonic development and therefore of evolution; but he avoided the
word evolution, as implying the derivative origin of species, and
used instead the word _development_, though it is hard to see in what
the words differ. Thus, it is evident that Agassiz laid the whole
foundation of evolution, solid and broad, but refused to build any
scientific structure on it; he refused to recognize the legitimate, the
scientifically necessary outcome of his own work. Nevertheless, without
his work a scientific theory of evolution would have been impossible.
Without Agassiz (or his equivalent), there would have been no Darwin.

There is something to us supremely grand in this refusal of Agassiz to
accept the theory of evolution. The opportunity to become the leader of
modern thought, the foremost man of the century, was in his hands, and
he refused, because his religious, or, perhaps better, his philosophic
intuitions, forbade. To Agassiz, and, indeed, to all men of that time,
to many, alas! even now, evolution is materialism. But materialism is
Atheism. Will some one say, the genuine Truth-seeker follows where she
seems to lead _whatever be the consequences_? Yes; whatever be the
consequences to one’s self, to one’s opinions, prejudices, theories,
philosophies, but not to _still more certain truth_. Now, to Agassiz,
as to all genuine thinkers, the existence of God, like our own
existence, is more certain than any scientific theory, than anything
can possibly be made by proof. From his standpoint, therefore, he was
right in rejecting evolution as conflicting with still more certain
truth. The mistake which he made was in imagining that there was any
such conflict at all. But this was the universal mistake of the age. A
lesser man would have seen less clearly the higher truth and accepted
the lower. A greater man would have risen above the age, and seen that
there was no conflict, and so accepted both. All thinking men are
coming to this conclusion now, but none had done so then.

Now, then, at last, the obstacle of supernaturalism in the realm of
Nature having been removed by the establishment of the doctrine of
correlation of natural forces, and the extension of this doctrine
to embrace also life-force; and now also a broad and firm basis of
carefully-observed facts and well-established laws of succession
of organic forms having been laid by Agassiz, when again, for the
third time, the doctrine of origin of species “by derivation with
modifications” was brought forward by Darwin in a far more perfect
form, with more abundant illustrative materials, and with a new
and most potent factor of modification--viz., divergent variations
and natural selection--it found the scientific world already fully
prepared, and anxiously waiting. I say _anxiously_ waiting--for the
supposed supernatural origin of species had been the one exception
to the otherwise universal law of cause and effect, or the law of
continuity. It was therefore in open contradiction to the whole drift
of scientific thought for five hundred years. Is it any wonder,
then, that the derivative origin of species was welcomed with joy by
the scientific world? For five hundred years, scientific thought,
like a rising tide which knows no ebb, had tended thitherward with
ever-increasing pressure, but kept back by the one supposed fact of
the supernatural origin of species. Darwin lifted the gate, and the
in-rushing tide flooded the whole domain of thought.

What, then, is the place of Agassiz in biological science? What is the
relation of Agassiz to Darwin--of Agassizian development to Darwinian
evolution? I answer, it is the relation of formal science to physical
or causal science. Agassiz advanced biology to the _formal_ stage;
Darwin carried it forward, to some extent at least, to the _physical_
stage. All true inductive sciences in their complete development pass
through these two stages. Science in the one stage treats of the _laws_
of phenomena; in the other, of the _causes_ or explanation of these
laws. The former must precede the latter, and form its foundation;
the latter must follow the former, and constitute its completion. The
change from the one to the other is always attended with prodigious
impulse to science.

To illustrate: Until Kepler, astronomy was little more than
an accumulation of disconnected facts concerning celestial
motions--abundant materials, but no science; piles of brick and stone,
but no building. Kepler reduced this chaos to beautiful order and
musical harmony by the discovery of the three great laws which bear his
name, and therefore he has been justly called the legislator of the
heavens--_the lawgiver of space_. But, had he been asked the _cause_
of these beautiful laws, he could only have answered, “The _first
cause_--the direct will of the Deity.” A good answer and a true, but
not scientific; because it places the question beyond the domain of
science, which deals only with second or physical causes. But Newton
comes forward and gives a _physical cause_. He shows that all these
beautiful laws are the necessary result of gravitation; and thus
astronomy becomes a physical science. So, until Agassiz, the facts
of geological succession of organic forms were in a state of lawless
confusion. Agassiz by establishing the three great laws of succession,
which ought to bear his name, reduced this chaos to order and beauty;
and, therefore, he might justly be called the legislator of geological
history--the _lawgiver of time_. But, when asked the cause of these
laws, he could only answer, and did indeed answer, “The plans of the
Creator.” A noble answer and true, but not scientific. Darwin now comes
forward and gives, partly at least, the cause of these laws. He shows
that all these beautiful laws are explained by the doctrine of “origin
of species by derivation with modifications”; that these laws are
not ultimate, but derivative from more fundamental laws of life; and
thus biology is advanced one step, at least, toward the causal stage.
Newton and Darwin substituted second causes for first cause--natural
for supernatural. They each in his own department broke the bonds of
supernaturalism in the domain of Nature.

One more important reflection: There are two, and only two, fundamental
conditions of material existence--_space_ and _time_. There are,
therefore, two, and only two, cosmoses--space-cosmos and time-cosmos.
These have been redeemed from confusion and reduced to law and order
and beauty--changed from chaos to cosmos--by science. For this result
we are chiefly indebted, in the one case, to Kepler and Newton; in the
other, to Agassiz and Darwin. The universal law, in the one cosmos, is
the _law of gravitation_; in the other, the _law of evolution_. Traced
by analysis to its deepest roots of philosophic truth, the one law
may be called the divine mode of sustentation; the other, the divine
process of creation.

Or again: we have all heard of the “music of the spheres”--a beautiful
and significant name used by the old thinkers for the divine order of
the universe--a music heard not by human ear, but only by the attentive
human spirit. Harmonic relation apprehended by _reason_ we call _Law_,
and its embodiment Science; the same apprehended by the imagination
and æsthetic sense, we call _Beauty_, and its embodiment _Art_,
_music_. Now, in music there are two kinds of harmony, simultaneous
and consecutive--chordal harmony and melody. These must be combined
to produce the grandest effect. So in cosmic order, too, there are
two kinds of harmonic relation--the _co-existent in space_ and the
_consecutive in time_. The law of gravitation expresses the universal
harmonic inter-relation of _objects_ co-existent in space, the law of
evolution, the universal harmonic relation of _forms_ successive in
time. Of the divine spheral music, the one is the chordal harmony, the
other the consecutive harmony or melody. Combined they form the divine
chorus which “the morning stars sang together.”




PART II.

_EVIDENCES OF THE TRUTH OF EVOLUTION._




CHAPTER I.

GENERAL EVIDENCES OF EVOLUTION AS A UNIVERSAL LAW.


Let us again remind the reader that evolution means, first of all,
_continuity_. The law of evolution, although it doubtless means much
more, means, first of all, a law of continuity, or _causal relation
throughout Nature_. It means that, alike in every department of Nature,
each state or condition grew _naturally_ out of the immediately
preceding. In a word, it means that, in the course of Nature, nothing
appears suddenly and without natural cause, but, on the contrary,
everything is the natural and usually the gradual outcome of a previous
condition. This is _now_ admitted by every one in regard to _nearly_
everything: evolutionists apply it to the whole course of Nature.
I said this is _now_ admitted by every one in regard to _nearly_
everything; but this has not always been so. The world has come to its
present position on this subject only by a very gradual process. Let
us then trace rapidly the history of the gradual change, for it will
prepare us for much that follows.

There was a time (and that not many decades ago) when all things, the
origin of which transcends our ordinary experience, were supposed to
have originated suddenly and without natural process--to have been made
at once, out of hand. There was a time when, for example, mountains
were supposed to have been made at once, with all their diversified
forms, of beetling cliffs and thundering waterfalls, or gentle slopes
and smiling valleys, just as we now find them. But _now_ we know that
they have become so only by a very gradual process, and are still
changing under our very eyes. In a word, they have been formed by a
_process of evolution_. We know now the date of mountain-births; we
trace their growth, maturity, decay, and death; and find even, as it
were, the fossil bones of extinct mountains in the crumpled strata
of their former places. There was a time when continents and seas,
gulfs, bays, and rivers, were supposed to have originated at once,
substantially as we now see them. _Now_, we know that they have been
changing throughout all geological time, and are still changing. Not,
however, change back and forth in any direction indifferently and
without goal, but gradual change from less perfect to more perfect
condition, with more and more complex inter-relations--i. e., by a
_process of evolution_. We are able now, though still imperfectly,
to trace some of the stages of this evolution. There was a time when
rocks and soils were supposed to have been always rocks and soils; when
soils were regarded as an original clothing made on purpose to hide the
rocky nakedness of the new-born earth. God clothed the earth so, and
there an end. _Now_ we know that rocks rot down to soils; soils are
carried down and deposited as sediments; and sediments re-consolidate
as rocks--the same materials being worked over and over again, passing
through all these stages many times in the history of the earth. In
a word, there was a time when it was thought that the earth with
substantially its present form, configuration, and climate, was made
at once out of hand, as a fit habitation for man and animals. _Now_
we know that it has been changing, preparing, becoming what it is by
a slow process, through a lapse of time so vast that the mind sinks
exhausted in the attempt to grasp it. It has become what it now is
by a _process of evolution_. The same change of view has taken place
concerning the origin of all the heavenly bodies. We may, therefore,
confidently generalize--we may assert without fear of contradiction
that _all inorganic forms_, without exception, have originated by a
process of evolution.

The proof of all this we owe to geology--a science born of the present
century. This science establishes the law of _universal continuity_ of
events, through infinite _time_, as astronomy does that of _universal
inter-relation_ of objects through infinite _space_. How great the
change these two sciences have made in the realm of human thought!
Until the birth of modern astronomy the intellectual _space-horizon_
of the human mind was bounded substantially by the dimensions of
our earth; sun, moon, and stars, being but inconsiderable bodies
circulating at a little distance about the earth, and for our behoof.
Astronomy was then but the geometry of the curious lines traced by
these wandering fires on the concave blackboard of heaven. With the
first glance through a telescope the phases of Venus and the satellites
of Jupiter, revealed clearly to the mind the existence of other
worlds besides and like our own. In that moment the idea of _infinite
space_, full of worlds like our own, was for the first time completely
realized, and became thenceforward the heritage of man. In that moment
the _intellectual horizon of man was infinitely extended_. So also
until the birth of geology, about the beginning of the present century,
the intellectual _time-horizon_ of the human mind was bounded by six
thousand years. The discovery about that time of vertebrate remains,
all wholly different from those now inhabiting the earth, revealed
the existence of other time-faunas, besides our own and the idea of
infinite time, of which the life of humanity is but an epoch, was
born in the mind of man; and again the intellectual horizon of man
was infinitely extended. These two are the grandest ideas, and their
introduction the grandest epochs, in the intellectual history of man.
We have long ago accepted and readjusted our mental furniture to the
requirements of the one, but the necessary readjustment to the other is
not yet complete.

All inorganic forms, then, it is admitted, have come by evolution. But
how is it with organic or living forms? Let us see.

Every one knows, because it is within the limits of ordinary
experience, that every _individual_ organism _now_ originates and
gradually becomes what we see it, by a natural process--that is, by
evolution. If, then, there be any exception, it must be only the _first
of each kind_. But what kind? There are many kinds of kinds; classes,
orders, families, genera, species, varieties. Now, many of these kinds
can be shown to have become what we see them by a gradual process
similar, at least, to evolution. Take for example, classes. The class
of fishes and the class of reptiles are _now_ widely distinct and
have little in common except a vertebrate structure; but, as already
shown, page 12, this extreme difference has not always existed. On
the contrary, the earliest representatives of these two classes so
merged into one another that each seemed either. From this common stock
the two classes were gradually separated, each going its own way and
becoming more and more widely distinct even to the present day. There
can be no doubt, therefore, that _these two classes_, as we now know
them, _have become_ what they are by a gradual process. Again: In the
whole realm of Nature there is not a class more distinctly separate
from every other and without intermediate links than birds. But this
has not always been so. They have gradually become so. The earliest
birds were so reptilian in structure and appearance that if we could
see them now we would be in doubt whether we should call them birds or
reptiles. Birds have gradually separated themselves from the reptilian
stem, becoming more and more bird-like from age to age, until now, at
last, the two classes are wholly separated and the intermediate links
destroyed. So far as external characters are concerned, birds may be
said to have finally and wholly released themselves from entangling
alliance with any other class.

Classes, then, it will be admitted, have undoubtedly become what we
now know them by a very gradual process following laws identical (as
we have already seen, page 19) with the laws of evolution. Shall we
try orders? Of the class Mammalia there are two well-recognized and
widely-distinct _orders_, viz., the Carnivores and the Herbivores. We
all know how widely diverse these are in form, in structure, in habits,
and in food. Has it always been so? Have these been made so at once?
By no means. They have gradually become so. The earliest mammals were
neither the one nor the other distinctively. They were _omnivores_,
completely intermediate in food, habits, form, and structure. From this
common stock the two orders have gradually separated, the carnivores
becoming more and more adapted to one mode of life and the herbivores
to another, by a process following the laws of evolution, as already
explained. Shall we try _families_ and _genera_? Marsh and Huxley have
shown us how completely the horse family (_Equidæ_) and the horse-genus
(_Equus_) illustrate the process of gradual becoming and the law of
evolution. Under their guidance, we see that the earliest traceable
ancestor of the horse family, before it was distinctively a horse
family at all, had on the fore-foot five toes in the Lower Eocene,
four toes in the Upper Eocene, and three toes in the Miocene; then we
see the two side-toes shortening up more and more in the Pliocene and
becoming rudimentary splints, leaving only one toe in the Quaternary
and present epochs. Thus, the side-splints in the foot of the modern
horse tell the story of its three-toed ancestry. Similar gradual
changes are clearly traceable in size, shape, structure of limbs, of
teeth, and of brain. In all respects the members of the horse family
have become more and more horse-like in the course of time.

This subject will be taken up and more fully illustrated, under the
head of special evidences, in a subsequent chapter. We here touch it
only sufficiently to illustrate this universal law of gradual becoming.

We have taken only a few examples, but the same is undoubtedly true of
all Taxonomic groups _above species_. Passing over these last for the
moment, we take next _races_ and _varieties_. These smaller groups are
admitted by all to be formed by a natural process, because not only
can we make them artificially, but all the intermediate links may be
found in Nature. So we have only _species_ remaining. Yes; species are
imagined by the old-school naturalist and by the anti-evolutionist of
to-day as the _ultimate elements_ of Taxonomy. This, then, is the _last
ditch_ upon which the defense of supernaturalism in the realm of Nature
is made. “Other groups,” they say, “may have gradually become what they
now are by the successive introduction of specific forms according
to a preordained plan which is well expressed by the formal laws of
evolution. But _species_ are without transition forms. _They_ come in
suddenly, remain unchanged while they continue, and finally pass out
suddenly, so far as specific characters are concerned. New species come
in their places by direct act of creation--by _substitution_, not by
transmutation.” This, then, is the last intrenchment. Can we give any
good evidence of gradual formation of species? I believe we can.

First, then, it is admitted that we can easily make varieties and
races artificially. We will not _now_ describe the process; we are all
familiar with the results, viz., the varieties of domestic animals
and of useful and ornamental plants; the extremely different breeds
of horses, cattle, sheep, dogs, pigeons, etc.; of wheat, cabbages,
turnips; of roses, dahlias, etc., etc. No one will doubt that the
extreme varieties of any of these, say greyhound and pug, if wild,
would be called distinct species, or even distinct genera. We do not
call them so, for two reasons: first, because we see them made; and,
second, because we find all intermediate links between them; and the
usual definition of species is that they can not be made, and they have
no intermediate links. Thus, then, the question is narrowed down to
_wild species_. They say: “We take our stand on these” (surely a very
narrow ground for so broad a philosophy). “We defy you to show gradual
formation with intermediate links.”

Now, in fact, by diligent search such intermediate links between
well-recognized species have been found in some cases, especially in
birds, on account of their great power of dispersal. Certain forms
have long been known from widely-separated regions, and universally
regarded as distinct species, as distinct as any. Then, by minute
examinations of intermediate regions, a complete series of intermediate
forms has been picked up. This has occurred not only in one case but in
many cases, and not in birds only but in many other classes--examples
increase with our increasing knowledge.[11] The only answer to such
evidence is that _these are not true species_. Now, see the fallacy
lurking here! They define species as ultimate elements of taxonomy, as
distinct and without intermediate links, and then require us to find
such intermediate links; and, finally, when with infinite pains some
such links are found, they say: “Oh! I see; we were mistaken; they are
only varieties!!” It is true that naturalists, when intermediate links
are found, usually put all together as one species, but this they do
purely for the sake of clearness of definition and description. It is
freely admitted by the evolutionist that species are _now_ usually
distinct and without intermediate links, these having been destroyed in
the struggle for life. This will be fully explained in another chapter.
It is also freely admitted that although intermediate links must have
existed at one time, their remains are rarely found. The reason of
this will also be explained hereafter. Nevertheless, in some cases, as
already seen, we do find them still existing. Now, we add that in some
cases, where they no longer exist, we find them in the form of fossil
remains. The most remarkable example of this is found in the gradual
changes in the forms of Planorbis in the fresh-water deposits of
Steinheim, as shown by the admirable researches of Hyatt.[12] We shall
discuss these also more fully in another place. Now, if there be any
such links at all, however rare, then every objection to the derivative
origin of species is removed.

Perhaps it may be well to make bare mention of another kind of
evidence, viz., the actual change of species under the eyes, by
the action of change of environment. The different species of the
genus _Artemia_ (a low form of crustacean) live in brine-pools. By
concentrating the brine of such a pool, one species (_A. salina_)
has been observed to change in successive generations into another
(_A. Muhlhausenii_), and the latter back again to the former by slow
freshening.[13] Again: The siredon and the amblystoma have always,
until recently, been regarded as not only distinct species, but
distinct genera of amphibians. Siredon was supposed to be a permanent
gill-breather, while amblystoma becomes by metamorphosis a pure
air-breather. Now, however, it is known that the former may change into
the latter. But the most curious part of the life-history of these
animals, is that if water be abundant the siredon reproduces freely,
and remains indefinitely a gill-breather; but if the water dries up
it changes into the lung-breathing amblystoma. We do not give this
as examples of change of species, for the change is in the individual
life, and therefore in the nature of metamorphosis, but as evidence
of the power of physical conditions in modifying the development of
organic forms and therefore of the manner in which gill-breathers were
probably transformed into air-breathers.

To sum up: 1. All _inorganic_ forms, without exception, have become
what we find them by a natural process--i. e., by evolution. 2. All
_organic_ or living forms within the _limits of observation_, i. e.,
every living thing, has become what we now see, by a gradual, natural
process--i. e., by evolution. 3. All taxonomic groups, except species,
have undoubtedly become what we now see them by a gradual process,
following the laws of evolution, and therefore presumably by a natural
process of evolution. 4. By artificial means, breeds, races, etc., very
similar, at least in many respects, to species, are seen to arise by
a gradual natural process--i. e., by evolution. 5. In some instances,
at least, natural species are observed to pass into one another by
intermediate links in such wise that we are forced to conclude that
they have been formed by a natural process.

May we not, then, safely generalize, and make the law universal? Is
not this a sufficient ground for confident induction? Even though
some facts are still inexplicable, is that a sufficient reason for
withholding assent to a theory which explains so much? In all induction
we first establish a law provisionally from the observation of a
comparatively few facts, and then extend it over a multitude of facts
not included in the original induction. If it explains these also,
the law is verified. The law of gravitation was first based on the
observation of a few facts, and then verified by its explanation of
nearly all the facts of celestial motion. There are some outstanding
facts of celestial motion still unexplained, but we do not, therefore,
doubt the law of gravitation. The same principle applied in biology
ought to establish the law of evolution, for it also explains all
the facts of biology as no other law can. But inductive evidence
differs from other kinds of evidence in one respect, which, in fact,
constitutes its strength to the scientific, but its weakness to the
popular mind. It is a kind of circumstantial evidence, but its force
does not consist in a few strong circumstances easily appreciated,
such as strike the popular mind, and force conviction, but rather in a
multitude of small circumstances, each by itself insignificant, but all
together pointing to one conclusion and demanding one explanation. Such
evidence is, indeed, overwhelming, but only to the mind that masters
it. The evidence for the law of gravitation is literally the whole
science of astronomy. So also the evidence for the law of evolution
is the whole science of biology. Neither of these laws can be proved
in a debating society, but only by a course of study. In the one case
the law has been universally accepted--not, however, on evidence, for
there are few indeed who appreciate the evidence, but on the authority
of scientific unanimity. In the other case there has not yet been time
enough for the already established unanimity to have its full effect.

Thus much, we believe, will be generally admitted as a very moderate
claim. Evolution is certainly a legitimate induction from the facts
of biology. But we are prepared to go much further. We are confident
that evolution is _absolutely certain_. Not, indeed, evolution as a
special theory--Lamarckian, Darwinian, Spencerian--for these are all
more or less successful modes of explaining evolution; nor evolution
as a school of thought, with its following of disciples--for in this
sense it is still in the field of discussion--but evolution as a law
of derivation of forms from previous forms; evolution as a law of
continuity, as a universal law of becoming. In this sense it is not
only certain, it is axiomatic. It is only necessary to conceive it
clearly, to see that it is a necessary truth. This may seem paradoxical
to some. I stop to justify it.

Physical phenomena we all admit follow one another in unbroken
succession, each derived from a preceding, and giving origin to a
succeeding. We call this the law of causation, and say that it is
axiomatic. We might call it a law of derivation. So also organic
_forms_ follow one another in continuous chain, each derived from a
preceding and giving origin to a succeeding. We call this a law of
derivation. We might call it a _law of causation_, and say that it too
is axiomatic. The origins of new phenomena are often obscure, even
inexplicable, but we never think to doubt that they have a natural
cause; for so to doubt is to doubt the validity of reason, and the
rational constitution of Nature. So also the origins of new organic
_forms_ may be obscure or even inexplicable, but we ought not on that
account to doubt that they had a natural cause, and came by a natural
process; for so to doubt is also to doubt the validity of reason, and
the rational constitution of organic Nature. The law of evolution
is naught else than the scientific or, indeed, the rational mode of
thinking about the origin of things in every department of Nature. In
a word, it is naught else than the law of necessary causation applied
to _forms_ instead of phenomena. Evolution, therefore, is no longer
a school of thought. The words _evolutionism_ and _evolutionist_
ought not any longer to be used, any more than _gravitationism_ and
_gravitationist_; for the law of evolution is as certain as the law of
gravitation. Nay, it is far more certain. The nexus between _successive
events in time_ (causation) is far more certain than the nexus between
_coexistent objects in space_ (gravitation). The former _is a necessary
truth_, the latter is usually classed as a contingent truth. I have
used and may continue to use the term evolutionist, but if so it is
only in deference to the views of many intelligent persons, who do not
yet see the certainty of the law.




CHAPTER II.

SPECIAL PROOFS OF EVOLUTION.

_Introductory._


It will be seen from the preceding chapter that we regard the law of
evolution in its wider sense, viz., the derivative origin of all forms,
organic or other, as axiomatic, and therefore requiring no further
proof. Among scientific men there is no longer any discussion of the
truth of this law, but only of the theories of the causes of the law.
We believe that to the scientific mind there is no other rational mode
of looking at the subject of origin of organic forms. To such a mind,
therefore, all that follows is but the deductive application of that
law in the explanation of the phenomena of organic Nature. But it takes
time for the popular mind to readjust itself to new and revolutionary
truth. Many minds, even among the most intelligent, have not yet
accepted this as the only rational mode of thought. Many men require
further _special proofs_ of the derivative origin of organic forms.
Even to those who accept evolution, these proofs will be interesting
as illustrations of such origin. We will attempt to bring out these
proofs under several heads, the most important of which are: 1. Proofs
from morphology, or the general laws of animal structure; 2. Proofs
from embryology; 3. Proofs from geographical distribution of organic
forms; and, 4. Proofs from artificial breeding. The subject is so vast
that all we can do is to touch lightly only the most salient points
under each of these heads; for, as we have already said, the evidence
is really nothing less than the whole science of biology. Preparatory
to this, however, it is necessary to bring out a little more fully than
before (page 29), though still only in outline, the two antagonistic
views, which may be called the old and the new, or the natural and the
supernatural, of the origin of new organic forms, especially species.

=Origin of New Organic Forms; the Old View briefly stated.=--According
to the old-school naturalists, species are the ultimate elements of
taxonomy: genera, families, orders, etc., may gradually change their
character from age to age, by the introduction of new species; but
species were supposed to be substantially _permanent_. It was necessary
to have some unit for convenience of description and classification,
and this was found to be the best because most stable. As in nearly
all cases of beliefs, this doctrine was held at first somewhat
loosely, as a provisional and convenient view--as a good working
hypothesis--but gradually, under pressure of controversy, became more
strictly formulated, and, as it were, hardened into a scientific
dogma, especially in the hands of Agassiz. According to this view,
the first pair or pairs of each specific kind originated we know not
how, but certainly _at once in its present form_ in full perfection,
and, therefore, presumably by _direct creative_ act of Deity; and then
afterward by the law of generation continued to produce others of the
same pattern indefinitely. Moreover, the first one or more pairs of
each kind multiplied and spread abroad in every direction, _each from
its own center of origin_, as far as physical conditions and struggle
for life with other species would allow. This idea explains tolerably
well the geographical distribution of species as we now find it. For
example, species on different continents are widely different, because
those on each have originated independently where we now find them, and
spread in all directions as far as physical conditions would allow, but
could not reach other continents because of the ocean-barrier. That
this is the only reason they are not there, is shown by the fact that,
if they are carried there, they usually do perfectly well. Even on the
same continent, for the same reason, species may be very different
if separated by impassable barriers such as high mountain-chains or
by climate. But wherever one group of species, originating in one
place, comes in contact on the margin of their range with another
group of species originating in another place, we see no evidence of
_transmutation_ of one form _into_ another, but only _substitution_ of
one fully-formed species _for_ another equally fully formed. Therefore,
we must conclude that physical conditions may limit the range of a
species, but can not transmute it into another. Thus, to say the least,
many of the facts of geographical distribution are well explained
by this idea of creative origin in specific centers and subsequent
permanence of specific form. We say _many_ of the facts; we will show
hereafter that _not all_ can be thus explained.

But the main question is not of geographical but of geological
distribution; not distribution in space, but succession in time.
Species do not continue forever. On the contrary, they have changed
many times in the course of geological history. As conditions become
unfavorable, species die out or become extinct, and others take their
place and carry forward the life and development of the organic
kingdom. Now, how do they change? According to this school of thought,
here also, as in geographical distribution, they are not transmuted
but replaced; here also physical conditions may destroy a species,
but can not transform it into another. As species die out, others are
created at once, out of hand and fully formed in their place; but in
accordance with a preordained plan consistently carried out and working
ever toward higher and higher conditions. Thus, life is continued on
the earth by the alternation of supernatural and natural processes; by
the alternate use of direct and indirect action of Deity: direct in
the introduction of first pairs, indirect through the natural process
of reproduction in the continuance and multiplication of the species.
Each species is made according to a pattern in the Divine mind, on a
sort of intellectual die, and then continues to reproduce a succession
of individuals of the same pattern as if struck from the same die
until the die is broken or worn out. Another die is made, of another
pattern, and individuals are struck from this; and so on, throughout
the whole geological history of the organic kingdom. Only, we must
add that the successive dies are made to follow one another according
to a plan which is expressed by the three laws already given on page
11. Thus, the origin of individuals is natural, the origin of species
supernatural; the making of dies is supernatural, the coinage is
natural.

We have stated this view in a too extreme form, in order to make it
clearer. We now, therefore, proceed to qualify somewhat. Specific types
were held, by writers of this school of thought, to be _substantially_
but not absolutely unchangeable. Successive individuals of the same
species were admitted to be not exactly alike. Such slight differences
were called _varieties_. It was admitted, indeed, that species
varied, but it was believed that such variations in any direction
were strictly limited in amount. A species may be compared to a right
cylinder standing on end. As such a cylinder may be tilted slightly
in one direction or another, without overthrowing its equilibrium,
the cylinder tending ever to right itself and return to its original
position, so a species may be varied slightly in one direction or
another without destroying its integrity, the species tending ever to
return to its normal or typical form. But as the cylinder, if pushed
too far from its normal position, is overthrown, so also a species,
if pressed too far in the way of variation from its typical form, is
destroyed, but not changed into another species. As cylinders may be
more or less rigid, depending upon the breadth of their bases, so also
some species are more rigidly set in their typical form, and some are
more plastic to influences causing variations, but in all cases there
is a limit to the amount of oscillation consistent with integrity.

=The New View briefly stated.=--According to Darwin, and all biologists
of the present day, species are variable _without limit_, if only the
causes of change are constant and slow enough in their operation,
and the time long enough. A species must be in harmony with its
environment, for this is the condition of its existence. Now, if the
environment change, the species must _tend_ to change slowly from
generation to generation, so as to readjust its relations in harmony
with the changing environment. If the change of environment be slow,
the readjustment may be successful, and the species will change
gradually into another form, so different that it will be called
a different species, especially if the intermediate gradations be
destroyed. If the change in the environment be too rapid, many species,
especially the more rigid, will be destroyed, while the more plastic
may survive by modification. Thus, at every step in the evolution
of the organic kingdom, some species have died without issue, while
others have saved themselves by changing into new forms in harmony
with the new environment. Comparing to a growing tree, some branches
overshadowed die, while others push on for light, forming new lateral
buds, and dividing as they grow. By continued divergent change species
gradually become genera, genera families, etc. Thus, varieties,
species, genera, families, orders, classes, etc., are only different
degrees of differences formed all in the same way. Varieties are only
commencing species, species commencing genera, and so on. There is
no making and wearing out of dies, and making of new ones; the whole
process is a natural one--the whole series is genetically connected. In
a perfect classification varieties, species, genera, families, orders,
classes, etc., are only different _degrees of blood-kinship_.

So much may be regarded as certain, and out of the field of discussion
among biologists of the present day. It is only in defining this
process more accurately, and especially in the _theory of the causes_
or _factors_ of evolution, that there are still difference and
discussion. The most probable view on this subject we now proceed to
give.

=Factors of Evolution.=--The causes of change or adaptive modification,
or the factors of evolution, are at least _four_ well known, and
probably many more still unknown: 1. The physical environment--heat and
cold, dryness and moisture--affects function of organs, and function
affects structure, and both changed function and changed structure are
inherited by offspring, and so increased from generation to generation,
becoming greater without limit. 2. Increased _use_ or _disuse_ of
organs enforced or permitted by change in the environment, physical
or organic, or both, induces change in form, size, and structure of
the organs; and this change is inherited by the offspring, and so
from generation to generation small differences are integrated until
they become great without limit. These two factors were recognized
by Lamarck. 3. “Natural selection,” or “survival of the fittest,”
among divergent varieties of offspring. This is the distinctive
Darwinian factor. In the two preceding factors the change is during
the _individual lifetime_, and reproduction is supposed to transmit
it unchanged to the offspring. In this factor, on the contrary,
the form and structure are supposed to remain unchanged during the
individual life, but for some unknown cause there are slight variations
in different directions (divergent) in the offspring from the same
parents. Now, when we remember that by reproduction the number of
individuals tends to increase by geometrical progression, and that
in each generation only a very few (on an average only two from all
the offspring of one pair) can survive, it is evident that among
these divergent varieties those will most likely survive which are
most in harmony with the external environment, and which possess the
most efficient organs of defense or of escape, or for food-taking.
The surviving offspring, therefore, will be on the average better in
these respects than their parents. It matters not how little better,
for the integration of even infinitesimal improvements from generation
to generation will eventually produce any required amount of change.
4. To the above Darwin has added also “_sexual selection_.” In
_natural_ selection there is struggle of _all_ for _food_, or _means
of living_. In sexual selection there is a struggle among the _males_
for possession of the _female_, and the _means of procreation_. The
one is connected with the nutritive appetite, the other with the
reproductive appetite. This mode of selection acts in two ways, by the
law of battle and the law of attractiveness. The strongest or the most
attractive males alone, or mainly, leave offspring, which, of course,
inherit their peculiarities; and these are increased indefinitely
by integration through successive generations, thus increasing the
strength or the beauty. Of these two laws, the law of battle is most
conspicuous among mammals, and the law of attractiveness among birds.
It is evident that this factor can not operate among many lower animals
which are hermaphroditic, nor among plants.

Of these acknowledged factors of evolution, the first two were known
to Lamarck and the older evolutionists. The third and fourth are
distinctively Darwinian. According to Darwin, while all these are
operative, the third is the most powerful; but Spencer accords this
distinction to the Lamarckian factors. Many American zoölogists take
the same view.

Such until very recently were all the recognized factors of evolution.
But, within the past year (1886) has taken place, it seems to us,
the most important advance in the theory of evolution since Darwin.
It is the suggestion by Mr. Catchpool,[14] and afterward the more
full elaboration by Dr. Romanes, of another factor, which he calls
“_physiological selection_.”[15]

The great objections to the sufficiency of the theory of evolution,
as left by Darwin, were twofold: 1. While natural selection accounts
completely for the formation of _useful_ structures or adaptive
modifications, and therefore for differences characterizing classes,
orders, families, and even genera--for these are all adaptive--it
can not so completely account for those constituting species; for
these consist mostly of _trivial_ differences in coloration, relative
proportion of parts, which are of _no perceivable use_ in the struggle
for life, and therefore could not be preserved and integrated by
natural selection. Therefore, according to Romanes, natural selection
is a theory of origin of adaptive structures rather than of origin of
species. Comparing to a growing tree, once admit lateral buds started,
and natural selection completely accounts for the growth in different
directions, and therefore for the profuse ramification; but the origin
of the lateral buds is not explained.

2. The second difficulty is as follows: Such commencing differences as
constitute varieties and species not only would not be preserved and
integrated by natural selection unless useful, but would immediately
be _swamped by cross-breeding_ with the parental form. But, as the
whole divergence commences in varieties, evidently it could not
commence at all unless this cross-breeding be in some way prevented.
This may, indeed, be done, without the assumption of any new factor
of evolution, by _migration_; and, hence, migration must be regarded
as an important agent in the creation of new forms, not only by the
effect of a new environment, but also by prevention of the swamping of
commencing species by cross-breeding with the parental form; but in a
crowded locality, without outlet for migration (the very conditions
most favorable for severe competitive struggle, and therefore for
most potent operation of natural selection; and therefore, also,
according to Darwin, for profuse diversification), commencing varieties
could not pass into species, because swamped by cross-breeding.
Once the divergence reaches the point of cross-sterility--i. e., of
species--then, indeed, by true breeding, characters, even though not
useful, may be preserved. But how is it to commence?

This difficulty has been severely felt by all Darwinists. It seems to
us that it is largely met by Dr. Romanes. According to Romanes, no
organ is so subject to varietal changes as the _reproductive_, and
these in no respect so much as in degrees of fertility. Unfortunately,
these changes are not visible, and must be judged of only by the
results. It is not uncommon, for example, to find sterility between
individuals (sexual incompatibility) who are both of them perfectly
fertile with other individuals. Similarly, cross-sterility, partial
or complete, is not uncommon between varieties or races, as Mr.
Darwin has long ago noticed. It very generally, as we know, occurs
between, and, in fact, is constantly used as a test of, species. Now,
this cross-sterility with parent stock, which we find so constant a
character of species, and which, therefore, must _have commenced as a
partial cross-sterility_ in varieties, is it _antecedent or consequent
to other variations_? It has been usual to suppose it consequent
to a certain amount of divergence, viz., that which constitutes,
or at least approaches, species. But, according to Romanes, it is
_antecedent_. Among many other variations, this is that one which
originates species, because it prevents reversion by cross-breeding
with the parent stock, and insures true breeding with its own kind.
In a word, it sexually isolates the species. Suppose, then, a species
multiplying indefinitely in one locality: trivial variations of many
kinds, and in many directions, occur among the offspring. These are
merged by cross-breeding into the original type, which, therefore,
remains unchanged. But, from time to time, among these variations
there occur some affecting the reproductive organs in such wise as to
produce partial or complete cross-sterility with the parent form. This
is the beginning of a new species. It breeds true with its own kind,
and therefore all the associated variations external and visible, and
therefore constituting species, although trivial and of no use in the
struggle for life, are preserved.

This view completely accounts for the cross-fertility of artificial
breeds equivalent in other respects to species; for cross-sterility
is not an end aimed at by the breeder, it being easy to prevent
cross-breeding, if desired, by artificial isolation. But, if this view
be true, species from widely-different geographical regions ought also
to be often cross-fertile, because, having been formed by geographical
isolation, sexual isolation was not a necessary factor in their
formation. This point deserves testing by careful observation.

It may be, and has been, objected to Dr. Romanes’s claims, that this is
no new factor; that physiological selection is only a form of natural
selection. This objection, it seems to us, is little more than a play
upon words. It certainly is selection, and by a _natural_ process,
and therefore in some sense a natural selection, but not in the sense
of Darwin. It is not a selection of individuals _fittest to survive_;
for cross-fertile individuals are as fit to survive as individuals,
though not as species, as are cross-sterile. Natural selection is
intent only on preserving the best individuals; physiological selection
on preserving the kind. Natural selection continues the direction of
progress unchanged; physiological makes new directions.

In addition to all these factors of _organic_ evolution, there is still
another far higher factor characteristic of man alone. This is the
_conscious, voluntary co-operation of the thing evolving--the spirit
of man--in the work of its own evolution_. This may be called the
_rational factor_. This, the most important factor of human evolution,
is usually ignored by writers on evolution--either as non-existent,
or else as lying beyond the domain of science. We will emphasize its
importance by taking it up more fully in the next chapter.

It will be observed that Darwin and his followers take divergent
variations of offspring simply as a known fact, upon which natural
selection operates to produce progressive modification; and, as the
cause of variation in offspring is wholly unknown, such variations are
often spoken of as fortuitous. But, of course, it is well understood
that nothing in Nature is really fortuitous. They may, however, for
all purposes of natural selection be thus regarded until we know
their cause. It is evident, then, that if we, with Darwin, take
natural selection, as the most important known factor, the really most
important cause of evolution is the _cause_ of varieties. This is the
_unknown_ fundamental factor. As Darwin reduced Agassiz’s three formal
laws of succession to more general laws of life, and thus made one
important step in the advance of biological science, so he who shall
explain the _cause_ of divergent variation will make another important
step by reducing the phenomena to still more general and fundamental
laws of life.

In conclusion, let me again impress upon the reader that all the doubt
and discussion, above described, as to the factors of evolution, is
entirely aside from the truth of evolution itself, concerning which
there is no difference of opinion among thinkers.




CHAPTER III.

THE GRADES OF THE FACTORS OF EVOLUTION AND THE ORDER OF THEIR
APPEARANCE.


We have given in the previous chapter six factors of evolution--viz.:
1. _Pressure of the environment._ 2. _Use and disuse of parts._
3. _Natural selection._ 4. _Sexual selection._ 5. _Physiological
selection._ 6. _Reason._ Let us now compare these as to their grade in
the scale of energy and as to the order of their introduction.

The first two or the Lamarckian factors are the lowest in position,
the most fundamental and universal, and therefore the first in
the order of appearance. They precede all other factors, and were
doubtless for a long time _the only ones in operation_. For, observe,
all the selective factors--i. e., those of Darwin and Romanes--are
conditioned on reproduction; for the changes produced by these are
not in the individual during life, but in the offspring at birth.
And not only so, but the operations of these factors are further
conditioned on _sexual modes_ of reproduction; for all the non-sexual
modes of reproduction--as, for example, by fissure and by budding--are
but slight modifications of growth, and the resulting multitude of
organisms may be regarded as in some sense _only an extension of the
first individual_. Of course, therefore, the identical characters of
the first individual are continued indefinitely, except in so far
as they are modified in successive generations by the effect of the
environment and by use and disuse--i. e., by the Lamarckian factors.
In sexual generation, on the contrary, the characters of two diverse
individuals are funded in a common offspring; and the same continuing
through successive generations, it is evident that the inheritance in
each individual offspring is infinitely multiple. Now, the _tendency
to variation_ in offspring _is in proportion to the multiplicity of
the inheritance_: for among the infinite number of slightly differing
characters, as it were, offered for inheritance in each generation,
some individuals will inherit more of one and some more of another
character. In a word, sexual reproduction by multiple inheritance
_tends to variation of offspring, and thus furnishes material for
natural selection_.[16]

Thus, then, I repeat, all the selective factors are absolutely
dependent on sexual modes of reproduction. But there was a time when
this mode of reproduction did not yet exist.[17] The sexual modes
developed out of non-sexual modes. If these non-sexual preceded sexual
modes of reproduction, it is evident that at first only Lamarckian
factors could operate. Evolution was then carried forward wholly
by changes in the individual produced by environment and by use and
disuse (acquired characters), inherited and increased by integration
through successive generations indefinitely. It is probable, therefore,
that the _rate_ of evolution was at first comparatively slow; unless,
indeed, as seems probable, the _earliest_ forms _were then_ and the
_lowest_ forms _are now_ more plastic under the influence of physical
conditions than are the present higher forms. Doubtless, now, in the
higher animals and plants, the Darwinian factors are by far the most
potent; for, among plants, where we can use these factors separately,
if we wish to _make_ varieties, we propagate by seeds (sexual
reproduction); but, if we wish to preserve varieties, we propagate by
buds and cuttings (non-sexual reproduction).

I have taken the two Lamarckian factors together, and showed that they
preceded the Darwinian. But even in the two Lamarckian factors there is
a difference in grade. Undoubtedly the lowest, the most fundamental,
and therefore the first introduced, was _pressure of the physical
environment_. For use and disuse of organs implies some degree of
volition and voluntary motion, and therefore already some advance in
the scale of evolution.

With the introduction of sex another entirely different and higher
factor was introduced, viz., _natural selection_, or selection of
the fittest individuals of a varying progeny. We have already seen
how sexual generation produces variation of offspring, and how this
furnishes materials for natural selection. As soon, therefore, as this
form of generation was evolved, this higher factor came into operation
and immediately assumed control; while the previous factors became
subordinate, though still underlying, conditioning, and modifying the
activity of the higher. The result was an immediate increase in the
rate of evolution. It is very worthy of note that it is in the higher
animals, such as birds and mammals, in which we have only the highest
forms of sexual reproduction, where the diversity of characters of
the two sexes funded in the offspring is the greatest, and where,
therefore, the variation in offspring is also greatest and natural
selection most active; it is precisely among these that the Lamarckian
factors are most feeble, because, during the most plastic period of
life, the offspring is removed from the influence of the physical
environment, and from use and disuse by its inclosure within the womb,
or within a large egg surrounded with abundant nutriment. Development
is already well advanced before Lamarckian factors can operate at all.

Next, I suppose, physiological selection, or Romanes’s factor, came
into operation. After the introduction of sex, it became necessary that
the individuals of some varieties should be isolated in some way, so
as to prevent the swamping of varietal characters, as fast as formed,
in a common stock, by _cross-breeding_. In very low forms, with slow
locomotion, such isolation might easily take place accidentally. Even
in higher forms, changes in physical geography or accidental dispersion
by winds and currents would often produce geographical isolation,
and thus, by preventing crossing with the parent stock, secure the
formation of new species from such isolated varieties. But, in order
to insure in all cases the preservation of commencing species, _sexual
isolation_, or partial or complete infertility of some varieties
with other varieties and with the parent stock, was introduced, as
I suppose, later. The process by which this takes place has already
been explained. According to Romanes, natural selection alone, with
cross-breeding, tends to _monotypal_ evolution; isolation of some kind
is necessary for polytypal evolution. The tree of evolution, under
the influence of natural selection alone, grows, palm-like, from its
_terminal bud_; isolation of varieties was necessary for the starting
of _lateral buds_, and thus for the profuse ramification which is its
most conspicuous character.

Next, I suppose, was introduced _sexual selection_, or contest among
the males, by battle or by display, for possession of the females,
and the success of the strongest or the most attractive; and the
perpetuation and increase of these superior qualities of strength
and beauty in the next generation. This, I suppose, was later,
because connected with a higher development of the psychical nature.
This is especially true where splendor of color or beauty of song
determines the selection. As might be supposed, therefore, this factor
is operative only among the highest animals, especially birds and
mammals.[18]

Next and last, and only with the appearance of _Man_, another entirely
different and far higher factor was introduced, viz., _conscious,
voluntary co-operation_ in the work of his own evolution--a conscious,
voluntary striving to _attain an ideal_. We have called this a factor,
but it is much more than a mere factor, co-ordinate with other factors.
It is, rather, a different kind of evolution. It is evolution on
a higher plane and by another nature. As _physical_ Nature works
_unconsciously_, using certain factors, so _spiritual_ nature works
_consciously_, co-operating and using the same factors. At first this
factor, if we still call it so, was extremely feeble. In the early
stages of his progress, man, like other animals, was largely urged
on by forces of organic evolution, unknowing and uncaring whither
he tended. But more and more, as civilization advances, this higher
and distinctively human factor becomes more and more dominant, until
now, in civilized communities, it takes control of evolution. Reason,
instead of Nature, now assumes control, though still using the methods
and factors of Nature. This _free_, self-determined evolution of the
race, in order to distinguish it from the _necessary_ evolution of the
organic kingdom, we call progress.

Now, in this whole process we observe two striking stages. The one is
the introduction of sex, the other is the introduction of reason.[19]
They may be compared to two equally striking stages in the development
of the _individual_. As the _ontogenic_ evolution receives fresh
impulse at the moment of fertilization, so the evolution of the organic
kingdom receives fresh impulse at the moment of introduction of sex. As
in ontogenic evolution the individual at birth enters upon a new and
higher plane, in which it co-operates in its own _physical_ growth,
so the organic kingdom, with the introduction of man, enters upon a
new and higher plane, in which man co-operates in the physical and
_spiritual_ growth of the race. With sex three new and higher factors
were introduced, and these immediately assumed control and quickened
the rate of evolution. With reason another and infinitely higher factor
is introduced, which, in its turn, assumes control, and not only again
quickens the rate, but elevates the whole plane of evolution. Moreover,
this voluntary, rational factor not only takes control itself, but
transforms all other factors and uses them in a new way and for its own
higher purposes.

This last is by far the greatest change which has ever occurred in
the history of evolution. In organic evolution Nature operates by
necessary law without the conscious voluntary co-operation of the thing
evolving. In human progress man voluntarily co-operates with Nature in
the work of evolution, and even assumes to take the process mainly into
his own hands. Organic evolution is by _necessary_ law, human progress
by _free_ or at least by freer law. Organic evolution is by a _pushing_
upward and onward from _below_ and _behind_, human progress by a
_drawing_ upward and onward from above and in front by the attractive
force of ideals. In a word, organic evolution is by the law of _force_,
human evolution by the law of _love_.

