Produced by Turgut Dincer and the Online Distributed
Proofreading Team at http://www.pgdp.net (This file was
produced from images generously made available by The
Internet Archive)










[Illustration: NATURE SERIES]

DEGENERATION.

[Illustration]




                            _NATURE SERIES._

                              DEGENERATION.
                                    A
                          CHAPTER IN DARWINISM.

                                   BY
                   PROFESSOR E. RAY LANKESTER, F.R.S.,
                    FELLOW OF EXETER COLLEGE, OXFORD.

                                 London:
                            MACMILLAN AND CO.
                                  1880.

         _The Right of Translation and Reproduction is Reserved_

                                 LONDON:
                       R. CLAY, SONS, AND TAYLOR,
                        BREAD STREET HILL, E. C.




    TO MY FRIEND

    ANTON DOHRN

    THESE PAGES

    Are Dedicated

    IN MEMORY OF OUR COMPANIONSHIP

    AT JENA AND NAPLES.

    E. R. L.

    _January, 1880._




DEGENERATION.




DEGENERATION.


It is the misfortune of those who study that branch of science which
our President has done so much to advance—I mean the science of living
things—that they are not able, in the midst of a vast assembly,[1] to
render visible to all eyes the actual phenomena to which their inquiries
are directed. Whilst the physicist and the chemist are able to make
evident to the senses of a great meeting the very things of which they
have to tell, the zoologist cannot hope ever to share with those who
form his audience the keen pleasure of observing a new or beautiful
organism; he cannot demonstrate by means of actual specimens the delicate
arrangements of structure which it is his business to record, and
upon which he bases his conclusions. It is for this reason that he who
would bring to the notice of laymen some matter which at the moment is
occupying the attention of biological students, must appear to be unduly
devoted to speculation—hypothesis—to support which he cannot produce
the facts themselves but merely the imperfect substitutes afforded by
pictures. It is perhaps not altogether a matter for regret that there
should be in one great branch of science, as there is in biology, so very
marked a disproportion between the facilities for demonstrating facts
and the general interest attaching to the theories connected with those
facts. We may be thankful that at the present day we are not likely, in
the domain of biology, to make the mistake (which has been made under
other circumstances) of substituting the mere inspection and cataloguing
of natural objects for that more truly scientific attitude which consists
in assigning the facts which come under our observation to their causes,
or, in other words, to their places in the order of nature. Though we may
rightly object to the attempt which is sometimes made to decry the modern
teachings of biology as not being “exact science,” yet we may boldly
admit the truth of the assertion that we biologists are largely occupied
with speculations, hypotheses, and other products of the imagination. All
true science deals with speculation and hypothesis, and acknowledges as
its most valued servant—its indispensable ally and help-meet—that which
our German friends[2] call “Phantasie” and we “the Imagination.” Our
science—biology—is not less exact; our conclusions are no less accurate
because they are only _probably_ true. They are “probably true” with a
degree of probability of which we are fully aware, and which is only
_somewhat_ less than the probability attaching to the conclusions of
other sciences which are commonly held to be “exact.”

These remarks are addressed to an Association for the advancement
of science—of science which flourishes and progresses by the aid of
suppositions and the working of the imagination. The Association has
been holding its annual sitting in various parts of the British Islands
for more than thirty years, and yet it is still a very common and widely
spread notion that science, that is to say, _true_ science according to
those who hold the notion, does not countenance hypotheses, and sternly
occupies itself with the exact record of fact. On the other hand, there
are many persons who run to an opposite extreme, and call by the name of
science any fanciful attempt to deal with or account for a certain class
of phenomena. The words “science” and “scientific” are used so vaguely
and variously that one might almost come to the conclusion that it would
be well for our Association to plainly state what is that thing for the
advancement of which its meetings are held. I cannot venture to speak
in the name of my colleagues; and no doubt a review of the work done
by the Association would most fitly explain what that body understands
by the word “science.” At the same time it is permissible to take this
opportunity of briefly stating what science is and what it is not, so far
as I am able to judge of the fitting use of the word.