It may be well to stop a moment and show briefly some of the
differences between organic and human evolution--differences which are,
of course, wholly the result of the introduction of this new factor:

1. In organic evolution “_the fittest_” are those most in harmony
with the physical environment, and therefore they survive. In human
evolution _the fittest_ are those most in harmony with _the ideal_, and
often, especially in the early stages, when the race is still largely
under the dominion of organic factors, they do not survive, because
not in harmony with the social environment. But, although the fittest
individuals may indeed perish, the _ideal_ survives in the race and
will eventually triumph.

2. In organic evolution the weak, the sick, the helpless, the unfit
in any way perish and _ought to perish_, because this is the most
efficient way of strengthening the _blood_ or _physical nature_ of the
species, and thus of carrying forward evolution. In human evolution
the weak, the helpless, the sick, the old, the unfit in any way are
sustained and _ought to be sustained_, because sympathy, love, pity,
strengthen the _spirit_ or _moral nature_ of the race. But let us
remember that in this material world of ours and during this earthly
life the spirit or moral nature is conditioned on the physical nature;
and, therefore, in all our attempts to help the weak we must be careful
to avoid poisoning the blood and weakening the physical vigor of the
race by inheritance. This gravest of social problems, viz., How shall
we obey the higher law of love and mutual help without weakening the
_blood_ of the race by inheritance and the spirit of the race by
removing the necessity of self-help?--this problem, I believe, can and
will be solved by a _rational education_, physical, mental, and moral.
I only allude to this. It is too wide a field to follow up here.

3. In organic evolution the bodily _form_ and _structure_ must
continually change in order to keep in harmony with the ever-changing
environment. In other words, organic evolution is by continual change
of species, genera, families, etc. There must be continual evolution
of new forms by modification. In human evolution, on the contrary, and
more and more as civilization advances, man modifies the environment so
as to bring it into harmony with himself and his wants, and therefore
there is no necessity of change of bodily form and structure or
making of new species of man. Human evolution is not by modification
of _form_--new species; but by modification of spirit--new planes of
activity, _higher character_. And the spirit is modified and character
elevated, not by _pressure_ of an _external physical environment_, but
by the _attractive_ force of an _internal spiritual ideal_.

4. The way of evolution toward the highest--i. e., from protozoan
to man and from lowest man to the ideal, the divine man--is a very
_straight and narrow way_, and few there be that find it. In the
case of organic evolution it is so straight and so narrow that any
divergence therefrom is fatal to upward movement toward man. Once get
off the track, and it is _impossible_ to get on again. No living form
of animal is on its way _manward_, or can by any possibility develop
into man. They are all gone out of the way. There is none going right;
no, not one. The organic kingdom developing through all geological
times may be compared to a tree whose trunk is deeply buried in the
lowest strata, whose great limbs were separated in early geological
times, whose secondary branches diverged in middle geological times,
and whose extreme twiglets, and also its graceful foliage, its
beautiful flowers, and luscious fruits, are the fauna and flora of
the present day. But this tree of evolution is an _excurrent stem_,
continuous through the clustering branches to the terminal shoot--man.
Once leave the stem as a branch, and it is easy to continue growing in
the direction chosen, but impossible to get back on the straight upward
way to the highest. In human evolution, whether individual or racial,
the same law holds, but with a difference. If individual or race gets
off the straight, narrow way toward the highest--the divine ideal--it
is hard, very hard to get back on the track. Hard, I say, but _not_
impossible, because man’s conscious voluntary effort is the chief
factor in his own evolution. By virtue of self-activity, through the
use of reason and co-operation in the work of evolution, man alone of
all created things is able to rectify an error of direction and return
again to the deserted way.

5. In organic evolution, when a higher factor appears, it immediately
assumes control, and previous lower factors sink into a subordinate
position, though still underlying and conditioning the higher. But in
human evolution, the higher rational factor, when it comes in with
man, not only assumes control, but transforms all other factors and
uses them in a new way and for its own higher purposes. In fact, as
already said, it is much more than a mere factor. It determines a
new kind of evolution--evolution on a new and higher plane though,
indeed, underlaid and conditioned by the laws of organic evolution. As
_external physical_ Nature uses many factors to carry forward organic
evolution, so the _internal spiritual_ nature, characteristic of man
alone, uses these same factors in a new way to carry forward human
evolution or progress. Thus, for example, one organic factor--the
environment--is modified or even totally changed so as to effect
suitably the human organism. This is _hygiene_. Again, use and
disuse--another factor--is similarly transformed. The various organs of
the body and faculties of the mind are deliberately used in such wise
and degree (determined by reason) as to produce the highest efficiency
of each part and the greatest strength and beauty of the whole. This
is _education_--physical, mental, moral. So also the selective factors
are similarly transformed, and _natural_ selection becomes _rational_
selection. We all know how this method is applied to domestic animals
and cultivated plants in the formation of useful or beautiful
varieties. Why should it not be applied also to the improvement of our
race in the selection of our mates in marriage, or in the selection of
our teachers, our law-makers, our rulers? Alas! how little even yet
does reason control our selection in these matters! How largely are we
yet under the law of organic evolution!

_Application of these principles to some questions of the day_:

I. Evolution, as a law of derivation of organic forms from previous
forms by descent with modifications, as already shown, is as certain
as the law of gravitation. This question has passed beyond the realm
of doubtful discussion; but the causes, the factors, the details of
the process of evolution are still under discussion. Both Darwin and
Spencer, the two great founders of the theory of evolution in its
modern form, acknowledge and insist on at least four factors, viz., the
two Lamarckian and the two distinctively Darwinian. The only difference
between them is in the relative importance of the two sets: Spencer
regarding the former and Darwin the latter as the more potent. But in
these latest times there has arisen a class of biologists, including
some of highest rank, such as Wallace, Weismann, and Lankester, who
out-Darwin Darwin himself in their exaltation of the most distinctive
Darwinian factor, viz., natural selection. They try to show that
natural selection is the sole and sufficient cause of evolution; that
changes in the individual, whether as the effect of the environment or
by use and disuse of organs, are not inherited at all; that Lamarck was
wholly wrong; that Darwin (in connection with Wallace) was the sole
founder of the true theory of evolution; and, finally, that Darwin
himself was wrong only in making any terms whatever with Lamarck. This
view has been called _Neo-Darwinism_.

Perhaps the reasons for this view have been most strongly put by
Weismann, and are based partly on experiments, but mainly on his
ingenious and now celebrated theory of the immortality of germ-plasm.
The animal body consists of two kinds of cells wholly different in
function--somatic cells and germ-cells, including in this last the
sexual elements both male and female. Somatic cells are specially
modified for the various functions of the body; germ-cells are
wholly unmodified. The somatic cells are for the conservation of
the _individual_ life, the germ-cells for the conservation of the
_species_. In the development of the egg the germ-cell multiplies
itself into a cell-aggregate, and then most of the resulting multitude
of cells are modified in various ways to form the tissues and organs
of the body--somatic cells; but a few are reserved and put aside
in an unmodified form in the sexual organs as germ-cells, to again
produce ova which again divide into somatic and germ-cells, and so on
indefinitely. Now, according to Weismann, inheritance is only through
_germ-cells_, while the environment affects only the _somatic cells_.
Therefore changes produced by the environment can not be inherited.
Sexual modes of generation were introduced for the purpose of producing
variability in progeny, and thus furnishing material for natural
selection, as this was the only means of evolutionary advance. Weismann
made many experiments on animals, especially by mutilation, to show
that somatic changes are not inherited.

A full discussion of this question would be unsuitable in a work like
this. We will therefore content ourselves with making three brief
remarks:

_a._ If the views presented in the early part of this chapter are true,
then the Lamarckian factors must be true factors, _because there was
a time when there were no others_. They were therefore necessary, at
least to start the process, even if no longer necessary at present.

_b._ But if these factors were ever operative, _they must be so
still_, though possibly in a subordinate degree. A lower factor is
not abolished, but only becomes subordinate to a higher when the
latter is introduced. Thus it may well be that Lamarckian factors are
comparatively feeble at the present time and among living species,
especially of the higher animals, and yet not absent altogether. In the
earliest stages of evolution there was a _complete identification of
germ-cells and somatic cells_--of the individual with the species. In
such cases, of course, any effect of the environment must be inherited
and increased from generation to generation. But the differentiation
of the germ and somatic cells was not all at once, nor is their
sympathetic relation completely severed. It was a _gradual process_,
and therefore the effect of the environment _on the germ-cells through
the somatic cells_ continued, though in decreasing degree, and still
continues. The differentiation in the higher animals is now so complete
that germ-cells are probably not at all affected by changes in somatic
cells, unless these changes are _long continued in the same direction,
and are not antagonized by natural selection_.

_c._ It is a general principle of evolution that the _law of the whole
is repeated with modifications in the part_. This is a necessary
consequence of the unity of Nature. We ought to expect, therefore,
and do find, that the order of the use of the factors of evolution is
the same in the evolution of the _organic kingdom_, in the evolution
of _each species_, and in the evolution of _each individual_. In all
these the physical factors are at first powerfully operative; these
become subordinate to organic factors, and these, in their turn, to
psychical and rational factors. Therefore, as the individual in its
early stages--i. e., in embryo and infancy--is peculiarly plastic
under the influence of the physical environment, and afterward becomes
more and more independent of these; so a species when first formed is
more plastic under the influences of Lamarckian factors, and afterward
becomes more rigid to the same. And so also the organic kingdom was
at first more plastic under Lamarckian factors, and has become less
so in the present species, especially in the higher animals. The
principal reason of this, as we have already seen, is the increasing
differentiation of germ and somatic cells, and the removal of the
former to the interior, where they are more and more protected from
external influence.

II. Some evolutionists--the materialistic--insist on making human
evolution identical in all respects with organic evolution. This, we
have shown, is not true. The very least that can be said is that a
new and far more potent factor is introduced with man, which modifies
greatly the process. But we may claim much more, viz., that evolution
is here on a different and higher plane. The factors of organic
evolution are, indeed, still present, and condition the whole process;
but they are not left to be used by Nature alone. On the contrary, they
are used in a new way and for higher purposes--by reason.

But by a revulsion from the materialistic extreme some have gone to the
opposite extreme. They would place human progress and organic evolution
in violent antagonism, as if subject to entirely different and even
opposite laws; but we have also shown that, although the distinctive
human factor is indeed dominant, yet it is underlaid and conditioned by
all the lower factors; that these lower factors are still necessary as
the agents used by reason.

III. We have already given the views of Weismann and Wallace, and some
reasons for not accepting them; but there is one important aspect
not yet touched. There are some logical consequences of these views
when applied to human evolution which seem to us nothing less than a
_reductio ad absurdum_. This brings into view still another contrast
between organic evolution and human progress.

In organic evolution, when the struggle for life is fierce and pitiless
as it is now among the higher animals, natural selection is undoubtedly
by far the most potent factor. It is at least conceivable (though
not probable) that at the present time organic evolution might be
carried on mainly or even wholly by this factor alone; but in human
evolution, especially in civilized communities, this is impossible.
If Weismann and Wallace be right, then alas for all our hopes of race
improvement--physical, mental, and moral!--for natural selection will
never be applied by man to himself as it is by Nature to organisms. His
spiritual nature forbids. Reason may freely use the Lamarckian factors
of environment and of use and disuse, but is debarred the unscrupulous
use of natural selection _as its only method_. As this is an important
point, we must explain.

All enlightened schemes of physical culture and hygiene, although
directed primarily to secure the strength, the health, and the
happiness of the _present generation_, yet are sustained and
ennobled by the conviction that the improvement of the individuals
of each generation enters by inheritance into the gradual physical
improvement of the race. All our schemes of education, intellectual
and moral, though certainly intended mainly for the improvement
of the individual, are glorified by the hope that the race also is
thereby gradually elevated. It is true that these hopes are usually
extravagant; it is true that the _whole_ improvement of one generation
is not carried over by inheritance into the next; it is true,
therefore, that we can not by education raise a lower race up to the
plane of a higher in a few generations or even in a few centuries: but
there must be at least a small residuum, be it ever so small, carried
forward from each generation to the next, which, accumulating from age
to age, determines the slow evolution of the race. Such are the hopes
on which all noble efforts for race-improvement are founded. Are all
these hopes baseless? They are so if Weismann and Wallace are right. If
it be true that reason must direct the course of human progress, and
if it be true also that selection of the fittest in the organic sense
is the only method which can be used by reason, then the dreadful law
of pitiless destruction of the weak, the helpless, the sick, the old,
must with Spartan firmness be voluntarily and deliberately carried out.
Against such a course we instinctively revolt with horror, because
contrary to the law of our spiritual nature.

But the use by reason of the Lamarckian factors is not attended with
any such revolting consequences. All our hopes of race-improvement,
therefore, are strictly conditioned on the efficacy of these
factors--i. e., on the fact that useful changes, determined by
education in each generation, are to some extent inherited and
accumulated in the race.




CHAPTER IV.

SPECIAL PROOFS, TAKEN FROM THE GENERAL LAWS OF ANIMAL STRUCTURE, OR
FROM COMPARISON IN THE TAXONOMIC SERIES.

_General Principles._


=Analogy and Homology.=--In biology those organs or parts in different
animals are said to be _analogous_ which, however different their
origin, have a general similarity of form and especially of function;
while those are called _homologous_ which, however different their
general appearance, and however different their function, yet may,
by close examination and extensive comparison, be shown to be
modifications of one another--to be, in fact, originally the same part
modified for different purposes. In the former the parts compared look
and behave as if they were the same, but are not; in the latter they
look and behave entirely differently, but are, in fact, the same part
in disguise.

We can best make this plain by examples. The wing of a bird and
the wing of a butterfly are analogous organs. They have the same
function--i. e., flying; and this function necessitates the same
general form of a flat plane. But they are not at all homologous; they
are not at all the same organ or part. They certainly have never been
formed one out of the other by modification. But the wing of a bird,
the fore-paw of a reptile or mammal, the wing of a bat, and the arm and
hand of a man, though so different in form and function, are homologous
parts. On close examination they are found to have the same general
structure, to be composed of essentially the same pieces, although they
are so greatly modified in order to adapt them to different functions,
that the general or superficial resemblance is now lost. Their
structure is precisely such as it would be if they had all originated
from some archetypal fore-limb by modifications in different directions
of its several parts. By extensive comparison in the taxonomic and
ontogenic series, all the intermediate gradations between these extreme
modifications may be picked up.

[Illustration: FIG. 2.--Lepidosiren.]

Another example. The lungs of a mammal and the gills of a fish are
analogous organs, since they have the same function of aëration of the
blood. But they are not at all homologous: they are not built on the
same plan; by no effort of the mind can we imagine that the former
could have come out of the latter by modification. On the contrary,
we have positive proof that it did not so come. But there is an organ
in the fish which is homologous with the mammalian lung, viz., the
air-bladder, or swim-bladder. We know it--1. Because we can trace in
the taxonomic series all the gradations from the one to the other. In
most fishes the air-bladder is wholly cut off from the gullet, and
only very feebly supplied with blood. It is used and can be used only
for flotation. In others, as the gar-pike, the swim-bladder is quite
vascular and opens by a tube into the throat. Through this opening
air is gulped down from time to time into the bladder, and again
from time to time expelled. In other words, this fish supplements
its gill-breathing by an imperfect lung-breathing. We have here
the beginning of a lung. In still other fishes, viz., the Dipnoi
(_lepidosiren_ and _ceratodus_, Fig. 2), the air-bladder becomes a
more perfect lung--i. e., a very vascular sacculated sac; and there is
not only an opening into the throat, but also from the throat to the
snout. In other words, we have for the first time _nostrils_. These
fishes completely combine gill-breathing with lung-breathing. The step
from these to the lowest amphibian reptiles is so small, that some have
classed the lepidosiren among amphibians instead of fishes. The siredon
or axolotl of New Mexico, the necturus or menobranchus of our Northern
lakes, and the siren of our Southern swamps, have both gills and lungs,
and breathe both air and water; but the lung is very imperfect, being
only a sacculated sac, like the air-bladder of the ceratodus and
lepidosiren. No one doubts that the air-breathing organ of an amphibian
is a true lung; yet we have traced all the gradations between it and
the air-bladder of a fish. We conclude, therefore, that if there be
any such thing as transmutation of organic forms, the lung of higher
animals must have been formed by the process above described.[20]

But we know it still more certainly--2. Because we can trace the change
from the one to the other in the ontogenic series. In the life-history
of the individual we can actually see the one thing change into the
other. The frog, as is well known, when first hatched, is a tadpole. It
has no legs, but locomotes by means of a vertically-expanded tail. It
has no lungs, but breathes water instead of air, by means of gills. It
is in all respects, therefore, a fish, and would be classed as such if
it remained in this condition. But it does not; it gradually loses its
tail and gills, and acquires legs and lungs, and breathes air only. Now
in this change whence came the lungs? From the gills by modification?
No; but from an organ similar in character and position to the
air-bladder of a ceratodus, or a lepidosiren. This organ has gradually
developed into a lung. The steps of the change are briefly as follow:
First, the breathing is wholly water-breathing by gills. Next, by the
development of this other organ, it is partly water-breathing by
gills, and partly air-breathing by lungs. Lastly, the gills gradually
dry up, and the lungs develop more and more, until the breathing is
wholly by lungs.

We have dwelt somewhat upon this example, because it is an excellent
example of what we mean by homology, and also because we will have
occasion to use it again. But so important, for all that follows in
this part, is a clear idea on the subject of homology, that it will be
best to familiarize the mind of the reader with it by means of a few
examples drawn from plants.

A potato is analogous to a root--a tuberous root like that of a
dahlia or a sweet-potato--but is not at all homologous with these.
On the contrary, it is homologous with a stem. It is essentially an
underground, leafless branch, which has thickened enormously at the
point by accumulation of starch. The evidence of this is found in
the fact that it has rudimentary leaves (scales) arranged in regular
spiral order of phylotaxis, each with its axillary bud (eyes). It is
still more clearly shown by the fact that buds above-ground which, if
let alone, would form leafy branches, may be made to become tubers by
covering them with earth or dead leaves, and thus excluding the light;
and, conversely, underground buds which, if let alone, would form
tubers, may be made to grow into leafy branches by exposing them to the
light.

Take another example: The broad, flat, elliptical, green masses so
characteristic of the cactus family, and usually called their leaves,
are indeed _analogous_ to leaves in color, form, and function; for
they are green and flat, and assimilate carbonic acid and water (CO2
and H2O) like leaves. But they are not, in truth, leaves, but modified
stems, for they have the essential structure of stems, with their
pith, wood, medullary rays, and bark, and may be traced through all
gradations into the ordinary cylindrical form of stems. Where are
their leaves, then? Their spines are their abortive leaves. These
are arranged spirally like leaves, and bear buds in their axils like
leaves. They are, in truth, leaves, modified to perform the function of
defensive armor; while their function has been delegated to the stem
flattened for this purpose.

[Illustration:

  FIG. 3.--A branch of young acacia, showing change from one form of
      leaf to the other; _a_, _b_, _c_, _d_, successive stages of
      change; _l_, _s_, leaf stalk which gradually changes into the
      blade in _c_, _d_, and _e_.
]

One more example: The acacias, of which there are fifteen to twenty
species in California, introduced from Australia, form two groups
having extremely different styles of leaves. We will call them the
feather-leaved and the simple-leaved acacias. In the former, the leaves
are very finely bipinnate, and the general aspect of the foliage is
extremely feathery and graceful. In the latter the leaves are simple,
ovate, and, curiously enough, set on edge; and the general aspect
of the tree is therefore rather stiff. It seems at first incredible
that leaves so different and aspects so diverse should belong to
plants of the same genus. But a little close examination shows that,
as usual, the botanists are right and the popular judgment wrong.
The plumose-leaf is the normal leaf-form for this genus. The simple
leaf is not only abnormal, but in a homological sense is not a
leaf at all--i. e., it does not correspond to the part called the
_blade_ in ordinary simple leaves of other trees. In the seedling of
the simple-leaved acacias, and sometimes for a considerable time in
the young tree, the leaves are all plumose. As the tree matures it
gradually changes its dress and puts on its _toga virilis_. The gradual
change from the one form to the other may easily be traced in the same
tree, and even often in the same branch (Fig. 3). The steps of the
change (_a_, _b_, _c_, and _d_) are shown in the following figure,
drawn from nature. It is seen, by bare inspection of the figure, that
the so-called leaf, _d_, of the simple-leaved acacias, is really the
vertically-expanded leaf-stalk, _l_, _s_, the true leaf or blade being
wholly aborted. The whole structure of this so-called leaf is different
from that of a true blade. For example, its style of ribbing is
parallel, its position is edgewise to the sky, its palisade cells are
on both sides alike, etc. To emphasize this difference, botanists call
such an apparent leaf a _phyllodium_, or phyllode.

After these illustrations we now repeat the definitions in different
words. Analogy has reference to _general resemblance_ of form
determined by _similarity of function_, however different the origins
of the parts compared may be. Homology has reference to _community
of origin_, however obscured to the superficial observer such common
origin may be by modifications necessary to adapt to different
functions. Observe, then, there are two ideas here which must be kept
distinct. One is common origin, always shown by deep-lying, essential
identity of structure; the other is adaptive modification for function.
Organs of the most diverse origin may resemble by adaptive modification
for the same function. This is analogy. Organs of the same origin
may assume very different appearance by adaptive modifications for
different functions. This is homology. In the latter case, which is
the one that concerns us, a profound study of essential structure
and structural relations to other parts, and especially extensive
comparison in the taxonomic and ontogenic series, will usually
detect the homology, or common origin, in spite of the obscurations
produced by adaptive modifications. It is seen, also, that analogy is
a superficial resemblance, easily detected by the popular eye, and
therefore embodied in popular language; while homology is a deep-seated
and essential resemblance, detected often only by profound study and
extensive comparison. Now, one of the strongest proofs of the truth
of evolution is taken from the homologies of animal structure. Common
origin completely explains homology. Every other explanation is
transcendental, and therefore unscientific.

=Primary Divisions of the Animal Kingdom.=--Now, the animal kingdom
consists of several primary divisions, called sub-kingdoms or
departments. The animals in these groups differ so essentially from
one another in their _plan of structure_, that it is difficult, if
not impossible, to trace any structural relation between them--to
imagine how the members of one could have been derived from those of
another--or conceive the common stem from which they all separated.
In other words, it is impossible, in the present state of knowledge,
to trace homology with any certainty from one group to another. But
within the limits of each primary group the homology is easy. Some
naturalists--Agassiz and Cuvier--have made four or five of these
primary groups. Some--Huxley--have made eight. Some make nine or
ten.[21] We will not trouble ourselves to settle this question; for
all agree to make _vertebrata_ and _articulata_ or _arthropoda_ two of
them, and all our illustrations will be drawn from these. Other groups
are too unfamiliar to the general reader to serve our purpose.

Now, as already stated, homology can not be traced with any certainty
between the primary groups, but within the limits of each group it may
be traced with ease and beauty. Analogy, however, being connected with
function, and function being universal, can be traced throughout the
animal kingdom. While, therefore, it is probable, nay, almost certain,
that all animals have had a common origin, we can not yet trace these
great departments by homology to that common origin. But the common
origin of each department is quite clear. For example, the structure of
all vertebrate animals is precisely such as would be the case if all
came from one primal vertebrate, variously modified to adapt to various
modes of life. Also, the structure of all arthropods is precisely
such as would be if all came from one primal arthropod, which, from
generation to generation, became gradually modified in different
directions, in order to adapt itself to various modes of life. But
between arthropods and vertebrates we can not yet clearly see a common
origin, although there doubtless was such.

These great departments may, therefore, be compared to _natural
styles of animal architecture_. As there are various styles of human
architecture--Oriental, Egyptian, Greek, Gothic--each of which may be
variously modified to adapt it to all the different purposes for which
buildings are made, without destroying, though perhaps obscuring, the
integrity of the style; so the different primary groups or departments
may be regarded as different styles of animal structure, each of which
may be and has been modified in many ways to adapt it to various habits
and modes of life, obscuring but not destroying the general style.
Or they may be compared to natural _machines_. As a steam-engine, by
modification, may be adapted to many kinds of purposes, obscuring,
perhaps, but not destroying the essential identity of structure;
even so the vertebrate machine by modification may be, and has been,
adapted to many kinds of purposes, and thus become a swimming-machine,
a crawling-machine, a flying-machine, a running-and leaping-machine,
without destroying, although obscuring, the essential identity of
structure. As in architecture, æsthetic principles of form may be
traced through each style, but not from style to style, while the
mechanical principles of construction run through all alike; so also
in animal architecture, the laws of form and styles of structure are
traceable with ease only within the limits of each primary group,
while the laws of function are traceable through all groups alike.
Or, again, and finally: Each of these departments may be compared
to a _tree_, with branches, twigs, and spray, all obviously coming
from one common stem, but each stem seems separate. They are, indeed,
probably, themselves only great branches of one common trunk, but their
connection is too remote and obscure to be made out clearly by means
of homology. Other evidences, however, drawn from other sources, as we
shall see hereafter, are not wholly wanting.




CHAPTER V.

PROOFS FROM HOMOLOGIES OF THE VERTEBRATE SKELETON.


The proposition to be established here is, that all vertebrates
have not only a common general plan of structure, but an essential
identity even in detail, although this identity is obscured by adaptive
modifications. We will try to show first a common general plan, and
then, taking parts most familiar to the general reader, will show
essential identity even in detail.

=Common General Plan.=--1. All vertebrate animals, and none other, have
an _internal_ jointed skeleton worked by muscles on the _outside_.
As we shall see hereafter, the relation of skeleton and muscle in
arthropods is exactly the reverse.

2. In all vertebrates, and in none other, the axis of this skeleton
is a jointed backbone (vertebral column) inclosing and protecting the
nervous centers (cerebro-spinal axis). These, therefore, may well be
called back-boned animals.

3. All vertebrates, and none other, have a number of their anterior
vertebral joints enlarged and consolidated into a box to form the
skull,[22] in order to inclose and protect a similar enlargement of
the nervous center, viz., the brain; and also usually, but not always,
a number of posterior joints, enlarged and consolidated to form the
pelvis, to serve as a firm support to the hind-limbs.

4. All vertebrates, and none other, have two cavities, inclosed
and protected by the skeleton, viz., the neural cavity above, and
the visceral or body cavity below, the vertebral column; so that a
cross-section of the body is diagrammatically represented by Fig. 4.

[Illustration:

  FIG. 4.--Diagram cross-section through the body of a vertebrate,
      showing the relation of skeleton to the cavities. _n_, neutral
      cavity; _v_, visceral cavity; _c_, centrum of vertebra.
]

5. All vertebrates, with few exceptions, and no other animals, have
two and only two pair of limbs. The exceptions are of two kinds,
viz.: _a_, some lowest fishes, amphioxus and lampreys, which probably
represent the vertebrate condition before limbs were acquired; and _b_,
degenerate forms like snakes and some lizards, which have lost their
limbs by disuse.

So much concerns the general plan of skeletal structures, and is
strongly suggestive of--in fact, is inexplicable without--common
origin. But much more remains which is not only suggestive, but
demonstrative of such origin. By extensive comparison in the taxonomic
and ontogenic series, the whole vertebrate structure in all its
details in different animals may be shown to be modifications one
of another. Sometimes a piece is enlarged, sometimes diminished, or
even becomes obsolete; sometimes several pieces are consolidated into
one; but, in spite of all these obscurations, corresponding parts may
usually be made out. This is the main subject of this chapter.

=Special Homology of Vertebrate Limbs.=--It would lead us much too far
into unfamiliar technicalities to take up the whole skeleton. We select
the limbs, both because their general structure is more familiar, and
because in them the two fundamental ideas of essential identity and of
adaptive modification are both admirably illustrated. The reason of
this is, that it is by the limbs that the organism chiefly reacts on
the environment, and is modified by it.

=Fore-limbs.=--In the accompanying figures (Figs. 5-18) we have
represented, side by side, the fore-limbs of many vertebrates, taken
from all the classes--mammals, birds, reptiles, and fishes. For
convenience of comparison, the corresponding parts are similarly
lettered in all. Also, in order to identify easily certain important
corresponding segments, we have drawn through them a continuous
dotted line. In man, nearly all the parts are present, and his limbs,
therefore, may be taken as a term of comparison; for man’s structure,
except his brain, is far less modified than that of many animals.

Note, then, the following points: 1. The collar-bone (clavicle) is
associated with wide separation of the shoulders, and the free use of
the fore-limb for prehension or for flight, but is gradually lost in
proportion as the fore-limb is brought nearer together and used for
support, because it is no longer wanted. I say _gradually_, for all
the steps of the passing away may be found. The useless rudimentary
condition is not uncommon.

[Illustration:

  FIGS. 5-9.--5. Fore-limb of man. 6. Dog 7. Hog. 8. Sheep. 9. Horse.
      _sc_, scapula; _c_, coracoid; _a_, _b_, two bones of fore-arm.
      (Taken from various sources and grouped.)
]

[Illustration:

  FIGS. 10-13.--10. Fore-limb of bat. 11. Bird. 12. Archæopteryx.
      13. Pterodactyl. (Lettered as in previous figures;
      grouped from various sources.)
]

2. The coracoid (_c_), it is seen, is a small, beak-like process
of the blade-bone (scapula) in man and mammals; but in birds (Fig.
11) and reptiles (Figs. 14, 18) it is a separate bone as large as
the blade-bone itself, jointed with the latter at the shoulder and
with the breast-bone (sternum) in front, thus making together a
strong shoulder-girdle for the attachment of the fore-limb. This was
undoubtedly the condition in the original or earliest walking animal,
viz., reptiles. It was inherited and retained by birds, because
necessary for powerful action of the wings in flight. In mammals
it gradually dwindled and became united with the blade-bone as a
process. In one mammal, the lowest and most reptilian living--the
ornithorhynchus--the coracoid is much like that of reptiles--a large,
flat bone, separated from the blade-bone and articulated with the
breast-bone. It is a significant fact that, in the mammalian embryo,
it is first developed as a separate bone and afterward united with the
scapula.

[Illustration: FIGS. 14-17.--14. Fore-limb of turtle. 15. Mole. 16.
Whale. 17. Fish.]

3. In man, monkeys, bears, and some other mammals, the limb is fairly
free from the body and the elbow half-way down the limb; while in
herbivores (Figs. 8, 9), such as the horse, ox, and deer, etc., the
elbow is high on the side of the body, and the limb is free only
from the elbow downward. Perhaps in these cases most observers do
not recognize it as an elbow at all. All gradations between these
extremes are easily traced. The free condition of the limb is evidently
the original one, the condition in herbivores being an extreme
modification associated with another modification mentioned under 5.

4. In man and in many mammals, and in all reptiles and birds, there are
two bones in the forearm (radius and ulna). In the more specialized
forms of hoofed animals (ungulates), such as horse and ruminants (Figs.
8, 9), there is apparently but one. Two is the normal and original
number; but one of them, the ulna, has gradually become smaller and
smaller, and finally is reduced to a short splint, and consolidated
with the radius as a process extending backward to form the point
of the elbow. In the horse family every step of this reduction and
consolidation may be traced in the course of its geological history.

[Illustration: FIG. 18.--Mosasaur.]

5. The _wrist_ of many mammals and all birds differs in structure from
that of man, chiefly in containing a smaller number of bones. The
normal number, as in man, seems to be eight. The decrease takes place
mainly by consolidation of two or more into one. In such cases usually
the embryo will show the bones still separate, thus revealing the
ancestral condition. Again, the _position_ of the wrist is noteworthy.
In man, monkeys, the bear family, and several other mammalian families,
and in all reptiles, the hand bends forward at the wrist, so that
the tread is on the whole palm (palmigrade). But, in all the most
specialized mammals, the wrist can not bend in this direction, and
therefore this joint can not be brought to the ground. The tread is
therefore on the toes (digitigrade), and the wrist is high up above
the ground. In the horse (Fig. 9), the ox, and many other mammals, for
example, the wrist is so high that it is not usually recognized as a
wrist, and is often called the _fore-knee_. Now, homologous parts ought
to have the same _scientific_ name; but to use the word “_hand_” in
the case of lower animals might produce confusion and misconception.
Therefore it has been agreed among comparative anatomists to use
instead the Latin word “_manus_” for all that corresponds, in any
animal, to the hand of man--i. e., all from the wrist downward.
The manus of a horse is about fifteen inches long. The manus of a
pterodactyl, such as that found by Marsh in the cretaceous strata of
the West, with an expanse of wings of twenty-five feet, was probably
not less than seven or eight feet long.

6. The number of palm-bones (metapodal) and toes deserves special
notice. In fishes, and in some extinct swimming reptiles, these are
or were very numerous, but in the earliest land-animals they became
five. This is the number now in nearly all reptiles, and in all the
more generalized mammals. It may be called the normal number for a
walking animal. In very many mammals, such, for example, as the dog
family, they are reduced to four, though the fifth often remains as a
useless, rudimentary splint and dew-claw (Fig. 6), thus showing the
process of dwindling in the ancestry. In hoofed animals the process of
gradual diminution is shown even in existing forms, and still better in
extinct forms. Confining ourselves, now, only to existing forms, in the
elephant there are five palm-bones and toes, and in the hippopotamus
there are four, all functional. In the hog (Fig. 7) there are still
four, but two are behind the others and much smaller, and do not touch
the ground--are not functional unless in soft ground. In the cow, deer,
etc., the palm-bones are reduced to two, and these are consolidated
into _one_ (canon-bone), and the toes are reduced to two efficient and
two useless rudiments. In the sheep and the goat (Fig. 8) these useless
rudiments are dropped, and there are two only. Finally, in the horse
(Fig. 9), the _toes_ are reduced to one, although the palm-bones are
still three, two of them, however, being reduced to rudimentary splints.

How is it with birds? Have these also palm-bones and fingers? Yes,
in birds (Fig. 11) there are three palm-bones and three fingers (the
fourth and fifth being wanting); one of them--the thumb--is free, and
sometimes carries a claw. In the earliest known and most reptilian
bird, the archæopteryx (Fig. 12), all the three fingers are free, have
the full number of joints, and all of them carry claws. In the embryo
of living birds the fingers are all free, as in the archæopteryx.

[Illustration: FIG. 19.--Restoration of Rhamphorhynchus phyllurus
(after Marsh). One-seventh natural size.]

7. Observe, finally, as an admirable illustration of different
adaptative modifications for the same purpose--flight--the structure
of the manus of flying animals. In the bat (Fig. 10), the flat
flying-plane is made by enormous elongation of the palm-bones and
finger-bones, their wide separation and the stretching of a thin
membrane between them. In the pterosaurs, or extinct flying reptiles
(Fig. 13), one finger only is greatly enlarged and elongated, and
the flying-membrane is stretched between it and the hind-leg (Fig.
19), while the other three fingers are free and provided with claws.
If it be asked which finger is it that is so greatly enlarged in
this animal, we answer, it is the _little finger_. In birds, on
the contrary, the manus is consolidated to the last degree, to
form a strong basis for attachments for the quills which form the
flying-plane, and which are themselves extreme modifications of the
scales of reptiles. But throughout all these extreme modifications the
same essential structure is detectable.

It is perhaps unnecessary to dwell upon the still greater modifications
of limbs for swimming, as in the whale (Fig. 16), the ichthyosaur,
mosasaur (Fig. 18), and the fish (Fig. 17). A careful inspection of the
figures, after what we have said, will be sufficient to explain them.
In the fish alone the upper segments of the limb, viz., shoulder-girdle
and humerus, are wanting, not being yet introduced, and the manus is
not yet differentiated into palm-bones and fingers, and the fingers
are indefinitely multiplied. All these characters are indications of
low position in the scale of evolution. The earliest vertebrates were
fishes. Limbs were not yet completely formed. In embryos of higher
animals, also, the outer segments are first formed.

=Hind-Limbs.=--Figs. 20 to 24 represent, in a similar way, the
hind-limbs of several animals--in this case all mammals. As before,
corresponding parts are similarly lettered, and a dotted line is
carried through certain prominent parts, especially the knee, heel,
instep, and toes. By careful inspection the figures explain themselves.
Nevertheless, it will be well to draw special attention to several of
the more important points:

[Illustration: FIGS. 20-24.--20. Hind-limb of man. 21. Monkey. 22. Dog.
23. Sheep. 24. Horse.]

1. See, then, the position of the knee. The thigh-bone in man, monkeys,
bears, and several other families of mammals, and all reptiles, is free
from the body, and the knee is far removed and half-way down the limb
(Figs. 20, 21). This is undoubtedly the original and normal condition
of land-animals. But in all the more highly specialized and swifter
animals the knee is brought nearer and nearer to the body, until, in
the swiftest of all, such as the ruminants and the horse (Figs. 23,
24), it is high up on the side of the body, in the middle of what is
usually called the thigh but which really includes the thigh and the
upper part of the lower leg or shank.

2. See, again, the position of the heel. In man, monkey, bear, and many
other mammals, and all _living_ reptiles, the heel is on the ground,
the tread is on the whole foot, plantigrade; while in all the more
specialized and agile animals, and especially in the swiftest of all,
such as the horse, the deer, etc., the heel is high in the air, and the
tread is digitigrade.

3. Observe, again: there are two degrees of digitigradeness. The one
we find in carnivorous or clawed digitigrades, the other in herbivores
or hoofed digitigrades. In the one the tread is on the whole length of
the toes to the balls, as in man when he _tip-toes_; in the other the
_tread is on the tip of the last joint alone_. All that in any animal
corresponds to the foot of a man--i. e., from the hamstring and heel
downward--is called, in comparative anatomy, the “_pes_.” The pes,
or foot of a horse, is eighteen inches long. It is easy to see what
spring and activity this mode of treading gives to an animal. Think how
helpless a horse would be if he trod on the whole foot, heel down!

4. Observe, again, the number of toes. In the process of specialization
there is a tendency for these to become fewer and stronger.[23] The
normal number, as already seen, is five. All the earliest mammals,
and many orders of mammals still living, have five; but in the most
specialized orders, such as the ungulates or hoofed animals, they
were steadily reduced in number in the course of evolution. In the
elephant there are still five, in the hippopotamus there are four, in
the rhinoceros three, in the goat two, in the horse one. Still more
the order of the dropping is regular. If an animal have but four toes,
it is usually the first, or great toe, or thumb, that is wanting, or
may be rudimentary. If, as in the rhinoceros, there are only three,
then No. 5, or little toe, is also wanting, and the existing toes are
Nos. 2, 3, and 4. If an animal has only two toes, as the goat, these
are Nos. 3 and 4; and if only one, as the horse, it is the third or
middle toe. Or, to put it more definitely: hoofed animals are divided
into two groups, even-toed (artiodactyl) and odd-toed (perissodactyl).
The even-toed may have four, as in the hippopotamus; or two, as in the
goat. The odd-toed may have three, as in the rhinoceros; or but one, as
in the horse. Now, both of these orders came by differentiation, far
back in the Eocene Tertiary, from a five-toed plantigrade ancestor.
After dropping No. 1 (thumb or great toe) it is not yet decided, so far
as number of toes is concerned, whether the resulting four-toed animal
shall become artiodactyl or perissodactyl. If the former, then the
two side-toes (Nos. 2 and 5) become shortened up, as in the hog; then
rudimentary, as in the ox and deer; and finally pass away entirely, as
in the goat. If, on the other hand, the four-toed animal is on the line
of perissodactyl evolution, it becomes first a three-toed animal by
dropping No. 5. Now, the two side-toes (Nos. 2 and 4) shorten up more
and more, and the middle toe increases in size, until finally, in the
modern horse, only the greatly enlarged middle toe (No. 3) remains.
We look with wonder and admiration at the _danseuse_ pirouetting on
the point of one toe. The horse is performing this feat all the time.
Yes, the one toe of a horse has all the three joints like ours. The
coffin-bone is the last joint, and the hoof is the nail.

[Illustration: _a b c d e f g_

  Equus: Quaternary and Recent.

  Pliohippus: Pliocene.

  Protohippus: Lower Pliocene.

  Miohippus: Miocene.

  Mesohippus: Lower Miocene.

  Orohippus: Eocene.

  FIG. 25.--Diagram illustrating gradual changes in the horse family.
      Throughout _a_ is fore-foot; _b_, hind-foot; _c_, fore-arm; _d_,
      shank; _e_, molar on side-view; _f_ and _g_, grinding surface of
      upper and lower molars (after Marsh).
]

=Genesis of the Horse.=--Every step of this process on the
perissodactyl line may be traced in the history of the genesis of
the horse. The beautiful form and structure of this animal were not
made at once, but by a slow process of integration of small changes
from generation to generation, and from epoch to epoch of the earth’s
history. The horse (as in fact did all ungulates) came from a five-toed
_plantigrade_ ancestor, but we are not able to trace the direct line
of genesis quite so far. The earliest stage that we can trace with
certainty, in this line of descent, is found in the eohippus of Marsh.
This was a small animal, no bigger than a fox, with three toes behind
and four serviceable toes in front, with an additional fifth palm-bone
(splint), and perhaps a rudimentary fifth toe like a dew-claw. This was
in early Eocene times. Then, in later Eocene, came the orohippus, which
differs from the last chiefly in the disappearance of the rudimentary
fifth toe and splint. (See Fig. 25.) Next, in the Miocene, came the
mesohippus and miohippus. These were larger animals (about the size of
a sheep), and had three serviceable toes all around; but in the former
the rudiment of a fourth splint in the fore-limb yet remained. Then,
in the Miocene, came the protohippus and pliohippus. These were still
larger animals, being about the size of an ass. In the former the two
side-toes were shortening up and the middle toe becoming larger. In
the latter the two side-toes have become splints. Lastly, only in
the Quaternary comes the genus _Equus_, or true horse. The size of the
animal is become greater, the middle toe stronger, the side-splints
smaller; but in the side-splints of the modern horse we have still
remaining the evidence of its three-toed ancestor.

Similar gradual changes may be traced in the two leg-bones, which
have gradually consolidated into one; in the teeth, which have become
progressively longer and more complex in structure, and therefore a
better grinder; in the position of the heel and wrist, which have
become higher above-ground; in the general form, which has become
more graceful and agile; and, lastly, in the brain, which has become
progressively larger and more complex in its convolutions--to give
greater battery-power, to make a more powerful dynamo--to work the
improved skeletal machine. See, then, how long it has taken Nature to
produce that beautiful finished article we call the horse!

       *       *       *       *       *

We have taken only limbs as examples of what is true of the whole
skeleton. To the superficial observer the bodies of animals of
different classes seem to differ fundamentally in plan--to be entirely
different machines, made each for its own purposes, at once, out of
hand. Extensive comparison, on the contrary, shows them to be the same,
although the essential identity is obscured by adaptive modifications.
The simplest, in fact the only scientific, explanation of the phenomena
of vertebrate structure is the idea of a primal vertebrate, modified
more and more through successive generations by the necessities of
different modes of life.

See, then, in conclusion, the difference between man’s mode of working
and Nature’s. A man having made a steam-engine, and desiring to use it
for a different purpose from that for which it was first designed and
used, will nearly always be compelled to add new parts not contemplated
in the original machine. Nature rarely makes new parts--never, if
she can avoid it--but, on the contrary, adapts an old part to the
new function. It is as if Nature were not free to use any and every
device to accomplish her end, but were conditioned by her own plans
of structure; as, indeed, she must be according to the derivation
theory. For example: In early Devonian times fishes were the only
representatives of the vertebrate type of structure. The vertebrate
machine was then a _swimming-machine_. In the course of time, when all
was ready and conditions were favorable, reptiles were introduced.
Here, then, is a new function--that of locomotion on land. We want a
_walking-machine_. Shall we have a new organ for this new function? No:
the old swimming-organ is modified so as to adapt it for walking. Time
went on, until the middle Jurassic, and birds were introduced. Here
is a new and wonderful function, that of flying in the air. We want a
_flying-machine_. We know how man would have done this; for we have
the result of his imagination in angels of Christian art and griffins
of Greek mythology. He would have added wings to already existing
parts, and this would have necessitated the alteration of the whole
plan of structure, both skeletal and muscular. Nature only modifies
the fore-limbs for this new purpose. If we must have wings, we must
sacrifice fore-legs. We can not have both without violating the laws of
morphology. Finally, ages again passed, and, when time was fully ripe,
man was introduced. Now we want some part to perform a new and still
more wonderful function. We want a _hand_, the willing and efficient
servant of a rational mind. We know, again, how man would have done
this, for we have the result in the centaurs of Greek mythology, in
which man’s chest, and arms, and head are added to the body of a
quadruped. But natural laws must not be violated, even for man. If we
want hands, we must sacrifice feet. Again, therefore, the fore-limbs
are modified for this new and exquisite function. Thus, in the fin of
a fish, the fore-paw of a reptile or a mammal, the wing of a bird, and
the arm and hand of a man, we have the same part, variously modified
for many purposes.

Many other illustrations might be taken from the skeleton and from
other systems, especially the muscular and nervous. But in the
muscular system the modifications have been so extreme that homology
is much more difficult to trace, and therefore requires more extensive
knowledge than we yet possess, and more extended comparison than has
yet been attempted. It has been traced with some success through
mammals, and probably will be through air-breathing vertebrates--i. e.,
also through birds, reptiles, and amphibians; but to trace it through
fishes seems almost hopeless. In the case of the nervous system, and
especially of the brain, it is again distinct; but this had better be
taken up under another head, viz., proofs from ontogeny, Chapter VI.

In the visceral organs homology is very plain, in fact too plain.
There is not modification enough in most cases even to obscure it,
because function is the same in all animals. These organs do not,
therefore, furnish good illustrations of that essential identity in the
midst of adaptive modification which constitutes the argument for the
derivative origin of structure. It is the organs of _animal life_ that
show this most perfectly, because it is these that take hold on the
environment and are modified by it. There are, however, a few striking
illustrations to be found among the visceral organs, especially the
blood-system. This, however, had better also be deferred to the chapter
on ontogeny.




CHAPTER VI.

HOMOLOGIES OF THE ARTICULATE SKELETON.


We have taken the vertebrate skeleton first, only because this
department is most familiar. But in reality, the most beautiful
illustrations of essential identity of structure in the midst of
infinite diversity of adaptive modification for different functions
and habits of life, and therefore of common origin from a primal form,
are found in the department of articulates. I use the old Cuvierian
department _articulata_, rather than the more modern _arthropods_,
because the former includes worms also. Now, whether worms should
be thus included with arthropods, or deserve a whole department to
themselves it matters not for our purposes. It is generally admitted
that arthropods probably descended from marine worms. They all have
the same general plan of skeletal structure. It will suit my purpose,
therefore, to regard worms as the lowest form of jointed animals.

Here, then, we have an entirely different plan of structure--a
different style of architecture and different mechanical principles
of machinery. Instead of a skeleton within and muscles acting on the
outside, we have the skeleton on the outside, and muscles acting from
within. Instead of two cavities, a neural and visceral, the skeleton
forms but one cavity, in which all organs are inclosed and protected.
Instead of finding the nerve-axis on the dorsal aspect of the body, we
find it on the ventral aspect.

[Illustration:

  FIG. 26.--Diagram section across an arthropod, showing the inclosing
      skeleton-ring and a pair of jointed appendages, _n_, nervous
      center; _v_, viscera; _b_, blood system.
]

Take any articulate animal, for example, a shrimp, a centiped, or
a beetle. Cut it across the body, and look at the end (Fig. 26).
We see a ring of bone (chitin) inclosing all the organs (nervous
system _n_, blood system _b_, and visceral system _v_), and a pair
of jointed appendages, perhaps legs, on each side. Now imagine these
parts repeated in a linear series. The rings repeated make a hollow,
jointed tube or barrel, the appendages repeated make a continuous row
of appendages on each side. Now this is exactly what we actually
find. The whole articulate skeleton is ideally made up of a series
of such repeated rings and appendages, modified according to the
position in the series, and the uses to which they are put. And then
the whole articulate department is made up of such articulate animals
again modified according to place in the scale of articulates. The
modification in the lower forms is slight, and therefore the identity
of the repeated parts is obvious; but as we go up the scale, and
the number and complexity of the functions increase, the adaptive
modification becomes greater and greater, until finally it so obscures
the essential identity, that it requires the most extensive comparison
in the taxonomic series and in the ontogenic series, to pick up the
intermediate links and establish the fact of common origin. In a word,
whether they so originated or not, it is certain that the structure of
articulate animals is exactly such as would be the case if all these
animals were genetically connected, and came originally from a primal
form something like one of the lower crustaceans, or, perhaps, a marine
worm.

[Illustration: FIG. 27.--Shrimp (Palæmonetes vulgaris).]

[Illustration: FIG. 28.--External anatomy of the lobster (after
Kingsley).]

It will be best to take an example from about the middle of the
scale, where the two elements, viz., essential identity and adaptive
modification, are somewhat evenly balanced, and both traceable with
ease and certainty. Take, then, a cray-fish, a lobster, or a shrimp.
This animal (Fig. 27) has twenty or twenty-one rings and pairs of
jointed appendages. The rings are some of them diminished, some
of them increased in size. Sometimes several are consolidated;
sometimes several are partially or wholly aborted. The appendages
are modified in shape and size, according to their position, so as
to make them swimming-appendages (swimmerets), walking-appendages
(legs), eating-appendages (jaws), and sense-appendages (antennæ). For
example, in the abdominal region, or so-called tail, we have seven
segments, all being perfect movable rings, each with its pair of
jointed appendages, except the last, or _telson_. The appendages of the
first ring (Fig. 28, B) are specially modified in the male as organs
of copulation (B′). The next four pairs are modified for swimmerets
(D′) and for use as holders of the eggs in the female. The appendages
of the sixth ring (G) are broad and paddle-shaped, and, together with
the telson or seventh ring (H), form the powerful terminal swimmer.
Going, now, to the cephalo-thorax: in this either a large number of
segments (thirteen or fourteen) are consolidated above to form the
upper shell or carapace; or else, as is more probable, two or three
of the anterior segments have enlarged and grown backward over, and
at the expense of the others, to form this shell. At any rate, it is
certain that the carapace is formed of the dorsal portions of a number
of segments consolidated together. Below, however, the segments are
all distinct, and have each its own pair of appendages. For example,
going forward in this region, the five next pairs of appendages are
greatly enlarged and very strong, and serve the purpose of locomotion.
They are _walking-appendages_. The next two or three pairs are smaller
and somewhat modified, but not so much as to obscure their essential
similarity to legs. Like legs, they are many-jointed, and like legs,
too, they have gills attached to them. They are called maxillipeds, or
jaw-feet. They are used like hands to gather food and carry it to the
mouth. They are _gathering-appendages_. Then follow three or four pairs
still more modified, and used for mastication. They are called maxillæ
and mandibles. They are _eating-appendages_. Then follow two pairs,
long, many-jointed, with the same kind of curious hinge-joints, which
we have in the legs, undoubtedly homologous with all the others, but
used for an entirely different purpose, and specially modified for that
purpose. They are the antennæ. They are delicate organs of touch and
of hearing, for the ear is situated in the basal joint of the anterior
pair. Last of all, there is still another pair, jointed and movable, on
the ends of which are situated the eyes. These last three, therefore,
are _sense-appendages_. Some writers make this last pair special
organs, not homologous with appendages.

[Illustration: FIG. 29.--Appendages of a prawn (after Cuvier).]

[Illustration: FIG. 30.--Appendages of Nebalia.]

For the sake of greater distinctness, we give the whole series of these
appendages in one of the higher forms, viz., the prawn (Palemon, Fig.
29, and in one of the lower forms, Nebalia, Fig. 30).

[Illustration: FIG. 31.--Vibilia, an amphibod crustacean (after Milne
Edwards).]

That these are really homologous parts is further shown by the fact
that in the case of other crustaceans, such as limulus, the same
appendages, i. e., the appendages of the same body segments, which in
the cases before mentioned are used as feet, become swimmers, while
the appendages corresponding to jaw-feet become walkers; and even what
corresponds to antennæ or sense-appendages, may, as in branchippus,
become powerful claspers. Finally, in all the lowest crustaceans, the
identity is evident, because all the segments and their appendages are
much alike in form and function (Fig. 31).

[Illustration: FIG. 32.--Lithobius forcipatus (after Carpenter).]

We have taken examples from near the middle of the articulate scale,
because, as already stated, both the essential identity and the
adaptive modifications are easily traced. If we go downward in the
scale, the structure becomes more and more generalized, and the rings
and appendages become more and more alike (Fig. 31), until in the most
generalized forms we have only a series of similar rings, with similar
pairs of appendages, except some necessary modifications to form the
head and tail. This is well shown in the centiped (Fig. 32), and still
better in marine worms (Fig. 33). In some marine worms the slight
modification to form the head takes place under our very eyes. These
often multiply by dividing themselves into two. When they do so, they
make a new head and new tail by slight modification of segments and
appendages (Fig. 33).

[Illustration: FIG. 33.--Syllis prolifera.]

If, on the other hand, we go up the scale, we find adaptive
modifications obscuring more and more the simple and obvious identity
of parts, until finally the identity can not be recognized without
extensive comparison in the taxonomic series and study of embryonic
conditions. In crabs--which is a higher form than cray-fish--the tail
or abdomen seems to be wanting, but is only very small and bent under
the body and thus concealed. In all essential respects the structure is
precisely like the cray-fish. In fact, in the embryo, we trace the one
form into the other; for the crab is at first a long-tailed crustacean
(Fig. 34).

[Illustration: FIG. 34.--Development of Carcinus mœnas. A, zoæa stage;
B, megalopa stage; C, final state (after Couch).]

Insects are the highest form of articulates. In these, therefore, we
find the modification is still greater than in crustaceans, though even
here the ring-and-appendage structure is plain enough in most cases.

One of the best evidences of high grade among animals is the gathering
of the segments into distinct groups, and especially the distinctness
of the _head_ as one of these groups. In worms and lower crustaceans
there is no grouping at all, the skeleton being a continuous series
of joints, only slightly modified at the anterior and posterior
extremities. In the higher crustacea, and in spiders and scorpions,
they are grouped into two regions, viz., cephalo-thorax and abdomen.
In insects they are grouped into three very distinct regions--head,
thorax, and abdomen. In insects, therefore, we find for the first
time the head distinctly separated from the rest of the body. This
is an evidence of high grade, because it shows the dominance of
head-functions.

[Illustration:

  FIG. 35.--External anatomy of Caloptenus spretus, the head and thorax
      disjointed; up, uropatagium; _f_, furcula; _c_, cercus (drawn by
      J. T. Kingsley).
]

The insect, such, for example, as a grasshopper, consists of seventeen
or eighteen segments (Fig. 35). Of these, four belong to the head,
three to the thorax, and about ten to the abdomen. Those of the abdomen
are all separated and movable; those of the thorax and head are more or
less consolidated. The appendages of the head-segments become antennæ
and jaw-parts, i. e., mandibles--maxillæ and labium; the appendages
of the thorac-segments become legs (the wings are not homologous with
appendages), while those of the abdomen are aborted. The steps of the
gradual consolidation on the one hand, and the abortion on the other,
may be traced in the embryo or larva--i. e., in the caterpillar or the
grub of a bee or a beetle. In the caterpillar, for example, there is
no grouping into three regions, there is no consolidation, and all the
segments have appendages. Again, the almost infinite variety in the
mouth-parts among insects, brought about by adaptive modifications for
biting, for piercing, and for sucking, and yet the essential identity
of all to the more simple and generalized structure of the grasshopper,
is an admirable illustration of the same principle. But to dwell upon
these minor points would carry us too far.

=Illustration of the Law of Differentiation.=--We have here, in the
modifications of segments and appendages of articulates, an admirable
illustration of the most fundamental law of evolution, viz., the law of
differentiation. As we have already seen (page 21), perhaps the most
beautiful and certainly the most fundamental illustration of this law
is found in the development of cell-structure. Commencing in the lowest
animals, and in the earliest embryonic stages of the higher animals,
from a condition in which all are alike, the _cells_ as we go upward
quickly diverge into different forms to produce different tissues and
perform different functions. Here, then, we have a perfect example of
essential identity and adaptive modification. It is the very best type
of differentiation. So also skeletal _segments_, commencing, in the
lowest articulates and in earliest embryonic stages of the higher, all
alike, as we go upward in either series, begin immediately to diverge
in various directions (divergent variation), taking different forms to
subserve different uses. Here, again, therefore, is an illustration
of the law of differentiation. Lastly, in the articulate department,
commencing with the lowest forms and earliest embryonic conditions,
and we may add earliest geological times, and going up either series
from generalized forms very much alike, the _individuals_ are gradually
differentiated into many special forms, in order to adapt them to
the diversified modes of life actually found in nature. Thus cells,
segments, individuals, are all alike affected by this most fundamental
law.

We have taken our illustrations from only the two departments of
vertebrata and articulata, because these are the most familiar to the
reader, and also have been most carefully studied. We have shown that
the general structure of all vertebrates is precisely what it would
be if they all had come from one primal vertebrate form, and that
of all articulates what it would be if all had come from one primal
articulate form. The only _natural_ explanation, and, therefore, the
only scientific explanation of this, is that _they were really thus
derived_. The same kind of evidence may be drawn from the study of
other departments, but to pursue the subject any further in this
direction would carry us beyond the limits which we have assigned. We
desire only to explain the nature, not to give all, of the evidence.
The examples given will be sufficient for the purposes of illustration.
The whole proof is nothing less than the whole science of comparative
anatomy.

Vertebrates, then, were derived from a primal vertebrate, articulates
from a primal articulate, and so for other departments. But whence were
these _primals_ derived? Are there any intermediate links between, any
deeply concealed common plan of structure underlying these primary
groups, showing a common origin? It must be confessed that, in their
_mature_ condition, there seems to be but little evidence of such.
These primary groups seem to be built on different plans, to be
fundamentally of different styles of architecture. Therefore Darwin,
in the true spirit of inductive caution--that true scientific spirit
which keeps strictly within the limits of evidence--commences with four
or five distinct primal kinds, from which by divergent variation all
animals were descended. Nevertheless, the truly scientific biologist
must ever strongly incline to believe that these also came from some
_primal animal_, and even that both animals and plants were derived
from some primal form of _living thing_; that as, in the taxonomic
series, the animal and vegetal kingdoms in their lowest forms merge
undistinguishably into one another; as in the ontogenic series the
animal and plant germ are one, so also in the phylogenic series the
earliest organisms were simply living things, but not distinctively
animal nor vegetal. Science, therefore, whose mission is to trace
origins as far back as possible, must ever strive to find connecting
links between the primary groups. Some such have been supposed to
have been discovered. Some find the origin of vertebrates among the
molluscoids (ascidians); some find the origins of both vertebrates and
articulates among marine worms (annelids). This point is still too
doubtful to be dwelt upon here. It may be that we seek in vain for such
connecting links among existing forms. It may well be that the point of
separation of these great primary groups (unless we except vertebrates)
was far lower even than these low forms. Both phylogeny and ontogeny
seem to indicate this. In the earliest fauna known, the primordial (for
if there was life in the archæan it was not yet differentiated into a
fauna), all the great departments, except the vertebrates, seem to
have been represented. In embryonic development, too, the point of
connection or even of similarity, between the great departments, is
found, as we shall see hereafter, only in the earliest stages--i. e.,
lower down than any but the lowest existing forms, viz., the protozoa.




CHAPTER VII.

PROOFS FROM EMBRYOLOGY, OR COMPARISON IN THE ONTOGENIC SERIES.


It is a curious and most significant fact that the successive stages of
the development of the _individual_ in the higher forms of any group
(ontogenic series) resemble the stages of increasing complexity of
differentiated structure in ascending the animal scale in that group
(taxonomic series), and especially the forms and structure of animals
of that group in successive geological epochs (phylogenic series). In
other words, the individual higher animal in embryonic development
passes through temporary stages, which are similar in many respects to
permanent or mature conditions in some of the lower forms in the same
group. To give one example for the sake of clearness: The frog, in its
early stages of embryonic development, is essentially a fish, and if
it stopped at this stage would be so called and classed. But it does
not stop; for this is a temporary stage, not a permanent condition.
It passes through the fish stage and through several other temporary
stages, which we shall explain hereafter, and onward to the highest
condition attained by amphibians. Now, if we could trace perfectly
the successive forms of amphibians, back through the geological epochs
to their origin in the Carboniferous, the resemblance of this series
to the stages of the development of a frog would doubtless be still
closer. Surely this fact, if it be a fact, is wholly inexplicable
except by the theory of derivation or evolution. The embryo of a
higher animal of any group passes _now_ through stages represented by
lower forms, because in its evolution (phylogeny) its ancestors _did
actually have these forms_. From this point of view the ontogenic
series (individual history) is a brief recapitulation, as it were, from
memory, of the main points of the philogenic series, or family history.
We say brief recapitulation of the _main_ points, because many minor
points are dropped out. Even some main points of the earliest stages of
the family history may be dropped out of this sort of inherited memory.

This resemblance between the three series must not, however, be
exaggerated. Not only are many steps of phylogeny, especially in
its early stages, dropped out in the ontogeny, but, of course, many
adaptive modifications for the peculiar conditions of embryonic life
are added. But it is remarkable how even these--for example the
umbilical cord and placenta of the mammalian embryo--are often only
modifications of egg-organs of lower animals, and not wholly new
additions. It is the similarity in spite of adaptive modifications that
shows the family history.

We will now illustrate by a few striking examples.

We can not do better than to take, again, as our first example, the
development of tailless amphibians, and dwell a little more upon it:

=1. Ontogeny of Tailless Amphibians.=--It is well known that the
embryo or larva of a frog or toad, when first hatched, is a legless,
tail-swimming, water-breathing, gill-breathing animal. It is
essentially a fish, and would be so classed if it remained in this
condition. The fish retains permanently this form, but the frog passes
on. Next, it forms first one pair and then another pair of legs;
and meanwhile it begins to breathe also by lungs. At this stage it
breathes equally by lungs and by gills; i. e., both air and water.
Now, the lower forms of amphibians, such as siredon, menobranchus,
siren, etc., retain permanently this form, and are therefore called
_perennibranchs_, but the frog still passes on. Then the gills
gradually dry up as the lungs develop, and they now breathe wholly by
lungs, but still retain the tail. Now this is the permanent, mature
condition of many amphibians, such as the triton, the salamander, etc.,
which are therefore called _caducibranchs_, but the frog still passes
on. Finally, it loses the tail, or rather its tail is absorbed and its
material used in further development, and it becomes a perfect frog,
the highest order (_anoura_) of this class.

Thus, then, in ontogeny the fish goes no further than the fish stages.
The perennibranch passes through the fish stage to the perennibranch
amphibian. The caducibranch takes first the fish-form, then the
perennibranch-form, and finally the caducibranch-form, but goes no
further. Last, the anoura takes first the fish-form, then that of the
perennibranch, then that of the caducibranch, and finally becomes
anoura. This is shown in the diagram, which must be read upward, line
by line.

[Illustration:

  FISH.      PERENNIBRANCH.     CADUCIBRANCH.      ANOURA.
                                                     ^
  FISH.      PERENNIBRANCH.     CADUCIBRANCH.--------^
                                     ^
  FISH.      PERENNIBRANCH-----------^
                   ^
  FISH.------------^

Diagram showing the stages of development of amphibians. (To be read
upward.)]

Now, this is undoubtedly the order of succession of forms in geological
times--i. e., in the phylogenic series. This series is indicated by
the arrows in the diagram. Fishes first appeared in the Devonian
and Upper Silurian in very reptilian or rather amphibian forms.
Then in the Carboniferous, fishes still continuing, there appeared
the lowest--i. e., most fish-like--forms of amphibians. _These were
undoubtedly perennibranchs._ In the Permian and Triassic higher forms
appeared, which were certainly caducibranch. Finally, only in the
Tertiary, so far as we yet know, do the highest form (anoura) appear.
The general similarity of the three series is complete. If we read the
diagram horizontally, we have the ontogenic series; if diagonally with
the arrows, we have both the taxonomic and the phylogenic series.

=2. Aortic Arches.=--But some will, perhaps, say that these stages
in the ontogeny are only examples of adaptive modifications--like
modifications for like conditions of life--and had better be accounted
for in this way, without reference to family history. We will,
therefore, take another example, which can not be thus accounted
for--an example in which there is no possible use _now_ for the
peculiar form or structure which we find. For this purpose we take the
case of the _course of circulation in vertebrates_.

[Illustration: FIG. 36.--Showing heart and outgoing blood-vessels of a
lizard (after Owen). The arrows show the course of the blood.]

[Illustration: FIG. 37.--A, heart and gill-arches of a fish; B, one
arch, with fringe (after Owen); H, the heart.]

If one examines the large vessels _going out_ from the heart of a
lizard, he will find _six aortic arches_--i. e., three on each side.
These all unite below to form the one descending abdominal aorta. This
is shown in the accompanying figure (Fig. 36), in which _a a′ a″_ and
_b b′ b″_ are the six arches. Now, there is no conceivable use in
having so many aortic arches. We know this, because there is but one in
birds and mammals, and the circulation is as effective, nay, much more
effective in these than in reptiles. The explanation of this anomaly is
revealed at once as soon as we examine the circulation of a _fish_,
which is shown in the accompanying figure (Fig. 37). The multiplication
of the aortic arches is here, of course, necessary, for they are the
_gill-arches_. The whole of the blood passes through these arches, to
be aërated in the gill-fringes. The use of this peculiar structure is
here obvious enough. If a lizard were ever a fish, and afterward turned
into a lizard, changing its gill-respiration for lung-respiration,
then, of course, the useless gill-arches would remain to tell the
story. Now, although a lizard never was a fish, in its _individual_
history or ontogeny, it was a fish in its family history or phylogeny,
and therefore it yet retains, by heredity, this curious and _useless_
structure as evidence of its ancestry.

[Illustration: FIG. 38.]

[Illustration: FIG. 39.

  FIGS. 38, 39.--Diagrams showing the change of the course of blood
      in the development of a frog. 38. The tadpole stage. 39. The
      mature condition. H, heart; G G′ G″, external gills; _g g′ g″_,
      internal gills; _c c_, connecting branches in the tadpole; _p p_,
      pulmonary branches.
]

That this is the true explanation is demonstrated by the fact that in
amphibians this very change actually takes place before our eyes in
the _individual history_. We have already seen that the individual
frog, in its tadpole state, is a gill-breather. It has therefore its
gill-arches (Fig. 38), three on each side, like a fish, and for the
same reason, viz., the aëration of the blood. But when its gills dry
up and lung-respiration is established, its now useless gill-arches
still remain as aortic arches, to attest their previous condition (Fig.
39). Now, the lizard undoubtedly came from an air-breathing, tailed
amphibian, and therefore inherited this form of arterial distribution.
In both lizard and amphibian the ultimate cause is an origin from
fishes, in which such arches are obviously necessary. The diagrams,
Figs. 38 and 39, are illustrations somewhat idealized, showing the
manner in which the change actually takes place in air-breathing
amphibians. Fig. 38 represents the tadpole stage, and Fig. 39 the
mature condition. In the former the gills are mostly external, G G′,
etc., but also internal, _g g′_, as in the fish. Observe in this
condition the small connecting vessels, _c c′_. When the external gills
dry up, these are enlarged, and the whole of the blood passes through
them, as shown in Fig. 39. It is seen, also, in Fig. 38, that a small
branch, _p_, goes from the lower gill-arches to the yet rudimentary
lung, _l_. When the gill-fringes have disappeared, the whole of the
blood of the lower arch goes through the now enlarged pulmonary branch
to the lungs, L, now in full activity, and the remainder of this arch
disappears, as shown by the dotted lines in Fig. 39.

The change which actually took place in the family history of the
lizard probably differed from the above only in being more simple, the
gills being only internal like the fish. The external gills complicate
the process a little in the case of the frog, but the principle is
precisely the same.

As already explained (pages 82-85), the large gap between fishes and
reptiles, as regards mode of respiration, is completely filled both
in the taxonomic series--i. e., in ganoids, dipnoi, and the mature
condition of the different orders of amphibians--and in the ontogeny
of the higher amphibians. Now, we add that the same is true of the
arterial distribution. We have just traced the change in the ontogeny
of the frog, but the steps of the same change are traceable in passing
from the typical fish (teleosts), through dipnoi and amphibians to
reptiles. Thus, again, the phylogeny, the taxonomy, and the ontogeny,
are in complete accord.

But the argument for evolution does not stop here. If birds and
mammals have come from reptiles, and therefore from fishes, we may
expect to find some evidences of the same kind still lingering in
the great arteries. And such we do find. It is a most curious and
significant fact that, in the early embryonic condition of birds and
mammals, including man himself, we find on each side of the neck
several gill-slits, each with its gill-arch, and therefore _several
aortic arches on each side_, precisely similar to what we have already
described. These arches are subsequently, some of them, obliterated;
some modified to form the one aortic arch, and some of them still more
modified to form the other great arteries coming from the heart to
supply the head and forelimbs.

[Illustration:

  FIG. 40.--Diagram of mammalian heart. _a_, aorta; _p_, pulmonary
      artery; _scs′c′_, subclavium on each side; _cc′_, carotids on
      each side.
]

[Illustration: FIG. 41.--Ideal diagram representing the primitive
aortic arches (after Rathke).]

This is so beautiful and convincing an example, and one so generally
unfamiliar, to even intelligent persons, not especially acquainted with
biology, that it is best to explain it more fully. In Fig. 40 we give
a mammalian heart and outgoing vessels, very slightly modified, so as
to suggest the process of change. In Fig. 41 we give an ideal diagram
representing the primitive aortic arches as they exist in the embryo of
mammals, birds, and reptiles. It represents, also, substantially, the
arches as they exist in the _mature_ condition in the most reptilian
fishes (dipnoi) and in some sharks, except that in these the arches
are of course furnished with gill-fringes. We will use this figure,
therefore, to represent both the embryonic condition of air-breathing
vertebrates and the mature condition of some fishes. The place of
the heart is indicated by the dotted circle. Fig. 36, on page 134,
shows what these arches become in reptiles (lizard). It is seen that
the two upper arches on each side are obliterated, as indeed they
already are in some teleost fishes. Fig. 42 shows what they become in
birds. The two upper arches are, of course, obliterated. The others
are all modified, each in a manner which may be readily understood
by comparison with Fig. 41. Finally, Fig. 43 shows what they become
in mammals and in man. In the bird (Fig. 42) the first pair of arches
become the two pulmonary arteries as they do also in the lizard. The
second pair become on the right side (left of the diagram) the aortic
arch, on the left side (right of the diagram) the left subclavian,
_s′c′_ (the right subclavian, _sc_, is a branch of the aortic arch).
The third pair become carotids, _cc_, while the fourth and fifth, as
already said, are aborted. In the mammal (Fig. 43), on the left side
(right of the diagram) the first arch becomes the pulmonary artery,
_p_. In the fœtus the continuation of this arch forms the ductus
arteriosus, which is afterward obliterated, as shown in the dotted
line. The second arch becomes the aortic arch, the third the left
exterior carotid. On the right side (left of the diagram) the first
arch becomes aborted; the second, the right subclavian, _sc_ (the
_left_ subclavian, _s′c′_, is a branch of the aortic arch); and the
third, the right carotid. Nos. 4 and 5, on both sides, as usual, are
aborted.

[Illustration: FIG. 42.--Modified for bird.]

[Illustration: FIG. 43.--Modified for mammal.]

[Illustration: FIG. 44.--Lancelet (Amphioxus lanceolatus). Magnified
two and one-half times.]

See, then, the gradual process of change through the whole vertebrate
department. In the lowest of all vertebrates, if vertebrate it may
be called (for what corresponds to its backbone is an unjointed,
fibrous cord), the amphioxus or lancelet (Fig. 44), there are about
forty gill-arches on each side. As we rise in the scale of fishes
these are reduced in number. In the lamprey, there are seven; in the
sharks, usually five; in ordinary fishes (teleosts), there are four or
sometimes only three on each side, the others being aborted. Thus far
the change is only by diminution of number in accordance with a law
universal in biology, that decrease in the number of identical organs
is evidence of advance in the grade of organization, provided that it
be associated with more perfect structure of the organ. The further
change is one of adaptive modification. In some reptiles (lizard) the
three gill-arches on each side all retain the form of aortic arches;
in some reptiles only two retain this form. In birds and mammals only
one arch is retained, in the form of aortic arch, the others being
modified to form the great outgoing vessels of the heart, or else
aborted. It may be well to observe that in birds the one aortic arch
turns to the right, while in mammals it turns to the left. This is
positive evidence that mammals could not have come from birds, nor
_vice versa_. They both came from reptiles, and, of the many reptilian
arches, a right one was retained by the bird branch, and a left one by
the mammalian.

In all the figures illustrating this subject, we have left out the
great _incoming_ vessels or veins, because we are not here concerned
with them, they not being transformed gill-arches.

Last of all, it may be well to stop a moment to show the cogency of
this evidence. If it were a question of the origin of some structure
not only useful (for all structures selected by Nature must be useful)
but the _best imaginable_, like the eye or the ear, for example; then,
if _we examined only the highest form_ or _the finished article_, there
are two ways in which it is possible to explain the adaptive structure.
We may either suppose that it was made at once out of hand, by some
intelligent contriver; or else that it was slowly made by a process
of evolution, becoming more and more perfect by a selection of only
the most perfect from generation to generation. But in the case of the
six aortic arches of the lizard, we are shut up to the one explanation
only, viz., by slow process of evolution. One arch is all that is
necessary, as is plainly shown by the use of only one in the more
perfect circulation of birds and mammals. If the thing were done out
of hand, unconditioned by the previous structure in fishes, to have
made six was surely but a bungling piece of work.

[Illustration: FIG. 45.--Fish-brain. A, side view; B, top view.]

[Illustration: FIG. 46.--Reptile-brain. A, side view; B, top view.]

[Illustration: FIG. 47.--Bird-brain. A, side view; B, top view.]

[Illustration: FIG. 48.--Mammal-brain. A, top view; B, side view.]

[Illustration: FIG. 49.--Man’s brain. A, side view; B, top view.]

=3. Vertebrate Brain.=--Another excellent example is the structure of
the vertebrate brain. The brain of an average fish is represented in
Fig. 45. It consists of four or five swellings, or ganglia, strung
along, one beyond another. Commencing behind, these are, first, the
medulla, _m_; then the cerebellum, _cb_; then the optic lobes, _ol_;
then the cerebrum and thalamus combined, _cr_; and last, the olfactive
lobes, _of_. Of these, it will be observed, the optic lobe is the
largest in the brain of the fish (Fig. 45). In the brain of the reptile
(Fig. 46) we have the same serial arrangement, of the same parts,
only that the cerebrum has now become the dominant part instead of
the optic lobes. In the average bird (Fig. 47) the cerebrum has grown
so large that it extends backward, and partly covers the optic lobes.
In the lower mammals (marsupials), the brain is much the same in this
respect, as in birds--i. e., the cerebrum only partly covers the optic
lobes, so that, looked at from above, the whole series of ganglia are
still visible. But in the average mammal (Fig. 48) the cerebrum is so
enlarged that it covers entirely the optic lobes and encroaches on the
cerebellum behind and the olfactive lobes in front. In some monkeys,
indeed, the cerebellum is nearly or even quite covered. Finally, in
man (Fig. 49), the cerebrum has grown so enormously that it covers
every other part and completely conceals them from view when the brain
is looked at from above. In front it not only covers but has grown far
beyond the olfactive lobes; behind it extends beyond and overhangs the
cerebellum; on the sides it overhangs and covers all. Looked at from
above, nothing is seen but this great ganglion. The ideal section (Fig.
50) represents all these stages diagrammatically in one figure. After
what has been said, the figure will be readily understood.

[Illustration: FIG. 50.--Ideal section showing all the above stages.]

[Illustration: FIG. 51.--Sub-fish Stage. _th_, thalamus; _ol_, optic
lobe; _m_, medulla.]

[Illustration:

  FIG. 52.--Fish-stage. _of_, olfactive lobe; _cr_, cerebrum; _th_,
      thalamus; _ol_, optic lobe; _cb_, cerebellum; _m_, medulla.
]

[Illustration: FIG. 53.--Reptile-stage.]

Now, it is a most remarkable fact that substantially these same
stages, which are permanent conditions in the taxonomic series, are
passed through as transient stages in the embryonic development of the
human brain, and in the order given above. The very early condition
of the human brain is represented in Fig. 51. It is evidently nothing
more than the intercranial continuation of the spinal cord, enlarged
a little into three swellings or ganglia. These are the early
representatives of the medulla, the optic lobes, and the thalamus;
which last may be regarded as the basal and most fundamental part of
the cerebrum. This stage may be regarded as lower than that of the
ordinary fish. I have called it, therefore, the _sub-fish stage_.
The cerebellum is a subsequent outgrowth from the medulla, as is
the cerebrum and olfactive lobes from the thalamus. Fig. 52 may be
said, therefore, to represent fairly the fish-stage. Henceforward the
principal growth is in the cerebrum and cerebellum, both of which are
subsequent outgrowths of the original simple ganglia, the medulla, and
the thalamus. The cerebrum especially increases steadily in relative
size, first becoming larger than but not covering the optic lobes (Fig.
53). This represents the reptilian stage. Next, by further growth,
it covers partly the optic lobes (Fig. 54). This may be called the
bird-stage. Then it covers wholly the optic lobes, and encroaches on
the cerebellum behind and olfactive lobes in front (Fig. 55). This is
the mammalian stage. Finally, it covers and overhangs all, and thus
assumes the human stage (Fig. 56).

[Illustration:

  FIG. 54.--Bird-stage. _of_, olfactive lobe; _cr_, cerebrum; _th_,
      thalamus; _ol_, optic lobe; _cb_, cerebellum; _m_, medulla.
]

[Illustration: FIG. 55.--Mammalian stage.]

[Illustration: FIG. 56.--Human stage.]

We have spoken thus far only of relative _size_; but progressive
changes take place also in complexity of structure--i. e., in the
depth and number of convolutions of the cerebrum and cerebellum. The
cerebrums of fish, of reptile, bird, and lower mammals are smooth.
About the middle of the mammalian series it begins to be convoluted.
These convolutions become deeper and more numerous as we go upward in
the scale, until they reach the highest degree in the human brain.
The object of these inequalities is to increase the surface of gray
matter--i. e., the extent of the force-generating as compared with
the force-transmitting part of the brain, or battery as compared with
conducting-wire. Now, in embryonic development the human brain passes
also through these stages of increasing complexity of organization.
Here also the ontogenic is similar to the taxonomic series.

Now, why should this peculiar order be observed in the building of the
individual brain? We find the answer, the only conceivable scientific
answer to this question, in the fact that _this is the order of the
building of the vertebrate brain by evolution_ throughout geological
history. We have already seen that fishes were the only vertebrates
living in the Devonian times. The first form of brain, therefore, was
that characteristic of that class. Then reptiles were introduced;
then birds and marsupials; then true mammals; and, lastly, man. The
different styles of brains characteristic of these classes were,
therefore, successively made by evolution from earlier and simpler
forms. In phylogeny this order was observed because these successive
forms were necessary for perfect adaptation to the environment at each
step. In taxonomy we find the same order, because, as already explained
(page 11), every stage of advance in phylogeny is still represented
in existing forms. In ontogeny we have still the same order,
because ancestral characteristics are inherited, and family history
recapitulated in the individual history.

[Illustration: FIG. 57.--A, brain of extinct Ichthyornis; B, modern
tern.]

[Illustration: FIG. 58.--A, brain of Eocene dinoceras; B, Miocene
brontothere; C, modern horse.]

But not only is this order found in the evolution of the whole
vertebrate department, but something of the same kind is found also
in the evolution of _each class_. The earliest reptiles, the earliest
birds, and the earliest mammals had smaller and less perfectly
organized brains than their nearest congeners of the present day.
This is shown in the accompanying figures (Figs. 57 and 58). To
carry out one example more perfectly: In the history of the horse
family, in connection with the changes of skeletal structure already
described (page 108), we have also corresponding changes in the
size and structure of the brain; _pari passu_ with the improvement
of the mechanism we have also increased engine-power and increased
muscular energy and therefore increased activity and grace. The brain
of a modern horse, though not very large, is remarkable for the
complexity of its convolutions. The great energy, activity, and nervous
excitability of the horse are the result of this structure.

=Cephalization.=--Thus, in going up the phylogenic, the taxonomic,
or the ontogenic series, we find a gradual process of development
headward, brainward, cerebrumward; or, more generally, we might say
that in all organic evolution we find an increasing dominance of the
higher over the lower, and of the highest over all. For example, in
the lowest plane of either series we find first the different systems
imperfectly or not at all differentiated. Then, as differentiation
of these progress, we find an increased dominance of the highest
system--the _nervous system_; then in the nervous system, the
increasing dominance of its highest part--the _brain_; then in the
brain the increasing dominance of its highest ganglion--the _cerebrum_;
and, lastly, in the cerebrum the increasing dominance of its highest
substance--the exterior gray matter--as shown by the increasing number
and depth of the convolutions. This whole process may be called
_cephalization_.

Shall the process stop here? When evolution is transferred from the
animal to the human plane, from the physiological to the psychical,
from the involuntary and necessary to the voluntary and free, shall not
the same law hold good? Yes! all social evolution, all culture, all
education, whether of the race or the individual, must follow the same
law. All _psychical advance is a cephalization_--i. e., an increasing
dominance of the higher over the lower and of the highest over all; of
the mind over the body, and in the mind of the higher faculties over
the lower; and, finally, the subordination of the whole to the highest
moral purpose.

[Illustration: FIG. 59.--Homocercal tail-fin. A, form; B, structure.]

[Illustration: FIG. 60.--Heterocercal or vertebrated tail-fin. A, form;
B, structure.]

=4. Fish-Tails.=--Still another and last example: It has long been
noticed that there are among fishes two styles of tail-fins. These
are the even-lobed, or homocercal (Fig. 59), and the uneven-lobed,
or heterocercal (Fig. 60). The one is characteristic of ordinary
fishes (teleosts), the other of sharks and some other orders. In
_structure_ the difference is even more fundamental than in _form_.
In the former style the backbone stops abruptly in a series of short,
enlarged joints, and thence sends off rays to form the tail-fin
(Fig. 59, B); in the latter the backbone runs through the fin to its
very point, growing slenderer by degrees, and giving off rays above
and below from each joint, but the rays on the lower side are much
longer (Fig. 60, B). This style of fin is, therefore, _vertebrated_,
the other _non-vertebrated_. Figs. 59 and 60 show these two styles in
form and structure. But there is still another style found only in the
lowest and most generalized forms of fishes. In these the tail-fin is
vertebrated and yet symmetrical. This style is shown in Fig. 61, A and
B.

[Illustration: FIG. 61.--Vertebrated but symmetrical fin. A, form; B,
structure.]

Now, in the development of a teleost fish (Fig. 58), as has been shown
by Alexander Agassiz,[24] the tail-fin is first like Fig. 61; then
becomes heterocercal, like Fig. 60; and, finally, becomes homocercal
like Fig. 59. Why so? Not because there is any special advantage in
this succession of forms; for the changes take place either in the egg
or else in very early embryonic states. The answer is found in the
fact that _this is the order of change in the phylogenic series_. The
earliest fish-tails were either like Fig. 61 or Fig. 60; never like
Fig. 59. The earliest of all were almost certainly like Fig. 61; then
they became like Fig. 60; and, finally, only much later in geological
history (Jurassic or Cretaceous), they became like Fig. 59. This order
of change is still retained in the embryonic development of the last
introduced and most specialized order of existing fishes. The family
history is repeated in the individual history.

[Illustration: FIG. 62.--Tail of the Archæopteryx.]

[Illustration: FIG. 63.--Tail of a modern bird.]

Similar changes have taken place in the form and structure of birds’
tails. The earliest bird known--the Jurassic Archæopteryx--had a long
reptilian tail of twenty-one joints, each joint bearing a feather on
each side, right and left (Fig. 62). In the typical modern bird, on the
contrary, the tail-joints are diminished in number, shortened up, and
enlarged, and give out long feathers, fan-like, to form the so-called
tail (Fig. 63). The Archæopteryx’ tail is _vertebrated_, the typical
bird’s _non-vertebrated_. This shortening up of the tail did not take
place at once, but gradually. The Cretaceous birds, intermediate in
time, had tails intermediate in structure. The Hesperornis of Marsh
had twelve joints. At first--in Jurassic--the tail is fully a half
of the whole vertebral column. It then gradually shortens up until it
becomes the aborted organ of typical modern birds. Now, in embryonic
development, the tail of the modern typical bird _passes through all
these stages_. At first the tail is nearly one half the whole vertebral
column; then, as development goes on, while the rest of the body grows,
the growth of the tail stops, and thus finally becomes the aborted
organ we now find. The ontogeny still passes through the stages of the
phylogeny. The same is true of all tailless animals. The frog is tailed
in the larval condition, because its ancestors were tailed amphibians.
Even man himself is endowed with a much more considerable tail, viz.,
eight or nine joints, in his early embryonic condition.[25]

We have taken all our examples from vertebrates, but quite as many
and as good examples might be found among articulates. Insects, in
the larval state, are worm-like in form. Hence it is probable that
the earliest progenitors of this class were worm-like. Again, some
insects have aquatic larvæ. The progenitors of these--in fact, of
all insects--were probably aquatic. Crabs, in a larval condition, are
long-tailed, and we know that the long-tailed crustaceans (Macrourans)
preceded the short-tailed (Brachyourans). Water-breathing animals
preceded air-breathers; the same is true in the ontogeny of the frog,
of many insects, and, we might add, even of mammals. For the breathing
of the _fœtus in utero_ is essentially by exposure of fœtal blood
to the oxygenated blood of the mother in a sort of _gill-fringes_
(placental tufts). But why should we multiply examples? The whole of
embryology, in every department, is made up of examples of the same law.

=Illustration of the Differentiation of the Whole Animal
Kingdom.=--Finally, the law of differentiation in the evolution of
the whole animal kingdom may be well illustrated by means of the
different directions taken in the development of the eggs of all the
various kinds of animals. Suppose, then, we have one thousand eggs,
representing all the different departments, classes, orders, families,
etc., of animals. Many of these may doubtless be identified by form
or size, or some other superficial character, as the eggs of this or
that animal, _but structurally they are all alike_. At first, i. e.,
as germ-cells, they all represent the _earliest condition_ of life on
the earth, and the _lowest forms_ of life _now_. If we now watch their
development, we find that some remain in this first condition without
further change. These we set aside. They are _Protozoa_. The remainder
continue to develop, but at first it would be impossible to say to
which of the several departments or primary groups they each belonged.
Then, by cell-multiplication, the original single cell becomes a
cell-aggregate. It may be compared now to a compound protozoan, such
as Foraminifera. The cell-aggregate then differentiates into layers,
and forms, in fact, a two-layered sac called a gastrula. This is the
structure of some of the lowest cœlenterates, such as the hydra. Thus
far all seem to go together. But now, for the first time, the primary
groups are declared. If it be a vertebrate, for example, the most
fundamental characters--the cerebro-spinal axis, the vertebral column,
and the double cavity, neural and visceral, are outlined. Suppose,
now, we set aside all other departments, and fix our attention on the
vertebrates. At first we could not tell which were mammals, birds,
reptiles, or fishes; but after a while the classes are declared. We
now set aside all other classes and watch the mammals. After a while
the order declares itself. We select the ungulates. Then the family is
declared, say the _Equidæ_; then the genus, _Equus_; and, lastly, the
species, _Caballus_.[26]

The same would be true if we followed any other line of development,
whether in vertebrates or in any other department. Observe, then, that,
in following any one line as we have done, there is an increasing
specialization, and, if we followed all the lines, an increasing
differentiation, like the branching and rebranching of a tree. Now,
this is the type and illustration of what took place in the development
of the animal kingdom. We conclude that the animal kingdom appeared
first as Protozoa, then as living cell-aggregates or compound
protozoans, then as gastrula or two-layered sacs with oral opening.
Then the great primary departments, unless we except the vertebrates,
commenced to separate. This took place before the primordial period;
for in the primordial fauna we have all the departments, except
vertebrates, already declared. This completely explains why it is that
we are able to trace homology only within the limits of each primary
group.

But the question has doubtless already occurred to the thoughtful
reader, “Why should the steps of the phylogeny be repeated in the
ontogeny?” The general answer is doubtless to be found in the law of
heredity--that wonderful law, so characteristic of living things. We
have compared it to a brief recapitulation from memory--the minor
points, especially if they be also early, dropping out. But can we
not explain it further? It is probable that we find a more special
explanation in “_the law of acceleration_,” first brought forward by
Prof. Cope. By the law of heredity each generation repeats the form and
structure of the previous, and in the order in which they successively
appeared. But there is a tendency for each successively-appearing
character to appear a little earlier in each successive generation;
and by this means time is left over for the introduction of still
higher _new_ characters. Thus, characters which were once adult are
pushed back to the young, and then still back to the embryo, and thus
place and time are made for each generation to push on still higher.
The law of acceleration is a sort of young-Americanism in the animal
kingdom. If our boys acquire knowledge and character similar to that of
adults of a few generations back, they will have time while still young
and plastic to press forward to still higher planes.

=Proofs from Rudimentary and Useless Organs.=--These have to a large
extent been anticipated under previous heads. The tails of birds and
the gill-arches of reptiles are rudimentary. The finger-bones of a
whale’s paddle or a turtle’s flipper may be regarded as useless, at
least so far as the exact number of constituent pieces is concerned;
for an extended surface, without visible joints or separate fingers, is
all that is seen, and apparently all that is required. The splint-bones
of a horse’s foot or the dew-claws of a dog’s foot are certainly
useless. We have already, in speaking of modifications of structure and
of embryonic conditions, given many examples of this kind, but it may
be well to add some striking examples with this special point in view.

If different orders of existing mammals were indeed made by gradual
modification of some generalized primal form, then it is evident that
these useless remnants of once useful parts would be most common in
the most highly modified forms. Now, of all mammals, the whales are
perhaps the most modified or changed from the original mammalian
form--so much modified, in fact, that the popular eye scarcely
recognizes them as mammals at all. Here, then, we might expect, and do
indeed find, many examples:

1. The baleen whales have no teeth, and no use for them. They have
instead a wonderful armature of fringed whalebone plates (baleen),
by means of which they gather their food.[27] Yet the embryo of
the whale has a full set of rudimentary teeth deeply buried in the
jawbone, and formed in the usual way characteristic of mammalian
teeth--i. e., by an infolding of the epithelial surface of the
gum--_but the teeth are never cut_; in fact, they reach their highest
development in mid-embryonic life, and are again absorbed. Why, then,
this waste of developmental energy? Why should teeth be formed only
to be reabsorbed without being cut? The only conceivable answer is,
because the ancestors of the whale, before the family of whales was
fairly established, had teeth which were gradually, from generation to
generation, aborted, because no longer used, the baleen plates having
taken their place. If whales were made at once out of hand as we now
see them, is it conceivable that these useless teeth would have been
given them?

2. Again, many whales have rudimentary pelvic bones, but no hind-limbs.
Why should there be pelvic bones, when the sole object of these bones
is to act as a basis for hind-limbs? In some whales, for example the
right whale, there are also rudiments of hind-legs, but these are
buried beneath the skin and flesh, and therefore, of course, wholly
useless. The only explanation of these facts is that the ancestors of
all the whales before they had become whales were quadrupeds, which
afterward took to the water, and little by little the hind-legs, for
want of use, dwindled away to the useless remnants which we now find.

3. Again, whales seem to be hairless, yet rudimentary hairs are
found in the skin. Their organs of smell are rudimentary, but made
on the pattern of those of mammals, not of fishes--i. e., they are
air-smelling, not water-smelling organs. From all these, as well as
many other facts, it is evident that the whales descended in early
Tertiary times from some marsh-loving, powerful-tailed, short-legged,
scant-haired quadruped by modifications gradually induced by increasing
aquatic habits.

Examples of such rudimentary organs might be multiplied without limit.
As might be expected, some are found even in man. Such, for example,
are the muscles for moving the ear, necessary in animals but useless
in man, and therefore rudimentary. Similarly useless in man are the
scalp-muscle, used by animals to erect the crest or bristles on the
head, and the skin-muscle of the neck and chest, used by animals
for shaking the skin of those parts. Most persons have lost the
power of using these. For my part I can use them all--ear-muscles,
scalp-muscle, skin-muscle--but they serve no useful purpose.

Again, and finally, in man and many mammals we find a slender,
worm-like appendage about three inches long, attached to the cæcum of
the large intestine. Anatomists and physiologists, under the influence
of that philosophy which maintains that every part of the fearfully
and wonderfully made human frame was _directly_ contrived to subserve
some useful purpose, have puzzled themselves to find the use of this.
It probably has no use; on the contrary, it is a continual source of
danger. If the human body had been made at once out of hand, it would
not have been there. How came it, then? It is the rudimentary remnant
of an organ--a greatly enlarged cæcum--which has served, and in some
mammals still serves, a useful purpose. All these cases are survivals;
they are organs which, like many customs in society, have outlived
their usefulness, but still continue by heredity.

But why multiply examples? All along the track of evolution organs
become useless by changes in the habits of their possessors. They are
not, however, shed or dropped bodily at once. No; they are _retained
by heredity_, but _dwindle by disuse_, more and more, until they pass
away entirely. But even when they are entirely gone in the adult, they
are often found still lingering in the embryo. They are among the
most obvious and convincing proofs of the origin of organic forms by
derivation.




CHAPTER VIII.

PROOFS FROM GEOGRAPHICAL DISTRIBUTION OF ORGANISMS.


It is well known that the kinds of organisms found in widely-separated
countries differ more or less conspicuously. The traveler in Australia
or in Africa finds all, the traveler in Europe nearly all, the animals
and plants wholly different from those he has been accustomed to see
at home. Even the visitor from the Atlantic to the Pacific coast, if
he observes at all, will find nearly all organisms strange to him.
The facts of geographical diversity of organisms are so numerous and
complex that, at first sight, they seem utterly lawless. Only recently
this subject has been redeemed from chaos and reduced to something like
order and law by the light thrown upon it by the theory of evolution.
We will give, in very brief outline, the most important facts, and then
show how they may be explained.