Science is certainly _not_ any and every kind of knowledge. Knowledge of
literature, of the beautiful things which have been written or otherwise
produced by human ingenuity, is not science. Knowledge of the various
manufacturing processes in use by civilised men is not science; nor
knowledge of the names of the stars, or of the joints of a beetle’s leg.
Science cannot be identified with knowledge of any particular _class_ of
objects, however detailed that knowledge may be. It is a common mistake
to consider all knowledge of raw products, of living objects or other
natural objects, as necessarily “science.” The truth is, that a man may
have great knowledge of these things as so many facts, and yet be devoid
of “science.” And, on the other hand, that which is properly called
science embraces not only such subject-matter as that just alluded to,
but also may find its scope in the study of language, of human history,
and of the workings of the human mind.

The most frequent and objectionable misuse of the word ‘science’ is
that which consists in confounding science with invention—in applying
the term which should be reserved for a particular kind of knowledge to
the practical applications of that knowledge. Such things as electric
lighting and telegraphs, the steam-engine, gas, and the smoky chimneys
of factories, are by a certain school of public teachers, foremost among
whom is the late Oxford Professor of Fine Art, persistently ascribed
to science, and gravely pointed out as the pestilential products of
a scientific spirit. They are, in fact, nothing of the kind. American
inventors and electric lamps, together with all the factories in
Sheffield, might be obliterated without causing a moment’s concern to
a single student of science. It is of the utmost importance for the
progress and well-being of science that this should be understood; that
the eager practical spirit of the inventor who gains large pecuniary
rewards by the sale of his inventions should not be confounded with
what is totally different and remote from it, namely, the devoted,
searching spirit of science, which, heedless of pecuniary rewards, ever
faces nature with a single purpose—_to ascertain the causes of things_.
It seems to me impossible to emphasise too strongly in such a place
and in such a meeting as this, that Invention is widely separate from,
though dependent on, Science. Invention is worldly-wise, and despises
the pursuit of knowledge for its own sake. She awaits the discoveries
of Science, in order to sell them to civilisation, gathering the golden
fruit which she has neither planted nor tended. Invention follows, it is
true, the footsteps of Science, but at a distance: she is utterly devoid
of that thriftless yearning after knowledge, that passionate desire to
know the _truth_, which causes the unceasing advance of her guide and
benefactress.

We may, it seems to me, say that of all kinds and varieties of knowledge
that only is entitled to the name “science” which can be described as
Knowledge of Causes, or Knowledge of the Order of Nature. It is this
knowledge to which the great founder of European science—Aristotle the
Greek—pointed as _true_ knowledge: τότε ἐπιστάμεθα ὅταν τὴν αἰτίαν
εἴδωμεν. Science is that knowledge which enables us to demonstrate so
far as our limited faculties permit, that the appearances which we
recognise in the world around us are dependent in definite ways on
certain properties of matter: science is that knowledge which enables,
or tends to enable us, to assign its true place in the series of events
constituting the universe, to any and every thing which we can perceive.

The method by which scientific knowledge is gained—knowledge of the
causes of nature—is precisely the same as that by which knowledge of
causes in every-day life is gained. Something—an appearance—has to be
accounted for: the question in both cases is “Through what cause, in
relation to what antecedent is this appearance brought about?” In
scientific inquiry, as in every-day life, a hypothesis—a provisional
answer or guess—is the reply; and the truth of that guess or hypothesis
is then _tested_. This testing is an essential part of the process. “If
my guess be true, then so-and-so as to which I can decide by inspection
or experiment, must be true also,” is the form which the argument takes,
and the inquiry is thus brought to a point where _observation_ can decide
the truth of the hypothesis or first guess. In every-day life we have
often to be content without fully testing the truth of our guesses, and
hurry into action based on such unverified suppositions. Science, on the
other hand, can always wait, and demands again and again the testing and
verification of guesses before they are admitted as established truths
fit to be used in the testing of new guesses and the building up of
scientific doctrine.

The delicately-reared imaginations of great investigators of natural
things have from time to time given birth to hypotheses—guesses at
truth—which have suddenly transformed a whole department of knowledge,
and made the causes of things quite clear which before seemed likely
to remain always concealed. So great is the value of hypothesis,
so essential to scientific discovery, that the most skilled and
highly-trained observer may spend his life in examining and scrutinising
natural objects and yet fail, if he is not guided by hypothesis, to
observe particular facts which are of the uttermost importance for the
explanation of the causes of the things which he is studying. Nature,
it has been said, gives no reply to a general inquiry—she must be
interrogated by questions which already contain the answer she is to
give; in other words, the observer can only observe that which he is led
by hypothesis to look for: the experimenter can only obtain the result
which his experiment is designed to obtain.

For a long time the knowledge of living things, of plants and of animals
could hardly be said to form part of the general body of science, for
the causes of these things were quite unknown. They were kept apart as
a separate region of nature, and were supposed to have been pitched, as
it were, into the midst of an orderly and cause-abiding world without
cause or order: they were strangers to the universal harmony prevailing
around them. Fact upon fact was observed and recorded by students of
plants and animals, but having no hypothesis as to the causes of what
they were studying, the naturalists of twenty years ago, and before that
day, though they collected facts, made slow progress and some strange
blunders. Suddenly one of those great guesses which occasionally appear
in the history of science, was given to the science of biology by the
imaginative insight of that greatest of living naturalists—I would say
that greatest of living men—Charles Darwin.

In the form in which Mr. Darwin presented his view to the world it was no
longer a mere guess. He had already tried it and proved it in an immense
series of observations; it had already been converted by twenty years’
labour on his part into an established doctrine, and the twenty years
which have passed since he published the _Origin of Species_ have only
served to confirm, by thousands of additional tests, the truth of his
original guess.

Space will not allow me to go fully into the history of the Darwinian
theory, but it is necessary for my present purpose that I should state
precisely what that theory is. It involves a number of subordinate
hypotheses which, together with the main hypothesis, furnish us with a
complete “explanation,” as it is called, of the facts which have been
ascertained as to living things; in other words, it assigns living things
to their causes, gives them their place in the Order of Nature.

It is a very general popular belief at the present day that the Darwinian
theory is simply no more than a capricious and anti-theological assertion
that mankind are the modified descendants of ape-like ancestors.

Though most of my readers, I do not doubt, know how imperfect and
erroneous a conception this is, yet I shall not, I think, be wasting
time in stating what the Darwinian theory really is. In fact, it is
so continuously misrepresented and misunderstood, that no opportunity
should be lost of calling attention to its real character. Bit by bit,
naturalists had succeeded in discovering the order of nature—so far that
all the great facts of the universe, the constitution and movements of
the heavenly bodies, the form of our earth, and all the peculiarities
of its crust, had been successfully assigned to one set of causes—_the
properties of matter_, which are set forth in what we know by the name
of the “laws of physics and chemistry.” Whilst geologists, led by Lyell,
had shown that the strata of the earth’s crust and its mountains,
rivers, and seas were due to the long-continued operation of the very
same general causes—the physico-chemical causes—which at this moment are
in operation and are continuing their work of change, yet the living
matter on the crust of the earth had to be excluded from the grand
uniformity which was elsewhere complete.

The first hypothesis, then, which was present to Mr. Darwin’s mind,
as it had been to that of other earlier naturalists, was this: “Have
not all the varieties or species of living things (man, of course,
included) been produced by the continuous operation of the _same_ set
of physico-chemical causes which alone we can discover, and which alone
have been proved sufficient to produce everything else?” “If this be
so,” Mr. Darwin must have argued (and here it was that he boldly stepped
beyond the speculations of Lamarck and adopted the method by which Lyell
had triumphantly established Geology as a science), “these causes must
still be able to produce new forms, and are doing so wherever they have
opportunity.” He had accordingly to bring the matter to the test of
observation by seeking for some case of the production of new forms
of plants, or of animals, by natural causes at the present day. Such
cases he found in the production of new forms or varieties of plants and
animals, by breeders. Breeders (the persons who make it their business
to produce new varieties of flowers, of pigeons, of sheep, or what not)
make use of two fundamental properties of living things in order to
accomplish their purpose. These two properties are, firstly, that no two
animals or plants, even when born of the same parents, are _exactly_
alike; this is known as Variation: secondly, that an organism, as a rule,
inherits, that is to say, is born with the peculiarities of its parents;
this is known as Transmission, and is simply dependent on the fact that
the offspring of any plant or animal is only a detached portion of the
parent—a chip of the old block, as the saying is. The breeder selects
from a number of specimens of a plant or animal a variety which comes
nearest to the form he wishes to produce. Supposing he wished to produce
a race of oxen with short horns, he would select from his herd bulls and
cows with the shortest horns, and allow these only to breed; they would
_transmit_ their relatively short horns to their offspring, and from
these again the cattle with the shortest horns would be selected by the
breeder for propagation, and so on through several generations. In the
end a very short-horned generation would be obtained, differing greatly
in appearance from the cattle with which the breeder started.