=Geographical Faunas and Floras.=--The group of animals and plants
inhabiting any locality, whether peculiar to that locality or not,
is called, in popular language, its fauna and flora. But, in a true
scientific sense, a fauna and flora is a _natural_ group of animals
and plants in one place, _differing_ more or less conspicuously
from other groups in other places, and _separated from them by
physico-geographical boundaries, or by physical conditions of some
kind._ The members of such a group can only exist in certain harmonic
relations with external conditions, and with one another. These
relations with one another are often complex and nicely adjusted,
so that change in one term is propagated through the whole series
of terms, giving rise often to the most unexpected results, until
finally a new equilibrium is established. Thus, the destruction of
certain insectivorous birds, in mere wanton sport, may give rise to the
multiplication of insect pests, and this to the destruction of certain
kinds of plants, and this to the diminution of certain herbivores, and
this in its turn to the disappearance of certain carnivores. It is well
known that the introduction of rabbits into New Zealand and Australia
has produced the most unexpectedly disastrous effect upon certain
crops, on account of the absence of the fierce and active carnivores
which keep in check their excessive multiplication in Europe.

Now, among the physical conditions which limit faunas and floras, and
separate them from each other, the most important and universal is
temperature.

=Temperature-Regions.=--If we travel from equator to pole, we pass
through mean temperatures varying from 80° to 0°. This gives rise
to a very regular zonal arrangement of plant-forms: 1. We have
first a region in which palms and palm-like forms are abundant and
characteristic, and which therefore may be called the region of palms.
It corresponds with the tropic zone. 2. We next have a region in which
hard-wood foliferous trees are most abundant and characteristic;
first mostly evergreens and then deciduous trees, and therefore may
be called the region of hard-wood forests. This corresponds with the
temperate-zone. 3. Then we find a region characterized predominantly by
pines and pine-like trees and birches, and may be called the region of
pines. This is the sub-Arctic region. 4. Then a region without trees,
but only shrubs and summer plants. This is the Arctic region. 5. And,
finally, an almost wholly plantless region of perpetual ice--the polar
region.

These regions are determined wholly by temperature, and therefore, in
going up a mountain-slope to snowy summits, we pass through similar
regions in smaller space. For example, in going from sea-level to
the summits of the Sierra, 14,000 to 15,000 feet high, we commence
in a region of predominantly hard-wood trees; but at 3,000 feet the
forests become almost wholly coniferous, at 11,000 to 12,000 feet the
vegetation becomes shrubby, and at 13,000 feet we reach perpetual snow.

We have taken plants first, because these, being fixed to the soil and
incapable of voluntary seasonal migrations, are more strictly and
simply limited by temperature--i. e., the arrangement of different
kinds in zones is more simple and conspicuous. But the same rule
holds also for animals. In passing from equator to pole, animal kinds
also change frequently, so that there are many temperature-faunas in
which the animals are all very different. In both animals and plants,
species, genera, families, etc., are limited by temperature. These are
familiar facts; we recall them to the reader in order that we may base
thereon a clearer definition of these limits.

=More Perfect Definition of Regions.=--1. The area over which any form
spreads is called its _range_. Now, the range of a species is more
restricted than that of a genus, because, when a species is limited by
temperature, another species of the same genus may carry on the genus.
For the same reason the range of a family is usually greater than that
of a genus, and so on for higher classification-groups. For example,
pines range on the slopes of the Sierra from about 2,000 feet to
11,000 feet, but not the same species. In ascending, we meet first the
nut-pine (_Pinus Sabiniana_), then the yellow-pine (_P. ponderosa_),
then the sugar-pine (_P. Lambertiana_), then the tamarack-pine (_P.
contorta_), and last, the _Pinus flexilis_, etc.

[Illustration: FIG. 64.]

2. Where two contiguous temperature-regions come in contact, there is
no sharp line between; on the contrary, they _shade gradually_, almost
imperceptibly, into one another, the ranges of species overlapping and
interpenetrating, and the two species coexisting on the borders of
their ranges. This is represented by the diagram (Fig. 64), in which
the horizontal lines represent the north and south ranges of species of
two groups, A and B, separated by the dotted line.

3. Species also pass out gradually on the borders of these ranges and
others come in gradually, so _far as number and vigor of individuals
are concerned_. If _a a′_ and _b b′_ (Fig. 65) represent the north
and south range of two species, and _b a′_ their overlap or area of
coexistence, then the height of the curves A and B will represent the
number and vigor of the individuals in different parts of the range.

[Illustration: FIG. 65.]

4. While, therefore, there is a shading of contiguous groups into each
other by overlap of species-ranges; while there is also a gradual
passing out of species so far as number and vigor of individuals
is concerned, yet, in _specific characters_ we observe usually no
such gradation. Species seem to come in on one border with all their
specific characters perfect, remain substantially unchanged throughout
their range, and pass out on the other border, still the same species.
In other words, one species takes the place of another, usually by
_substitution_, not by _transmutation_. It is _as if_ species had
originated, no matter how, each in its own region, and had spread
in all directions as far as physical conditions and struggle with
other species would allow. This important subject will be more fully
discussed later.

5. We have thus far spoken of species as limited by temperature alone,
but they are limited also by _barriers_. If, then, there be an east and
west barrier, such as a high mountain-range, or a wide sea or desert,
there will be no shading or gradation of any kind, because the barrier
prevents overlapping, interpenetration, and struggle on the margins.
For example: The species north and south of the Himalayas, or north
and south of Sahara, are widely different. It is, again, _as if_ they
originated each where we find them and spread as far as they could, but
the physical barrier prevented mingling and shading.

6. There are temperature-regions south as well as north of the equator.
Now, although the climatic conditions are quite similar, the species of
corresponding temperature-regions north and south are wholly different.
It is, again, as if they originated where we find them, and were kept
separate by the barrier of tropical heat between. If carried over, they
often do perfectly well.


_Continental Faunas and Floras._

If the land-surfaces were continuous all around the globe, there is
little doubt that each temperature region with its characteristic
species would also be substantially continuous. There would, it is
true, be some local variations dependent upon soil and humidity,
etc., but substantially the same species would exist all around.
The distribution would be almost wholly zonal. But the intervening
oceans are complete barriers to continental species. Hence we ought to
expect, and do find, that the faunas and floras of different continents
are almost totally different. Each apparently originated on its own
continent, and did not spread to other continents, only because they
could not get there. It is necessary to explain this in more detail.

[Illustration: FIG. 66.--Polar projection of the earth. 1, tropical; 2,
temperate; 3, sub-arctic; 4, arctic; 5, polar regions.]

Fig. 66 represents a polar view of the earth, showing the eastern and
western continents, and the five temperature zones already described.
Now, if we examine the species in each region, commencing at the pole,
we find that those of Nos. 5 and 4 are almost identical all around.
The reason is obvious. The continents come close together there, with
ice-connection if not land-connection all around. There is but one
circumpolar region. But, as soon as we come down to No. 3 and No. 2,
the species on the two continents are nearly all different, because
there is an impassable barrier between, either in the form of ocean
or of Arctic cold. For example, the animals and plants inhabiting the
United States are almost wholly different from those in Europe, not
only in species, but even largely in genera and to some extent in
families. There are some exceptions to this rule, but these are of the
kind which prove the rule, or rather the principle on which the rule
is founded. These exceptions are mainly of three kinds: 1. _Introduced
species._--All our weeds, many garden-plants, and many animal pests are
of this kind. They were not found here when America was discovered,
only because they could not get here; for, when brought here, they
do so well that they often overrun the country and dispossess the
native species, as we ourselves have done the Indians. 2. _Hardy or
else wide-migrating species._--Hardy species have wide range; they
may belong to No. 4 as well as No. 3. If so, they range down to No. 3
on both continents. Migrating birds, such as ducks and geese, etc.,
breed in summer in No. 4, and migrate southward in winter on both
continents from the common circumpolar ground. 3. _Alpine species._--It
is a curious fact that species on tops of snowy mountains in temperate
regions of the two continents are wonderfully similar, though so
completely isolated. We are not yet prepared to discuss this point.
We shall do so later. Suffice it to say now that it can be completely
explained.

In region No. 1 the continental diversity is still greater. Not only
species and genera, but whole families and even orders, are peculiar
to each continent. The great pachyderms--elephant, rhinoceros,
hippopotamus--are peculiar to the Eastern; the edentates--sloths and
armadillos--to the Western. The humming-birds, those gems of the
forests, of which there are over four hundred species, and the whole
cactus family, are peculiar to America, while the tailless monkeys are
equally characteristic of the Eastern Continent.

The continents do not come together again toward the south, and,
therefore, as might be expected, the great difference between the two
persists to the southern points. The faunas of the southern points of
South America, Africa, and Australia are very different.

=Subdivisions of Continental Faunas and Floras.=--Besides the
subdivisions of continental faunas, north and south, determined
by temperature as already explained, if there be in any continent
an impassable barrier running north and south, there will be a
corresponding difference in the species on the two sides, east and
west. We give but one example: The North American Cordilleras or Rocky
Mountains, with their high ranges and desert plains, constitute a very
great barrier between the eastern and western portions of the United
States. Hence, we find an extraordinary difference between the species
inhabiting California and those found in the eastern portion of the
country. Speaking generally, all the species and many of the genera are
peculiar. The exceptions, too, are significant. Leaving out introduced
species, of which there are many, they are mostly strong-winged or
widely-migrating birds, such as the turtle-dove, the turkey-buzzard,
the bald eagle, and, of course, many water-birds.

=Special Cases.=--If any body of land is widely separated from
all other lands by deep seas, we invariably find a corresponding
peculiarity of its species. Thus, the species inhabiting Australia and
Madagascar are perhaps the most peculiar in the world. We do not dwell
further on these, because we will discuss them hereafter. There is a
little group of very small islands--the Galapagos--about six hundred
miles off the western coast of South America, and surrounded on all
sides by deep sea. These islands are stocked with a collection of
curious animals not found elsewhere on the surface of the earth; but
among them are no mammals at all. We might multiply examples without
limit. Even the rivers emptying in the same sea sometimes have each
its peculiar species of mussels. In the Altamaha River there are
several species of unios--such, for instance, as the wonderful spinous
unio--not found elsewhere. How came they there? Howsoever they may have
come there, they are now kept isolated there by barriers of land and of
salt water.

Many other curious details will come up in our discussion of the origin
of diversity.

=Marine Species.=--Precisely the same principles apply here; but
diversity in the case of marine species is perhaps less marked, and
certainly less general, because of the universal oceanic connection.
Open-sea species are therefore almost universal. But many marine
species are confined to shallow water, and therefore to shore-lines.
The species on the two shores of the same ocean, or the two coasts of
the same continent, are different, being isolated east and west by
barriers of deep sea or of land, and north and south by temperature.
Also about isolated lands, like Australia and Madagascar, the species
are peculiar.

Thus, then, species, genera, etc., are limited in every direction;
north and south by temperature, and in all directions by barriers,
in the form of oceans, deserts, and mountain-chains. Add to these,
peculiar climates and soils, and we see that, from this point of view,
the whole surface of the earth may be divided and sub-divided into
regions, sub-regions, provinces, etc. It would carry us too far to
explain the primary and secondary divisions adopted by Mr. Wallace, and
the somewhat different ones suggested by Mr. Allen. Our main object is
to discuss the _cause_ of this diversity, and especially to show the
light shed upon it by the theory of evolution. We have only given a
sketch of the facts sufficient for this purpose.


_Theory of the Origin of Geographical Diversity._

It will be observed that all along we have assumed a sort of
provisional theory. We have said in every case, it is _as if_ organic
forms originated where we find them, and have gone thence wherever
they could--as far in every direction as physical conditions and
struggle with competing species would allow. This view has been
formulated as the “theory of specific centers of origin.” There would
be less objection to this as a first provisional theory did it not
assume a supernatural _mode_ of origin. But, in the minds of those
who hold it, it has usually assumed expressly or tacitly the form of
“_specific centers of creation_,” thus implying the immutability of
specific types and the supernaturalism of specific origin (page 68). In
this latter or usual form it completely fails to account for the facts
given above. For, if this were the mode of origin, each species ought
in every case to be perfectly adapted to its own environment, and to no
other. But, on the contrary, introduced species often flourish better
than in their own country, and better than the natives of their new
homes. In the less objectionable form of “specific centers of origin,”
without defining the mode of origin, it accounts well for many of the
more obvious facts of geographical diversity, as it _now_ exists, but
not all. According to this view, the amount of diversity ought to be in
strict proportion to the completeness of isolation, or impassableness
of the separating barriers; but this is not _exactly_ true. There is
another element, not yet mentioned, which is just as important as
impassableness, but which until recently has been left entirely out
of account. This is the element of _time_--the amount of time since
the barrier was set up, or during which it has continued to exist.
These two elements, it is true, are closely connected with each other;
for, since all changes in physical geography have taken place very
slowly--since barriers in the form of mountain-ranges and seas have
increased by slow process of growth--it is evident that impassableness
is, to some extent, a measure of time. But they are by no means in
strict proportion. The one or the other may predominate.

Now, this time-element connects geographical distribution with changes
of physical geography and climate in _geological_ times, and especially
with the _latest_ of these changes, viz., those occurring during the
_Glacial epoch_. During that remarkable epoch extraordinary changes
of climate, from extreme Arctic rigor to great mildness, enforced
wide migrations of species southward and northward; while concomitant
changes of physical geography, by elevation of the earth’s crust over
wide areas, opened highways between previously-isolated continents,
permitting migrations in various directions, and by subsequent
depression again isolating the migrated species in their new homes.
It is evident, then, that the recognition of the element of almost
unlimited time at once introduces into the question of geographical
distribution the _idea of evolution_. If the study of geographical
distribution, as _it now exists_, and as a part of science of physical
geography, gave rise naturally to the theory of “specific centers of
origin,” the study of the same, in connection with geological time,
and as a part of geological science, now demands its explanation by the
theory of evolution.

It must be borne in mind, then, that geographical diversity of
organisms is not a question of the present epoch only. There has
been geographical diversity in every previous geological epoch; it
is, therefore, a question of geology as well as of biology. It is
probable, however, that diversity has increased with the course of
geological times, and is greater now than ever before. In other words,
in the evolution of the organic kingdom, the law of differentiation
has prevailed here, as in other departments of biology. A clear
statement of the causes of the _present_ distribution of organisms
must embrace also the causes of geographical diversity _generally_.
We give, therefore, at once a brief statement of what seems to us the
most probable view, and shall then proceed to show how it explains the
present distribution.

=Most Probable View of the General Process.=--Bearing in mind, then,
this time-element, the phenomena of geographical diversity are best
explained by the following suppositions: 1. A gradual progressive
movement (evolution) of the organic kingdom, marching, as it were,
abreast, at equal rate along the whole line--i. e., in all parts of
the earth, and throughout all geological times, under the action of
all the forces or factors, and following all the laws, of evolution
already explained (pages 19 and 73). If this were all, there would be
no _geographical_ diversity, although _organic diversity_ might be
as great as it is now. There would be differentiation of forms and
structure everywhere, but no differentiation of groups in different
localities. 2. Under the influence of different conditions in
different places, more or less isolated from one another by climatic
or physical barriers, the onward movement (evolution) of organic
forms takes different directions and different rates, and gives rise
to local groups, which become more and more differentiated, without
limit as time goes on. This element, acting by itself throughout all
geological times, would ere this have produced an extreme geographical
diversity, such as does not anywhere exist. 3. From time to time, at
long intervals, extensive changes of physical geography and climate,
produced by crust elevations, partly enforce by change of temperature,
and partly permit by opening of gateways, extensive migrations and
dispersals of species, by which mingling and struggle for life and
final readjustment takes place, and extreme diversity is prevented.
Such mingling of different faunas and floras on the same ground,
and the severe struggle for life that thus ensues, and the survival
of the fittest in many directions, are, as already shown, among the
most powerful factors of evolution. They tend to _increase organic_
diversity, but to _diminish geographical_ diversity. 4. At the close
of such great periods of change as indicated in the last, by contrary
movement of the earth-crust--i. e., subsidence--new barriers are set up
and new isolations are produced, and the process of divergence again
commences and increases steadily so long as the barriers continue to
exist.

Now, the last of these periods of great changes and extensive
migrations, and subsequent isolations, was the Glacial epoch. It was
this epoch, therefore, which mainly determined the present geographical
distribution of species. Thus, the present distribution is a key to the
directions of the last great migrations, and therefore to the nature of
the changes in physical geography and climate which then occurred; and,
conversely, the character of these changes, determined in other ways,
_furnishes the only key to the present distribution of species_.

Before applying the foregoing principles in the explanation of special
cases, it may be well to give a very brief outline of the condition of
things during the Glacial epoch.

In America, during this epoch, by increasing cold the southern margin
of the great northern ice-sheet crept slowly southward, until it
reached the latitude of about 38° to 40°. Arctic species were thus
driven southward slowly, from generation to generation, until they
occupied the whole of the United States, as far as the shores of
the Gulf, while temperate species were forced still farther south,
into Central and South America. This period of extreme rigor and
southward migration was followed by a period of great mildness,
during which the ice and its accompanying Arctic conditions retreated
northward, followed by Arctic species. More than one advance and
retreat, apparently, occurred during this time. Again, during the
same time, brought about by northern elevation, there was broader
connection than now exists between North and South America, and free
migrations between, in both directions, enforced by extreme changes
in temperature. Also, during this or previous time, there were broad
connections between North America and Asia, in the region of Behring
Strait, and between America and Europe, in high-latitude regions, and
extensive migrations of faunas and floras between were thus permitted.
The necessary result of all these migrations of species, partly
enforced by changes of climate, partly permitted by opening of gateways
since closed, was exceptionally rapid changes in organic forms. This
was the result of two causes: First, the severer pressure of a changing
physical environment; and, second, a severer struggle for life between
the natives and the invaders.

In Europe, during the same time and from similar causes, there were at
least three or four different faunas struggling together for mastery
on the same soil. First, there were the Pliocene indigenes, who had,
if any, pre-emption right to the soil; second, invaders from Arctic
regions, driven southward by increasing cold; third, invaders from
Asia, permitted by the removal of the old sea-barrier which once
extended from the Black Sea to the Arctic, and of which the Caspian and
Aral are existing remnants, and thus opening a gateway for migration
which has remained open ever since; fourth, invaders from Europe and
Asia into Africa, and sometimes back again into Europe, by opening
of gateways through the Mediterranean, which have been since closed.
One of these highways was through Gibraltar, and one from Italy to
Africa through Sicily. As in America, so here, in even greater degree,
the severe pressure of changing environment and the severe struggle
for life produced rapid changes of organic forms. Many species were
destroyed; others saved themselves by modifications adapted more
perfectly to the changed conditions. There is little doubt that
man came into Europe with the Asiatic invasion, and was one of the
principal agents of change, especially in the way of destruction of
many old forms.

Such is a very brief outline of the last great geological change and
its general results. Being the last, this one has left the strongest
and most universal impress on the _present_ geographical distribution.
But similar changes by crust oscillations, if not also by extreme
changes of climate, have repeatedly occurred in geological times, and
some of the most remarkable geographical faunas and floras are the
result of these earlier geological changes. We will now give a few
examples illustrating these principles:

1. _Australia_ is undoubtedly more peculiar in its fauna and flora than
any other known country. Not only are all its species peculiar, not
found elsewhere on the face of the earth, but its genera, its families,
and even many of its orders of animals and plants, are also peculiar.
These facts are so familiar that it is unnecessary to dwell on them.
I need only mention, among plants, the whole of the simple-leaved
acacias, already mentioned on page 86, of which there are so many
species, and the whole family of the eucalyptids, of which there are
several hundred species. Among animals I need mention only the order
of monotremes, or egg-laying mammals, and nearly the whole order of
marsupials, or pouched animals, of which there are over two hundred
species. On the other hand, the true typical mammals are entirely
absent, with the exception of a few bats and a few rats, which have
evidently been accidentally introduced from abroad.

Another very noteworthy fact, which must be taken in connection with
the last, is that Australian forms are far less advanced in the race of
evolution than those of any other country--i. e., that many old forms
which have long ago become extinct elsewhere are still retained there.
A few examples will suffice. The marsupials just mentioned are an old
form once universally distributed, but now nearly extinct everywhere,
except in Australia; the cestracion, or Port Jackson shark, and the
ceratodus, are Palæozoic and Mesozoic forms retained only in Australia.

What is the explanation of these remarkable facts? We find the
sufficient answer in the fact that Australia has been long isolated
from all other countries. While geographical changes in geological
times have mingled more or less the organic forms of other countries,
and the sharp struggle for life has produced more rapid advance and
the production of many new and higher forms better armed for the
battle of life, Australia has remained isolated from competition, and
therefore comparatively unprogressive.

Can we tell when Australia was finally isolated? Approximately we can.
The class of mammals is divided into two groups, which differ widely
from each other; so widely, that they are called sub-classes. These
are placental mammals, or true typical mammals, and non-placental or
reptilian mammals. The non-placentals include only the marsupials and
the monotremes (ornithorhyncus and echidna). The monotremes actually
lay eggs and incubate them. In the marsupials the embryo has no
placental connection with the mother, and is born in a very imperfect
condition, utterly unfit for independent life, and placed in the pouch
(marsupium), and _permanently_ attached there to the teat until it is
capable of independent life; after which only it voluntarily nurses
like other new-borns. In other words, the gestation commenced in the
womb is completed in the pouch. The uterine gestation in the opossum
is only seventeen days, while the marsupial gestation is about two
and a half months. In a kangaroo seven feet high in sitting position
the embryo at birth is only one inch long--a pink, hairless, almost
amorphous mass. The monotremes are pure oviparous animals, like birds
and reptiles. The marsupials might well be called _semi-oviparous_.
In pure egg-layers the whole embryonic development is outside of the
body; in pure young-bearers the whole is within the body; in marsupials
it is partly within and partly without. Now--1. The monotremes are
found nowhere but in Australia and the neighboring New Guinea. 2. The
marsupials are also all confined to the Australian region, except a few
oppossums in America. 3. There are some two hundred and thirty species
of non-placentals in the Australian region. 4. As already said, there
are no true mammals at all in Australia, except a few bats and rats
which have come accidentally from abroad. 5. But non-placentals existed
abundantly in _Mesozoic times everywhere_, both in Europ-Asia and in
America, while true mammals did not appear at all on the surface of
the earth until the _Tertiary_, when they almost immediately became
very abundant everywhere, except in Australia. _Evidently, therefore,
Australia was isolated before the Tertiary._ The enormous difference
between its fauna and flora and those of other countries is due to
at least three things: 1. So long an isolation necessarily produced
great divergence of forms. This alone, however, would not affect the
_grade of organization_. 2. Saved from wide migrations, and especially
invasions from Eurasia, the great field of competitive struggle, it was
left far behind in the race of evolution. Hence many of its forms are
archaic; its mammalian fauna, for instance, is still in the Mesozoic
stage. 3. Its distance from other large continents is so great that
accidental colonization has been very slight, only extending to a few
bats and a few rats.

I stop a moment to insist on the effect of competitive struggle in
developing organic forms strong for the battle of life. Of all the
continents, Eurasia has been the scene of most frequent geological
changes, and therefore the arena of fiercest competitive struggle
through wide and frequent migrations. Eurasian species, therefore, are
the strongest of all. They have conquered wherever they have gone.
Species in isolated regions are usually the weakest. The great moas
and the dodo could not have continued to exist unless protected in a
sort of bomb-proof. Kangaroos would now be quickly exterminated by the
introduction of fierce Eurasian carnivores.

2. _Africa._--The fauna of that part of Africa north of Sahara is
essentially Mediterranean--i. e., a sub-group of the Eurasian. Sahara,
rather than the Mediterranean Sea, is the true intercontinental
barrier. The true African region, therefore, is south of Sahara. Now,
according to Mr. Wallace, whom I mainly follow here, the true African
mammalian fauna consists of two very different groups of animals. The
one is a group of very small, curious animals, mostly low forms of
insectivores and lemurs, very peculiar to this region, though more
resembling those of Madagascar than of any other region; the other
is a group of large and powerful animals which dominate the region.
These latter are similar to, though not identical with, those which
inhabited Eurasia in Pliocene times. The great carnivores, pachyderms,
and ruminants of the region are examples of this group. Now, the
explanation of these facts is as follows: The indigenes of Africa are
the animals of the first group. Africa, in Tertiary times, was isolated
from the great field of combat, Eurasia, and therefore its animals were
small, of low grade, and peculiar. During later Tertiary (Pliocene)
times, then, Africa was inhabited by animals of the first group, while
Eurasia was dominated by animals of the second group. These two groups
were then separated by the Desert of Sahara, or else by a sea in that
region. Some time during the Glacial epoch geographical changes removed
this barrier, and climatic changes drove the Eurasian animals southward
into Africa, where, finding congenial climate, they took possession
of the continent, dominating the feebler natives. Subsequently they
were isolated there by the formation of the desert, and the process
of divergence commenced, and has gone on to the formation of many
new forms. Meanwhile the change, partly by extinction and partly by
modification, has gone on still more rapidly in Eurasia, but in a
different direction. Hence, Africa is regarded as one of the primary
faunal regions.

3. _Madagascar._--This, next to the Australian, is probably the most
peculiar faunal region known. There is probably not a single mammalian
species found there which is known to occur anywhere else. It is
remarkable also as the principal home of that strange, generalized,
ancient form of monkeys--the lemurs. And yet its animals, though
very different, have a distant resemblance to those of Africa; not,
however, to the present dominant type, but to those we have called
the indigenes. Not one of the northern invaders is found there. The
obvious conclusion from these facts is, that Madagascar was formerly
united with Africa, and both were occupied by the same mammalian fauna
(which may be called African indigenes, although they were considerably
different from their descendants of the present day), but became
separated before the northern invasion. The effect of this invasion
was to hasten the steps of change in the indigenous fauna of Africa,
partly by extermination, partly by modification, while the isolated
portion in Madagascar went on at the usual slow rate of change in
isolated regions. The time since the separation (which was certainly
during the Tertiary period) has been sufficiently long to produce very
great divergence in both, but _especially in the African indigenes_. In
the fauna of Madagascar, therefore, we have a nearer approach to the
original fauna of both. On account of this long isolation, we have here
many ancient types which are extinct elsewhere. The lemurs are such an
ancient type. These are a wonderfully-generalized type of monkeys--a
connecting link between monkeys and other mammals, especially
insectivores. As might be supposed, from the law of differentiation,
already explained (page 11), they are the earliest form, the
progenitors, of monkeys. In fact, in early Tertiary times, they were
found not only in Africa and Madagascar, but all over the earth, as the
only representatives of the monkey family. The true monkeys were not
introduced until the mid-Tertiary. In Eurasia and in America (which at
that time was probably connected with Eurasia) wide migrations and
frequent conflicts of faunas produced comparatively rapid evolution
of new and higher forms, while in isolated Africa old types continued
until the invasion. Madagascar was spared this invasion, and therefore
old types are still preserved there. At present, at least three
quarters of all lemurs are confined to Madagascar, although a few
species are still found in Africa and in the great East Indian islands.

4. =Island-Life.=--Mr. Wallace has divided islands into two kinds,
continental and oceanic islands. The division is undoubtedly a good
one, although we may not always be able to refer an example with
certainty to the one or the other class. _Continental_ islands are
those on the borders of continents, and separated from the latter
only by _shallow water_. _Oceanic_ islands are those, usually very
small, found in the midst of the ocean, with abyssal depth all about.
Continental islands may be regarded as appendages to the neighboring
continent--as outliers of continents separated by submergence, and
have, in fact, been thus formed. Oceanic islands have been formed
geologically recently by volcanic action building up from the
sea-bottom. Continental islands have a continental structure--i. e.,
they are composed of stratified as well as of igneous rocks. Their
structure is a record of geological history, like that of the
neighboring continent. Oceanic islands are composed wholly of volcanic
rocks; or, if there be any stratified rocks, these are only of the most
recent date. As examples of continental islands we have New Zealand
as an appendage of Australia, the great East Indian (Borneo, Java,
Sumatra, etc.) and the Japanese Islands, etc., as appendages of Asia;
the British Islands, appendages of Europe; the West Indian Islands,
appendages of America; Madagascar, an appendage of Africa, etc., etc.
As examples of oceanic islands we have the Azores and Bermudas in the
Atlantic, and the Polynesian islands in mid-Pacific.

_a. Continental Islands._--Now, the fauna of continental islands, as
might be expected from the mode of origin of these islands, is similar
to, though not identical with, that of the neighboring continent; the
amount of difference being in proportion to the _length of time since_
they were separated and the _width of the separation_. _Madagascar_,
for example, has been long separated from its parent continent, and by
a wide and deep channel. Its fauna, therefore, differs greatly from
that of Africa, although resembling it more than that of any other
country. The separation of _New Zealand_ from Australia has been not
quite so long, and the divergence, therefore, is not so great. These
two will be sufficient illustrative examples of long separation, and
therefore of great differentiation of forms.

[Illustration: FIG. 67.--Map of outline of coast of Western Europe, if
elevated 600 feet (after Lyell).]

On the other hand, the British Isles are an excellent example of
comparatively recent separation. These isles have probably been several
times united and separated from Europe, but we are here concerned only
with the more recent. They are now separated from the continent and
from one another only by shallow seas. An elevation of less than six
hundred feet--geologically a very small change--would bare the bottoms
of the Irish and English Channels and the North Sea, and connect these
islands with one another and with the continent (Fig. 67). Now, it is
well known that there were during the Glacial epoch, and subsequently,
several oscillations of level sufficient to connect and separate
these islands. In the mid-Glacial epoch the British Islands, by
submergence, were nearly obliterated, being reduced to an archipelago
of small islets representing the high mountains of Wales and Scotland.
The Pliocene fauna and flora were, therefore, largely exterminated.
During the close of that epoch they were elevated above the present
condition and broadly connected with the continent (Fig. 67), and the
newly-exposed land was taken possession of by European species, man
among the number. Still later--i. e., at the beginning of the present
epoch--the islands by subsidence were again separated, but not widely,
from the continent. This is the condition now. What, then, was the
result? 1. The fauna and flora of the British Isles are substantially
the same, but _less rich_ in species than that of Continental Europe,
some of the European species being wanting. This shows that the last
connection was not a long one; the colonization had not been completed
before re-isolation. 2. This poverty of species is more conspicuous in
Ireland, because colonization is progressive in space as well as in
time. Some species had not reached so far when Ireland was re-isolated
from England. The conspicuous absence of snakes, for example, is thus
accounted for. There is, we all know, another theory to account for
this, but we prefer the natural one. 3. The difference between British
and European fauna and flora is very small, it is true, but there is
some difference, varietal if not specific. The reason is, that the time
since separation is too small to produce much divergence, and the width
of the existing barriers not great enough to prevent colonization by
accidental causes.

The continental islands of the southern coast of Asia are good examples
of an intermediate condition as to the length of time since separation,
and of the consequent degree of differentiation of the faunas and
floras.

_Coast-Islands of California._--We give one more example, and dwell
upon it a little, because it occurs on our own coast.

The recent studies of Mr. E. L. Greene on the flora of the islands off
the coast of California have brought to light some facts which are an
admirable illustration of the principles laid down above.

On looking at a good map of California, any one will observe eight
or ten islands, some of them of considerable size, strung along the
coast from Point Conception southward, and separated from the mainland
by a sound twenty to thirty miles wide. They are in structure true
continental islands--outliers of the mainland separated by a subsidence
of a few hundred feet. Moreover, the date of their separation is known.
They were certainly connected with the mainland during the later
Pliocene and early Quaternary, for bones of the mammoth, characteristic
of that time, have been found on one of them.[28] They were therefore
separated during the Glacial epoch.

The main peculiarities of the flora of these islands are the following:

1. Out of nearly three hundred species of plants gathered by Mr.
Greene, about fifty are wholly peculiar to these islands. 2. Of the
remaining two hundred and fifty species, nearly all are distinctively
Californian. In other words, the distinctively Californian forms are
very abundant, while the common American forms are rare--i. e., the
island flora is distinctively Californian, with many peculiar species
added.

I explain these facts as follows: The whole coast-region of California
is geologically very recent, having emerged from the sea as late as
the beginning of the Pliocene epoch. As soon as emerged it was of
course colonized from adjacent parts. Since that time its peculiar
flora has been formed by gradual modification. The environment has been
sufficiently peculiar, the isolation sufficiently complete, and the
time sufficiently long, to make a very distinct group of organisms. It
is one of Mr. Wallace’s primary divisions of the Ne-arctic region.

During late Pliocene and early Quaternary times, as already said, the
islands were still a part of the mainland, and the whole was occupied
by the same species, viz., the distinctively Californian species
now found in both, together, as I suppose, with the peculiar island
species. During the oscillations of the glacial times the islands were
separated by subsidence of the continental margin. Simultaneously with
this subsidence, or subsequently thereto, came the invasion of northern
species, driven southward by glacial cold. Then came the mingling of
invaders with natives, the struggle for mastery, the extermination
of many forms--viz., the peculiar island species--and the slight
modification of others, and the final result is the California flora
of to-day. But the island flora was spared this invasion by isolation.
Therefore the invading species are mostly wanting, the distinctive
island species were saved, and the result is the island flora of
to-day. The island flora, therefore, somewhat nearly represents the
Pliocene indigenes of both.

It will be observed that this case is somewhat like that of Madagascar,
but with a characteristic difference. In the case of Madagascar, the
separation has been long. The extreme peculiarity of its fauna is the
result partly of progressive divergence and partly of many forms saved
by isolation. In the case of the coast-islands of California, the time
has not been long enough for any great divergence by modification. The
peculiarity of its species is due almost wholly to species saved by
isolation.[29]

_b. Oceanic Islands._--We have seen that faunas and floras of
continental islands are somewhat similar to those of the neighboring
continent, though with varying degrees of difference--the amount of
difference, or divergence by evolution, being in proportion to the
amount of time and the impassableness of the separating barriers. But
oceanic islands have never been connected with any continent. They
are new land formed in the midst of the ocean by volcanic action.
When they first appeared they were, of course, without inhabitants
of any kind, animal or vegetal. How were they peopled? We answer by
_waifs_ from here and there--by _castaways from other lands_. The
dominance of particular kinds will depend on the direction of winds
and currents, bringing from some lands more than others, and upon the
kinds of animals or seeds of plants most liable to be successfully
carried across wide seas. Their faunas and floras, therefore, are
characterized by a mixture of species resembling, though not usually
identical with, those of various lands, with a predominance of those
of some one land, and by the singular and complete absence of mammals
and amphibians, these being unlikely to be transported by floating
timber, as are small reptiles and insects, etc. Among mammals, however,
there is a significant exception in favor of bats, the reason being
both their power of flight and their habit of concealment in hollow
trees, etc. To this explanation, however, we must add that divergence
by isolation will meanwhile go on in proportion to time. The Azores,
for example, have been peopled from Europe, Africa, and America, but
mostly from Europe, on account of the prevailing winds and currents
being favorable to colonization from that direction. There are many
curious peculiarities in the species, however, because colonization is
very slow, and divergent variation has been going on _pari passu_. The
Bermudas, on the other hand, have been colonized mainly from America,
because of the current of the Gulf Stream.

These few examples are sufficient for our purpose, which is only to
illustrate the causes of geographical distribution. If any one desires
to pursue this interesting subject, we would refer him to that most
fascinating book, Mr. Wallace’s “Island-Life.”

5. =Alpine Species.=--These afford an admirable illustration of the
fact that in isolated faunas and floras the amount of difference is
proportioned not only to the completeness of isolation, but also and
mainly to the _time of isolation_.

It is well known that Alpine species--i. e., those species inhabiting
the region bordering the perpetual snow of lofty mountains--are very
similar to one another, even in the most distant localities, where
their isolation from one another is as complete as possible; as, for
example, in the high Alps of Europe, the high mountains of Colorado
and California. Why is this? We find the key to this mystery in the
additional fact that _they are similar also to Arctic species_. A
somewhat full explanation is here necessary.

During Miocene times, magnolias and taxodiums (bald cypress),
like those in forests and swamps of Carolina and Louisiana, and
sequoias and libocedrus like those now in California, and many other
temperate-region forms of plants, grew abundantly in Greenland,
and northward certainly to 75° north latitude. At that time there
could not have been any perpetual polar ice, and therefore no Arctic
species, unless on _high mountains in polar regions_. In Pliocene
times perpetual polar ice, and therefore Arctic species, probably
commenced to appear. As the cold of the Glacial epoch came on and
increased in severity, the polar ice extended southward as a general
ice-sheet, until it reached in America 40° and in Europe about 50°
north latitude. In the United States its margin can be traced as
a distinct moraine through Long Island, middle New Jersey, middle
Pennsylvania; thence, less distinctly, following the Ohio River,
crossing the Mississippi; thence following the Missouri, on its south
side, into Montana. By the increasing cold, Arctic species were driven
slowly southward, generation after generation, until they occupied
the whole of the United States to the Gulf, and the whole of Europe
to the Mediterranean. As these species on the two continents came
from a _common home_ in polar regions, they were similar to one
another, except in so far as some slight divergent modification may
have been produced during their southward travel. When the glacial
rigor declined, and the ice-sheet gradually retreated to its present
position, Arctic species, following the snow-edge, went also northward,
on both continents, to their present home in polar regions. But there
was an alternative way of migration left open which was embraced by
certain plants and insects. While on both continents most individuals
went northward, some of them went upward, following the snow-edge into
high mountains, and were left _stranded there_. Thus it has come to
pass that the plants and insects of high mountains in temperate regions
of different continents, though so widely separated and impassably
isolated, are extremely similar to one another. But, though similar,
they are rarely identical. The time has been long enough for some but
not very great divergent modification. It is impossible to conceive a
more beautiful illustration of the principles we have been trying to
enforce.

       *       *       *       *       *

Thus, then, undoubtedly all the phenomena of geographical distribution
of species are most rationally explained on the principle of slow
evolution--changes, different in different places, and increasing with
the time of isolation and its completeness.

=Objection.=--The only objection which can be raised against this
view is the manner in which contiguous geographical faunas and floras
pass into one another when they are _limited not by barriers but
by temperature_. In passing from equator to poles, over continuous
land, we of course pass through many successive faunas and floras,
limited wholly or mainly by temperature. Now, if species are indeed
indefinitely modifiable, then on the borders of contiguous faunas or
floras, where one species disappears and another closely allied but
adapted to a colder temperature takes its place, the one species (say
the anti-evolutionists) ought to be gradually _transmuted_ into the
other, so that all the gradations may be traced. But this is certainly
not usually the fact. On the contrary, a species may indeed pass out
gradually, and another come in gradually, so far as _number and vigor
of individuals are concerned_; but, in _specific character_, they
may be said, usually at least, to come in suddenly, with all their
characters perfect, remain unchanged throughout their whole range, and
pass out suddenly at its borders. Another species takes its place,
overlapping in range and coexisting on the borders of both; this also
continues unchanged, as far as it goes, and so on. The change from one
fauna to another is apparently not by _transmutation_ of one species
_into_ another by gradations, but by _substitution_ of one perfect
species _for_ another perfect species. As a broad general statement,
the condition of things is precisely such as would be the case if
specific types were substantially immutable by physical conditions, but
were originated in some inscrutable way (created) in the regions where
we now find them, and have spread in every direction as far as physical
conditions and struggle with other species would allow them--their
ranges therefore interpenetrating and overlapping one another on their
borders.

Two characteristic examples will make our meaning clear. There is not
a more characteristic tree known than the sweet-gum, or liquidambar.
This tree grows from the borders of Florida to the shores of the
Great Lakes. It may indeed be most numerous and vigorous somewhere in
the middle region, and may die out gradually in number and vigor of
individuals on the borders of its range, but in specific character it
is substantially the same throughout, easily recognizable by its dense
wood, its winged bark, its five-starred leaf, its spinous burr, and its
fragrant gum. Physical conditions may diminish its number and vigor,
and limit its extension, but seem powerless to essentially modify its
specific character. It seems to give up its life rather than change its
nature.

Another striking example: The sequoias (redwood and big-tree) are
entirely confined to California, and there are only two species now
existing, viz., the redwood (_S. sempervirens_) of the Coast Ranges,
and the big-tree (_S. gigantea_) of the Sierra Nevada. Doubtless they
are most numerous and vigorous somewhere in the middle of their range,
and die out gradually in number and vigor on the borders north and
south, being replaced there by other genera better adapted to the
physical conditions; but in specific character they remain essentially
unchanged throughout. They are everywhere the same--easily recognizable
by wood, bark, leaf, and burr. Both in this case, and in the previous
one of the sweet-gum, it is as if they were created perfect in their
present localities, and have spread in all directions as far as
physical conditions and the struggle with other competing species would
allow; but physical conditions seem powerless to change them into any
other species by adaptive modification.

=Answer.=--We have, we believe, stated the objection fairly. The
answer is, that the elements of _time_ and of _migrations_ have not
been taken into the account. In fact, this objection was conceived and
formulated before the idea of geological time was fully assimilated by
the human mind, and our theories of origin adjusted to it. If these
species did indeed originate where we now find them, and _in the
present geological epoch_, the argument might at least be entertained;
but this is not the fact. We know something of the geological history
of all these species, and the history of the migrations of some of
them. We know that sweet-gums were abundant and of _many species_ in
the United States in Tertiary times, and all have become extinct except
this remnant. Whatever of modifications there were must be looked
for at or about the time of its origin in Tertiary times, not now.
Species, like individuals, are plastic only when young. This one has
already become rigid, and all the more so as it is a remnant widely
separated from other species. For competition is strongest and most
effective with nearest allies. Present species are mostly isolated
remnants--terminal twiglets of the tree of life. Twiglets are of course
widely separated at their visible ends. Their points of union with
other twiglets must be sought below.

In the case of the sequoias, we know something also of the history of
their migrations. In Miocene times they were abundant, and of many
species in circumpolar regions. Some twenty-four species of fossil
sequoias are known, fourteen of which are Tertiary. By the cold of
the Glacial epoch they were driven slowly southward, both in America
and in Europe--in America as far as Southern California. After the
Glacial epoch, and the return of temperate conditions, they doubtless
attempted to go northward again; but these great changes were too much
for them; they were wholly exterminated in Europe, and nearly so in
America. A few were left stranded high up on the slopes of the Sierra
Nevada, and on the cool, moist slopes of the Coast Ranges. The species
now in California are not identical with those found in the Miocene
strata of Greenland; but the difference is only what we might expect
after such extensive migrations and such long and severe struggle for
life. Further, it is noteworthy that the Miocene species fall into two
groups, viz., the yew-like leaved and the cypress-like leaved. These
are represented to-day in California, the one by the redwood, the other
by the big-tree. They are evidently direct descendants of the Miocene
species, though somewhat modified.

But it will be objected that there ought to be some cases of
transitional forms showing transmutation--in fact, there ought to
be some cases of species now forming under our eyes. There are, we
believe, examples of such cases. But intermediate forms are not likely
to be maintained long, especially if migrations occur to give rise to
severe conflict of forms. In that case the intermediate forms are soon
eliminated, and species become distinct. This important point will be
discussed more fully in the next chapter.




CHAPTER IX.

PROOFS FROM VARIATION OF ORGANIC FORMS, ARTIFICIAL AND NATURAL.


As already stated, page 40, the use of the method of experiment in
the field of biology is, unfortunately, very limited. Nevertheless,
it is already beginning to be used more and more in the department
of physiology, and may be used also, to a limited extent, in the
department of morphology. It is true that direct _scientific_
experiments, for the express purpose of producing permanent
modifications of form, and thus testing the theory of evolution, are of
comparatively little value as yet, because the all-important element
of time is wanting. The steps of evolution are so slow, and the time
necessary to produce any sensible effect is usually so great, that, in
comparison, man’s individual lifetime is almost a vanishing quantity.
But, from time immemorial, experiments have been _unconsciously_
made by man on domestic animals and food-plants, which bear directly
on this subject. All domestic animals and food-plants, and many
ornamental flowering plants, have been subjected for ages to a process
of artificial selection acting upon natural variation of offspring.
As wild species are modified, we believe, indefinitely by divergent
variation and _natural_ selection, so domestic species are modifiable
certainly largely, perhaps indefinitely, by divergent variation
and _artificial_ selection by man. We all know the extraordinary
modifications which have thus been gradually brought about in domestic
animals, such as dogs, horses, sheep, pigeons, etc.; in food-plants,
as cereal grains, garden-vegetables, etc., and in ornamental plants,
as roses, dahlias, pinks, etc. We can only give very briefly the
principles of the process by which these extreme modifications are
produced, referring the reader to works specially devoted to this
subject for more complete accounts.

Let it be borne in mind, then (_a_), that inheritance is not only
from the immediate parents, but from the whole line of ancestry. The
inheritance from the immediate parents is, doubtless, usually greater
than from any other _one_ term of the ancestral series--the effect on
the offspring of any previous generation becomes, doubtless, less and
less as the distance from the offspring increases--yet the _sum_ of
the ancestral inheritance is far greater than the immediate parental.
Let it also be borne in mind (_b_) that true breeding from one form
for many generations creates a fund of heredity in that form, and thus
tends to produce fixity, rigidity, or permanence in that form.

[Illustration: FIG. 68.]

Now, the method of producing artificial breeds, sometimes consciously,
sometimes unconsciously, is, briefly, as follows: Suppose it be
desired to obtain a variety of an animal, say a dog, having a
certain character. We start from a common type, _a_ (Fig. 68). If
this type were allowed to breed naturally, the slight divergent
variation of offspring represented by the radiating lines would
neutralize one another by interbreeding, the individual differences
would be “_pooled_” in a common stock, and the species would remain
substantially constant. But if among all these slightly divergent
varieties we select one, _b_, which seems in the right direction, and
ruthlessly destroy all the others (indicated by crossing them out by
the circular line), and breed this variety, _b_, only, we shall get
again a number of divergent varieties. It may be that the larger number
of these will be backward, in the direction of the original type _a_,
on account of the ancestral heredity in that direction, but some will
again be in the desired direction. Let all the varieties other than
the desired one, but especially the backward-going or reverting ones,
be again destroyed, and the one kind only selected which seems to be
in the right direction, viz., _c_. As we push the form thus from
generation to generation in the desired direction, especially if we
attempt to hasten too much the process, the resistance to movement--if
I may use the expression--in that direction becomes greater and greater
(shown by the decreasing distances between the successive points of
divergence, _a_, _b_, _c_, _d_, etc.), and the tendency to reversion
becomes stronger (shown by the greater number and length of the
backward-going lines), until finally it is almost impossible to push
any farther. We will suppose that _x_ is such a limit. But if, now,
we breed true on the point _x_, destroying the reversions or backward
variations for many generations, we will gradually accumulate a fund
of ancestral heredity on this point which increases with every added
generation, until finally the tendency to reversion becomes small. The
variety _breeds true_ without further interference, or with only very
general superintendence. Such a permanent variety is called a _race_.
After a race is firmly established for a sufficient length of time,
and the tendency to reversion is lost, it may itself become a new
point of departure for the formation of new varieties or races, in the
same or other directions. Thus, during even the brief history of man,
have been formed races of the different domestic animals, and useful
and ornamental plants, differing so greatly from each other that, if
found in the wild state, they would unhesitatingly be called different
species, or even in some cases different genera.