Now we know of no facts which forbid us to suppose that could a breeder
continue his operations indefinitely for any length of time—say for a few
million years—he could convert the short-horned breed into a hornless
breed; that he could go on and thicken the tail, could shorten the
legs, get rid of the hind limbs altogether by a series of insensible
gradations, and convert the race into forms like the Sirenia, or
sea-cows. But if he could do this, you have only to give him a longer
time still and there is no obstacle remaining to the conversion, by the
same kind of process, of a polyp into a worm, or of a worm into a fish,
or even of a monkey into a man.[3]

So far we have supposed the interference of a breeder who selects and
determines the varieties which shall propagate themselves; so far we
have not got a complete explanation, for we must find a substitute in
nature for the _human selection_ exercised by the breeder. The question
arises, then, “Is there any necessary selective process in nature which
could have operated through untold ages, and so have represented the
selective action of the breeder, during an immense period of time?”
Strangely enough, Mr. Darwin was led to the discovery of such a cause
existing necessarily in the mechanical arrangements of nature, by reading
the celebrated book of an English clergyman, the Rev. Mr. Malthus, _On
Population_. On happening to read this book, Mr. Darwin himself tells
us that the idea of “natural selection” flashed upon him. That idea is
as follows. Not only among mankind, but far more largely among other
kinds of animals and of plants, the number of offspring produced by
every pair is immensely in excess of the available amount of the food
appropriate to the particular species in question. Accordingly, there is
necessarily a struggle for existence—a struggle among all those born for
the possession of the small quantum of food. The result of this struggle
is to pick out, or select, a few who survive and propagate the species,
whilst the majority perish before reaching maturity. The fact that no
two members of a species are alike has already been shown to be the
starting-point which enables the breeder to make _his_ selection. So,
too, with _natural_ selection in the struggle for existence; the fact
that all the young born of one species are not exactly alike—but some
larger, some smaller, some lighter, some darker, some short-legged, some
big-eyed, some long-tongued, some sharp-toothed, and so on—furnishes the
opportunity for a selection. Those varieties which are best fitted to
obtain food and to baffle their competitors, gain the food and survive,
the rest perish.

We have, then, to note that the hypothesis that there _must be a
selection_—which was framed or deduced as a “test hypothesis” from the
earlier hypothesis that species have arisen by the action of causes still
competent to produce new forms—led Mr. Darwin to the discovery of this
great cause—the “_natural selection_,” or “survival of the fittest,”
in the struggle for existence. Just as the breeder can slowly change
the proportions of the animals or plants on which he operates, so in
inconceivably long periods of time has this struggling of varieties, and
the consequent natural selection of the fittest, led to the production,
from shapeless primitive living matter, of all the endless varieties of
complicated plants and animals which now people the world. Countless
varieties have died out, leaving only their modified descendants to
puzzle the ingenuity of the biologist.

Of the tens and hundreds of thousands of intermediate forms we know
nothing by direct observation. They have perished as better fitted forms
ousted them in the never-ending conflict. But we feel sure that they once
were in existence, and can infer what was their structure, and what were
their peculiarities, by the study of the structure and attributes of
their now living descendants.