Now, if art can vary form so greatly, and in so short time, why may
not Nature in limitless time? If art by artificial selection, why not
Nature by natural selection? Nature is as rigid in selection and as
ruthless in destruction: why may we not expect similar or even much
greater results? The process is similar in the two cases--i. e.,
selection among varieties in offspring, only that the selection
is natural instead of artificial, and the process is so slow that
there is little tendency to reversion in the latter case. Suppose,
then, we have a gradually changing physical environment, or climate.
Among the divergent varieties of any species in each generation,
those would be preserved which are most in accordance with the new
climate, and the others would perish. This is natural selection, or
survival of the fittest. Add to this the effect of the change in
the organic environment. All species are modified by the changing
physical environment; but these modified species again all affect
one another in the competitive struggle for life, and the strongest
or swiftest, or most cunning, survive (natural selection). Add to
this, again, the struggle among the males for possession of the
females--for reproductive opportunities--by which only the strongest
and most courageous, or the most beautiful and attractive, leave
progeny which inherit their peculiarities (sexual selection). Add to
these, finally, _migrations_, voluntary among higher and involuntary
dispersals among lower animals and plants, and the consequent mingling
of faunas and floras--the migrations subjecting them to great change
of environment, both physical and organic, and the mingling producing
fiercer struggle for life--and we have in powerful operation many
causes of modification. Add, I say, all these causes of modification
together, and then make the process slow and continuous through
unlimited time, and where is the limit to the degree of change?
Commencing in any species, from any point of departure, there are
formed first slight modifications which would be called varieties; then
these modifications, continuing in the same direction, form races;
these races by wider separation become species, and species in their
turn become genera, etc. Comparing, again, to a growing tree, varieties
are swelling buds; when they grow into twigs, they are species; when
they branch again into different species, the branching stem becomes a
genus, etc.

We have thus far spoken only of the various forms of one factor, viz.,
the Darwinian factor of selection, whether natural or artificial.
We have dwelt upon this one, because the natural and the artificial
processes are so similar, and the artificial is so controllable. But
there are other factors in operation, in art as well as in nature. We
have already spoken (p. 73) of other factors of natural change. We
have shown how changing physical environment affects _function_, and
function affects _form and structure_, and how these slight changes are
integrated by heredity through many generations. We have also shown how
_use_ or _disuse_ increases or diminishes the size and change the form
of parts, and these changes, also, however slight, are integrated by
heredity.

Now, these factors are operative also in domestication of animals
and cultivation of plants. No environment is so new and peculiar as
domestication and cultivation. The soil and temperature in plants,
food and housing of domesticated animals, tend to change form and
structure of the offspring, although in a way which it is difficult
intelligently to control, and thus are prolific of varieties from
which to select. In fact, they often give rise to great and unexpected
modifications, called sports, which form points of departure for new
varieties and races. Now, in nature, not only are all these causes
and factors of change in constant operation, but they act together in
a peculiarly complex way. All the members of a fauna and flora, and
the physical environment of any locality, constitute together a most
complex and delicately adjusted system of correlated parts. A change in
one part is propagated through the whole system; also, a change in one
factor affects all other factors. When we add to this the large amount
of time, in comparison with individual human life and observation,
necessary to produce visible change of form, we can easily understand
why the process is still imperfectly understood, although the _fact_ is
certain.

But it will be asked, Are there, then, no differences between the
artificially made extreme varieties equivalent, so far as difference
of form is concerned, to species, and real natural species? There
are. If there were not, there would never have been any doubt about
the derivative origin of natural species. But if it be asked, Are not
these differences fundamental, and therefore fatal to the argument for
evolution derived from this source? we answer, we think not. We will
deal frankly and fairly with these differences.

=First Difference, Reversion.=--The strong tendency of artificial
varieties to reversion, even during the process of formation, and
especially their complete reversion to the original type if the hand
of man be withdrawn--i. e., if left to themselves, or become wild--is
supposed to show an essential difference between such varieties,
however extreme, and true species--is supposed, in fact, to prove an
indestructible permanency of specific types. Nature disowns these
artificial forms, and as it were brands them with bastardy. Not only
so, she strives ever to destroy them. The supporting hand of man is
necessary to sustain them. Left to themselves and to Nature, they
quickly revert to the original type. If all the extreme varieties of
dogs, from the greyhound and Newfoundland, on the one hand, to the
terrier and lap-dog on the other, were turned loose on an isolated
island, uninhabited by man but full of other animals, and left there
to shift for themselves--and the island were visited again after a
lapse of a hundred or a thousand years--it is probable that a uniform
species, something like to, though perhaps not identical with, the
wolf, would be found. They would have reverted to the original or
nearly the original wild type from which they were produced by
domestication. All or nearly all that was done by man would have been
undone by Nature. This reversion is one test of species.

But the reason of this tendency to reversion is obvious: First, the
time was too short, the rate of change was too rapid, in the artificial
formation of these varieties. There was not time enough to accumulate
a fund of heredity on each successive stage of the change. Therefore
the form is unstable and the tendency to revert is strong. Compare the
fleeting days and the hurrying impatience of man with the infinite time
and the divine patience of Nature! But mere instability is not the
principal cause of reversion. Secondly, in the case of artificial forms
in a wild state, _natural selection compels reversion_. Every species
in a wild state must of course be in harmony with the environment. But
artificially made forms are in harmony with the artificial environment
of domestication, but not with the environment of nature. In nature
the fittest survive, but artificial breeds are not fit to survive in a
state of nature. They are therefore quickly destroyed in the struggle
for life, or must be modified. Nature immediately begins to select
the fittest, and gradually in the course of time produces one or more
uniform species, similar to that from which they came, or perhaps to
what they would have been by this time if left to the operation of
natural causes under the conditions supposed. But natural species, if
they are formed, as the derivationists suppose, by the operation of
natural causes, can not revert unless the conditions revert; for the
same causes which operated to produce, still continue to operate to
keep, the species. Take an example:

The form, the habits, and the instincts of the pointer have been made
by a slow process of artificial selection of divergent varieties of
offspring, and by training of individuals continued and its effects
accumulated through many generations. But this form and these habits
and instincts, so laboriously produced, would be quickly destroyed by
Nature. The pointer, left to himself, must either change or become
extinct, because not adapted to the wild state. Such instincts and
habits would not only be of no use, but would be incompatible with
success in the struggle for life. But suppose for a moment that these
habits and instincts were useful to the animal in a wild state;
evidently they would be instantly seized upon by natural selection,
and not only perpetuated but intensified until a very distinct species
would be produced. The same is true of all other races of dogs. If the
Newfoundland, the greyhound, and the pug were all turned loose in a
forest, and if each of these kinds were admirably adapted to some place
in the economy of Nature--for some special mode of food-getting without
corresponding disabilities in other directions (as must be the case
if made by natural selection)--there can be no doubt they would each
survive, and their characters intensified; intermediate forms would
disappear (for reasons which we shall see presently), and we would
soon have three distinct species, or perhaps we would even call them
distinct genera.

=Second Difference, Intermediate Forms.=--Natural species are
distinct--marked out with hard and fast lines--while artificially-made
races, even though in their typical forms they differ as much or more
than natural species, shade into one another by insensible gradations.
In answer and explanation of this difference we remark: If species or
modified forms of any kind, whether natural or artificial, are made by
natural causes, and not at once out of hand by supernatural creation,
then of course there must have been gradations in the process of
making. Now, in the artificial case, the whole process as well as the
result lies within the limits of observation, while in the natural case
only the final result. But it will be asked, Why are the gradations
not seen also in the final result? We answer, because the intermediate
forms are eliminated in the struggle for life, and not reproduced by
cross-breeding. If artificial races always bred true--i. e., without
crossing, as natural species do--they would probably soon be as
sharply demarked. Cross-breeding is the great cause of the shadings
between domestic races. This brings me to the third and most important
difference.

=Third Difference, Cross-Fertility.=--Artificially-made races breed
freely and without repugnance with one another, and the offspring
of such cross-breeding is indefinitely fertile. Natural species
will not usually unite with one another, being prevented by sexual
repugnance and other causes. Or, if they do sexually unite, there is
either no offspring, or else the offspring is sterile, and therefore
the intermediate form dies out in the first generation; or else the
offspring is imperfectly fertile, and therefore the intermediate form
is eliminated in a few generations, and the species remain distinct;
or else the offspring is more fertile with the parent stocks, and
therefore revert to the parent stocks, and still the species remain
distinct. Such infertile, or imperfectly fertile, offspring--the result
of crossing of species--are called hybrids.

This is regarded as a most important test of true species, as
contrasted with varieties or races. There are two bases on which
species may be founded. Species may be based on _form_, morphological
species; or they may be based on _reproductive functions_,
physiological species. By the one method a _certain amount of
difference_ of form, structure, and habit, _constitutes species_;
according to the other, if the two kinds breed freely with each other
and the offspring is indefinitely fertile, the kinds are called
varieties, but if they do not they are called species. The two tests,
however, do not always accord. Every now and then we find undoubted
morphological species which may be crossed and produce indefinitely
fertile offspring. Yet it is certainly true that species are usually
cross-sterile, while varieties, whether natural or artificial, are
cross-fertile.

In explanation of this important difference, let it be observed that
there are here two things which must be kept distinct in the mind,
although they are, doubtless, closely allied--viz., sexual repugnance
(psychological element) and cross-sterility (physiological element).
The former is found, of course, only in the higher animals, where
fertilization is _voluntary_. The latter is universal among all
living things. This latter, therefore, is the more fundamental and
essential element, and the former may be regarded as its psychical
sign in the higher animals. It is of this latter, therefore--i. e.,
cross-sterility--that we shall speak mainly.

Suppose, then, we have growing together in the same locality many
species of pines or oaks, or other anemophilous trees. The whole air
is filled with the pollen of many species, and every germ-cell must
receive many kinds of male cells, and yet there are no hybrids, but,
on the contrary, the species remain distinct. So also in case of
hermaphrodite animals, where the fertilization is involuntary; many
aquatic species are found together in the same locality, and the water
is filled with sperm-cells of many different species. Many kinds of
sperm-cells must fall on each germ-cell, and yet there are no hybrids;
the species remain distinct. In all such cases we must suppose that
there is, among the different kinds of male cells, a struggle for the
possession of the germ or female cell, or a sort of sexual selection by
the female cell among the competing male cells, and the fittest--the
most in accord; i. e., those of the same species--prevail. This is
universal. But in the higher animals, in addition to the prepotency
of male cells of the same species, and comparative infertility in
case of union of those of different species, sexual attraction and
sexual repugnance contribute to the same result, and species are thus
doubly separated. Thus sexual selection is of two kinds: selection of
individuals for union (psychical), and selection of sperm-cells for
fertilization (physiological). The one kind is usually the sign of the
other--attraction the sign of fertility, and repugnance of sterility.

But in the domestic state it is all otherwise. Free competition between
individuals or between cells is not allowed. Thus, for example, among
plants, crossings may be forced and hybrids made in gardens which would
never occur in Nature. The florist prevents fertilization in the same
kind and compels fertilization of a different kind. If male cells of
the same kind were allowed to compete, the result would be different.
Doubtless the same method would succeed in many lower animals. So also
in higher animals free competition and sexual selection for union are
often not allowed, and therefore animals of different species, such as
the horse and the ass, unite, which would not do so if they were free
to select as in the wild state. These two are widely distinct species,
sometimes even called genera, and therefore the offspring is infertile;
but two closely allied species, such as two species of wolf, or of the
fox, in a domestic state would probably not only unite but produce
indefinitely fertile offspring. In fact, it is almost certain that the
dog was made by a mixture of several species of wolf, most, perhaps
all, of them now extinct.[30] On the other hand, it is not at all
certain that the extreme varieties of dogs have not passed the limit
of greatest attraction, and therefore of greatest cross-fertility, and
that, if allowed free choice, as in Nature, they would not breed true,
or tend to breed true, with their own kind, and intermediate kinds die
out in the struggle for life.

=Law of Cross-breeding.=--Before going any further in this discussion,
it is necessary to bring out another point of extreme importance in the
formation of varieties, both natural and artificial--a point which I
believe throws light upon the very significance of sex itself--I refer
to the effect of cross-breeding.

It is a curious and most significant fact that different varieties,
both natural and artificial, are, up _to a certain limit_, not only
cross-fertile and cross-attractive, but even more so than individuals
of the same variety. Long experience has shown that very close breeding
of the same variety for a long time fixes the _kind_ but _weakens_ the
_stock_, especially in fertility, while judicious crossing of varieties
strengthens the stock, increasing its fertility, and especially
producing _plasticity_ or _variability_. Therefore breeders, if they
wish to preserve a valuable variety, breed close; but, if they wish to
make new varieties, cross-breed. But we have already seen that species
are usually cross-sterile. Therefore there must be some regular law of
increase to a maximum, and again decrease to zero. It is this law that
I now wish to investigate.

In the lowest animals and plants multiplication of individuals and
the continuance of the kind are independent of sex, and therefore
in such there may be no sex at all. The sexual elements are not yet
differentiated. An individual divides itself into two; each grows to
the original size and again divides into two, and so on, it may be
indefinitely. In this lowest form of reproduction the individual is
sacrificed to the kind, or else we may regard the kind as an extension
of the individual, and reproduction as a modification of growth. But
there are other sexless modes of reproduction, found in nearly all
plants and many lower animals, in which the individuality is not
sacrificed. The next step in the ascending scale is reproduction by
_budding_. In this case a bud is formed which grows into a perfect
individual, and may remain attached to the parent stalk, forming
together a compound individual, as in most plants and many lower
animals, such as the coral; or it may separate and assume independent
life, as in some plants and many lower animals. In still other animals,
as in many hydrozoa, the budding function is relegated to a special
part, which thus becomes a reproductive _organ_. The next step is the
placing of the budding organ, for greater safety, in an _interior
cavity_. This is the case with aphids. Now, why would not this be an
excellent mode of reproduction for all animals, man included? Why
was sex introduced at all? There are very sufficient reasons, of
many kinds, which may come up later; but the fundamental reason, in
connection with evolution, is _the funding of individual differences
in a common offspring, thereby giving to the offspring a tendency to
divergent variation_.

Now, _non-sexual_ reproduction is _absolute true breeding_. The law
of like producing like is absolute. Heredity is all-powerful, and
tendency to variation is _nil_. These modes of reproduction are in
fact but a modification of growth and an extension of the individual.
Evolution-changes in animals produced in this way only must be very
slow, since the most powerful factor of evolution, viz., natural
selection among divergent varieties of offspring, would be wanting.
In the earliest times, therefore, before sex was yet declared,
we may imagine that physical environment was the great and only
factor of change. Sexual reproduction introduces the new element of
variation of offspring from which Nature makes her selections; and
this element of variation is apparently the result of the union of
_diverse_ individuals, and the funding of these differences in a common
offspring, and thus a double inheritance of individual characteristics
from the parents and a multiple inheritance of the same from the
ancestry. See, then, with this end in view, the pains Nature has
taken to make the difference between the uniting individuals and the
diversity of inheritance by the offspring as great as possible, and
yet the gradual way in which she has accomplished it. As already said,
the lowest form of reproduction is that by _fission_. Next comes
budding in _any_ part indifferently. Next comes the relegation of the
budding function to a particular part. This is the first appearance
of a reproductive _organ_. Next comes the placing of this organ, for
greater safety, within. Thus far all is non-sexual reproduction--all
a modification of growth--an extension of the individual, like the
propagation of plants by cuttings and by buds. Then comes sexual
reproduction in its lowest forms.

It may be well to stop here, to show the entire difference between this
and non-sexual modes. The latter, we have seen, is only a modification
of growth, an extension of the individual. Now, sexual reproduction
is the opposite of all this. Growth is a constant multiplication of
cells. One cell is ever becoming two similar cells--or, if we call them
individuals, one individual is ever becoming two similar individuals.
But in sexual reproduction we have an exactly reverse process. Reduced
to its simplest terms, sexual reproduction is the fusion of _two
diverse_ cells, sperm-cell and the germ-cell, to form _one_ cell,
the ovule--literally, a diverse twain forming one flesh. In its
higher forms it is the union of diverse _individuals_ to bring about
the same result. Instead of one cell becoming two, it is two cells
becoming one; instead of one individual becoming two in the offspring,
it is two individuals becoming one in the offspring. But this great
change was not brought about at once, but only in the most gradual
manner. First, the sexual elements--sperm-cell and germ-cell--are
separated, but _in the same organ_. Then the organs--spermary and
ovary--are separated, but in the _same individual_. This is the
condition of self-fertilizing hermaphroditism so common among plants
and lower animals. Then comes cross-fertilizing hermaphroditism; and
Nature takes much pains and uses many ingenious devices to prevent
self-fertilization and insure cross-fertilization. Now, for the
first time, we have slight individual differences funded in a common
offspring. Then, in order to absolutely forbid self-fertilization, and
at the same time allow greater differences in the crossing individuals
than could be attained in hermaphroditic individuals, the sex organs
are separated in _different individuals_, and fertilization can
only take place by _voluntary union_. Then, to insure the union of
suitable individuals, and forbid the ban between unsuitable, there are
introduced sexual attraction and repulsion. Then, last of all, the
difference between the two sex-individuals becomes greater and greater
as we go up. It is conspicuous only in vertebrates and some insects,
and very conspicuous only in birds and mammals.

We see, then, as we go up the taxonomic, and undoubtedly also the
phylogenic series, that there is a cross-breeding of more and
more diverse individuals, a funding of more and more divergent
characteristics in a common offspring. Why is this? I answer, for the
sake of _better results in the offspring_. This is abundantly shown
by direct experiment. In hermaphroditic plants in which there may
be either self-fertilization or else cross-fertilization with other
individuals of the same species, the latter produces better results in
number and vigor of offspring. But there are other advantages, more
difficult to prove but none the less certain, and of the greatest
importance in evolution: First, as already stated, complexity of
inheritance, like complexity of composition in a chemical substance,
gives instability to the embryo, and thus liability to variation in the
offspring; and this in its turn furnishes the material for selection
of the fittest. Again, it seems to me that there is a direct tendency
to improve the offspring by a sort of struggle in the embryo among the
various qualities inherited from both sides, and a survival of the best
and strongest--a sort of pre-potency of strong qualities.

Can divergence of uniting individuals and the funding of diverse
characteristics go any further? It may. The differences of the uniting
individual may be still further increased, and the resulting offspring
still further improved by the cross-breeding of different varieties
of the same species, for we thus add varietal differences to sexual
differences in the uniting individuals. It is well known that too
close breeding, or consanguineous breeding, or breeding in and in, as
it is variously called, if continued long, has a bad effect on the
offspring, weakening the stock, while judicious crossing of varieties
within certain limits of difference has a good effect, strengthening
the stock and increasing its fertility. It probably does so in two
ways: one direct, by funding many diverse qualities from both sides,
and the survival in the offspring of the strongest and best; the other
indirect, by giving _plasticity_, instability to the embryo, and
variability to the offspring, and therefore abundant material for the
operation of selection, either by man or by Nature. We said, “within
certain limits of difference.” If the difference is extreme, as in
extreme varieties and races, then the effect becomes again bad, and
more and more so as the limit of specific difference is approached;
at which limit at last Nature shuts down and forbids the bans. Thus,
then, there is in cross-breeding a regular law of effect, increasing to
a maximum and again decreasing, which may be graphically represented
by a curve (Fig. 69). In this figure the horizontal line represents
the ordinary level of the type; distances on this line represent
differences, individual, varietal, or specific; ordinates above or
below represent the effect, good or bad, of crossing. Thus s s′
represent two species, and the line between represents their specific
differences; _r r′_ represent different races or permanent varieties;
_v v′_ two strong varieties; _d d′_ ordinary individual differences; _c
c′_ close resembling or consanguineous individuals. The undulating line
represents the effect of crossing these various kinds. It is seen that
“in-and-in breeding,” _c c′_, produces bad effect (negative ordinates);
breeding of ordinary individual differences, _d d′_, keeps the stock at
the ordinary level--in its typical form; crossing two strong varieties,
_v v′_, produces maximum good effect (positive ordinates); crossing
decided races produces again bad effects, which become infinitely bad
as we approach species, S S′.[31]

[Illustration: FIG. 69.]

It is generally admitted that long-continued very close breeding has a
bad effect. Even in plants, Darwin has shown that cross-fertilization
has better effect than self-fertilization, this last being of course
the closest possible breeding. But it is probable that the principal
bad effect is not on the stock but _on the process of evolution_. Very
close breeding weakens the stock, ordinary breeding of individual
differences maintains the stock at the ordinary level and fixes it.
Cross-breeding of varieties strengthens the stock, and also (and this
is its main advantage) produces plasticity in the stock, gives rise
to strong divergent variations, or even sports, and thus becomes a
main agent in evolution. It is probable, moreover, that the higher
the function the more sensitive is it to these effects of breeding.
Therefore, the effect is greater in man than in any other animal. It is
true that many have doubted the bad effect of close breeding in man,
and have brought forward formidable statistics to substantiate their
position; but these doubtless take no account of the most important
function, the psychic, and especially the most important element in
every function, so far as evolution or progress is concerned, viz.,
_plasticity_ or capability of progressive improvement. The tendency
of consanguineous breeding, or even the breeding of persons of like
character and experiences, as in an isolated community, is, if not to
deteriorate the physique, at least to fix, stereotype the character,
and thus to check social progress. Contrarily, the crossing of
varieties of the same race seems not only to strengthen but, by the
diverse inheritance, to produce plasticity of character and capacity
for progress. But the difference between the primary races seems too
great for crossing with advantage. Some degree of sexual repugnance
which undoubtedly exists between the primary races is the psychical
sign of this fact.[32]

If, now, we go back to what we said before taking up this subject of
the effect of cross-breeding, we at once see that there is an apparent
flaw in all our reasonings. If close in-and-in breeding produced
better and more numerous offspring than cross-breeding between slight
varieties, then, indeed, such varieties would be preserved, and
increase in divergence from generation to generation until they became
species. Or, in any case, if, in any way, divergence could reach the
point of extreme varieties or races, or what are called sub-species,
then commencing cross-sterility would complete the separation, and thus
form true species. But how can the process of progressive divergence
begin, when slight varieties are even more fertile by cross-breeding
than by close breeding? Is it not evident that, with every generation,
the slight varieties would cross-breed with one another and with the
parent stock, and thus all varietal differences would be funded into
a common stock, and the type would be preserved unchanged? This, as
already pointed out (p. 76), has always been the chief difficulty
in the way of imagining how varieties can grow into species; and
the difficulty is _only increased_ by our discussion of the law of
cross-breeding. Now, just here, Dr. Romanes’s most important and
prolific idea comes to our help, and, as it seems to us, completely
solves the difficulty.

According to Dr. Romanes, no organ is so subject to variation as
the reproductive, and this in no respect so much as in degrees and
kinds of fertility--we might almost say so subject to freaks of
cross-sterility. Now, suppose we start with any well-defined species
in a state of nature. With every generation there are many slightly
divergent individual varieties, some greater and some less; but these
are all immediately swamped by crossing with one another and with the
parent stock, and the species remains unchanged. But suppose among
these divergent variations there arise, from time to time, some which
affect the reproductive organs in such wise that the variety, though
perfectly fertile with its own kind, is infertile, or imperfectly
fertile, with other varieties, and especially with the parent stock.
The change may be only in the _time_ of flowering in plants, or season
of heat in animals, or it may be actual infertility in sexual union.
Right here we have the beginning of a new species. The variety is
sexually isolated from the parent stock by cross-sterility, and
therefore all its peculiarities, however trivial, are preserved by
true breeding. Cross-breeding is necessary to make species, but true
breeding preserves them. Cross-breeding tends ever to make varieties,
but immediately destroys them again. This constant forming and
swamping, separating and again merging of varieties, like mixing of
dough, makes the whole mass (stock) more and more plastic and subject
to variety. This plasticity finally gives rise to varieties of the kind
which produces species by sexual isolation. By continued merging the
centrifugal forces continually increase, but are continually repressed
by crossing, until finally varieties break away to form species.

Now it is easy to see, from this point of view, why artificial
varieties are cross-fertile. It is because in artificial breeding we
are intent only on making varieties in form, size, color, etc., and not
at all on making any characterized by cross-sterility with the parent
stock. Cross-sterility with the parent stock, or with other varieties,
would be of no advantage, because we control the breeding, and can
breed true if we desire. Sexual isolation is not necessary, because
we can use physical isolation. On the contrary, such cross-sterility
would be a positive disadvantage to the breeder, by limiting the range
of his experiments just where they would be most prolific in making
new varieties. Hence, as might be expected, all domestic varieties are
cross-fertile, unless it be the extreme varieties, which may, in some
instances, have passed the limit of greatest fertility.

If this idea be true, then species which have originated in the same
locality ought to be always cross-sterile, but species which have
grown up apart, in widely separated geographical regions, ought to be
sometimes cross-fertile, because they were isolated by physical not by
sexual barriers. Such, Dr. Romanes thinks, is a fact. It is, however,
a very important point, which ought to be carefully investigated. We
say “_sometimes_.” It is probable that most geographical species also
are cross-sterile; for, although the isolation by cross-sterility of
slight varieties be the main cause of the origin of species, yet a
species formed by isolation of any other kind will gradually become
cross-sterile with other species. Although cross-sterility be the main
cause of divergence, yet divergence beyond a certain limit, however
caused, will bring about cross-sterility, because the reproductive
organs will partake of the general change going on in every part.

=Application.=--Suppose, then, a species breeding naturally in a wild
state. Individual varieties are constantly being formed and again
funded back into the common stock by cross-breeding. If the varieties
thus formed be decided, the cross-breeding will strengthen the stock,
and especially will preserve and increase its plasticity or tendency to
variation. Finally, among the widely divergent varieties there is one
affecting the reproductive organs of several individuals in such wise
that they are infertile, or imperfectly fertile, with the parent stock,
though perfectly fertile among themselves. These form a new species,
which continue to increase indefinitely.

=Objection answered.=--This view completes the answer to an objection
which is often made to evolution: “If natural species are formed by
transmutation, why is it we do not find intermediate links? Why is not
organic nature made up only of individual forms, shading insensibly
into each other in such wise that classification becomes a mere device
to handle more conveniently complex material? Why is it that groups,
especially species, are marked out with hard and fast lines?” We
have heretofore answered this by saying that intermediate forms are
eliminated. So they are, but how? Dr. Romanes’s idea of physiological
selection largely answers this. It is by the funding of _ordinary_
varieties into a common parental stock by crossing, and separating
_specific_ varieties by cross-sterility. Thus the organic field is
broken up into points about which variations oscillate. As every mass
of matter, when closely examined, is found to consist of aggregations
about centers of _cohesive_ attraction as discrete granules or
crystals, and only exceptionally do we find a homogeneous vitreous
structure; even so organic forms aggregate about points of _sexual_
attraction, and the whole mass consists of discrete species, and only
exceptionally--i. e., in domestication--do we find insensible shadings.
Now, species are the smallest aggregate of individuals, as granules
are of molecules. Species are more distinctly marked out by hard and
fast lines than are other taxonomic groups only because they are the
_last_, going downward, that are cross-sterile--because right here is
the change from cross-sterility to cross-fertility.

If this view be true, then in _the same locality_ species ought to be
always distinct and without shadings. If we find shadings at all, it
ought to be in intermediate geographical regions, where isolation is
not sexual but physical. Now, this is exactly what we find to be the
fact. _Innumerable examples of such intermediate forms in intermediate
geographical regions_ are now known, especially among birds and
reptiles, and examples have so increased in modern times, by closer
study, that naturalists, especially ornithologists, have been compelled
to resort to a trinomial nomenclature in order to designate these
geographical sub-species.[33]

If any further explanation is necessary, it will probably be found in
the following suggestions:

1. The number of individual varieties constantly being formed is
almost infinite, but the number of places in nature is very limited.
Now, among the infinite number of slight individual varieties formed
with every generation, the competitive struggle will be severest
between those most nearly alike, because they are competitors for the
_same_ place. Only one kind succeeds, viz., the fittest. Intermediate
forms are, therefore, exactly those which are eliminated in the most
wholesale way. 2. Add to this the fact that, as soon as divergence,
from whatsoever cause, reaches a certain point, sexual repugnance
or cross-sterility, or both, come in to perpetuate and increase the
separation already commenced. 3. Add to this, again, that migrations
in higher animals, and involuntary dispersals in lower animals and
in plants, and the mingling together of different faunas and floras,
produces a still fiercer struggle for life, especially between natives
and invaders, and thus great numbers of forms are destroyed; all but
the fittest are weeded out, and therefore the distinctness of the
remainder is greatly increased. Periods of great changes of physical
geography and of climate, and therefore of wide and general migrations,
are also periods of great weedings-out of unfit forms. Thus it
happens that existing faunas and floras are little else than isolated
_remnants_.

To illustrate, again, by a growing tree: If all the buds of a tree
lived and grew, they would soon become so numerous that they would
together form a solid hemispherical mass, like a coral-head, with no
room between for leaf or light or air. But ninety-nine one-hundredths
of buds die in the struggle for light and air, and therefore the
survivors are distinct growing points, widely separated from each
other. Species are such extreme, but separated, twiglets of the tree of
life.

=Objection.=--But it will be objected, again: The twig-_points_
are, indeed, separate, but the twigs themselves must meet somewhere
lower down, where they began to grow. Intermediate links may be
wanting _now_, but they must, of course, have existed once--i. e., in
previous geological times, and therefore ought to be found fossil. In
distribution in space or geographically, organic kinds may be marked
off by hard-and-fast lines, but, if their derivative origin be true,
in their distribution in _time_ or geologically, there ought to be
many examples of insensible shadings between them. In fact, if we
only had all the extinct forms, the organic kingdom, taken as a whole
and throughout all time, ought to consist not of species at all, but
simply of individual forms, shading insensibly into each other, like
the colors of the spectrum, and our classification ought to be a mere
matter of convenience, having no counterpart in nature. But this is
not the fact. On the contrary, the law of distribution in time is
apparently similar in this respect to the law of distribution in space,
already given (page 169). As in the case of _contiguous_ geographical
faunas, the change is apparently by _substitution_ of one species _for_
another, and not by _transmutation_ of one species _into_ another.
So also in _successive_ geological faunas, the change seems rather
by substitution than by transmutation. In both cases species seem to
come in suddenly, with all their specific characters perfect, remain
substantially unchanged as long as they last, and then die out and
are replaced by others. Certainly this looks much like immutability
of specific forms, and supernaturalism of specific origin. We have,
we believe, satisfactorily explained this in the case of geographical
distribution (page 201), but how can we explain it in the case of
geological distribution?

=Answer.=--1. The reason for this, given by Darwin and other
evolutionists, is the extremely fragmentary character of the geological
record. If the existing faunas and floras are but isolated remnants,
the rest having been _destroyed_ by migrations and conflicts, how
much more are fossil faunas and floras but fragmentary remnants, the
rest having been _lost_, partly because never preserved, and partly
by destruction of the record! If from this cause existing species are
widely separated, how much more ought we to expect to find fossil
species distinct and widely separated!

This is undoubtedly in most cases a true and sufficient answer, yet we
think the fragmentariness of the geological record has been overstated.
While it is true that there are many and wide gaps in the record; while
it is true, also, that even where the record is continuous many forms
may not have been preserved, yet there are some cases, especially
in the Tertiary fresh-water deposits, where the record is not only
continuous for hundreds of feet in thickness, but the abundance of
life was very great, and the conditions necessary for preservation
exceptionally good. In such cases the number of fossil species found
on each horizon seems to be as great as in existing faunas over equal
space. The record in these cases seems to be continuous and without
break, and crowded with fossil forms; and yet, although the species
change greatly, and perhaps many times, in passing from the lowest to
the highest strata, we do not usually, it must be acknowledged, find
the gradual transitions we would naturally expect, if the change were
effected by gradual transformations. The incompleteness of the record,
therefore, although a true and important cause, is not the whole cause.

In further and completer answer to this greatest of all objections, we
will throw out the following suggestions:

2. We must remember that considerable latitude is allowed by the
anti-derivationists to _variation of species;_ so much so, indeed, that
it is often difficult to draw the line between well-marked varieties
and closely-allied species. Now, according to the derivationist,
these strong varieties, breeding usually true, are naught else than
commencing species.

3. On every side and everywhere, both in existing faunas and in fossil
forms, but especially in the latter, we find innumerable examples of
transitions, or intermediate forms, between all the _higher groups_,
such as genera, families, orders, and classes. It is, in fact, by means
of these that the great law of differentiation from generalized types
has been established. It is, therefore, only between _species_ that
such intermediate forms are rare.

4. But even between species such intermediate forms, though rare, have
been pointed out, both in existing and in extinct faunas. But the
opposition contend that, in all such cases, the previously supposed
species are only varieties. We have already (page 61) spoken of the
obvious fallacy involved in this position. Species are first defined
as forms distinct and without intermediate links, and then we are
challenged to find such links; and when, with much labor, we find them,
they say the supposed species are not species, but only varieties.
But there are some cases in which this subterfuge will not do. There
are cases in which the transitions are between forms so extreme that
they can not, by any stretch of the term, be called varieties. We will
select and dwell upon but one striking example, viz., the fossil forms
of the Tertiary fresh-water deposits of Steinheim.

In Würtemberg, near the little village of Steinheim, are found certain
strata of sand and lime, which are evidently deposits from a small
lake of Tertiary times. The deposits are extremely rich in fossil
shells, especially of the different species of the genus _Planorbis_.
As the deposits seem to have been continuous for ages, and the fossil
shells very abundant, this seemed to be an excellent opportunity to
test the theory of derivation. With this end in view, they have been
made the subject of exhaustive study by Hilgendorf in 1866,[34] and by
Hyatt in 1880.[35] In passing from the lowest to the highest strata
the species change greatly and many times, the extreme forms being so
different that were it not for the intermediate forms they would be
called not only different species but different genera. And yet the
gradations are so insensible that the whole series is nothing less
than a demonstration, in this case at least, of origin of species by
derivation with modifications. The accompanying plate of successive
forms (Fig. 70), which we take from Prof. Hyatt’s admirable memoir,
will show this better than any mere verbal explanation. It will be
observed that, commencing with four slight varieties--probably sexually
isolated varieties--of one species, each series shows a gradual
transformation as we go upward in the strata--i. e., onward in time.
Series I branches into three sub-series, in two of which the change of
form is extreme. Series IV is remarkable for great increase in size
as well as change in form. In the plate we give only selected stages,
but in the fuller plates of the memoir, and still more in the shells
themselves, the subtilest gradations are found.

[Illustration: FIG. 70.--Transformations of Planorbis (after Hyatt).

  _Series IV._ 1, Pl. levis: Undorf. 2, Pl. Steinheimensis;
      3, tenuis-Steinheimensis; 4, tenuis; 5, discoideus; 6,
      trochiformis-discoideus; 7, trochiformis: Steinheim.

  _Series III._ 8, Pl. levis: Undorf. 9, Pl. oxystomus; 10, supremus;
      11, supremus var. turrita: Steinheim.

  _Series II._ 12, Pl. levis: Undorf. 13, Pl. crescens-parvus; 14, 15,
      crescens: Steinheim.

  _Series I._ _Sub-series 3._ 16, Pl. levis: Undorf. 17, Pl.
      minutus-levis; 18, minutus; 19, 20, triquetrus: Steinheim.
      _Sub-series 2._ 21, Pl. minutus; 22, 23, denudatus-minutus; 24,
      denudatus var. distortus: Steinheim. _Sub-series 1._ 25, Pl.
      costatus-minutus; 26, costatus; 27, 28, costatus var--: Steinheim.

  The specimens from Undorf all belong to an older Tertiary period than
      that at Steinheim.
]

This case is striking, partly because it is a very favorable one,
but mainly because it has been so carefully studied. There can be no
doubt that equally careful study would reveal the same transition
in many other cases. Nor are such transitions confined to the lower
forms of life, though they are probably more abundant there. According
to Cope, the nicest gradations may be traced between some of the
extinct mammalian species so abundant in the Tertiary deposits of the
West--especially between the species of the extinct generalized
family of _Oredontidæ_[36] The same is probably true of the many
extinct species of the horse family.

It is interesting to observe that the details of the process of change
in the forms of _Planorbis_ are in accord with Dr. Romanes’s views.
The change does not seem to have been uniform but somewhat paroxysmal.
The forms seem to remain stable for a long time, and then a few break
into several different forms, while the more rigid die out. It is as if
cross-breeding had kept the type true, but at the same time increased
its tendency to variation, until finally one or more varieties became
sexually isolated and thus formed new species.

5. But still the question remains: Why are transitional forms _rare_ in
all cases, especially between species--so rare that they are eagerly
sought and highly prized? I believe that the true reason of this is
that _the steps of evolution are not always uniform_.

Nearly all evolutionists have assumed and even insisted on uniformity,
as the opposite of catastrophism and of supernaturalism, and therefore
as essential to the idea of evolution. They say that the constancy of
the action of the forces of change necessitates the uniformity of the
rate of change. But, in fact, this is not always nor even usually true.
Causes or forces are constant, but phenomena everywhere and in every
department of Nature are _paroxysmal_. The forces producing storms
and lightning, and volcanoes and earthquakes, are or may be constant;
yet the phenomena are in the highest degree paroxysmal. Wherever in
nature we have a constant force and a strong resistance, we find more
or less paroxysmal action. For this reason the wind blows in puffs,
the friction of wind on water produces waves, water running in small
pipes issues in pulses. The reason is obvious, as may be seen by
the following examples: Suppose lifting forces within the earth are
resisted by crust-rigidity. The forces accumulate uniformly until the
resistance gives way, and suddenly we have an earthquake. Water running
with great resistance in small pipes is checked, but soon accumulates
additional force, which overcomes the resistance, only to be again
checked, and so on, and therefore runs in pulses. Now, the course of
evolution of the whole earth may be likened to such a current; there
are forces of movement and forces of resistance--progressive forces
and conservative forces. The progressive force is accumulative, the
resisting force is constant. Thus, in all evolution or history,
whether of the earth or of society, there are periods of comparative
quiet, during which the forces of change are gathering strength, and
periods of revolution or rapid change, during which these forces show
themselves in conspicuous effects.

Now, that there have been such periods of rapid revolutionary change
in the history of the earth, there can be no doubt. The history of the
earth is marked by periods of comparative quiet, during which life was
exceptionally abundant and prosperous, and change of organic forms
slow and uniform--separated by periods of disturbance, revolution,
rapid changes of physical geography and climate, and consequently of
comparatively rapid and sweeping changes in organic forms. These form
the division-lines between great eras of the earth’s history, and
are always marked by extensive unconformity of the strata, showing
the changes of physical geography above spoken of, and by apparently
sudden and sweeping change in life-forms, showing the great changes of
climate and other physical conditions. Unfortunately, in all cases of
unconformity of strata, there is, of course, a break in the continuity
of the record; and when the unconformity is very general a portion of
the record may be irrecoverably lost. The consequence is, that there is
an apparent break also in the continuity of life-forms. It looks, at
first sight, like wholesale extermination of old and recreation of new
forms. But undoubtedly the break in the continuity of life is apparent
only, as is shown by the loss in the record. If we could recover the
whole record, as indeed we sometimes do, we should find in all cases
that there is no break in the continuity of evolution, but only more
rapid rate of change at these times. But to this cause of rapid rate
of progress--i. e., change of physical environment--we must add change
of organic environment induced by the physical. We have already seen
(p. 179) that extensive changes in physical geography and climate are
always accompanied by wide migrations and dispersals of species, the
mingling of faunas and floras, and the severer struggle for life,
and the sweeping weeding-out of all but the fittest, and the change
of these latter, making them still fitter. These two causes of rapid
change, viz., change of climate and migrations, together with the loss
of record, we believe completely account for those sweeping changes,
not only of species but even of genera, families, and orders which
characterize the passage from one great era to another.

But this does not yet explain the apparent discontinuity between
_consecutive_ species in the same locality in continuous, conformable
strata, or the rarity of transitional forms when one species takes the
place of another in an apparently continuous record. In such continuous
deposits the successive faunas do indeed gradate insensibly into one
another, but apparently as in contiguous geographical regions (p. 200)
by substitution, not by transmutation. How shall we explain this?

On this point I throw out some suggestions: 1. In the modification of
species, too, as well as in other progressive changes, we may imagine
two forces operating, one progressive, the other conservative--the
one external, the other internal. The external progressive force
consists of all the factors of change already mentioned, the internal
conservative is the law of heredity, of like producing like. A changing
environment tends continually and increasingly to change of organisms,
but change is resisted by heredity, which tends to adhere, within
narrow limits, to the same form. But since the external force or
tendency to change increases constantly--since the discord between the
environment and the organism becomes ever greater, there must come a
time when either the species is destroyed, or else the resistance of
heredity gives way, and rapid change takes place. The alternative is
presented to the species to transform or perish; and in one or perhaps
in two or three generations we have an amount of change which, under
other circumstances, might take a hundred generations to accomplish.
These rapid changes are in fact exactly what in artificial varieties
we call sports. We do not know all the conditions which determine
sports in domestication, and still less what determines large and
widely-divergent variations, and therefore rapid origin of many
divergent species, in geological history. But one thing seems probable,
viz., that, when a species begins to change, it continues to change
easily and in many directions. When resistance gives way it takes some
time, many generations, for heredity to gather force again. Hence,
young species are plastic, fluent, because heredity, on any one point,
has not yet accumulated. But as soon as a stable form is again reached,
then, by accumulating a fund of heredity, the form tends to become more
and more rigid, until often it becomes too rigid to yield to modifying
influences, and therefore becomes extinct. By far the greater number
of species do thus become extinct and leave no progeny, while the few
more plastic forms are modified in several directions, and the number
of forms may, after a little time, be undiminished or even increased.

2. As to the _cause_ of rapid changes of form during revolutionary
or critical periods in the earth’s history, Brooks has introduced
an idea which is very suggestive, and deserves serious attention.
We have above spoken of the progressive element as external. Brooks
regards both elements as internal, and represented by the two sexes.
The male represents the progressive, the female the conservative
element. The one tends to divergent variation, the other to fixity
of type by heredity. I think we will all admit that, as a general
rule, in man (and probably all the higher animals) the male is more
highly differentiated into many divergent forms--the female is more
like the type-form of the species. In man, the male is certainly more
diversified in form, in expression, and in character. If they have the
keenest ear for musical pitch, they are also most often music-deaf;
if they have the sharpest perception of color, they are also most
often color-blind; if among them we find the brightest intellects, we
also find the dullest and most stupid; if there are among them more
geniuses, so, also, there are more cranks. The same is also, probably,
true of other animals, in proportion to their grade of organization.
The operation of these two equally necessary elements is well shown
in every advancing society. The initiative of every movement, in all
directions, good or bad, is determined by the male; the conservation
of whatever balance of good there may be, seems to be mainly by the
female. The male tries all things, the female holds fast that which
is good. By the one society gains a little in each generation; by the
other the gain is conserved and made a new point of departure. The one
is ever building hastily a scaffolding and platform; the other ever
consolidating into a permanent structure. Now, according to Brooks,
what is true in the plane of social progress is true also in the lower
plane of organic evolution. In sexual union, and in the resulting
offspring, the sperm-cell is the element which tends to divergent
variation, and the germ-cell to fixity of type, through heredity. In
artificial breeding, then, we ought to make new varieties by proper use
of the sire; we ought to preserve them true by proper management of the
dam.

But, again, it is believed that in many lower animals, especially
insects, the high-feeding of the mother, and consequent good condition
of the ovum, tends to the production of female offspring. It seems
almost certain that, in butterflies, the sex is not yet declared
in the caterpillar stage. According to the careful experiments of
Mrs. Treat,[37] if the caterpillars be well fed, they become female
butterflies; but, if poorly fed, they make males. One purpose of this
provision of Nature is, doubtless, to provide for the greater draught
on the vitality of the female in reproduction.

Now for the application. In good times in the history of a species,
when everything is prosperous, external conditions are favorable, and
food is abundant, females are in excess, and individuals are greatly
multiplied. Under these conditions, evolution would be slow and
uniform. But in _bad_ times in the history of a species, when external
conditions were unfavorable, not only would there be excess of males,
but these, through the influence of the changing environment, as well
as through the dominance of the male element, would be more than
usually varied in character. Among the strongly divergent varieties
thus formed, the fittest--i. e., those most in accord with the changing
environment--would survive and leave offspring partaking of their
character. We have already repeatedly said that the severer pressure of
a rapidly-changing environment determines correspondingly rapid changes
in organic forms. It may do so in many ways; but, according to Brooks,
one of the most important ways is by determining an excess of the male
element.

In brief, then, the causes of rarity of transitional forms among
fossils are--1. The change being, for the reasons given, comparatively
rapid, the _number of generations_ between consecutive species are
few, perhaps only one. 2. Times of rapid change are also times of
unfavorable conditions, and therefore the number of _individuals_
in each generation is small, and all the smaller--in Brooks’s
view--because of the fewness of females. When we remember that fossils
are but a small fraction of the actual faunas and floras of the
time, surely these two causes go far toward explaining the rarity of
links between _species_. 3. Add to these the existence of periods of
wide-spread changes in physical geography and climate, and consequent
wide migrations and dispersals of species, and we sufficiently account
for those sweeping changes in species, genera, families, and orders,
which mark the limits of the great eras, and which are made still more
abrupt, and apparently supernatural, by the loss of record at these
times.[38]

=Objection.=--There is still one more objection which will be made. We
have drawings of plants, animals, and men, by Egyptian artists, who
lived at least three thousand years ago, and the species of the one and
the races of the other are still the same. Still better, we have among
the wrappings of Egyptian mummies the very plants themselves, leaves
and flowers perfectly preserved, and even colors almost perfect. Yet
the species are exactly the same as grow in Egypt to-day. If species
are made by gradual transmutation, surely there ought to have been some
change in three thousand years.

=Answer=.--It may be well to note that this apparent permanence is true
of _races_ of men as well as of _species_ of animals and plants. But
the very men who insist on permanence of species are equally insistent
on the variability of varieties and races. The objection, therefore,
proves too much. We shall not insist on this, however, because as
derivationists we regard races as naught else than commencing species,
and therefore subject to the same laws. We are not striving for triumph
in debate, but only for truth. The true answer will, we believe, be
found among the following suggestions:

1. Three thousand years seems a long time in human history, but in
geological history it is but a day. This, the usual answer, is no doubt
a true one, but hardly, we think, sufficient. When we remember the
enormous change which has taken place in faunas and floras since the
end of the Tertiary, if change still continues at the same rate, surely
it ought to be distinctly perceptible in three thousand years.

2. But we must remember that such changes are usually more or less
paroxysmal; not, indeed, so sudden as to break the continuity of life,
but far more rapid at some times than at others. The last critical
or revolutionary period of rapid change was the Glacial epoch. Since
that time--i. e., during the human period--a new equilibrium has been
established, and the changes in organic forms have been very slow.

3. Remember, again, that in evolution _all_ species do not change. On
the contrary, most become rigid, and either remain unchanged, almost
indefinitely, or else die out and leave no descendants. Only the more
plastic forms change into other species, but usually into several
other species, and thus the number of forms may be undiminished, even
though the larger number of old forms leave no descendants. It is true,
therefore, of this as well as of other epochs, that the greater number
of species are permanent.

4. It is not impossible--indeed, it is in exact accordance with the
laws of evolution--that organic forms are more permanent now than
ever before. Evolution is a growth; the forces of growth must exhaust
themselves. Evolution proceeds by constant differentiation and
specialization, but extreme specialization always arrests evolution.
In ontogenic evolution, for example, cell-structure becomes more
and more specialized, but also thereby more and more rigid, and,
when specialization is complete, evolution stops, and cell-forms are
permanent. It is this which limits the cycle of every evolution. So is
it precisely with evolution of the organic kingdom, except that the
cycle is much longer. Here, also, every step is by specialization, and
yet specialization fixes the form, and finally arrests the advance on
that line. Thus, throughout the whole geological history of the earth,
the larger number of forms, by specialization, become rigid and perish,
while the fewer, more generalized, and more plastic forms take up the
march and carry it forward a step, only to be themselves specialized
and fixed. If we compare, again, to a tree: each twig finishes its
growth, flowers, fruits, and dies; other buds take up the growth and
carry it forward. By specialization the highest condition of a certain
form of life is attained, but other possibilities are shut off. Extreme
specialization is the flowering and fruiting--the end and completion
of twig-life. Now, obviously, this specialization and respecialization
can not go on forever. When it is complete in every direction it must
cease, and forms become permanent, or else perish. When it flowers it
must die.

Now, is not the advent of man in many ways a sign of the completeness
of organic evolution? Certain it is that with man there begins an
entirely new form of evolution. Certain it is that with man evolution
is transferred from the organic to the social plane, from the material
to the psychical. Certain it is that the forces, the conditions
and results of this evolution, are wholly different from those of
the other. In organic evolution the organism must conform to the
environment; in human evolution the environment is made to conform to
the wants of the organism. The one is unconscious and involuntary,
passive under the dominating laws of Nature; the other is conscious,
voluntary progress toward an ideal, _by the use_, among other means,
of the laws of Nature. The one is by change of external form--i. e.,
change of species--the other by change of brain-structure. Now, does
not the commencing of the cycle of this new evolution imply the
closing of that of the old? The two may overlap somewhat now, but it
is evident that, when the cycle of human evolution culminates, when
highly civilized man shall have taken possession of the whole earth,
the whole organic kingdom must be readjusted to his wants. All organic
forms must be either domesticated or destroyed. Organic forms will no
longer be modified by natural but wholly by artificial selection.

       *       *       *       *       *

There are many other supposed objections which have been urged, but
these are mostly not objections to evolution, but only to some _special
theory_ of evolution--Darwinian, Spencerian, Lamarckian, or other.

=Origin of Beauty=.--For example, it has been urged that natural
selection can only account for _useful_ structures; but _beauty_ is
as universal and as conspicuous in nature as _use_. In many cases
Darwin has shown that beauty is useful, and in such cases it is, of
course, seized upon by selection and intensified. Thus, the gorgeous
coloring of birds and insects is largely due to sexual selection.
Beauty is attractive, and therefore the most beautiful prevail in
securing reproductive opportunities. This character is, therefore,
perpetuated in the offspring, and intensified from generation to
generation. But, of course, this can apply only to higher animals,
in which the sexes are separate and sexual union voluntary. It can
not apply to self-fertilizing hermaphrodites; and yet in these, also,
we often find the most gorgeous coloring. Again, Darwin has very
ingeniously and successfully explained the case of the beauty and
fragrance of flowers of hermaphroditic plants by another principle,
viz., that of _insect-selection_. Insects are attracted by the most
showy and fragrant flowers, and thus become the means of carrying
pollen from flower to flower, insuring fertilization, and especially
cross-fertilization. The most beautiful and fragrant flowers are most
certain to be fertilized, and thus beauty and fragrance become useful
to the plant, and therefore are selected and intensified.

These and many other cases of beauty may doubtless be explained by
showing that it is useful; but beauty which is without any use can
not be explained by natural selection. Now, as already said, the
most gorgeous beauty is lavishly distributed even among the lowest
animals, such as marine shells and polyps, where no such explanation
is possible. The process by which such beauty is originated and
intensified is wholly unknown to us.

=Incipient Organs=.--Again, Mivart has drawn attention to another
difficulty in the way of natural selection as an explanation even of
useful organs. Darwin does not, of course, attempt to account for the
_origin_ of varieties. As we have already seen, he assumes divergent
variation of offspring as the necessary material on which natural
selection operates. He who shall explain the origin of varieties will
have made another great step in completing the theory of evolution. But
not only does not natural selection explain the _origin_ of varieties,
but neither can it explain the _first steps_ of advance toward
usefulness. An organ must be already useful before natural selection
can take hold of it to improve it. It can not make it useful, but only
_more useful_. For example, if fins commenced as buds from the trunk,
it is difficult to see how they could be of any use, and therefore
how they could be improved by natural selection until they were of
considerable size, and especially until muscles were developed to move
them. Until that time they would seem to be a hindrance to be removed
by natural selection, instead of a use to be preserved and improved. It
would seem that many organs must have passed through this _incipient
stage_, in which their use was prospective.

Much that is very interesting might be said on these and similar points
of difficulty, but all this lies entirely aside from the scope of
this work. As already said, these are not objections to evolution or
derivation, but only to _Darwinism_, or any other special theory, as a
_sufficient explanation_ of the process of evolution. They only show
that we do not yet fully understand this process; that there are still
other and perhaps greater factors of evolution than is yet dreamed of
in our philosophy.

In the foregoing chapters on special evidences, and especially in the
last two, the reader will observe many points of doubt, discussion, and
difference of opinion. Let it not be concluded on that account that the
_law of evolution_ is still in the region of uncertainty. It can not be
too strongly insisted on that the fact of evolution as a universal law
must be kept distinct from the causes, the factors, the conditions, the
processes, of evolution. The former is certain, the latter are still
imperfectly understood.




PART III.

_THE RELATION OF EVOLUTION TO RELIGIOUS THOUGHT._




CHAPTER I.

INTRODUCTORY.


From what has preceded, the reader will perceive that we regard the
law of evolution as thoroughly established. In its most general
sense, i. e., as a law of continuity, it is a necessary condition of
rational thought. In this sense it is naught else than the universal
law of necessary causation applied to forms instead of phenomena. It
is not only as certain as--it is far more certain than--the law of
gravitation, for it is not a contingent, but a necessary truth like the
axioms of geometry. It is only necessary to conceive it clearly, to
accept it unhesitatingly. The consensus of scientific and philosophical
opinion is already well-nigh, if not wholly, complete. If there are
still lingering cases of dissent among thinking men, it is only because
such do not yet conceive it clearly--they confound it with some special
form of explanation of evolution which they, perhaps justly, think not
yet fully established. We have sometimes in the preceding pages used
the words evolutionist or derivationist; they ought not to be used any
longer. The day is past when evolution might be regarded as a school
of thought. We might as well talk of gravitationist as of evolutionist.

If, then, evolution as a law be certain, if, moreover, it is a law
affecting not only one part of Nature--the organic kingdom--and one
department of science--biology--but the whole realm of Nature and every
department of science, yea, every department of thought, changing our
whole view of Nature and modifying our whole philosophy, the question
presses upon us, “What will be its effect on religious belief, and
therefore on moral conduct?” This is a question of gravest import.
To answer it, however imperfectly, is the chief object of this work.
Except for this, it would probably never have been undertaken. All that
goes before is subsidiary to this.

But I will doubtless be met at the very threshold by an objection
from the scientific side. Some will say--because it is the fashion
now to say--that as simple, honest truth-seekers, we have nothing to
do with its effect on religion and on life. They say we must follow
Truth wherever she leads, utterly regardless of what may seem to us
moral consequences. This I believe is a grave mistake, the result of a
reaction, and on the whole a wholesome and noble reaction, against the
far more common mistake of sacrificing truth to a supposed good. But
the reaction, as in most other cases, has gone much too far. There is
a true _philosophic_ ground of justification for the reluctance with
which even honest truth-seekers accept a doctrine which seems harmful
to society. Effect on life is, and ought to be, an important element
in _our estimate of the truth of any doctrine_. It is necessary for me
to show this, in order to justify this part of my work.

=Relation of the True and the Good.=--There is a necessary and
indissoluble connection between truth and usefulness. We all at once
admit this connection in one direction. We all admit that a truth must
eventually have its useful application. It may not be _now_, nor in ten
years, nor in a century, nor even in a millennium, but some time in the
future it will vindicate its usefulness. No truth is trivial or useless
in its relation to human life, for man is a part of Nature, and his
life must be in accordance with the laws of Nature. Every one admits
this, but not every one admits the converse proposition, viz., that
whatever doctrine or belief, in the long run and throughout the history
of human advancement, has tended to the betterment of our race, must
have in it an element of truth by virtue of which it has been useful;
for man’s good can not be in conflict with the laws of Nature. Also,
whatever in the long run and in the final outcome tends to the bad in
human conduct, ought to be received, even by the honest truth-seeker,
with distrust as containing essential error. The reason of this will
now be further explained.

=Relation of Philosophy to Life.=--There are three primary divisions
of our psychical nature, viz., sensuous, intellectual, and volitional
or moral. There are three corresponding primary processes necessary
to make a complete rational and satisfactory philosophy: (1) There
is first the _instreaming_ of the external world through the senses,
as impressions. These we call facts or phenomena. (2) The elaboration
of these facts within, by the _intellect_, into a compact, consistent
structure. This we call knowledge. (3) The outgoing of this knowledge
by the _will_ into the world as right or wise conduct. Now these three
are all equally necessary. All these three portions of our complex
nature are equally urgent to be satisfied.[39] But, unfortunately,
scientific workers are too apt to think only 1 and 2 necessary--that
true facts elaborated into consistent theory are all we need care for.
Theologians and metaphysicians, on the other hand, seem to think only 2
and 3 necessary. They elaborate a theory consistent in all its parts,
exquisitely woven in beautiful and delicate pattern, and apparently
satisfactory in its application to the right conduct of life, but are
less careful to inquire whether it is in harmony with facts derived
from the senses. But, we repeat, all three are equally necessary. The
first gathers the materials, the second constructs the edifice, the
third, by _use_, by practical application, _tests_ whether it be a fit
building to live in, whether it is constructed on sound architectural
principles. The tendency of the olden time was to neglect the first,
the tendency of the present time is to neglect the third. But we repeat
with stronger emphasis that this third element is equally necessary.
All admit that successful application in art is the surest test of
the truth of science. Now, social conduct is the art corresponding to
our philosophy of life, and therefore is the sure test of its truth.
It follows, therefore, that unless all these three primary divisions
of our nature are satisfied by any doctrine, there must result an
ineradicable confusion and discord in our psychical nature, and
cordial acceptance is not only impossible but irrational. We insist
upon this the more because it has become the fashion in these latter
days of dominance of science, to say that to inquire into effects on
society is inconsistent with the scientific spirit, and unworthy of the
honest truth-seeker. But, observe, I am speaking of effects on society
only as a _test of truth_. I would not swerve a hair’s breadth from
absolute devotion to truth. It is necessary, indeed, to inquire into
effects on society, but we must inquire only in the patient spirit
characteristic of the truth-seeker. Whatever is really true will surely
vindicate itself by its beneficence, if we will only wait patiently for
final results. Evolution is no exception to this universal truth. It
will surely vindicate its beneficence, but we must wait yet a little
while--not very long.

So much it was necessary to say in justification of the inquiry which
constitutes this third part of our work. But, after this justification,
the question returns with additional emphasis, “What will be the effect
of the universal acceptance of the law of evolution on religious
thought, and through this on the right conduct of life?”

There can be no doubt that evolution, as a law affecting all science
and every department of Nature, must fundamentally affect the whole
realm of thought, and profoundly modify our traditional views of
Nature, of God, and of man. There can be no doubt that we are now on
the eve of a great revolution. But, as in all great revolutions, so
in this, the first fears as to its effects are greatly exaggerated.
To many, both friends and foes of Christianity, evolution seems to
sweep away the whole foundation, not only of Christianity, but of all
religion and morals, by demonstrating a universal materialism. Many are
ready to cry out in anguish, “Ye have taken away our gods, what have we
more? Ye have destroyed our dearest hopes and noblest aspirations, what
more is left worth living for?” But I think all who are at all familiar
with the history of the so-called conflict between religion and science
will admit this is not the first time this cry has been raised against
science. They have heard this danger-cry so often that they begin
to regard it as little more than a wolf-cry--scientific wolf in the
religious fold. It may not be amiss, then, to stop a moment to trace
rapidly the main points of this conflict--to discuss the various forms
of this scientific wolf.

First, then, it came in the form of the _heliocentric theory of
the planetary system_. We once thought the earth the center of the
universe, and so firm that it can not be moved. But science shows that
it moves about the sun, and spins unceasingly on its axis. Every one
has heard of the terror of the sheep produced by this discovery, and
the nearly tragic results to the bold scientist. But now we look back
with wonder that there should have been any trouble at all. Would any
Christian now consent to give up the grand conceptions of Nature and
of God thus opened to the human mind--the idea of infinite space full
of worlds, of which our earth is one, moving in silent harmony as in a
mystic dance? Verily, this wolf has proved itself a harmless, nay, a
very noble beast, and lies down in peace with the lambs.

Next, it came in the shape of the _law of gravitation_, as sustentation
of the cosmos by law and resident forces. The effect of this on
religious thought was even more profound, though less visible on the
surface, because only perceived by the most intelligent. It seemed
at that time to remove God from the course of Nature. This was the
real ground of the skepticism of the last century, and also the real
motive of Voltaire’s ardent advocacy of Newton’s views before these
were generally accepted in France. But now, who would give up this
grand idea--this conception of law pervading infinite space--the same
law which controls the falling of a stone guiding also the planetary
orbs in their fiery courses? This is indeed the divine spheral music,
inaudible but to the ear of science, accompanying the celestial dance.

Next, it came in the form of the _antiquity of the earth_ and of the
cosmos. The earth which we had fondly thought made specially for us
about six thousand years ago; sun, moon, and stars, which we had vainly
imagined shone only for our behoof--these, science tells us, existed
and each performed its due course inconceivable ages before there was a
man to till the ground or contemplate the heavens. Some of my readers
may still remember the horror, the angry dispute which followed the
promulgation of these facts. But now, who would consent to give up the
noble conception of infinite time thus opened to the human mind and
become forever the heritage of man?

Next, it came in the form of the _antiquity of man_. It is probable,
nay, certain, that man has inhabited the earth far longer than we had
previously supposed we had warrant for believing. The controversy on
this question and the dread of its result has indeed not yet entirely
subsided. Some timid people still look askance at this wolf, but I
think all intelligent people accept it and find it harmless.

Next, and last, it comes now in the form of _evolution_--of the origin
of all things, even of organic forms, by _derivation_--of _creation
by law_. We are even now in the midst of the terror created by this
doctrine. But what is evolution but law throughout infinite time? The
same law which now controls the development of an egg has presided
over the creation of worlds. Infinite space and the universal law
of gravitation; infinite time and the universal law of evolution.
These two are the grandest ideas in the realm of thought. The one is
universal sustentation, the other universal creation, by law. There is
one law and one energy pervading all space and stretching through all
time. Our religious philosophy has long ago accepted the one, but has
not yet had time to readjust itself completely to the other. A few more
years, and Christians will not only accept, but love and cherish this
also for the noble conceptions it gives of Nature and of God.

But some will exclaim, “Noble conceptions of God, say you! Why, it
utterly obliterates the idea of God from the mind. All other conflicts
were for outworks--this strikes at the citadel. All others required
only readjustment of claims, rectification of boundaries betwixt
science and religion--this requires nothing less than unconditional
surrender. Evolution is absolute materialism, and materialism is
incompatible with belief in God, and therefore with religion of any
kind whatsoever!” Before proceeding any further, it becomes necessary
to remove this difficulty out of the way.




CHAPTER II.

THE RELATION OF EVOLUTION TO MATERIALISM.


It is seen in the sketch given in the previous chapter that, after
every struggle between theology and science, there has been a
readjustment of some beliefs, a giving up of some notions which really
had nothing to do with religion in a proper sense, but which had
become so _associated_ with religious belief as be to confounded with
the latter--a giving up of some line of defense which ought never to
have been held because not within the rightful domain of theology at
all. Until the present the whole difficulty has been the result of
misconception, and Christianity has emerged from every struggle only
strengthened and purified, by casting off an obstructing shell which
hindered its growth. But the present struggle seems to many an entirely
different and far more serious matter. To many it seems no longer
a struggle of theology, but of essential religion itself--a deadly
life-and-death struggle between religion and materialism. To many,
both skeptics and Christians, evolution seems to be synonymous with
blank materialism, and therefore cuts up by the roots every form of
religion by denying the existence of God and the fact of immortality.
That the enemies of religion, if there be any such, should assume and
insist on this identity, and thus carry over the whole accumulated
evidence of evolution as a demonstration of materialism, although
wholly unwarranted, is not so surprising; but what shall we say of the
incredible folly of her friends in admitting the same identity!

A little reflection will explain this. There can be no doubt that there
is at present a strong and to many an overwhelming tendency toward
materialism. The amazing achievements of modern science; the absorption
of intellectual energy in the investigation of external nature and
the laws of matter have created a current in that direction so strong
that of those who feel its influence--of those who do not stay at
home, shut up in their creeds, but walk abroad in the light of modern
thought--it sweeps away and bears on its bosom all but the strongest
and most reflective minds. Materialism has thus become a fashion of
thought; and, like all fashions, must be guarded against. This tendency
has been created and is now guided by science. Just at this time it is
strongest in the department of biology, and especially is evolution its
stronghold. This theory is supposed by many to be simply demonstrative
of materialism. Once it was the theory of gravitation which seemed
demonstrative of materialism. The sustentation of the universe by law
seemed to imply that Nature operates itself and needs no God. That time
is passed. Now it is evolution and creation by law. This will also
pass. The theory seems to many the most materialistic of all scientific
doctrine only because it is the _last_ which is claimed by materialism,
and the absurdity of the claim is not yet made clear to many.

The truth is, there is no such necessary connection between evolution
and materialism as is imagined by some. There is no difference in this
respect between evolution and any other law of Nature. In evolution,
it is true, the last barrier is broken down, and the whole domain of
nature is now subject to law; but it is only _the last_; the march
of science has been in the same direction all the time. In a word,
evolution is not only not identical with materialism, but, to the deep
thinker, it has not added a feather’s weight to its probability or
reasonableness. Evolution is one thing and materialism quite another.
The one is an established law of nature, the other an unwarranted and
hasty inference from that law. Let no one imagine, as he is conducted
by the materialistic scientist in the paths of evolution from the
inorganic to the organic, from the organic to the animate, from the
animate to the rational and moral, until he lands, as it seems to him,
logically and inevitably, in universal materialism--let no such one
imagine that he has walked all the way in the domain of science. He
has stepped across the boundary into the domain of philosophy. But,
on account of the strong tendency to materialism and the skillful
guidance of his leaders, there seems to be no such boundary; he does
not distinguish between the inductions of science and the inferences
of a shallow philosophy; the whole is accredited to science, and the
final conclusion seems to carry with it all the certainty which belongs
to scientific results. The fact that these materialistic conclusions
are reached by some of the foremost scientists of the present day adds
nothing to their probability. In a question of science, viz., the law
of evolution, their authority is deservedly high, but in a question
of philosophy, viz., materialism, it is far otherwise. If the pure
scientists smile when theological philosophers, unacquainted with the
methods of science, undertake to dogmatize on the subject of evolution,
they must pardon the philosophers if they also smile when the pure
scientists imagine that they can at once solve questions in philosophy
which have agitated the human mind from the earliest times. I am
anxious to show the absurdity of this materialistic conclusion, but I
shall try to do so, not by any labored argument, but by a few simple
illustrations.

1. It is curious to observe how, when the question is concerning a
work of Nature, we no sooner find out how a thing is made than we
immediately exclaim: “It is not made at all, it became so of itself!”
So long as we knew not how worlds were made, we of course concluded
they must have been created, but so soon as science showed _how_ it
was probably done, immediately we say we were mistaken--they were not
made at all. So also, so long as we could not imagine how new organic
forms originated, we were willing to believe they were created, but,
so soon as we find that they originated by evolution, many at once say,
“We were mistaken; no creator is necessary at all.” Is this so when the
question is concerning a work of man? Yes, of one kind--viz., the work
of the magician. Here, indeed, we believe in him, and are delighted
with his work, until we know how it is done, and then all our faith
and wonder cease. But in any honest work it is not so; but, on the
contrary, when we understand how it is done, stupid wonder is changed
into intellectual delight. Does it not seem, then, that to most people
God is a mere wonder-worker, a chief magician. But the mission of
science is to show us how things are done. Is it any wonder, then, that
to such persons science is constantly destroying their superstitious
illusions? But if God is an honest worker, according to reason--i. e.,
according to law--ought not science rather to change gaping wonder into
intelligent delight--superstition into rational worship?

2. Again, it is curious to observe how an _old truth_, if it come only
in a _new form_, often strikes us as something unheard of, and even
as paradoxical and almost impossible. A little over thirty years ago
a little philosophical toy, the gyroscope, was introduced and became
very common. At first sight, it seems to violate all mechanical laws,
and set at naught the law of gravitation itself. A heavy-brass wheel,
four to five inches in diameter, at the end of a horizontal axle, six
or eight inches long, is set rotating rapidly, and then the free end
of the axis is supported by a string or otherwise. The wheel remains
suspended in the air while slowly gyrating. What mysterious force
sustains the wheel when its only point of support is at the end of
the axle, six or eight inches away? Scientific and popular literature
were flooded with explanations of this seeming paradox. And yet it was
nothing new. The boy’s top, that spins and leans and will not fall,
although solicited by gravity, so long as it spins, which we have seen
all our lives without special wonder, is precisely the same thing.

Now, evolution is no new thing, but an old familiar truth; but,
coming now in a new and questionable shape, lo, how it startles
us out of our propriety! Origin of forms by evolution is going on
everywhere about us, both in the inorganic and the organic world. In
its more familiar forms, it had never occurred to most of us that it
was a scientific refutation of the existence of God, that it was a
demonstration of materialism. But now it is pushed one step farther
in the direction it has always been going--it is made to include also
the origin of species--only a little change in its form, and lo, how
we start! To the deep thinker, now and always, there is and has been
the alternative--materialism or theism. God operates Nature or Nature
operates itself; but evolution puts no new phase on this old question.
For example, the origin of the individual by evolution. Everybody knows
that every one of us individually became what we now are by a slow
process of evolution from a microscopic spherule of protoplasm, and yet
this did not interfere with the idea of God as our individual maker.
Why, then, should the discovery that the species (or first individuals
of each kind) originated by evolution destroy our belief in God as the
creator of species?

3. It is curious and very interesting to observe the manner in which
vexed questions are always finally settled, if settled at all. All
vexed questions--i. e., questions which have tasked the powers of
the greatest minds age after age--are such only because there is
a real truth on both sides. Pure, unmixed error does not live to
plague us long. Error, when it continues to live, does so by virtue
of a germ of truth contained. Great questions, therefore, continue
to be argued _pro_ and _con_ from age to age, because each side
is in a sense--i. e., from its own point of view--true, but wrong
in excluding the other point of view; and a true solution, a true
rational philosophy, will always be found in a view which combines and
reconciles the two partial, mutually excluding views, showing in what
they are true and in what they are false--explaining their differences
by transcending them. This is so universal and far-reaching a principle
that I am sure I will be pardoned for illustrating it in the homeliest
and tritest fashion. I will do so by means of the shield with the
diverse sides, giving the story and construing it, however, in my own
way. There is, apparently, no limit to the amount of rich marrow of
truth that may be extracted from these dry bones of popular proverbs
and fables by patient turning and gnawing.

We all remember, then, the famous dispute concerning the shield,
with its sides of different colors, which we shall here call white
and black. We all remember how, after vain attempts to discover the
truth by dispute, it was agreed to try the scientific method of
investigation. We all remember the surprising result. Both parties to
the dispute were right and both were wrong. Each was right from his
point of view, but wrong in excluding the other point of view. Each
was right in what he asserted, and each wrong in what he denied. And
the complete truth was the combination of the partial truths and the
elimination of the partial errors. But we must not make the mistake of
supposing that truth consists in _compromise_. There is an old adage
that truth lies in the middle between antagonistic extremes. But it
seems to us that this is the place of _safety_, not of truth. This is
the favorite adage, therefore, of the timid man, the time-server, the
fence-man, not the truth-seeker. Suppose there had been on the occasion
mentioned above one of these fence-philosophers. He would have said:
“These disputants are equally intelligent and equally valiant. One side
says the shield is white, the other that it is black, now truth lies
in the middle; therefore, I conclude the shield is gray or neutral
tint, or a sort of pepper-and-salt.” Do we not see that he is the only
man who has no truth in him? No; truth is no heterogeneous mixture of
opposite extremes, but a stereoscopic combination of two surface views
into one solid reality.

Now, the same is true of all vexed questions, and I have given this
trite fable again only to apply it to the case in hand.

There are three possible views concerning the origin of organic forms
whether individual or specific. Two of these are opposite and mutually
excluding; the third combining and reconciling. For example, take the
individual. There are three theories concerning the origin of the
individual. The first is that of the pious child who thinks that he was
made very much as he himself makes his dirt-pies; the second is that
of the street-gamin, or of Topsy, who says: “I was not made at all,
I growed”; the third is that of most intelligent Christians--i. e.,
that we were made by a process of evolution. Observe that this latter
combines and reconciles the other two, and is thus the more rational
and philosophical. Now, there are also three exactly corresponding
theories concerning the origin of species. The first is that of many
pious persons and many intelligent clergymen, who say that species were
made at once by the Divine hand _without natural process_. The second
is that of the materialists, who say that species were not made at all,
they were derived, “they growed.” The third is that of the theistic
evolutionists, who think that they were _created_ by a process of
evolution--who believe that making is not inconsistent with growing.
The one asserts the divine agency, but denies natural process; the
second asserts the natural process, but denies divine agency; the third
asserts _divine agency by natural process_. Of the first two, observe,
both are right and both wrong; each view is right in what it asserts,
and wrong in what it denies--each is right from its own point of view,
but wrong in excluding the other point of view. The third is the only
true rational solution, for it includes, combines, and reconciles the
other two; showing wherein each is right and wherein wrong. It is the
combination of the two partial truths, and the elimination of the
partial errors. But let us not fail to do perfect justice. The first
two views of origin, whether of the individual or of the species, are
indeed both partly wrong as well as partly right; but the view of the
pious child and of the Christian contains by far the more essential
truth. Of the two sides of the shield, theirs is at least the whiter
and more beautiful.

But, alas! the great bar to a speedy settlement of this question and
the adoption of a rational philosophy is not in the head but in the
heart--is not in the reason but in pride of opinion, self-conceit,
dogmatism. The rarest of all gifts is a truly tolerant, rational
spirit. In all our gettings let us strive to get this, for _it_
alone is true wisdom. But we must not imagine that all the dogmatism
is on one side, and that the theological. Many seem to think that
theology has a “_pre-emptive right_” to dogmatism. If so, then modern
materialistic science has “_jumped the claim_.” Dogmatism has its roots
deep-bedded in the human heart. It showed itself first in the domain
of theology, because there was the seat of power. In modern times it
has gone over to the side of science, because here now is the place of
power and fashion. There are _two dogmatisms_, both equally opposed
to the true rational spirit, viz., the old theological and the new
scientific. The old clings fondly to old things, only because they
are old; the new grasps eagerly after new things, only because they
are new. True wisdom and true philosophy, on the contrary, tries all
things both old and new, and holds fast only to that which is good and
true. The new dogmatism taunts the old for credulity and superstition;
the old reproaches the new for levity and skepticism. But true wisdom
perceives that they are both equally credulous and equally skeptical.
The old is credulous of old ideas and skeptical of new; the new is
skeptical of old ideas and credulous of new. Both deserve the unsparing
rebuke of all right-minded men. The appropriate rebuke for the old
dogmatism has been already put in the mouth of Job in the form of a
bitter sneer: “No doubt ye are the people, and wisdom shall _die_ with
you.” The appropriate rebuke for the new dogmatism, though not put into
the mouth of any ancient prophet, ought to be uttered--I will undertake
to utter it here. I would say to these modern materialists, “No doubt
ye are the men, and wisdom and true philosophy were _born_ with you.”

Let it be observed that we are not here touching the general question
of the personal agency of God in operating Nature. This we shall take
up hereafter. All that we wish to insist on now is that the process and
the law of evolution does not differ in its relation to materialism
from all other processes and laws of Nature. If the sustentation of
the universe by the law of gravitation does not disturb our belief in
God as the sustainer of the universe, there is no reason why the origin
of the universe by the law of evolution should disturb our faith in God
as the creator of the universe. If the law of gravitation be regarded
as the Divine mode of sustentation, there is no reason why we should
not regard the law of evolution as the Divine process of creation. It
is evident that if evolution be materialism, then is gravitation also
materialism; then is every law of Nature and all science materialism.
If there be any difference at all, it consists only in this: that, as
already said, here is the _last_ line of defense of the supporters of
supernaturalism in the realm of Nature. But being the last line of
defense--the last ditch--it is evident that a yielding here implies
not a mere shifting of line, but a change of base; not a readjustment
of details only, but a _reconstruction of Christian theology_. This, I
believe, is indeed necessary. There can be little doubt in the mind of
the thoughtful observer that we are even now on the eve of the greatest
change in traditional views that has taken place since the birth of
Christianity. But let no one be greatly disturbed thereby. For as then,
so now, change comes not to destroy but to fulfill all our dearest
hopes and aspirations; as then, so now, the germ of living truth has,
in the course of ages, become so encrusted with meaningless traditions
which stifle its growth, that it is necessary to break the shell to set
it free; as then, so now, it has become necessary to purge religious
belief of dross in the form of trivialities and superstitions. This
has ever been and ever will be the function of science. The essentials
of religious faith it does not, it can not, touch, but it purifies and
ennobles our conceptions of Deity, and thus elevates the whole plane of
religious thought.

It will not, of course, be expected of me to give, even in briefest
outline, a system of reconstructed Christian thought. Such an attempt
would be wholly unbecoming. Time, very much time, and the co-operation
of many minds, bringing contributions from many departments of thought,
is necessary for this. In a word, it can only itself come by a gradual
process of evolution. But from the point of view of science some very
fundamental changes in traditional views are already plain. Of these
the most fundamental and important are our ideas concerning God,
Nature, and man in their relations to one another. These will form the
subject of the next three chapters.




CHAPTER III.

THE RELATION OF GOD TO NATURE.


We have already said that evolution does not differ essentially from
other laws of Nature in its bearing on religious belief. It only
reiterates and enforces with additional emphasis what Science, in all
its departments, has been saying all along. The difficulties in the
way of certain traditional views have pressed with ever increasing
force upon the thoughtful mind ever since the birth of modern science.
All along, an issue has been gathering, but put off from time to time
by compromise, until now, at last, the issue is forced upon us and
compromise is exhausted. The issue (let us look it squarely in the
face) is: Either God is far more closely related with Nature, and
operates it in a more direct way than we have recently been accustomed
to think, or else (mark the alternative) Nature operates itself and
needs no God at all. There is no middle ground tenable.

Let us trace rapidly the growth of this issue. The old idea and the
most natural to the religious mind was the direct agency of God in
every event and phenomenon of Nature. This view is nobly expressed
in the noblest literature in the world--in the Hebrew and Christian
Scriptures: “He looketh on the earth and it trembleth. He toucheth
the hills and they smoke.” “He maketh his sun to rise on the evil and
on the good, and sendeth his rain on the just and on the unjust.” But
now comes Science and explains all these phenomena by natural laws and
resident forces, and we all accept her explanation. Thus, one by one
the phenomena of Nature are explained by the operation of resident
forces according to natural laws, until the whole course of Nature,
as we now know it, has been, or will be, or conceivably may be, thus
explained.

Thus has gradually grown up, without our confessing it, a kind of
scientific polytheism--one great Jehovah, perhaps, but with many agents
or sub-gods, each independent, efficient, and doing all the real work
in his own domain. The names of these, our gods, are gravity, light,
heat, electricity, magnetism, chemical affinity, etc., and we are
practically saying: “These be your gods, O Israel, which brought you
out of the land of Egyptian darkness and ignorance. These be the only
gods ye need fear, and serve, and study the ways of.”

What, then, is practically the notion which most people seem to have of
the relation of Deity to Nature? It is that of a great master-mechanic
far away above us and beyond our reach, who once upon a time, long
ago, and once for all, worked, created matter, endowed it with
necessary properties and powers, constructed at once out of hand this
wonderful cosmos with its numberless wheels within wheels, endowed
it with forces, put springs in it, wound it up, set it a-going, and
then--_rested_. The thing has continued to go of itself ever since.
He might have not only rested but _slept_, and the thing would have
gone of itself. He might not only have slept but _died_, and still
the thing would have continued to go of itself. But, no, I forget.
He must not sleep or die, for the work is not absolutely perfect.
There are some things too hard even for Him to do in this masterful,
god-like way. There are some things which even He can not do except in
a ’prentice-like, man-like way. The hand must be introduced from time
to time to repair, to rectify, to improve, especially to introduce new
parts, such as new organic forms.

Such was the state of the compromise until twenty-five years ago.
Nature is sufficient of itself for its _course_ and continuance, but
not for _origins_ of at least _some_ new parts. Such was the state of
the compromise until Darwin and the theory of evolution. But, now,
even this poor privilege of occasional interference is taken away.
Now, origins, as well as courses, are reduced to resident forces
and natural law. Now, Nature is sufficient of itself, not only for
sustentation, but also for creation. Thus, Science has seemed to push
Him farther and farther away from us, until now, at last, if this view
be true, evolution finishes the matter by pushing Him entirely out of
the universe and dispensing with Him altogether. This, of course, is
materialism. But this is no new view now brought forward for the first
time by evolution. On the contrary, evolution only finishes what
science has been doing all along.

See, then, how the issue is forced. Either Nature is sufficient of
itself and wants no God at all, or else this whole idea, the history
of which we have been tracing, is radically false. We have here given
by science either a demonstration of materialism or else a _reductio
ad absurdum_. Which is it? I do not hesitate a moment to say it is a
reductio ad absurdum. And I believe that evolution has conferred an
inestimable benefit on philosophy and on religion by forcing this issue
and compelling us to take a more rational view.

What, then, is the alternative view? It is the utter rejection with
Berkeley and with Swedenborg of the independent existence of matter
and the real efficient agency of natural forces. It is the frank
return to the old idea of direct divine agency, but in a new, more
rational, less anthropomorphic form. It is the bringing together
and complete reconciliation of the two apparently antagonistic and
mutually excluding views of _direct agency_ and _natural law_. Such
reconciliation we have already seen is the true test of a rational
philosophy. It is the belief in a God not far away beyond our reach,
who once long ago enacted laws and created forces which continue of
themselves to run the machine we call Nature, but a God _immanent_,
a God resident _in_ Nature, at all times and in all places directing
every event and determining every phenomena--a God in whom in the most
literal sense not only we but all things have their being, in whom all
things consist, through whom all things exist, and without whom there
would be and could be nothing. According to this view the phenomena of
Nature are naught else than objectified modes of divine thought, the
forces of Nature naught else than different forms of one omnipresent
divine energy or will, the laws of Nature naught else than the regular
modes of operation of that divine will, invariable because He is
unchangeable. According to this view the law of gravitation is naught
else than the mode of operation of the divine energy in sustaining
the cosmos--the divine method of sustentation; the law of evolution
naught else than the mode of operation of the same divine energy in
originating and developing the cosmos--the divine method of creation;
and Science is the systematic knowledge of these divine thoughts and
ways--a rational system of natural theology. In a word, according to
this view, there is no real efficient force but spirit, and no real
_independent_ existence but God.

But some will object that this is pure _Idealism_. Yes, but far
different from what usually goes under that name. The ideal philosophy
as usually understood regards the external world as having no real
objective existence outside of _ourselves_--as objectified mental
states of the _observer_--as literally such stuff as dreams are made
of--as a mere phantasmagoria of trooping shadows having no real
existence but in the mind of the dreamer, and each dreamer makes his
own world. Not so in the idealism above presented. According to _this_
the external world is the objectified modes, not of the mind of the
observer, but of the mind of God. According to this, the external world
is not a mere unsubstantial figment or dream, but for _us_ a very
substantial objective reality surrounding us and conditioning us on
every side.

Again, it will be objected that this is pure _Pantheism_. Again, we
answer “yes.” Call it so if you like, but far different from what goes
under that name, far different from the pantheism which sublimates
the personality of the Deity into all-pervading unconscious force,
and thereby dissipates all our hopes of personal relation with him.
Properly understood, we believe this view completely reconciles the
two antagonistic and mutually excluding views of impersonal pantheism
and anthropomorphic personalism, and is therefore more rational than
either. The discussion of this most important point can only come up
after the next chapter, because the argument for the personality of
Deity is derived, not from without by the study of Nature, but from
within in our own consciousness. We therefore put off its discussion
for the present.

But, finally, some will object, “We can not live and work effectively
under such a theory unless, indeed, we escape through pantheism.” It
may, alas! be true that this view brings us too near Him in our sense
of spiritual nakedness and shortcoming. It may, indeed, be that we can
not live and work in the continual realized presence of the Infinite.
It may, indeed, be that we must still wear the veil of a practical
materialism on our hearts and minds. It may, indeed, be that in our
practical life and scientific work we must still continue to think
of natural forces as efficient agents. But, if so, let us at least
remember that this attitude of mind must be regarded only as our
ordinary work-clothes--necessary work-clothes it may be of our outer
lower life--to be put aside when we return _home_ to our inner higher
life, religious and philosophical.




CHAPTER IV.

THE RELATION OF MAN TO NATURE.


There are two widely distinct views concerning the relation of man
to Nature; the one as old as the history of human thought, the other
only now urged upon us by modern science. According to the one, man
is the counterpart and equivalent of Nature. He alone has--in fact
is--an immortal spirit, and therefore he belongs to a world of his
own. According to the other, man is but a part, a very insignificant
part of Nature, and connected in the closest way with all other parts,
especially with the animal kingdom. He has no world of his own, nor
even kingdom of his own: he belongs to the animal kingdom. In that
kingdom he has no department of his own: he is a vertebrate. In the
department of vertebrates he has no privileged class of his own: he is
a mammal. In the class of mammals he has no titled order of his own:
he is a primate, and shares his primacy with apes. It is doubtful if
he may enjoy the privacy of a family of his own--the Hominidæ--for the
structural differences between man and the anthropoid apes are probably
not so great as between the sheep family and the deer family.

Now it is evident that these two are only views from different points,
psychical and structural. From the psychical point of view it is simply
impossible to exaggerate the wideness of the gap that separates man
from even the highest animals. From this point of view man must be
set over as an equivalent, not only to the whole animal kingdom, but
to the whole of Nature besides. From the structural point of view,
on the contrary, it is impossible to exaggerate the closeness of the
connection. Man’s body is identified with all Nature in its chemical
constituents, with the body of all animals in its functions, with all
vertebrates, especially mammals, in its structure. Bone for bone,
muscle for muscle, ganglion for ganglion, almost nerve-fiber for
nerve-fiber, his body corresponds with that of the higher animals.
Whether he was derived from lower animals or not, certain it is that
his structure even in the minutest details is precisely such as it
would be if he were thus derived by successive slight modifications.

Now, of these two views, the latter has been in recent times enormously
productive in increasing our knowledge. Anatomy has become truly
scientific only through comparative anatomy; physiology through
comparative physiology; embryology through comparative embryology.
Sociology is fast following in the same line, and becoming scientific
through comparative sociology. Is not the same true also of psychology?
Will not psychology become truly scientific only through comparative
psychology, i. e., by the study of the spirit of man in relation to
what corresponds to it in lower animals? But this view and this method,
when pushed to what seems to many their logical conclusion, end in
identification of man with mere animals, of spirit with mere physical
and chemical forces, immortality with mere conservation of energy,
and thus leads to blank and universal materialism. Thus, while it
increases our knowledge, it destroys our hopes. Is there any escape?
There is. The two extreme views given above are not irreconcilable. As
already said, they are only views from different points, and therefore,
although both true, are equally one-sided and partial, and a true and
rational philosophy, in this as in all other cases of vexed questions,
is found only in a higher view, which combines and reconciles these
mutually excluding extremes. Can we find such a view? I think we can.

Let us first, however, trace some of the stages of this scientific
materialism. There are two main branches of the argument for
materialism: one derived from _brain-physiology_, the other from
_evolution_. As we wish to be perfectly fair, we will present and even
press the argument in both these directions, although the latter alone
bears directly on the subject in hand.

In recent times, physiology has made great and, to many, startling
advances in the direction of connecting mental phenomena with
brain-changes. Physiologists have established the correlation of
vital with chemical and physical forces,[40] and probably in some
sense, at least, of mental with vital forces. They have proved, in
every act of perception, first a physical change in a nerve-terminal,
then a propagated thrill along a nerve-fiber, and then a resulting
change, physical or chemical, in the brain; and in every act of
volition, a change first in a brain-cell, then, a return thrill along
a nerve-fiber, and a resulting contraction of a muscle. Even the
velocity of the transmission to and fro has been measured, and the
time necessary to produce brain-changes estimated. They have also
established the existence of physical and chemical changes in the
brain corresponding to every change of mental state, and with great
probability an exact quantitative relation between these changes of
brain and the corresponding changes of mind. In the near future they
may do more: they may localize all the different faculties and powers
of the mind, each in its several place in the brain, and thus lay the
foundations of a truly scientific phrenology. In the far-distant future
we may possibly do much more. We may connect each kind of mental state
with a different and distinctive kind of brain-change. We may find, for
example, a right-handed rotation of atoms associated with _love_, and
a left-handed rotation associated with _hate_, or a gentle sideways
oscillation associated with _consciousness_, and a vertical pounding
associated with _will_. Now, suppose all this, and even much more, be
done in the way of associating, both in degree and in kind, mental
changes with brain-changes. What then? “Why,” say the materialists,
“we thereby identify _mind_ with _matter_, mental forces with material
forces. Thought, emotion, consciousness and will become products of the
brain, in the same sense as bile is a product of the liver, or urea a
product of the kidneys.”

Such is, in brief, the argument. Now, the answer: We may do all
we have supposed and much more. We may push our knowledge in this
direction as far as the boldest imagination can reach, and even
then we are no nearer the solution of this mystery of the relation
of brain-changes and mental changes than we are now. Even then it
would be impossible for us to conceive _how_ brain-changes produce
mental changes or _vice versa_. Physical changes in sense-organs,
transmitted along nerve-fibers, determine changes in brain-substance.
So much is intelligible. But now there appear--how it is impossible
to imagine--consciousness, thought, emotion, etc.--phenomena of an
entirely different order, belonging to an entirely different world. So
different, that it is impossible to imagine the nature of the nexus
between, or to construe the one in terms of the other. Brain-cells are
agitated and thought appears: Aladdin’s lamp is rubbed, and the genie
appears. There is just as much intelligible causal relation between the
two sets of phenomena in the one case as in the other.

Now, this mystery is not of the nature of those which disappear under
the light of knowledge. On the contrary, science only brings it out in
sharper relief, and emphasizes its absolute unsolvableness. Suppose
an absolutely perfect knowledge, perfect in degree, but human in kind.
Suppose an ideally perfect science--a science which has so completely
subdued its domain, and reduced it to such perfect simplicity, that
the whole cosmos may be expressed in a single mathematical formula--a
formula which, worked out with plus signs, would give every phenomenon
and event which shall ever occur in the future, and with minus signs
every phenomenon and event which has ever occurred in the past. Surely,
this is an ideally perfect science. Yet, even to such a science, the
relation of brain-changes to mental states would be as great a mystery
as now. It would even come out in stronger relief, because so many
other apparent mysteries would disappear. Like the essential nature of
matter or the ultimate cause of force, this relation lies evidently
beyond the domain of science. It requires some other _kind_ of
knowledge than human to understand it.

But materialists insist so much on the identity of brain-physiology
with psychology, that even at the risk of tediousness we will multiply
illustrations in order, if possible, to make this point still clearer.
Suppose, then, we exposed the brain of a living man in a state of
intense activity. Suppose, further, that our senses were absolutely
perfect, so that we could see every change, of whatever sort, taking
place in the brain-substance. What would we see? Obviously nothing but
molecular changes, physical and chemical; for to the outside observer
there is absolutely nothing else there to see. But the subject of
this experiment sees nothing of all this. His experiences are of a
different order, viz., consciousness, thought, emotions, etc. Viewed
from the _outside_, there is--there can be--nothing but motions; viewed
from the _inside_, nothing but thought, etc.--from the one side, only
_physical_ phenomena; from the other side, only _psychical_ phenomena.
Is it not plain that, from the very nature of the case, it must ever
be so? Certain vibrations of brain molecules, certain oxidations with
the formation of carbonic acid, water, and urea on the one side,
and there appear on the other sensations, consciousness, thoughts,
desires, volitions. There are, as it were, two sheets of blotting-paper
pasted together. The one is the brain, the other the mind. Certain
ink-scratches or blotches, _utterly meaningless_ on the one, soak
through and appear on the other as _intelligible writing_, but how we
know not, and can never hope to guess. But when the paste dissolves,
_shall the writing remain_? We shall see.

But some will object. There is nothing specially strange and unique
in all this, for the same mystery underlies the essential nature of
all kinds of force and matter, and therefore all phenomena. True
enough, but with this difference. Physical and chemical forces and
phenomena are indeed incomprehensible in their essential nature; but
once accept their existence, and all their different forms are mutually
convertible, construable in terms of each other and all in terms of
motion. But it is impossible by any stretch of the imagination to
thus construe mental forces and mental phenomena. It may, indeed, be
impossible to conceive _how came_ the plane of material existence, but,
standing on that plane, all phenomena fall into intelligible order. But
there is another plane above this one, having no intelligible relation
with it. We must climb up and stand on this before its phenomena fall
into intelligible order. In a word, material forces and phenomena are,
indeed, a mystery, but only of the _first order_. But mental and moral
forces and phenomena are a mystery even from the standpoint of the
other, and are therefore a mystery of the _second order_--a mystery
within a mystery.

We repeat, then, with additional emphasis after this examination, that
we can not imagine between physical and psychical phenomena a relation
of cause and effect _in the same sense_ in which we use these terms
in physical science, although in some sense there is doubtless such a
relation. If man were the only animal we had to deal with, there would
be no standing ground left for materialism. But there is still another
difficulty which sticks deeper. It is that suggested by the _law of
evolution_ and enforced by the _comparative method_.

=Relation of Man to Animals.=--Man, we say, is endowed with, _is_, in
fact, an immortal spirit. What is spirit? We know things only by their
phenomena; what are the phenomena of spirit? Consciousness, will,
intelligence, memory, love, hate, fear, desire--surely these are some
of them. But has not a dog or a monkey all these? Pressed with this
difficulty, some have indeed felt compelled to accord immortal spirit
to higher animals. But we can not stop here. If to these, then also to
all animals; for we have here only a sliding scale without break. Can
we stop now and make it coextensive with sentiency? No; for the lowest
animals and lowest plants merge into each other so completely that no
one can draw the line between them with certainty. We must extend it to
plants also. Shall we stop here and make immortal spirit coextensive
with life? We can not; for life-force is certainly correlated with,
transmutable into, and derivable from, physical and chemical forces. We
must extend it into dead nature also. Therefore, everything is immortal
or none. Our boasted immortality by continued extension becomes
thinner and thinner until it evaporates into thin air. It becomes
naught else than _conservation of energy_, and not, as we had hoped,
conservation of _self-conscious personality_. This may be interesting
as a scientific fact; but of what value to us personally is a continued
existence of our spiritual forces as heat, light, electricity, or
any other form of unconscious force? Thus, then, if once we pass the
gap between man and the higher animals, there is no possibility of a
stopping-place anywhere.

Such is the difficulty presented by comparison in the _taxonomic_
series. Take now the _embryonic_ series. Each one of us, individually,
was formed gradually by a process of evolution, from a microscopic
spherule of protoplasm undistinguishable in structure from the lowest
forms of protozoal life. Now, in this gradual process of evolution,
where did immortal spirit come in? Was it in the germ-cell? Then why
deny it to the protozoan? Was it at the quickening, or at the birth,
or at the moment of first self-consciousness, or at some later period
of capacity of abstract thought? Again, when it did come in, was it
something superadded or did it grow out of something already existing
in the embryo or the infant?

Or take the _evolution series_ from protozoan to man. This we have
already seen is similar in outline to the other two. Now, in the
gradual evolution of the animal kingdom throughout all geological time,
terminating in man, when did immortal spirit come in? Did it enter with
life, or with sentient life, or somewhere in the ascending scale of
animals, or with the advent of man? If with man, was it some new thing
added at once out of hand, or did it grow out of something already
existing in animals?

This last, we are persuaded, is the only tenable view--the only view
that can effect that reconciliation between the two extreme, mutually
excluding views now usually held, which, as already seen, is the true
test of a rational philosophy. I believe that the spirit of man _was_
developed out of the _anima_ or conscious principle of animals, and
that this, again, was developed out of the lower forms of life-force,
and this in its turn out of the chemical and physical forces of Nature;
and that at a certain stage in this gradual development, viz., with
man, it _acquired_ the property of immortality precisely as it now,
in the individual history of each man at a certain stage, acquires
the capacity of abstract thought. This is, in brief, the view which I
wish to enforce. The reader must understand, however, that this is _my
own view_ only, a view for which I have earnestly contended for twenty
years. It appeals, therefore, not to authority, but only to reason. I
wish now to present it as briefly as possible.

First, then, I would draw attention to the fact that there is nothing
wholly exceptional in such transformation with the sudden appearance of
new powers and properties; but, on the contrary, it is in accordance
with many analogies in the lower forces, and therefore _a priori_
not only credible but probable. For example, force and matter may
be said to exist _now_ on several distinct planes raised one above
another. There is a sort of taxonomic scale of force and matter. These
are, 1, the plane of elements; 2, the plane of chemical compounds;
3, the plane of vegetal life; 4, the plane of animal life; and 5,
the plane of rational and, as we hope, immortal life. Each plane has
its own appropriate force and distinctive phenomena. On the first
operates physical forces, producing physical phenomena only--for the
operation of chemical affinity immediately raises matter to the next
plane. On the second plane operates, in addition to physical, also
chemical forces, producing all those changes by action and reaction,
the study of which constitutes the science of chemistry. On the
third plane, in addition to the two preceding forces, with their
characteristic phenomena, operates also life-force, producing the
distinctive phenomena characteristic of living things. On the fourth
plane, in addition to all lower forces and their phenomena, operates
also a higher form of life-force characteristic of animals, producing
the phenomena characteristic of sentient life, such as sensation,
consciousness, and will. On the fifth plane, in addition to all the
preceding forces and phenomena, we have also the forces and phenomena
characteristic of rational and moral life.

Now, although there are doubtless great differences of level on each
of these planes, yet there is a very distinct break between each.
Although there are various degrees of the force characteristic of each,
yet the difference between the characteristic forces is one of kind
as well as of degree. Although energy by transmutation may take all
these different forms, and thus does now circulate up and down through
all these planes, yet the passage from one plane upward to another is
not a gradual passage by sliding scale, but _at one bound_. When the
necessary conditions are present, a new and higher form of force at
once appears, _like a birth_ into a higher sphere. For example, when
hydrogen and oxygen are brought together under proper conditions, water
is born--a new thing with new and wholly unexpected properties and
powers, entirely different from those of its components. When CO2, H2O,
and NH3 are brought together under suitable conditions, viz., in the
green leaves of plants, in the presence of sunlight, living protoplasm
is then and there born, a something having entirely new and unexpected
powers and properties. It is no gradual process but sudden, like birth
into a higher sphere.

Now, there is not the least doubt that the same is true of the order
and manner of the _first appearance_ of the natural forces in the
phylogenic series. In the history of the evolution of the cosmos,
the forces of Nature have appeared successively and suddenly when
conditions became favorable. There was a time in the history of the
earth when only physical forces existed, chemical affinity being held
in abeyance by the intensity of the heat.[41] By gradual cooling,
chemical affinity at a certain stage came into being--was born, a
new form of force, with new and peculiar phenomena, though doubtless
derived from the preceding. Ages upon ages passed away until the
time was ripe and conditions were favorable, and life appeared--a
new and higher form of force, producing a still more peculiar group
of phenomena, but still, as I believe, derived from the preceding.
Ages upon ages again passed away, during which this life-force
took on higher and higher forms--in the highest foreshadowing and
simulating reason itself--until finally, when the time was fully ripe
and conditions were exceptionally favorable, spirit, self-conscious,
self-determining, rational, and moral, appeared--a new and still higher
form of force, but still, as I am persuaded, derived from the preceding.

Now, that these forces are really of derivative origin is proved by the
fact that we see every step of this process taking place daily under
our very eyes. I pass over the conversion of physical into chemical
force because this is admitted on all hands. I begin, therefore, with
vital force. Sunlight falling on green leaves disappears as light
and reappears as life--is consumed in doing the work of decomposing
CO2, H2O, and NH3, and the C, H, O, and N thus set free from
previous combination unite to form living protoplasm.[42] Again, in
the embryonic history of every animal we see the next change take
place--i. e., the emergence of the psychic out of the vital. In the
germ-cell, in the egg, and even in the early stages of the embryo,
there is no distinctive animal life--i. e., no consciousness, nor
volition, nor response of any kind to stimulus. At a certain stage
distinctive animal or psychic life appears. We call it quickening.
Materials for psychology are now present for the first time. In man
alone, and that only some time after physical birth, we see the last
change. The new-born child has animal life only. The emergence of
self-consciousness--a change so wonderful that it may well be called
the birth of spirit--takes place only at the age of two to three years.
Now for the first time we have phenomena distinctive of humanity.

But some will ask, “How is this consistent with immortality?” In
answer, let me again remind the reader that with every new form of
force, with every new birth of the universal energy into a higher
plane, there appear new, unexpected, and, previous to experience,
wholly unimaginable properties and powers. This last birth is of course
no exception. Why may not immortality be one of these new properties?
But this point is so important that we must treat it more fully.

Remember, then, the view of the relation of God to Nature, already
explained. Remember that the forces of Nature are naught else than
different forms of the one omnipresent Divine energy. Remember that, as
just shown, this Divine omnipresent energy has taken on successively
higher and higher forms in the course of cosmic time. Now this upward
movement has been wholly by _increasing individuation_, not only
of matter, but also _of force_. This universal Divine energy, in a
generalized condition, _unindividuated_, diffused, pervading all
Nature, is what we call physical and chemical force. The same energy in
higher form, individuating matter, and itself individuated, but only
yet very imperfectly, is what we call the life-force[43] of plants. The
same energy, more fully individuating matter and itself more fully
individuated, but not completely, we call the _anima_ of animals. This
anima, or animal soul, as time went on, was individuated more and more
until it resembled and foreshadowed the spirit of man. Finally, still
the same energy, completely individuated as a separate entity and
therefore self-conscious, capable of separate existence and therefore
immortal, we call the spirit of man.

According to this view, the vital principle of plants and the anima
of animals are but different stages of the development of spirit in
the womb of Nature: _in man at last it came to birth_. In plants and
animals it was in deep embryo sleep--in the latter, quickened, indeed,
but not viable--still unconscious of self, incapable of independent
life, with physical, umbilical connection with Nature; but now at last
in man, separated from Nature, capable of independent life, born into
a new and higher plane of existence. Separated, but not wholly: Nature
is no longer _gestative_ mother, but still _nursing_ mother of spirit.
As the _organic embryo_ at birth reaches independent _material_ or
_temporal_ life, even so _spirit embryo_ by birth attains independent
_spiritual_ or _eternal_ life.

Although birth is its truest correspondence and best illustration, yet
we may vary the illustration in many ways:

1. Nature may be likened to a level water-surface. This represents
unindividuated physical and chemical force. On this surface some
individuating force pulls up a portion of the water into a _commencing_
drop. This represents the condition of spirit in plants. Or by greater
force the surface may be lifted higher into a nipple-like eminence
_simulating a drop_, or even into an almost complete drop with only
a neck-like connection with the general surface. This represents the
condition of spirits in the higher animals. In all these cases, even
though the drop be nearly completed, if we remove the individuating
or lifting force, the commencing drop is immediately drawn back by
cohesion and refunded into the general watery surface. But, once
complete the drop, and there is no longer any tendency to revert, even
though the lifting force is removed. This represents the condition of
spirit in man.

2. Or Nature may, again, be likened to a water-surface beneath which
the anima of animals is deeply and tranquilly submerged, wholly
unknowing of any higher, freer world above. In man spirit emerges above
the surface into a higher world, looks down on Nature beneath him,
around on other emerged spirits about him, and upward to the Father of
all spirits above him. Emerged, but not wholly free--head above, but
not yet foot-loose.

3. Or, again: As a planet must break away from physical, cohesive
connection with the central sun (planet-birth) in order to enter into
higher gravitative relations, which thenceforward determine all its
movements in beautiful harmony; as the embryo must break away from
physical umbilical connection with the mother in order to enter into
higher spiritual bonds of love, which thenceforward determine all
their mutual relations--even so spirit must break away from physical
and material connection with the forces of Nature, which are but the
omnipresent Divine energy, in order thereby to enter into higher
relations of filial love to God and brotherly love to man.

4. As the new-born child differs little in grade of physical
organization from the mature but unborn embryo, but at the moment
of birth there is a sudden and complete change, not so much in the
grade of organization but in the whole plane of existence--a change
absolutely necessary for further advance, for another cycle of life;
even so at the moment of the origin of man, howsoever this may have
been accomplished, there may have been no great change in the _grade_
of _psychical_ structure, but yet a complete change in the _plane_ of
psychical life--a change absolutely necessary for further advance, for
another cycle of evolution. In both cases there is a sudden entrance
into a new world, the sudden appearance of a new creature with entirely
different capacities--a passing out of an old world, a waking up in
a new and higher. According to this view, man alone is a _child_ of
God, capable of separate spirit-life--separate but not yet wholly
independent of Nature. As already said, Nature is no longer gestative
mother, but still nursing mother of spirit--we are weaned only by
death.

5. Or, again: As in passing up the _organic_ scale, we find all grades
of completeness of organic individuality, an increasing individuation
of bodily form which completes itself as a perfect organic individual
only in the higher animals, so, also, in passing up the _dynamic_
scale, force or energy is individuated more and more until the process
reaches completeness as a spirit-individual or dynamic individual--a
person only in man. _Organic_ individuality completes itself in
animals. _Psychic_ individuality only in man.

6. One more illustration and the last. The animal body may be likened
to an exquisitely adjusted instrument of communication between two
worlds--the material world without and the spiritual world within. The
key-boards of this marvelous instrument are the nerve-terminals of the
sense-organs in contact with the material world, and the brain-cells
in touch with the spirit-world. External Nature plays on the one by
sensation and determines changes in spirit. Spirit plays on the other
by will and muscular contraction, and determines changes in external
Nature. Now, in animals spirit is fast asleep or at most dreaming, or
even perhaps somnambulistic, but at least unconscious of _self_, and
acts only by stimulus--only responds in some sense automatically as
sleepers do. In man spirit is wide awake and may respond automatically
like animals, or may choose not to respond at all. Moreover, it acts
freely in its own domain--the world of ideas--_without external
stimulus_; or of its own free-will may _initiate_ changes in the
external world. With God all phenomena commence at the _spirit-end_.
In animals all commence at the _matter-end_, and by automatic response
terminate in the same. Man alone lives in both worlds, partakes of both
natures, and acts according to either method.

The more we reflect on this subject, the more we shall be convinced
that completed spirit individuality explains, as nothing else can, all
that is characteristic of man. It is this which constitutes person, or
the self-acting ego. It is this which constitutes self-consciousness,
free-will, and moral responsibility. And out of these, again, grows,
the recognition of relations to other moral beings and to God, and
therefore ethics and religion. Out of these, also, grows the capacity
of indefinite voluntary progress. This also means separate life,
spirit-viability, or immortality. Self-consciousness especially seems
to me the simplest sign of separate entity or spirit-individuality,
and its appearance among psychical phenomena _the very act of
spirit-birth_. We may imagine man to have emerged ever so gradually
from animals: in this gradual development the moment he became
conscious of self, the moment he turned his thoughts inward in wonder
upon himself and on the mystery of his existence as separate from
Nature, that moment marks the birth of humanity out of animality.
All else characteristic of man followed as a necessary consequence.
I am quite sure that, if any animal, say a dog or a monkey, could be
educated up to the point of self-consciousness (which, however, I am
sure is impossible), that moment _he_ (no longer _it_) would become a
moral responsible being, and all else characteristic of moral beings
would follow. At that moment would come personality, immortality,
capacity of voluntary progress; and science, philosophy, religion,
would quickly follow.

We have emphasized self-consciousness as the most fundamental sign of
spirit-individuality; but a difference of exactly the same kind is
found running through the whole gamut of human faculties as compared
with corresponding faculties in animals. As animal consciousness is
related to human self-consciousness, so exactly is animal will to human
free-will, animal intelligence to human reason, animal sign-language to
rational grammatical speech of man, constructive art of animals to true
rational progressive art of man. In every one of these the resemblance
is great, but the difference is immense, and not only in degree but
also in kind. In every case it is like shadow and substance, promise
and fulfillment, or, still better, it is like embryo and child. The
change from one to the other is like to a birth into a higher sphere,
the beginning of another cycle of evolution. We would like to follow
this idea out in detail, but it would lead us beyond the scope of this
work. Those who desire to do so we would refer to an article by the
author on the “Psychical Relation of Man to Animals.”[44]

But it will be objected that there are other births of energy from
lower to higher condition; but such births do not insure continued
existence in the higher condition. In the gradual evolution of energy
described on page 316, when a portion rises from physical to chemical,
from chemical to vital, or from vital to sentient, it does not remain
ever after in the higher condition--there is no immortality on the
higher plane. On the contrary, all these lower forms of energy are
continually ascending and descending; transformation is downward as
well as upward. Why should there be an exception in this last birth?
In these successive upward metamorphoses of energy why should the last
only be permanent? I answer: Because it reaches at last its final goal,
viz., complete individuation, as free, self-acting spirit; it reaches
again the spiritual plane from which it sprang, and becomes thereby
a partaker of the Divine nature; because it comes at last into moral
relations with the absolute--the Divine--and therefore above the plane
of shifting changes. If the scale of energy be likened to a ladder with
many rounds, reaching from the plane of matter to the plane of spirit,
then so long as energy is on the ladder it ascends and descends; but,
once it reaches the plane of free spirit, it is in a wholly new world
in which eternal ascent is the law.

Perhaps I can best bring out the reasonableness of my view by comparing
it with other possible alternative views.

There are three possible views as to the nature, the origin,
and the destiny of the human spirit: (1.) That it pre-existed
always--uncreated, underived, eternal, both ways--backward as well
as forward. Therefore, as it never began, so it will never end. It
is _immortal of its own right_. This is substantially the view of
Plato, of Leibnitz, and perhaps some other philosophers. (2.) That
it is derived from God _directly_--created at once _without natural
process_; that at the moment of creation of the first man Adam, and
at some unknown time and in some inscrutable way in the history of
each individual, it was _injected into the body from the outside_,
and at the same time _endowed_ with immortality. This, I take it, is
the orthodox view. (3.) That it was indeed derived from God, but not
directly; created indeed, but only by natural process of evolution;
that it indeed pre-existed, but only as embryo in the womb of Nature,
slowly developing through all geological times, and finally coming
to birth as _living_ soul in man. Thus it _attains_ immortality at a
certain stage of development, viz., at spirit-birth. This is the view I
have striven to enforce.

I hold up these three views: Which is the more rational? The view of
Plato--that of self-existent, uncreated, eternal spirit--I think few
will entertain at this time of the world’s day. The usual orthodox
view I have shown is surrounded with insuperable difficulties; is
wholly unscientific and irrational. What is there left but the view
presented above? Plato is right in asserting pre-existence, but wrong
in denying creation. The usual view is right in asserting creation, but
wrong in denying natural process. The view I have presented asserts
pre-existence in embryo and creation by natural process. It therefore
combines and reconciles the two extreme views, and is more rational
than either.

=Some General Conclusions.=--There are still two or three thoughts so
closely connected with what we have already said that we can not pass
them over:

1. We have seen that every mental state corresponds with a particular
brain state, and every mental change with a brain change. We have,
therefore, here, two series, physical and psychical, corresponding
with each other, term for term. For every change in the one there is
a corresponding change in the other, both in kind and amount. Now, is
not this the test of the relation of cause and effect? It certainly is.
Yes, there must be a causal relation here, even though we are not able
to understand the nature of the causal nexus. But which is cause and
which effect? If the view above presented be correct, then in animals
_brain changes_ are in all cases the _cause_ of psychical phenomena.
In man alone, and only in his higher activities, _psychic_ changes
precede and determines brain changes. In man alone brain changes
are determined not only by external but by _internal_ impressions.
Man alone perceives not only objects--_material things_--but also
relations and properties _abstracted_ from the objects, i. e., _ideal
things_; and, moreover, not only relations between objects, but also
relations between relations or ideas. In man alone there is an inner
world--microcosm--the _things_ of which are _thoughts_, ideas, etc.
This _self-acting power_ of spirit on _the things of itself_, instead
of merely reacting as played upon by external nature, is characteristic
of man, and is a necessary result and a sign of severance, partial at
least, of physical bond with Nature.

2. Again, I have used the term vital _principle_. I must justify it.
I know full well that it is the fashion to ridicule the term as a
remnant of an old superstition which regards vital force as a sort of
supernatural entity unrelated to other forces of Nature. No one has
striven more earnestly than myself to establish the correlation of
vital with physical and chemical forces;[45] and yet, if the view above
presented be true, there is a _kind_ of justification even for the
term vital _principle_--much more, vital _force_. There is a kind of
reason and true insight in the personification of the forces of Nature,
and especially of vital force. All forces, by progressive dynamic
individuation, are on the way toward entity or personality, but fully
attain that condition only in man.

3. Again, to perceive relations and properties abstracted from material
things, to form abstract or general ideas, to form not only _per_cepts
but also _con_cepts, is admitted to be a characteristic of man--a
characteristic on which all our science and philosophy rest. From time
immemorial the vexed question has been debated, “Have such abstract
or general ideas any _real_ existence, or are they mere _names_ of
figments of the mind?” This is the famous question of _realism_ and
_nominalism_. Now, if our view be correct, then there is one most
fundamental abstraction, viz., _self_, which is indeed a _reality_.
Self-consciousness is the direct recognition of the one reality,
spirit, of which all others are the sign and shadow--the true reality
which underlies and gives potency to all abstractions or ideas. Do
we not find in this view, then, the foundation of a true realism, or
rather a complete reconciliation of realism and nominalism?

4. Thus, then, Nature, through the whole geological history of the
earth, was gestative mother of spirit, which, after its long embryonic
development, came to birth and independent life and immortality in man.
Is there any conceivable meaning in Nature without this consummation?
All evolution has its beginning, its course, its end. Without
spirit-immortality this beautiful cosmos, which has been developing
into increasing beauty for so many millions of years, when its
evolution has run its course and all is over, would be precisely as if
it had never been--an idle dream, an idiot tale signifying nothing. I
repeat: Without spirit-immortality the cosmos has no meaning. Now mark:
It is equally evident that, _without this gestative method of creation
of spirit_, the whole geological history of the earth previous to man
would have no meaning. If man’s spirit were made at once out of hand,
why all this elaborate preparation by evolution of the organic kingdom?
The whole evolution of the cosmos through infinite time is a gestative
process for the birth of spirit--a divine method of the creation of
spirits.

Thus, again, man is born of Nature into a higher nature. He therefore
alone is possessed of two natures--a lower, in common with animals,
and a higher, peculiar to himself. The whole mission and life-work of
man is the progressive and finally the complete dominance, both in the
individual and in the race, of the higher over the lower. The whole
meaning of sin is the humiliating bondage of the higher to the lower.
As the _material_ evolution of Nature found its goal, its completion,
and its significance in man, so must man enter immediately upon a
higher _spiritual_ evolution to find its goal and completion and its
significance in the ideal man--the Divine man. As spirit, unconscious
in the womb of Nature, continued to develop by _necessary_ law until
it came to birth and independent life in man, so the new-born spirit
of man, both in the individual and in the race, must ever strive by
_freer_ law to attain, through a newer birth, unto a higher life.




CHAPTER V.

THE RELATION OF GOD TO MAN.


In the two preceding chapters we have discussed the relation of God
to Nature and of man to Nature. There is still another relation, if
possible, of still more vital importance to us, viz., the _relation of
God to man_. This, of course, introduces the question of revelation--a
subject which I approach with some reluctance. I feel I am treading
on holy ground, and must do so with shoes removed. If it be asked,
How is evolution concerned with the subject of revelation? I answer
Evolution emphasizes and enforces the reign of law taught by all
science, and makes it at last _universal_. Many conclude, therefore,
that, if evolution be true, a belief in the possibility of any form
of revelation is irrational. I do not think this follows, and I will
give my reasons. I do so, however, very briefly, because we are not yet
ready to formulate our views except in the most general way.

If man be indeed something more than a higher species of animal; if
man’s spirit be indeed a spark of Divine energy individuated to the
point of self-consciousness and recognition of his relation to God; if
spirit embryo, developing in the womb of Nature through all geological
time, came to birth and independent spirit-life in man, and thus man
alone is a _child of God_ as well as a product of Nature--if all this
be true, then it is evident that this wholly _new_ relation requires
also a wholly different mode of Divine operation. If God operates on
Nature only by regular processes, which we call _natural laws_, then he
_must_ operate on spirit in a different and a more direct way, and this
we call _revelation_. If to the student of Nature it is inconceivable
that He should operate on Nature except by natural laws (for this is
the name we give to His chosen mode of operation there), then to the
student of theology it is equally inconceivable, if our view of man
be true, that He should not operate on spirit in some more direct and
higher way, i. e., by revelation.

But some will ask, Is not this a palpable violation of law? I think
not. All divine operations are, must be, according to reason, i. e.,
according to law. The operation of the divine on the human spirit,
i. e., revelation, must therefore be according to law, but a higher
law than that which governs Nature, and, therefore, from _the point
of view of Nature_, supernatural. There is nothing wholly unique in
this. Life is a higher form of force than the physical and chemical.
Life-phenomena are therefore super-physical, and if we confined the
term Nature to dead Nature they would be supernatural. So the free,
self-determined acts of spirit on spirit, even of the spirit of man
on the spirit of man, much more of the Spirit of God on the spirit
of man, may be according to law, and yet from the natural point of
view be supernatural. It is true that, in the complex of phenomena,
material and spiritual inextricably woven together, which go to make
up human life, Science must ever strive to reduce as much as possible
to material laws, for this is her domain, and she is bound to extend
it; but, if our view of man be true, there will always remain a
large residuum of phenomena--a whole world of phenomena--which will
never yield, because clearly beyond her domain. Standing on the
lower material plane, these phenomena are wholly super-material, and
therefore incomprehensible from the material point of view. We must
rise and stand on the higher plane before these also are reduced to
law, but a higher law than that operating on the lower plane. If,
therefore, science insists on banishing the supernatural from the realm
of Nature, theology may reasonably insist on its necessity, _in this
sense_, in the realm of morals and religion.

If, then, the direct influence of the Spirit of God on the spirit of
man be what we call revelation, then there is evidently no other kind
of revelation possible; and, furthermore, such revelation is given to
all men in different degrees. It is given to all men as conscience;
in greater measure to all great and good men as clearer perception of
righteousness; in pre-eminent measure to Hebrew prophets and Christian
apostles; but supremely and perfectly to Jesus alone. But there is, and
in the nature of things there can be, _no test of truth but reason_.
We _must_ fearlessly, but honestly and reverently, try all things,
even revelations, by this test. We must not regard, as so many do,
the spirit of man as the passive amanuensis of the Spirit of God.
Revelations to man must of necessity partake of the imperfections of
the medium through which it comes. As pure water from heaven, falling
upon and filtering through earth, must gather impurities in its course
differing in amount and kind according to the earth, even so the pure
divine truth, filtering through man’s mind, must take imperfections
characteristic of the man and of the age. Such filtrate must be
redistilled in the alembic of reason to separate the divine truth from
the earthy impurities.




CHAPTER VI.

THE OBJECTION, THAT THE ABOVE VIEW IMPLIES PANTHEISM, ANSWERED.


It will be observed that the views presented in the last three
chapters are closely connected with one another, and all conditioned
on the “Relation of God to Nature,” urged in Chapter III. Now it will
doubtless be objected to this view, especially as applied in Chapter IV
on the “Relation of Man to Nature,” that it is naught else than pure
pantheism; that it destroys completely the personality of Deity, and
with it all our hopes of communion with him, and all our aspirations of
love and worship toward him; that, according to this view, God becomes
only the soul or animating principle of Nature, operating everywhere
but unconsciously like the vital principle of an organism; that the
whole cosmos becomes in fact a great organism, developing under the
operation of _resident_ force according to _necessary_ law, only that
_we_ apotheosize this omnipresent force and call it God; and finally,
that God is naught else than an abstraction, created like other
abstractions or general ideas wholly by the human mind, and having no
objective existence. Furthermore, it will be said, that according to
this view, this omnipresent unconscious energy individuates itself by
necessary law of evolution more and more until it reaches, _for the
first time in man_, self-consciousness and immortality, and thus that
man himself is the only self-conscious immortal being in existence, and
therefore the only being worthy of reverence and worship. Thus, this
view leads to humanity-worship or rather to _self-worship_.

I feel the full force of this objection. I answer it as follows: I
freely admit that, following up this scientific line of thought alone,
we are carried strongly in the direction of pantheism. But there is
nothing strange or exceptional in this. In all the deepest questions,
single lines of thought inevitably carry us to extreme one-sided views.
This seems to be the necessary result of the essentially two-fold
nature of man, self-conscious spirit in a material body, the relation
between which is, and must ever be, inscrutable. On this account
there is and must be a fundamental antithesis in human philosophy,
i. e., two lines of thought, the material and spiritual, which lead
to two apparently irreconcilable views.[46] We have already seen
that a rational philosophy, whenever we are able to reach such, is
always found in a higher and more comprehensive view, which includes,
combines, and reconciles two one-sided, partial, and mutually excluding
views. But spirit and matter, or mind and brain, or God and Nature,
is _the_ fundamental antithesis which underlies and is the cause of
all other lesser antitheses. This antithesis, therefore, is absolutely
fundamental, and therefore forever irreconcilable. We must accept
both sides, even though we can not clearly perceive the nature of
their relation. We must be content with compromise where we can not
effect complete reconciliation. We must frankly acknowledge that the
antagonism is apparent only, and the result of the limitation of our
faculties, and believe that, if we could only rise to a high enough
point of view, like all other antitheses, this also would disappear in
a rational philosophy.

Now, to apply these principles. No one, we admit, can form a clear
conception of how immanence of Deity is consistent with personality,
and yet we must accept both, because we are irresistibly led to each
of these by different lines of thought. Science, following one line of
thought, uncorrected by a wider philosophy, is naturally led toward the
one extreme of pantheistic immanence; the devout worshiper, following
the wants of his religious nature, is naturally led toward the other
extreme of anthropomorphic personality. The only rational view is to
accept both immanence and personality, even though we can not clearly
reconcile them, i. e., immanence without pantheism, and personality
without anthropomorphism. We have already seen in the third chapter,
how following the scientific line of thought, we are logically driven
to immanence. We wish now to show how, following another line of
thought, we are as logically driven to personality. On this most
difficult subject, however, all we are prepared to do is to throw out
some brief suggestions, in the hope that they may be carried out more
perfectly by some thoughtful reader; scatter some seed-thoughts, in the
hope that, falling haply on good soil, they may spring up and bear more
fruit than I have been able to produce.

1. In the gradual individuation of the universal Divine energy
described in Chapter IV, there must of course be a corresponding growth
of a kind of independent self-activity which reaches completeness
in man, and in fact constitutes what we call self-consciousness
and free will. The exact nature of the relation of Deity or of the
general forces of Nature to this gradually individuated portion, I do
not undertake to define. And how this idea of partial self-activity
comports with the absoluteness of Deity we can not clearly understand.
But this fact need not specially disturb us here; for this is only one
branch of the wider question of the moral agency of man in relation to
the absolute sovereignty of God, or the freedom of man in relation to
necessary law in Nature.

2. =Personality behind Nature.=--We have already shown that, if the
brain of a living, thinking man were exposed to the scrutiny of an
outside observer with absolutely perfect senses, all that he would
or could possibly see would be molecular motions, physical and
chemical. But the subject himself, the thinking, self-conscious spirit,
would experience and observe by introspection only consciousness,
thought, emotion, etc. On the _outside_, only physical phenomena;
on the _inside_ only psychical phenomena. Now, _must not the same
be necessarily true of Nature also?_ Viewed from the outside by the
scientific observer, nothing is seen, nothing can be seen, there is
nothing else to be seen, but motions, material phenomena; but behind
these, on the other side, on the _inside_, must not there be in this
case also psychical phenomena, consciousness, thought, will; in a word,
_personality_?[47] In the only place where we do get behind physical
phenomena, viz., in the brain, we find psychical phenomena. Are we not
justified, then, in concluding that in all cases the psychical lies
behind the physical? The human brain is a wonderful instrument, by
means of which, in some inscrutable way, viz., in our own experience,
we do get behind, on the other side, on the inside of some material
phenomena, and in so far become partakers of the Divine nature. But
behind other phenomena of Nature we may never hope to penetrate either
by observation or experience, but only in dim way by highest reason.
Science, even in the case of the brain, can not pass from the one kind
of phenomena to the other. If she would study the _inside_ she must
abandon the _outside_--she must abandon the microscope and take to
introspection. If she would study the phenomena of the higher platform,
she must leave the lower and climb up and stand on the higher. If this
be true of the brain where the two kinds of phenomena are brought
so close together, how much more is it true of the phenomena of the
cosmos. We can never hope, either by observation or by experience,
to pass beyond the veil. We must abandon the methods of science and
reach it, if at all, in some other way. Not the clear-sighted but the
pure-hearted shall see God in Nature.

Thus, then, we see that our own self-conscious personality behind
brain phenomena compels us to accept consciousness, will, thought,
personality behind Nature. Now I assert that, once get this abstract
idea in the mind, and by a necessary law of thought it gradually
expands without limit, and eventually reaches the form of infinite
consciousness, will, thought, etc., and therefore of an infinite
person. This law of indefinite expansion may be illustrated by
the ideas of space and time. The animal, and, indeed, the infant,
understands space and time only in their relation to itself, but has
not yet abstracted these from their contents. This comes only with
the birth of self-conscious personality. But, so soon as the abstract
idea of space is acquired, by a necessary law of mental activity
it expands without limit, and finally becomes the idea of infinite
space. Similarly, so soon as the idea of time as abstracted from its
contents is conceived, it inevitably expands without limit and grows
into the idea of infinite time. So is it precisely with the idea of
self-conscious personality. The animal or the very young child is
indeed conscious of its body and of external objects in their mutual
relations, but not of self, as abstracted from its contents. The
animal never attains it, the child does. Now, so soon as this idea of
self-conscious personality--of a spiritual entity underlying material
phenomena--appears, by a necessary law of mental activity it expands
without limit, and inevitably reaches the idea of an infinite self, an
infinite person, God, behind the phenomena of Nature.

But some will object that this idea of infinite personality
is inconceivable. True enough; but _the opposite is far more
inconceivable_. The ideas of infinite space and infinite time are
also inconceivable, yet we must accept them, because the idea of all
space or all time being limited is still more inconceivable; for
if we think of space or time as limited, immediately there comes
the question, “What is there beyond the limit?” There is therefore
this wide difference between these two inconceivables: the one is
so only in the sense of transcending the power of our mind, but the
other is unthinkable, self-contradictory, absurd. So also is it with
self-conscious personality. The idea of an infinite self, i. e., God,
is indeed inconceivable, but only in the sense of transcending our
power of comprehension; but the idea of the consciousness behind the
cosmos as being limited or finite is more than inconceivable, it is
unthinkable, self-contradictory, absurd; for immediately comes the
question, “What is there beyond which limits it?” To the Greek mind
Zeus was limited; therefore of necessity came also the idea of Fate,
superior to and limiting Zeus himself. To them, therefore, Fate was the
real God--the absolute.

3. _Divine Personality._--I have used the word personality as
expressing the nature of God. But let me not be misunderstood. I
well know we can not conceive clearly of an infinite, unconditioned
personality. Deeply considered, it seems nothing short of a
contradiction in terms. All I insist on is this: In our view of the
nature of God, the choice is not between personality and something
_lower_ than personality, viz., an _unconscious force_ operating
Nature by _necessity_, as the materialists and pantheists would have
us believe; but between personality as we know it in ourselves and
something inconceivably _higher_ than personality. Language is so
poor that we are obliged to represent even _our_ mental phenomena by
physical images. How much more, then, the Divine nature by its human
image! Self-conscious personality is the highest thing we know or can
conceive. We offer him the very best and truest we have when we call
him a Person; even though we know that this, our best, falls far short
of the infinite reality.

4. =Cause in Nature.=--We have thus far spoken only or principally
of self-consciousness, but the same precisely is true of another
essential attribute of personality, viz., _free-will_. Every one
admits causative force or forces operating in Nature. Science has shown
that all the different kinds of force are but different forms of one
omnipresent energy. Now, looking abroad on Nature from the outside,
this omnipresent energy seems to modern science as simply resident,
inherent in matter itself, and therefore as operating unconsciously
and by necessity. But the question occurs, “Whence did we get the idea
of force, energy, _causation_?” I answer unhesitatingly: We get it
not from without by observation of Nature, but from within through
consciousness; not from the outside view, but from, the inside view of
phenomena. We can not conceive of phenomena without force, of effects
without cause, because we are intensely conscious of being ourselves
through our wills an active cause of external phenomena. If we were
merely passive observers, not active causers of changes in the external
world, then these external phenomena would seem to us merely to shift
and change and succeed each in a certain order. We might note the
order and determine the laws of sequence, and thus form a science;
but it would never enter into our minds to imagine any causal or
dynamical nexus between them. In the mind of such passive observer,
but not doer--thinker, but not worker--would be completely realized
the only thorough-going and consistent materialistic philosophy,
i. e., a philosophy in which, like Comte’s, cause and force have no
place--are in fact banished as a superstition from science. But the
clear consciousness of essential energy, of causative force within, the
certainty that we ourselves, through our wills and by the conscious
exertion of force do determine changes in the external world, compels
us to attribute all changes to causative force of some kind, and
naturally enough, until the interference of science, to a personal will
like our own. Thus by a necessary law we project our internal states
into external Nature.

But see now the steps of evolution of this idea. At first, i. e.,
in the uncultured races, and also in childhood, external forces
take the form of a personal will like our own residing in _each
object_, and controlling its phenomena as our wills control our bodily
movements (fetichism). Then, as culture advances, it takes next
the form of several personal wills controlling each the phenomena
of a different department of Nature (polytheism). Finally, in the
highest stage of culture, it takes the form of one personal will
controlling the phenomena of the whole cosmos (monotheism). To the
religious but unscientific mind in all these stages the personal
will is anthropomorphic. But we have already seen (Chapter III) how
anthropomorphism has been driven by science from one department after
another, until now at last by evolution it is driven out of Nature
entirely, and to those following this line of thought alone, the
phenomena of Nature are relegated to forces inherent in matter, and
operating by laws necessary and fatal; and not only so, but material
forces are made to invade even the realm of consciousness, and reduce
this also to material laws. Thus the savage _e_jects his own conscious
personal will into every separate object of Nature; the modern
materialist _in_jects material forces into the realm of consciousness.
But, as already seen, a rational philosophy admits these two antithetic
views, and strives to combine and reconcile them. This reconciliation,
as far as it is possible for us, is found in a personal will immanent
in Nature, and determining directly all its phenomena.

Thus it is evident that the idea of a causal nexus between successive
phenomena is a primary conception, and therefore ineradicable and
certain. Even from the purest evolution point of view it must be true,
for, if man’s mind grew out of the forces of Nature, this idea must
represent a fact in Nature. Also, analysis shows that all causative
force originates in _will_. Lastly, culture and reason, by a necessary
law of expansion, carry us upward to the conception of one infinite
sustaining and creative will. Science may sometimes obscure but can
not destroy this idea. Evolution, which was supposed by some to have
destroyed it for ever, has only temporarily obscured it in the minds
of the unreflecting, by the supposed identity of evolution with
materialism. From this temporary eclipse it now emerges with still
greater clearness and far greater nobleness. For, observe: All the
effects known to us in Nature are finite; therefore a personal will,
which determines these _separately_ by successive acts, as we do, must
also be finite like ourselves. But a will, which by _one eternal_ act
ever-doing, never done, determines the evolution and the sustentation
of an infinite cosmos, must itself be infinite. Thus only in the
doctrine of universal evolution do we rise to a just conception of God
as an infinite cause.

5. =Design in Nature.=--As the idea of _cause_ and force is related
to _will_, so precisely is the idea of _design_ related to _thought_.
We get this also, not from without, but from within. Adaptation of
means to ends is in our experience the result of thought, and we can
not conceive it to result otherwise. The effect of science can not be
to destroy this primary conception--which, indeed, like all primary
conceptions, is ineradicable, and already more certain than anything
can be made by proof--but only to exalt and purify our conceptions
of the designer. For, observe: In any case of _adaptive_ structure,
whether in the animal body or in planetary relations, the evidence of
design is not in the materials, but in the _use_ of the materials; not
in the _parts_, but in the _adjustment_ of the parts for a purpose.
Design, purpose, adjustment, _adaptation_, are not material things,
but relations or intellectual things, and therefore perceivable only
by thought, and conceivable only as the result of thought. It is
simply impossible to talk about such adaptive structures without using
language which implies design. The very word “_adaptive_” implies it.
It is impossible even to think of such structures without implicitly
assuming intelligence as the cause. It makes no particle of difference
_how_ the material originated, or whether it ever originated at all;
it matters not whether the adaptation was done at once out of hand,
or whether by slow process of modification; it matters not whether
the adaptive modification was brought about by a process of natural
selection, or by pressure of a physical environment; whether without
law or according to law. The removal of the result from man-like
directness of separate action can not destroy the idea of design,
but only modify our conception of the Designer. What science, and
especially evolution, destroys, therefore, is not the idea of design,
but only our low anthropomorphic notions of the mode of working of the
Designer.

Precisely the same change takes place here under the influence of
science as has taken place in all our notions concerning God. The
uncultured savage sees a _separate_ god in every object. As culture
advances, his gods become fewer and nobler, until, in the most advanced
states, man recognizes but one infinite God, the creator and sustainer
of all. God is still in every phenomenon, but no longer as a separate
God, but only as the separate manifestation of the One. Thus culture
takes away our gods, but only to compel us to seek him in nobler forms
until we reach the only true God. But, even after the conception of the
one God is reached, how many seem to regard him as altogether such a
one as ourselves; but science shows us that his ways are not like our
ways, nor his ends as our ends. Thus science, more than all other kinds
of culture, simplifies while it infinitely ennobles and purifies our
conceptions of Deity.

Again, the same change takes place in our sense of _mystery_. I
suppose most people imagine that it is the special mission of science
to destroy all mystery. Many seem to think that superstition, or even
religion, is inseparably connected with ignorance and mystery, and
all must disappear together before the light of science. But not so.
There is only a gradual progressive change--an evolution in the form of
mystery as well as in the form of religion. To the savage everything is
a _separate_ mystery. The function of science is, indeed, to destroy
these separate mysteries, by explaining them; but, in doing so, it only
reduces them to fewer and grander mysteries, and these again to still
fewer and grander, until, in an ideally perfect science, all separate
and partial mysteries are swallowed up in the one all-embracing
infinite mystery--the mystery of existence. There is still mystery
in each object, but no longer a separate mystery--only a separate
manifestation of the one overwhelming mystery.

Or, again, and finally: The same change occurs in our ideas of
_creation_. At first every object is a separate creation--a
manufacture. With advancing science these separate, creative acts
become fewer and nobler, until now, at last, in evolution, all
are embraced and swallowed up in _one eternal_ act of creation--a
never-ceasing procession of the divine energy. Every object is still a
creation, but not a separate creation--only a separate manifestation of
the one continuous creative act.

Now, precisely the same change must take place in our conception of
design in Nature. To the uncultured there is a distinct and separate
design in every separate work of Nature. But, as science advances, all
these distinct, separate, petty, man-like designs are merged into fewer
and grander designs, until, finally, in evolution at last, we reach
the conception of the one infinite, all-embracing design, stretching
across infinite space, and continuing unchanged through infinite time,
which includes and predetermines and absorbs every possible separate
design. There is still design in everything, but no longer a separate
design--only a separate manifestation of the one infinite design.

Thus, then, our own self-consciousness and will and thought give rise,
necessarily, to the conception of an infinite self-consciousness, will,
and thought--i. e., God. The necessity to believe in self-conscious
spirit behind bodily phenomena compels us to believe also in an
infinite self-conscious spirit behind cosmic phenomena. Looking at the
operations of this ever-active spirit, whether in the one case or the
other, _from the outside_, it looks like unconscious energy inherent
in matter itself, and therefore like necessity, or fate. But, looked
at from the inside _in the one case_, the brain, we perceive only
self-conscious, free activity of spirit. Therefore, we are compelled
to acknowledge in the other case, the cosmos, also, the same source
of all activity, the same cause of all phenomena. We are compelled to
acknowledge an infinite immanent Deity behind phenomena, but manifested
to us on the outside as an all-pervasive energy. But some portion of
this all-pervasive energy again individuates itself more and more, and
therefore acquires more and more a kind of independent self-activity
which reaches its completeness in man as self-consciousness and
free-will. We said, “_a kind of_ independent self-activity.” How this
comports with the absoluteness of God we can not understand, any more
than we can understand how it comports with invariable law in Nature.
We simply accept them both as primary truths, even though we can never
hope to reconcile them completely, because we can not understand the
exact nature of the relation of spirit to matter. We can not look at
the outside and the inside at the same time. If we could understand
the relation of psychical phenomena to brain-changes, then might
we hope to understand far more perfectly than now the relation of
God to Nature. But as in the one case, the brain, although we can
not understand the _nature_ of the relation, yet we are sure of the
intimacy of the connection of the two series, psychical and physical,
term for term; so in the other case, the cosmos, although we can not
understand the exact _nature_, we are sure of the intimacy of the
connection, _term for term_--every material phenomenon and event with a
corresponding psychical phenomenon as its cause.




CHAPTER VII.

SOME LOGICAL CONSEQUENCES OF THE DOCTRINE OF THE DIVINE IMMANENCY.


The doctrine of the Divine immanency carries with it the solution of
many vexed questions. In fact, in its light these questions simply pass
out of view as no longer having any significance. Several of these
questions have been alluded to in an indirect way in the previous
chapter and in Chapter III. We take them up distinctly here, and show
their relation to evolution.

Religious thought, like all else, is subject to a law of evolution,
and therefore passes through regular stages. Of these stages, three
are very distinct and even strongly contrasted. They correspond in
a general way to the three stages of Comte, which he has misnamed
the _theological_, the _metaphysical_, and the _positive_. We will
illustrate by many examples.


I. _Conception of God._

This, the most fundamental conception of all religion, has passed from
a gross anthropomorphism to a true spiritual theism, and the change
is largely due to science and especially to the theory of evolution.
There are three main stages in the history of this change: (1.) The
first is a _low_ anthropomorphism. God is altogether such a one as
ourselves, but larger and stronger. His action on Nature, like our
own, is _direct_; his will is wholly man-like, capricious and without
law. (2.) The second is still anthropomorphism, but of a nobler sort.
God is not _altogether_ like ourselves. He is man-like; yes, but
also _king-like_. He is _not_ present in Nature, but sits enthroned
above Nature in solitary majesty. He acts on Nature, not directly but
indirectly, through physical forces and natural laws. He is an absentee
landlord governing his estate by means of appointed agents, which are
the natural forces and laws established in the beginning. He interferes
personally and by direct action only occasionally, to initiate
something new or to rectify something going wrong. This idea culminated
and found the clearest expression in the eighteenth century, and was
the necessary result of the scientific ideas then prevalent, viz.,
ideas of pre-established _stability_ of cosmic order and _fixedness_ of
organic types. God was the great _artificer_, the great _architect_,
working, as it were, on foreign material and conditioned by its nature.
He established all things as they are in the beginning, and they have
continued so ever since.

This conception still lingers in the religious mind, and is in fact the
prevailing one now. It is a great advance on the preceding, but, alas!
it removes God beyond the reach of our love. He is the architect of
worlds, the artificer of the eye, the sovereign ruler of the universe,
but not our Father. We are his creatures, his subjects, but not his
children.

(3.) The third and last stage in this development is true spiritual
theism. God is immanent, resident in Nature. Nature is the house
of many mansions in which he ever dwells. The forces of Nature are
different forms of his energy acting directly at all times and in
all places. The laws of Nature are the modes of operation of the
omnipresent Divine energy, invariable because he is perfect. The
objects of Nature are objectified, externalized--materialized states
of Divine consciousness, or Divine thoughts objectified by the Divine
will. In this view we return again to _direct_ action, but in a nobler,
a spiritual, Godlike form. He is again brought very near to every one
of us and restored to our love, for in him we live and move and have
our being. In him all things consist, by him all things exist. This
view has been held by noble men in all times, especially by the early
Greek fathers, but is now verified and well-nigh demonstrated by the
theory of evolution. No other view is any longer tenable.

The idea of God is of course the most fundamental of all religious
ideas, and a change in this carries with it many other changes. Some of
these necessary outcomes, especially the nature, the origin, and the
destiny of the human spirit, and its relation to the Divine spirit, I
have already treated in previous chapters. But there are others which
flow so directly and obviously that they may be presented in brief
space.


II. _Question of First and Second Causes._

Among the most obvious of these is the question of first and second
causes. This distinction, I suppose, did not exist in early thought.
As a popular view, it was mainly due to the physical science of the
eighteenth century. It was a necessary corollary of the idea of God
as the great architect sitting outside of Nature and acting on Nature
as on foreign material. According to this view, God is the original
and primary cause of all things; but he _delegates_ his power to
_secondary_ forces, such as gravity, heat, electricity, etc., which
are therefore the immediate causes of phenomena. I believe that most
persons hold this view still. But it is now being displaced by the
idea of God immanent or resident in Nature as already explained. This
view is a complete _identification_ of first and second causes. All
causes are mere modes of the first cause. They seem to us secondary,
necessary, and unconscious only because they act according to
invariable law. But law itself is only the mode of operation of a
perfect will. Thus we have the same three stages of evolution here
also: (1.) First, all is first cause, direct, man-like, capricious,
lawless. (2.) Then the first cause acts king-like, indirectly by many
appointed agents subject to pre-enacted laws. These agents or secondary
causes directly determine all natural phenomena. (3.) Lastly, come the
complete combination and reconciliation of these two. All is by first
cause and direct action, like the first. All is by invariable law like
the second, the law being only the mode of operation of a perfect will.


III. _Question of General and Special Providence._

So also providence, general and special, is only another phase of the
same question and solved in the same way. At first all is _special_
providence--the result of caprice or favoritism and without law. Then
all or nearly all is general providence operating by invariable law;
but from time to time the general law is broken through for special
purposes when necessary. Is not this the prevailing view now? Lastly,
these two must be combined and reconciled in a third. All is alike
general and special: general--i. e., according to law; special--i. e.,
by direct action. There is no real distinction between the two. The
distinction vanishes in the light of a higher view.


IV. _The Natural and the Supernatural._

In precisely the same category falls the question of the natural and
the supernatural. The same three stages are evident here also, and the
same solution: 1. First all is supernatural and lawless, and Nature is
viewed with stupid wonder and abject fear. 2. Then Nature is reduced to
mechanical laws and made subject to man. Wonder and fear give place to
indifference and even perhaps to contempt. We practically live without
God in the world. It requires, now, _miracles_ or a violent breaking
through of law in order to startle us out of our stupidity and awaken
in us a sense of the Divine presence. 3. But we must come lastly to a
higher philosophy. We must recognize that all is natural and all is
supernatural according as we view it, but none more than another. All
is natural--i. e., according to law; but all is supernatural--i. e.,
above Nature, as we usually regard Nature, for all is permeated with
the immediate Divine presence. Wonder in the contemplation of Nature
returns, or rather exalted reverence and rational worship are given
in place of open-mouthed wonder and superstitious fear. Once clearly
conceive the idea of God permeating Nature and determining directly all
its phenomena according to law, and the distinction between the natural
and the supernatural disappears from view, and with it disappears also
the necessity of miracles as _we usually understand miracles_. In fact,
the word as we usually understand it has no longer any meaning.

I must stop a moment to explain, lest I be misunderstood; and to
enforce, lest it be thought I speak lightly.

Miracle, in the sense of violation of law, is simply impossible,
because law is the expression of the essential nature and perfection
of God. It is as impossible for God to perform a miracle in this sense
as it is for him to lie, and for the same reason, viz., that it is
contrary to his essential nature. In what sense, then, is a miracle
possible? I answer, only as an occurrence or a phenomenon _according to
a law higher than any we yet know_. If we define Nature as phenomena
governed by physical and chemical laws and forces, then life becomes
supernatural and miraculous--because higher than Nature as we define
it. If we reduce the phenomena of life to law and include these
also in our definition of Nature but limit it there, then the free,
self-determined phenomena of reason become supernatural because above
our definition of Nature. There may well be still other and higher
modes of Divine activity, the law of which we do not and may never
understand. These are above our present definition of Nature, and
therefore to us supernatural or miraculous. But, even if miracles in
the ordinary sense were possible, is it not evident that the ordinary
processes of Nature are far more wonderful, more truly Godlike, than
any such miracle?


V. _Question of Design in Nature._

So, again, the question of design or purpose or mind in Nature is
similarly solved. It has been said, it is continually now being
said, that evolution has destroyed forever the teleological view
of Nature--i. e., the idea of design in Nature. Yes, if we mean
the man-like, cabinet-making, watch-making design of Paley and
older writers--a separate petty design for each separate object. It
has indeed destroyed this, but only to replace it by a far nobler
conception--a truly Godlike design, a design embracing all space and
running through all time, including and absorbing all possible separate
designs and predetermining them by a universal law of evolution.

Or the same question may be put in another way as “Mind _vs._
Mechanics in Nature.” In the evolution of thought on this subject at
first all was _mind_, but lawless, capricious, like our own. Then
one department after another of Nature was reduced to mechanical,
physical, necessary law, until all have been or will be or conceivably
may be thus reduced, and mind seems driven out of Nature entirely.
The friends of religion in despair cry out for at least some small
corner left for mind. Thus I find in recent numbers of an English
scientific periodical, “Nature,” a discussion concerning mind as _one_
of the factors of evolution.[48] Is it not amusing, if it were not
so sad?--God the Divine mind as _one of the factors_ of evolution!
The true solution is very simple. All is mind or none; so also all
is mechanics or none. It _is all mind through mechanics_. It is all
mechanics from the outside; it is all mind from the inside. To science
all is mechanics; to theology all is mind. It is the duty of philosophy
to reconcile these two opposites by the higher view that mechanics is
but the mode of operation of the Divine mind. There is only one form of
evolution, viz., human progress, in which mind--but the _human_, not
the Divine mind--is _one_ of the factors of evolution. But to think and
speak thus of God in relation to Nature is to place him on the human
plane. It is gross anthropomorphism.[49]


VI. _Question of the Mode of Creation._

I might multiply examples almost without limit, of questions the
solution of which depends on this one of the relation of God to Nature.
I give one more--Creation.

The creation of the universe _at once_--in the beginning--out of
nothing--and then _rest ever since_. This old anthropomorphic idea is
now replaced by that of continuous creation--unhasting, unresting,
by an eternal process of evolution. For if the universal law of
gravitation is the Divine mode of sustentation of the universe, the no
less universal law of evolution is the Divine process of creation.




CHAPTER VIII.

THE RELATION OF EVOLUTION TO THE IDEA OF THE CHRIST.


What think ye of Christ? This is indeed in many ways a test-question,
and we ought frankly to meet it. I have feared heretofore to touch this
question. I now only throw out some brief suggestions--scatter some
seed-thoughts. Does Evolution have anything to say on this also? I
think it does. This I proceed to show:

As organic evolution reached its goal and completion in _man_, so human
evolution must reach its goal and completion in the _ideal man_--i. e.,
the Christ. According to this view, the Christ is the ideal man, and
therefore--(mark the necessary implication)--and therefore the Divine
man. We are all as men (as contradistinguished from brutes)--we are
_all_, I say, _sons of God_; the Christ is the well-beloved Son. We
are _all_ in the image of God; he is the express and _perfect image_.
We are all partakers in various degrees of the Divine nature; in him
the Divine nature is completely realized. It is not necessary that the
ideal man--the Christ--should be perfect in knowledge or in power; on
the contrary, he must grow in wisdom and in stature, like other men;
but he must be _perfect in character_. _Character is essential spirit._
All else, even knowledge, is only environment for its culture. In the
dazzling light of modern science we are apt to forget this. Character
is the _attitude_ of the human spirit toward the Divine Spirit. If I
should add anything to this definition, I would say it is spiritual
_attitude_ and spiritual _energy_. In the Christ this attitude must be
wholly right; the harmony--the union with the Divine--must be perfect.
This perfect union gives, of necessity, also fullness of spiritual
energy.

Now, I wish to show that, although the Christ as thus defined must
be human--yes, even more intensely human than any one of us--yet by
the law of evolution we ought to expect him to differ from us in an
inconceivable degree, and especially in a superhuman way. This I do by
a series of illustrations.

We have said that the Christ is the ideal and therefore the Divine
man--that he is the goal and completion of humanity. But in evolution
a goal is not only a completion of one stage, but also the beginning
of another and higher stage--on a higher plane of life with new and
higher capacities and powers _unimaginable from any lower plane_. Let
me illustrate:

1. As man is the ideal--the goal and completion of animal evolution,
and yet is he also a birth into a higher plane of life--the spiritual;
so the Christ, the ideal man, may be only the goal and completion of
human evolution, and yet is he also a birth into a new and higher
plane--_the Divine_.

2. As the human spirit pre-existed in embryo in animals, slowly
developing through all geological times, until it came to birth and
immortality in man, so the Divine spirit is in embryo in man in various
degrees of development, and comes to birth and completion of Divine
life in the Christ.

3. As animals reached, finally, _conscious relations_ with God in
man, even so man reaches _union_ with God in the Christ. As man, the
ideal animal, is a union of the _animal_ with the _spiritual_; so the
Christ, the ideal of human evolution, is a union of the _human_ and the
_Divine_.

4. Finally: As with the appearance of man there were introduced new
powers and properties unimaginable from the animal point of view, and
therefore from that point of view seemingly supernatural--i. e., above
their nature--so with the appearance of the Christ we ought to expect
new powers and properties unimaginable from the human point of view,
and therefore to us seemingly supernatural--i. e., _above our nature_.

The Christ as defined above--i. e., as the _ideal man_--is undoubtedly
a true object of rational worship. There are two and only two
fundamental moral principles, viz., love to God and love to man. Both
of these must be embodied in a rational worship. The one must be
embodied in the worship of an Infinite Spirit--God; the other in the
worship of the ideal man--the Christ.

But some one will object that, admitting all this, it is impossible
that the goal, the ideal, should appear until the _end of the course_
of evolution. To him I answer: This is indeed true of animal evolution,
but not of human evolution. We have already seen (see p. 88 _et seq._)
that there is an essential difference in this regard between these
two kinds of evolution. In addition to all the factors of organic
evolution, in human progress there is a new and higher factor added,
which immediately takes precedence of all others. This factor is _the
conscious voluntary co-operation of the human spirit in the work of its
own evolution_. The method of this new factor consists essentially in
the formation, and especially in the _voluntary pursuit, of ideals_. In
organic evolution _species_ are transformed by the _environment_. In
human evolution _character_ is transformed by _its own ideal_. Organic
evolution is by _necessary_ law--human evolution is by voluntary
effort, i. e., by _free_ law. Organic evolution is _pushed_ onward and
upward from behind and below. Human evolution is _drawn_ upward and
forward from above and in front by the attractive force of ideals. Thus
the ideal of organic evolution can not appear until the end; while the
attractive ideals of human evolution _must_ come--whether only in the
imagination or realized in the flesh--but must come somehow _in the
course_. The most powerfully attractive ideal ever presented to the
human mind, and, therefore, the most potent agent in the evolution of
human character, is _the Christ_. This ideal must come--whether in the
imagination or in the flesh I say not, but--must come somehow _in the
course_ and not at the end. At the end the whole human race, drawn
upward by this ideal, must reach the fullness of the stature of the
Christ.

But it will be again objected that all ideals are relative and
temporary; that we are in fact drawn onward and upward by many
successive ideals, one beyond another, in the course. Ideals are but
mile-stones which we put successively behind us while we press on to
another; they are successive rounds of an infinite ladder which we put
successively beneath us while we rise higher. This one also we shall
eventually put behind us and pass on.

To this I have two answers: Admitted that in many ways such is the
course of progress; but who has been able to reach this ideal and
conceive a higher? When this one is reached and completely realized in
our personal character, it will be time enough to propose another.

Again, it is true that in many ways we have advanced and are still
advancing by the use of partial ideals; but this use of partial and
relative ideals is itself in only a temporary stage of evolution. At
a certain stage we catch glimpses of the _absolute_ moral ideal. Then
our gaze becomes fixed, and we are thenceforward drawn upward forever.
The human race has already reached a point when the absolute ideal of
character is attractive. This Divine ideal can never again be lost to
humanity.




CHAPTER IX.

THE RELATION OF EVOLUTION TO THE PROBLEM OF EVIL.


The problem of evil has tasked the power and baffled the skill of the
greatest thinkers in every age. It would be folly in me to imagine that
I can solve it. Its complete solution is probably impossible in the
present state of science. Yet I can not doubt that on this, as on every
important question relating to man, the theory of evolution will throw
new and important light. All I can hope to do is to throw out some
brief suggestions on the subject.

If evolution be true, and especially if man be indeed a product of
evolution, then what we call evil is not a unique phenomenon confined
to man, and the result of an accident, but must be a great fact
pervading all nature, and a part of its very constitution. It must have
existed in all time in different forms, and subject like all else to
the law of evolution. Let us, then, trace rapidly some of the steps of
this evolution.

1. _External Physical Evil in the Animal Kingdom._--As already seen in
previous chapters, the necessary condition of evolution of the organic
kingdom is a _struggle_ for life--a conflict on every side, with a
seemingly _inimical_ environment and a survival of only the strongest,
the swiftest, or the most cunning--in a word, the fittest. Now, suppose
the course of organic evolution finished in the introduction of man,
and from this vantage-ground we look back over the course and consider
its result. Shall we call that evil which was the necessary condition
of the progressive elevation which culminated so gloriously? Evil
doubtless it seemed to the individual, struggling animal, but is this
worthy to be weighed in comparison with the evolution of the whole
organic kingdom until it culminated in man? Is it not rather a _good_
in disguise? I suppose human arrogance may be willing enough to admit
it in _this_ case, where animals only are sufferers.

2. _Physical Evil in Relation to Man._--But organic evolution,
completed in man, was immediately transferred to a higher plane, and
continued as social evolution; material evolution is transformed into
psychical evolution; unconscious evolution, according to _necessary_
law, to conscious voluntary progress toward a recognized goal, and
according to a _freer_ law. But in this transformation the fundamental
conditions of evolution do not change. Man also is surrounded on every
side with what at first seems to him an _evil environment_, against
which he must ever struggle or perish. Heat and cold, tempest and
flood, volcanoes and earthquakes, savage beasts and still more savage
men. What is the remedy--the only conceivable remedy? Knowledge of
the laws of Nature, and thereby acquisition of power over Nature. But
increasing knowledge and power are equivalent to progressive elevation
in the scale of psychical being. This conflict with what seems an evil
environment is, therefore, the necessary condition of such elevation.
It is not too much to say that, without this condition, except for this
necessity for struggle, man could never have emerged out of animality
into humanity, or, having thus emerged, would never have risen above
the lowest possible stage. Now suppose, again, this ideal to have been
attained--suppose knowledge of physical laws and power over physical
forces to be complete--suppose physical nature completely subdued,
put beneath our feet, and subject to our will, and, from the high
intellectual position thus attained, we look back over the whole ground
and consider the result. Shall that be called evil which was obviously
the necessary condition for attaining our then elevated position? Evil
it doubtless seemed to the individuals who fell, and still seems to us
who now suffer, by the way in the conflict; but is physical discomfort
or even physical death of the individual to be weighed in comparison
with the psychical elevation of the individual, and especially of the
race? Evidently, then, physical evil even in the case of man is only
_seeming_ evil, but _real_ good.

3. _Organic Evil--Disease._--But there is a more dreadful form of evil
than that which results from _external_ physical nature--an evil far
more subtle and difficult to understand, and therefore to conquer.
I mean _internal_ organic evil--disease in its diversified forms
and with its attendant weakness and suffering, inscrutable often in
its causes, insidious in its approaches, contagious, infectious,
spreading from house to house, carrying suffering and death in its
course, and leaving sorrow and desolation behind. Is there any remedy
which can transmute this evil into good? There is. It is again
knowledge--knowledge of the laws, and power over the forces, of
_organic nature_. Is it not evident that complete knowledge of the laws
of health and the causes of disease would put this evil also under our
feet? Is it not evident that a perfect knowledge of the laws of health,
and a perfect living according to these laws, would so entirely subdue
this evil that men would no longer die except by natural decay or by
accident? Is it not evident, also, that the race will not attain this
knowledge unless it be forced upon us by the necessity of avoiding the
dread evil of disease?

Now suppose, again, this ideal attained, suppose this dread evil
subdued by complete knowledge, and again from our elevated intellectual
position we look back over the ground. Shall we call that evil which
was the necessary condition of our intellectual elevation? Evil,
doubtless, it seems to us individuals who have suffered and are still
suffering through our ignorance; but is such individual suffering or
even individual death to be weighed against the psychical elevation of
the individual and evolution of the race? Ought not the individual to
be willing to suffer thus much vicariously for the race? Is not this
seeming evil also a _real_ good?

May we not, then, confidently generalize? May we not say that all
physical evil is good in its general effect--that every law of Nature
is beneficent in its general operation, and, if sometimes evil in
its specific operation, is so only through our ignorance? Partly
by survival of the fittest, and partly by intelligence, man, like
other animals, brings himself in accord with the laws of Nature, and
thus appropriates the good and avoids the evil, and Nature becomes
beneficent only. But, also unlike any other animal, man by rational
knowledge makes the laws of Nature his servants, and uses them for his
own purposes, thus increasing his power and elevating the plane of his
life.

4. _Moral Evil._--But there is still another form of evil, the most
dreadful of all. This one may be called _the_ evil, in some sense, _the
only evil_. It is that of which all other forms are but the shadows
cast backward and downward along the course of evolution and on lower
stages of existence. This consummation of all evil is _sin_--_moral
disease_--more dreadfully contagious and deadly than any organic
disease. What shall we say now? Is there any rational explanation of
this evil? Is there any possible-reason or excuse for an all-wise,
all-powerful Ruler afflicting man alone of all His creatures with this
greatest of all evils? In all other cases, the individual and the race
sacrifice themselves for a time _physically_ for the sake of final
spiritual elevation; but this _is spiritual debasement_. In all other
cases, there is a sacrifice in the _course_ in order to attain the
_goal_, but this is a missing of the goal itself. Is there any view
which mitigates this evil, any philosophic alchemy which can transmute
this evil into good? Age after age the human mind has prostrated
itself in helpless paralysis before this problem. Most thinkers have
been content to say, “Thou hast ordered it so. Thou art good. It must
be right.” But many, and among them some of the best minds, have
said, “Either God is not all-good, or else not all-wise, or else not
all-powerful, or else there is no God at all.” Does evolution shed any
light on this dread problem? I believe it does.

We have said that all other evils are but shadows of this one, cast
backward and downward on earlier stages of evolution and lower forms of
existence. But from the evolution point of view these earlier and lower
forms of evil are rather to be regarded as _fore_shadowings of the
reality to come. They are but earlier and lower stages of the evolution
of the _same thing_--embryonic conditions of the now full-grown evil.
If so, then the same law must apply here also, though, as we shall see,
with a difference. Here, also, the individual as well as the race finds
himself surrounded by what seems an evil environment, against which
he must struggle. The spirit of man is inclosed and conditioned by a
lower environment, which he must subdue or perish. Here, then, is again
a deadly conflict: “a law in the members warring against the law of
the spirit, and bringing it into captivity”; a law of selfism warring
against the law of love, and bringing it into subjection; solicitations
to debasement on the one hand, and solicitations to wrong others on the
other. How shall it be overcome? What is the remedy? Again I answer,
Knowledge of and conformity to the _laws of the moral world_. But, as
in other cases, so in this: this knowledge of and conformity to law,
which is the true goal of humanity, will not be attained unless it is
forced upon us by necessity and in self-defense--i. e., by evil.

Now suppose, once more, this knowledge and conformity be complete, and
the ideal of humanity be attained, and from this final and highest
position we look back over the whole ground. Shall that be called evil
which from the very nature of a moral being and the laws of evolution
was obviously the necessary condition of attaining the goal? Shall
we not from this final position call it a good in disguise? Evil,
doubtless, it seems to us who suffer and stumble and mayhap fall by the
way; but shall the mishap of the individual be weighed as an equivalent
against the evolution of the race and the attainment of its goal?

Ah! there is the rub. It is all well enough to talk of sacrificing
the _physical_ individual to the race, but not so the _spiritual_. If
we believe in the immortality of the human spirit, if we do indeed
stand related to God in the manner explained in Chapter IV, then
moral evil in the individual has an entirely peculiar and an eternal
significance--then the individual human spirit has an infinite worth
and can not be sacrificed to the race; for the evolution of the race
itself is only in order to the perfecting of individual human souls.
What shall we say now? I answer: The sacrifice is not necessary. There
is in the realm of morals _alone_ a way of escape--a saving element
which redeems the individual without violating the law. Let me explain.

It will, I think, be admitted by all that _innocence_ and _virtue_ are
two very different things. Innocence is a _pre-established_, virtue
a _self-established_, harmony of spiritual activities. The course of
human development, whether individual or racial, is from innocence
through more or less discord and conflict to virtue. And virtue
completed, regarded as a condition, is holiness, as an activity, is
spiritual freedom. Not happiness nor innocence but virtue is the goal
of humanity. Happiness will surely come in the train of virtue, but
if we seek primarily happiness we miss both. Two things must be borne
steadily in mind: virtue is the _goal of humanity_; virtue can not be
given, it must be _self-acquired_.

Now we have already seen that in all evil the remedy, which not
only cures it but transmutes it into good, is knowledge of law and
conformity of conduct thereto--a true science and a successful art--in
a word, knowledge of the laws of God and obedience to these laws. In
the physical world ignorance of these laws is necessarily fatal, but
not so in the moral world. Ignorance here is not necessarily fatal
though dangerous. By the very nature of a moral being, the essential
thing is not knowledge but _character_ or virtue--the _will_ to know
and the _effort_ to obey. In the physical realm, knowledge is the goal;
in the moral realm, knowledge is only in order to virtue. Therefore,
in the case of the individual struggling with moral evil within and
without, the victory is always in his power. If he fails, it is his
own fault. His utmost effort in this field must be successful, because
the result is not external, but internal and in the realm of moral
freedom. The spirit of man is self-acting and in some sense, though
not absolutely, self-existing, and can not be ruined except by its own
act. In the moral world, where the goal is not knowledge but character,
attainment must be in proportion to honest endeavor in the right spirit.

Evil, then, has its roots in the necessary law of evolution. It is a
necessary condition of all progress, and pre-eminently so of moral
progress. But some will ask, “Why could not man have been made a
perfectly pure, innocent, happy being, unplagued by evil and incapable
of sin?” I answer: The thing is impossible even to omnipotence, because
it is a contradiction in terms. Such a being would also be incapable of
virtue, would not be a moral being at all, would not in fact be man.
We can not even conceive of a moral being without freedom to choose.
We can not even conceive of virtue without successful conflict with
solicitations to debasement. But these solicitations are so strong and
so often overcome us, that we are prone to regard the solicitations
themselves as essential evil instead of our weak surrender to them.

All evolution, all progress, is from lower to higher plane. From a
philosophic point of view, things are not good and evil, but only
higher and lower. All things are good in their true places, each under
each, and all must work together for the good of the ideal man. Each
lower forms the basis and underlying condition of the higher; each
higher must subordinate the lower to its own higher uses, or else it
fails of its true end. The physical world forms the basis and condition
of the organic, yet the organism rises to a higher plane only by
ceaseless conflict with and adaptation to the physical environment,
which therefore seems in some sense evil. The organic world in its
turn underlies and conditions and _nourishes_ the rational moral
world. As the senses are the necessary feeders of the intellect, so
the appetites are the necessary feeders of the moral nature. Yes, even
the lowest sensual appetites are the necessary basis and nourishers
of our highest moral sentiments. And yet the struggle for mastery of
the higher spiritual with the lower animal is often so severe that the
latter seems to many as _essential evil_ to be extirpated, instead of
a useful _servant_ to be controlled. This view is asceticism. Now the
whole view of evil usually held is a kind of asceticism, and therefore,
like asceticism, must be only a transition phase of human thought. All
that we call evil both in the material and the spiritual world is good,
so long as we hold it in subjection as servants to the spirit, and only
becomes evil when we succumb. All evil consists in the dominance of the
lower over the higher; all good in the rational use of the lower by
the higher. Asceticism may, indeed, be the best philosophy for some.
If we can not subdue the lower nature, we must try to extirpate it,
and thus at any cost set free the higher from humiliating bondage. If
we can not practice the higher virtue of _temperance_ in _all_ things,
we must even try the lower virtue of _total abstinence_ in _some_
things. If our right eye offends, we must not hesitate to pluck it
out; but let us not imagine that one eye is better than two--let us
clearly understand that thereby our spiritual nature is sadly maimed,
and therefore that the highest virtue, which is spiritual beauty and
strength, can not thus be attained. True virtue consists, not in the
extirpation of the lower, but in its subjection to the higher. The
stronger the lower is, the better, _if only_ it be held in subjection.
For the higher is nourished and strengthened by its connection with the
more robust lower, and the lower is purified, refined, and glorified by
its connection with the diviner higher, and by this mutual action the
whole plane of being is elevated. It is only by action and reaction of
all parts of our complex nature that true virtue is attained.




FOOTNOTES:


[1] The term _Chorology_, used by Haeckel, nearly covers the ground.

[2] _Ontos-gennao_ (individual-making, or genesis of the individual).

[3] _Taxis, nomos_ (relating to science of arrangement).

[4] This statement is general; it will be modified hereafter.

[5] _Phule-gennao_ (kind-making); genesis of the race.

[6] This formulation of the laws of organic succession was given by
me in 1860, before I knew anything of either Darwin’s or Spencer’s
evolution. They were my own mode of formulating Agassiz’s views.

[7] Genesis without previous life--spontaneous generation.

[8] Fishes were first introduced in the later Silurian; but became
dominant in the Devonian.

[9] Amphibians were introduced in the Carboniferous, but true reptile
not until the Permian.

[10] Of course I mean downward in _social function_. Individually the
scavenger may be nobler than the statesman.

[11] Cope, “Science,” vol. ii, p. 274, 1883.

[12] Boston Society of Natural History--anniversary memoir, 1880. Also,
“American Naturalist,” June, 1882.

[13] “Archives des Sciences,” vol. liv, 1875.

[14] “Nature,” vol. xxxi, p. 4, 1884.

[15] See abstract of Dr. Romanes’s views, “Nature,” vol. xxxiv, pp.
314, 336, 362. Also, discussions of the same by Meldola, Galton,
Wallace, etc., in immediately subsequent numbers.

[16] This subject is more fully treated in chapter IX, p. 240 _et seq._

[17] See an article entitled “Genesis of Sex,” “Popular Science
Monthly,” 1879, vol. xvi, p. 167.

[18] Mr. Wallace has recently, in his work on “Darwinism,” taken
strong ground against this Darwinian factor. He thinks, for example,
that sexual vigor is the cause of both the splendor of color and the
pertinacity which secures the female. We see little difference in this
way of putting it. Our object, however, is not to argue the question of
what are true factors, but simply to give the most accepted, and, as it
seems to us, also the most probable view.

[19] By _reason_ I mean the faculty of dealing with the phenomena of
the _inner world of consciousness and ideas_. Animals live in one
world--the outer world of _sense_; man in two--the outer world of
sense, like animals, but also in an inner and higher world of _ideas_.
All that is characteristic of man comes of this capacity of dealing
with the inner world. In default of a better word I call it reason. If
any one can suggest a better word, I will gladly adopt it.

[20] While all comparative anatomists agree that the lung is a
diverticulum from the œsophagus, like the air-bladder of the gar-fish,
some think that it is a _different_ diverticulum, which is seen first
in the dipnoi.

[21] Undoubtedly the true principle on which primary groups ought to be
made is, _identity of general plan of structure_, or _traceableness of
homology throughout_. For these groups are the great primary branches
of the tree of life, and classification ought to represent degrees of
genetic relationship. This was Agassiz’s principle, although he did not
admit the genetic relation. This principle has been, it seems to us,
too much neglected by later systematists.

[22] The Amphioxus, the lowest of all vertebrates--if vertebrate it may
be called--is an exception to 2 and 3. In this animal the vertebrate
type is not yet fully declared.

[23] This is only one example under a general law which it may be
well to stop a moment to illustrate. A repetition of similar parts
performing the same function is always an evidence of low organization,
and as we rise in the scale of organization such parts usually become
fewer and more efficient. Thus, to give one example, myriapods, as
their name indicates, have hundreds of locomotive organs--lower
crustaceans perhaps thirty or forty. As we go up, they are reduced to
fourteen (tetradecapods), then to ten (decapods), then in spiders to
eight, in insects to six, in vertebrates to four, and in man to two.
A similar reduction in number, but increase in efficiency, is found
in toes, _when they are used for support and locomotion only_. In man
we find the normal number of five (1), because his hands are used for
grasping and the functions of the fingers are not the same; and (2),
because man’s development was almost wholly _brainward_. In other
respects his structure is far less specialized than most other mammals.
He can not compete with carnivores in strength and ferocity, nor with
herbivores in fleetness. In the struggle for life, therefore, there
was nothing left for him but increase in intelligence. Probably four
is the smallest number of locomotive organs consistent with highest
efficiency. In retaining but two legs for locomotion, man has lost in
locomotive efficiency, but by the sacrifice he liberates two limbs for
higher functions.

[24] “Proceedings of American Academy of Arts and Sciences,” vol. xiv,
May, 1878.

[25] Fol., “Archives des Sciences,” vol. xiv, p. 84, 1885; “Science,”
vol. vi, p. 92, 1885.

[26] Of course, this is a purely imaginary case. The conditions of
development of the eggs of higher animals forbid continuous watching
the process. Yet we do observe in different individuals all these
stages in mammals as well as other animals.

[27] These baleen plates are not modifications of teeth, as might at
first be supposed, but rather of the transverse gum-ridges found on the
roof of the mouth of many mammals, and conspicuous in the horse.

[28] “Proceedings of the California Academy of Science,” vol. v, p.
152. 1873.

[29] For fuller discussion of this subject, see “Bulletin of the
California Academy of Science,” No. 8, 1887, and “American Journal of
Science,” for Dec., 1887.

[30] “Origin of Races of the Dog.” “Annals and Magazine of Natural
History,” vol. xvii, p. 295. 1886.

[31] Mr. Galton (“Nature,” August 26, 1886) has used a diagram similar
to the above (which I first used in 1879) to illustrate the law of
sexual attraction and repugnance.

[32] This subject is more fully discussed by the author in an article
entitled “Genesis of Sex,” in “The Popular Science Monthly,” vol. xvi,
p. 167, 1879.

[33] For examples of this the reader is referred to Cope, “Bulletin
of the National Museum,” No. 1; and to Coues’s “Key to North American
Birds,” last edition.

[34] “Monatsbericht d. k. Preuss. Akademie d. Wissenschaft zu Berlin,”
for July, 1866.

[35] “Genesis of Tertiary Species of Planorbis at Steinheim.” A. Hyatt,
Anniversary Memoir of the Boston Society of Natural History, 1880.

[36] In a letter to the author, dated February 13, 1887, Prof. Cope
says: “Such transitions of species are clearly indicated in the
_Oreodontidæ_, where such different forms as _O. gracilis_ and _O.
Culbertsoni_ are connected by intergradations.”

[37] “American Naturalist,” 1873; “Popular Science Monthly,” June, 1873.

[38] For a fuller development of this subject the reader is referred to
an article by the author, entitled “Critical Periods in the History of,
and their Relation to, Evolution” (“American Journal of Science,” vol.
xiv, p. 99, 1877).

[39] “Reflex Action and Theism,” William James, “Unitarian Review” for
November, 1881.

[40] See an article by the author on this subject, “American Journal of
Science,” series ii, vol. xxviii, p. 305, 1859, and in “Popular Science
Monthly,” vol. iv, p. 156, 1873.

[41] All chemical compounds are dissociated by sufficient heat.

[42] The origin of vital from chemical force in the green leaves of
plants can not be doubted; but this does not, of course, explain the
mystery of the _first origin of life on the earth_, for one condition
of the change _now_ is the _contact of living matter_.

[43] I know it is the fashion to ridicule the use of the terms
vitality, vital force, as a remnant of an old superstition; and yet the
same men who do so use the terms gravity, electricity, chemical force,
etc. Vital force is indeed _correlated_ with other forces of Nature,
but is none the less a distinct _form_ of force, far more distinct
than any other unless it be the still higher form of psychical, and
therefore it better deserves a distinct name than any lower form. Each
form of force gives rise to a peculiar group of phenomena, and the
study of these to a special department of science. Now, the group of
phenomena called vital is more peculiar, more different from other
groups than these are from each other, and the science of physiology
is a more distinct department than either physics or chemistry, and
therefore the form of force, which determines these phenomena, is more
distinct and better entitled to a name than any physical or chemical
force.

[44] “Princeton Review” for May, 1884.

[45] “Popular Science Monthly,” December, 1873.

[46] For a fuller statement of this antithesis, see an article by the
author entitled “Evolution in Relation to Materialism,” “Princeton
Review,” for March, 1881.

[47] Johnstone Stoney, “Nature,” vol. xxxi, p. 422.

[48] “Nature,” vol. xxxiv, p. 385. 1886.

[49] So, again, see a book recently published (“Nature,” vol. xliii, p.
460, 1891), entitled “Whence comes Man, from Nature or from God?” The
answer is plain. From both--from God through Nature. Evolution is the
method of creation.




INDEX


  Acceleration, law of, 178.

  African fauna explained, 204.

  Agassiz, his greatest result, 29, 43;
    relation to evolution, 32, 37, 43;
    relation to Darwin, 46;
    compared with Kepler, 47.

  Ages of geological history, 16.

  Alpine species explained, 215.

  Amphibians, development of, 150.

  Analogy and homology, 99.

  _Anima_ of animals, 313, 317.

  Animal architecture, styles of, 209.

  Animal kingdom, primary divisions of, 107.

  Animals, relation of man to, 311;
    spirit embryonic in, 311.

  Antiquity of man, religion and, 282;
    of the earth, religion and, 281.

  Aortic arches, proofs of evolution from, 151.

  Arthropods, 132.

  Artificial production of varieties, 222.

  Australia, fauna and flora of, explained, 200;
    when isolated, 202.


  Barriers limit faunal and floral regions, 188.

  Beauty, origin of, 269.

  Birds’ tails, changes of, 174.

  Brain, vertebrate, proofs of evolution from, 162;
    vertebrate, changes of, in phylogenic series, 168;
    relation to mind, 327, 338.

  Brain-physiology as a basis for materialism, 306.

  Branching tree illustrates evolution, 13-15, 18, 110, 250.

  Brooks, W. K., on the cause of variations, 262.


  Californian coast-islands, fauna and flora of, 211.

  Causation, idea of, from within, 342.

  Cause, first and second, 354.

  Cells, somatic and germ, 93.

  Centers of creation, specific, 194.

  Cephalization, 171.

  Chambers, his views on evolution, 34.

  Changes slow at present, 266.

  Christ, the, 359;
    relation of evolution to, 359;
    as an agent in human progress, 363.

  Close-breeding, effects of, 236, 243.

  Coast-islands of California, fauna and flora of, 211.

  Comparison, method of, 41.

  Conflict between religion and science, 280.

  Continental faunas and floras, 188.

  Continental island life, 208.

  Continuity, law of, 53;
    law of, applied to inorganic forms, 54;
    to organic forms, 56.

  Cope’s law of acceleration, 178.

  Creation, special, 30, 69;
    specific centers of, 194;
    changes in our notions of, 348;
    question of mode, 358.

  Cross-breeding, law of, 236.

  Cross-fertility of artificial varieties, 232.

  Cross-sterility, 77, 234.

  Cyclical movement, law of, 16, 22.


  Darwin, relation to Agassiz, 46;
    compared with Newton, 48;
    factors of evolution discovered by, 74;
    objections to his theory of evolution, 76.

  Derivation, origin of inorganic forms by, 54;
    origin of organic forms by, 56.

  Design, idea of, from within, 345;
    argument from, not destroyed by evolution, 346;
    changes in our ideas of, 348;
    in Nature, question of, 357.

  Differentiation, law of, 11, 19;
    law of, in embryonic development, 19;
    law of, illustrated, 144;
    of the animal kingdom illustrated, 176.

  Disease, necessity of, 367.

  Divine energy, forms of, 318.

  Divisions of the animal kingdom, 117.

  Dogmatism, theological and scientific, 293.

  Domestication, changes produced by, 222.


  Egg, development of, 3, 19.

  Egyptian species unchanged in three thousand years, 265.

  Embryology, proofs of evolution from, 148.

  Environment, physical, 73.

  Evil, problem of, relation of evolution to, 365;
    physical, necessity of, 366;
    a condition of progress, 366, 373;
    organic, necessity of, 367;
    moral, necessity of, 369.

  Evolution, what is, 3, 8;
    scope of, 3;
    type of, 3, 8;
    examples of, 5;
    popularly limited to the organic kingdom, 7;
    progressive change in, 9;
    laws of, 11;
    illustrated by branching tree, 13-15, 18, 90, 250;
    misconception of, 14;
    produced by resident forces, 27;
    germs of the idea, 32;
    relation of Agassiz to, 32, 37, 43;
    Lamarck’s views on, 33;
    Chambers’s views on, 34;
    obstacle to, removed, 35;
    confliction with religion imaginary, 45;
    how related to gravitation, 49;
    general evidences of, 53;
    artificial, 60;
    observed, 62;
    certainty of, 65;
    special proofs of, 67;
    factors of, 73, 81;
    human contrasted with organic, 88;
    monotypal and polytypal, 85;
    proofs of, from the vertebrate skeleton, 111;
    from the articulate skeleton, 132;
    from embryology, 148;
    from development of amphibians, 150;
    from aortic arches, 151;
    from vertebrate brain, 162;
    from rudimentary organs, 179;
    from geographical distribution of organisms, 183;
    explains geographical diversity, 195;
    objection to this view, 217;
    answer, 219;
    proofs of, from artificial modifications, 222;
    factors of, operative in domestication, 228;
    paroxysmal, 257;
    material, nearly completed, 267;
    thoroughly established, 275;
    relation to religion, 276, 282;
    relation to materialism, 284;
    necessitates great change in religious thought, 295;
    of forces, 315;
    relation to revelation, 331;
    pantheistic objection answered, 335;
    relation to problem of evil, 365.

  Experimental method largely fails on plane of life, 40.


  Factors of evolution, 73;
    their grades and order of introduction, 81;
    Lamarckian, 81;
    selection, 82-85;
    Darwinian, 83;
    rational, 86.

  Faculties, evolution of, 23.

  Faunas and floras, geographical, 183;
    continental, 188;
    marine, 192;
    special cases of distinct, 192;
    of Australia, 200;
    of Africa, 204;
    of Madagascar, 205;
    of continental islands, 208;
    of the coast-islands of California, 211;
    of oceanic islands, 213;
    of lofty mountains, 215.

  Fish-tails, changes of, in development, 172;
    in evolution, 174.

  Fishes, age of, 17.

  Floras and faunas, geographical, 183.

  Force, vital, correlation of, 36;
    planes of, 314;
    evolution of, 315;
    idea of, from within, 342.

  Forces, resident, evolution by, 27;
    of Nature are forms of Divine energy, 317;
    different planes of, 314.

  Fore-limbs, vertebrate, homologies of, 113.


  Generation, spontaneous, 15.

  Geographical faunas and floras, 183;
    diversity, theory of, 193;
    diversity explained by evolution, 195;
    present diversity determined by Glacial epoch, 198;
    objection to this view, 217;
    answer, 219.

  Geological record, imperfection of, 252.

  Glacial epoch determined distribution of species, 195, 198, 215;
    changes during, in America, 198;
    in Europe, 199.

  God, relation of, to Nature, 297;
    immanence of, in Nature, 300;
    relation of, to man, 326;
    personality of, 332;
    necessary belief in, 344;
    different forms of conception, 351.

  Good and the true, relation of, 277.

  Grasshopper, external anatomy of, 143.

  Gravitation, relation of, to evolution, 49;
    and religion, 281.

  Gyroscope, 288.


  Heliocentric theory and religion, 280.

  Hind-limbs, vertebrate, homologies of, 121.

  Horse, genesis of, 126.

  Homologies of vertebrate skeleton, 111;
    of vertebrate fore-limbs, 113;
    of vertebrate hind-limbs, 121;
    of articulate skeleton, 132.

  Homology and analogy, 99;
    only within primary divisions, 108.

  Hyatt, A., on Planorbis, 254.


  Ideal, relative and absolute, 364.

  Idealism, true and false, 301.

  Immortality in accord with law, 316.

  Individuality, organic, 325;
    spiritual, 325.

  Innocence and virtue compared, 372.

  Inorganic forms, law of continuity applied to, 54.

  Intermediate forms between artificial varieties, 232.

  Islands, continental and oceanic, 207.


  Kepler compared with Agassiz, 47.


  Lamarck, evolutionary views of, 33, 74.

  Law of differentiation, 11, 19;
    of progress of the whole, 13, 22;
    of cyclical movement, 16, 22;
    of continuity, 53;
    of continuity applied to inorganic forms, 54;
    to organic forms, 56;
    of differentiation illustrated, 144;
    of acceleration, 178;
    of cross-breeding, 218, 236.

  Laws of evolution, 11, 19.

  Lepidosiren, 101.

  Life, nature of, 35;
    imperfectly subject to experiment, 40;
    relation of, to philosophy, 277.

  Limbs, vertebrate, homology of, 113.

  Links, connecting, 12, 57, 145;
    connecting, elimination of, 248;
    connecting, usually absent from geological faunas, 251.

  Liquidambar, 218, 220.

  Lobster, external anatomy of, 136.

  Lungs, formation of, 100.


  Madagascan fauna explained, 205.

  Mammals, age of, 17.

  Man, age of, 18;
    relation of, to Nature, 304;
    relation of, to animals, 311;
    spirit of, in relation to the forces of Nature, 313, 316;
    relation of God to, 331.

  Marsupials, 201.

  Materialism, relation of, to evolution, 284;
    basis for, in brain-physiology, 306;
    basis for, in evolution, 311.

  Methods, scientific, 38.

  Migration favors diversification, 77.

  Mind, relation of, to brain, 327, 338;
    _versus_ mechanics in Nature, 340.

  Miracles, question of, 356.

  Mollusks, age of, 16.

  Monotremes, 201.

  Mystery, changes in our sense of, 347.


  Nature, relation of God to, 297;
    immanence of God in, 300;
    relation of man to, 304;
    has no meaning without spirit, 329;
    mind _versus_ mechanics in, 340.

  Natural and supernatural, 355.

  Neo-Darwinism, 93;
    relation of, to human progress, 97.

  Newton compared with Darwin, 48.

  Nominalism and realism reconciled, 329.


  Obstacle to evolution removed, 35.

  Oceanic island life, 213.

  Ontogenic series, 9, 40.

  Organic forms, views of origin of, 29, 68, 72, 292;
    law of continuity applied to, 56.

  Organs, incipient, 270.

  Origin of varieties unexplained, 270.


  Pantheism, true and false, 302, 335.

  Paroxysmal evolution, 257.

  Personality behind Nature, 338.

  Personality of God, 337, 341.

  Philosophy and life, relations of, 277.

  Phylogenic series, 10, 41.

  Planorbis of Steinheim, 254.

  Primal animals, 145.

  Progress of the whole, law of, 13, 22.

  Progressive change in evolution, 9.

  Providence, question of general and special, 355.


  Ranges of organic forms, 186.

  Realism and nominalism reconciled, 329.

  Record, geological, imperfection of, 252.

  Religion, so-called conflict of, with evolution, 45, 280.

  Religious thought to be reconstructed, 295.

  Reproduction, methods of, 237.

  Reptiles, age of, 17.

  Revelation, relation of evolution to, 331;
    not inconsistent with the laws of Nature, 332;
    nature of, 333.

  Reversion of artificial forms, 229.

  Romanes, G. J., his idea of physiological selection, 76, 84;
    the idea applied, 245.

  Rudimentary organs, proofs of evolution from, 179;
    organs in man, 181.


  Selection, sexual, 74, 85;
    natural, 74, 79, 83;
    physiological, 75, 79, 84;
    natural, compared with artificial, 225;
    physiological, applied, 245.

  Self-consciousness the sign of spirit-individuality, 325.

  Sequoia, 219, 220.

  Sexes, characters of, compared, 262.

  Shrimp, external anatomy of, 134.

  Sin a condition of moral evolution, 350.

  Skeleton, vertebrate, homologies of, 111;
    articulate, homologies of, 132;
    articulate, general structure of, 134.

  Society, progress of, 25.

  Space and time the two fundamental conditions of material
          existence, 48.

  Species, natural, more permanent than artificial varieties, 229;
    more distinct, 232;
    cross-sterile, 232.

  Spirit embryonic in animals, 311;
    of man related to _anima_ of animals, 313;
    to forces of Nature, 313, 316;
    origin of illustrated, 320-322;
    Plato’s view, 326;
    orthodox view, 326;
    no meaning in Nature without, 329.

  Steinheim, Planorbis of, 254.

  Supernatural and the natural, 355.


  Taxonomic series, 9, 40.

  Temperature-regions, 184.

  Tread, plantigrade and digitigrade, 123.

  True and the good, relation of, 277.

  Truth tested by effect on life, 277;
    not compromise, 291.

  Types, generalized, 13.


  Use and disuse of organs, 73.

  Useless structures, how produced, 76.


  Variation depends on sexual reproduction, 238;
    caused by unfavorable conditions, 264.

  Varieties, artificial production of, 222, 235;
    artificial production of, illustrated, 224;
    natural and artificial, compared, 228;
    origin of, unexplained, 270.

  “Vestiges of Creation,” 34.

  Virtue and innocence compared, 372.

  Vital principle, 328.

  Voluntary social progress, 26.


  Weismann’s views, 93.

  Whales, rudimentary organs of, 180.


THE END.




Transcribers’ Notes:


Punctuation, hyphenation, and spelling were made consistent when a
predominant preference was found in this book; otherwise they were not
changed.

Simple typographical errors were corrected; occasional unbalanced
quotation marks retained.

Ambiguous hyphens at the ends of lines were retained.

Subscripts in chemical formulas are represented here as simple numbers,
such as H2O and NH3.

Illustrations were printed mid-paragraph but have been moved between
paragraphs, usually near to text that references them.

Footnotes have been collected and repositioned just before the Index.

Some in-line paragraph headings are in boldface and some are in
italics; this emphasis has been retained.

Index not checked for proper alphabetization or correct page references,
but a reference to page 274 was a typographical error and has been
changed to 174.

Page 155: Text refers to _c c′_ in Figs. 38-39, but neither figure
appears to contain a _c′_ label.