If all the forms of life at present living are the modified offspring of
a smaller number of ancestral forms which have died out, and if these
again were the modified descendants produced by ordinary parentage of a
single original living thing—then the whole series of forms that have
_ever_ lived could, if we had them before us, be arranged in the form of
a great family-tree—the various branches presenting a perfect gradation
of forms arranged one after another, leading down from the terminal twigs
(which would represent the latest forms produced) to larger and larger
branches, until the common trunk representing the original ancestor would
be reached. Our actual means of observing the genealogical affinities of
different kinds of animals and plants may be understood by a further use
of the metaphor of a genealogical tree in shape like an elm or an oak.
Suppose the genealogical tree completely written out—a perfect record—to
be sunk in muddy water so that only its topmost branches and twigs
are here and there visible—then you have a fair notion of the present
condition of the great family of organisms. Only the topmost twigs remain
visible, the rest of the great family-tree of living beings is hidden
from view, submerged beneath the muddy waters of time. Naturalists have,
however, undertaken to reconstruct this great genealogical tree. It is a
main object now in the study both of zoology and of botany to find out
what are the cousinships, what the exact genetic relationships of all
the various species of plants and animals, and so to show, even to the
minutest detail, in what particular ways physico-chemical causes have
brought about and modified the forms of living things.

The task is not quite so difficult as the comparison to a submerged
forest-tree would lead one to expect; at the same time it is more
difficult than those who have boldly attempted it appear to believe. We
have one great help in the carefully worked out systematic classification
of animals and plants according to their structure. We are justified in
assuming as a general law that animals or plants of like structure have
descended from common ancestors—that is to say, that the same kind of
organisation (especially where a number of elaborate details of structure
are involved) has _not been twice_ produced by natural selection. Thus
we are entitled to conclude that _all_ the animals which have a backbone
and pharyngeal gill-slits combined—the Vertebrates, as we call them—have
descended from a common parent; that all the animals with a muscular
foot-like belly and lateral gill filaments, the Molluscs, have also had a
common parent, and so on.

A classification according to structure goes then a long way towards
mapping out the main lines of the family-tree of organisms. We are
further assisted in the task by the fossil remains of extinct organisms
which sometimes give to us the actual ancestors of forms now living. But
the most remarkable aid to the correct building-up of the pedigree of
_animals_ at least (and the remarks which follow are confined to that
division of the organic world), is afforded by the changes—the phases
of development—which every animal exhibits in passing from the small
shapeless egg to the adult condition. The aid which we here obtain
depends on the following facts. Just as we suppose any one animal—say
a dog—to have developed by slow change through an immense series of
ancestors which become simpler and simpler as we recede into the past
until we reach a small shapeless lump of living matter devoid of
structure, so do we find actually as a matter of fact, which any one can
see for himself, that every individual animal begins its individual life
as a structureless particle which is thrown off from its parent, and is
known as the _egg-cell_ (Fig. 1). Gradually passing through a series of
more and more elaborated conditions of structure, that egg grows into the
adult dog. The changes which have taken countless ages in the one case,
are accomplished in a few weeks in the other.

And now we have to note the important fact which makes this process
of development so intensely interesting in relation to the pedigree
of the animal kingdom. There is very strong reason to believe that
it is a general law of transmission or inheritance, that structural
characteristics appear in the growth of a young organism in the order
in which those characteristics have been acquired by its ancestors. At
first the egg of a dog represents (imperfectly, it is true,) in form and
structure the earliest ancestors of the dog; a few days later it has the
form and structure of somewhat later ancestors; later still the embryo
dog resembles less remote ancestors; until at last it reaches the degree
of elaboration proper to its immediate forefathers.

[Illustration: FIG. 1.—An egg: a single corpuscle of protoplasm with
nucleus _b_ _c_, and body _a_.]

Accordingly the phases of development or growth of the young are a brief
recapitulation of the phases of form through which the ancestors of the
young creature have passed. In some animals this recapitulation is more,
in others it is less complete. Sometimes the changes are hurried through
and disguised, but we find here and there in these histories of growth
from the egg most valuable assistance in the attempt to reconstruct the
genealogical tree. The history of the development of the common frog is a
good illustration of the _kind_ of evidence in question.

[Illustration: FIG. 2.—Tadpoles and young of the Common Frog. 1, Recently
hatched (twice natural size); 2 and 2_a_, same enlarged to show the
external gills; 3 and 4, later stages with gill slits covered by a
membrane leaving only the spiracle (see Fig. 16) as an exit for the
respired water; 5, with hind legs appearing; 6, with both fore and hind
legs; 7, atrophy of the tail; 8, young frog.]

The frog’s egg first gives rise to a little aquatic creature with
external gills and a tail—the tadpole—which gradually loses its gills
and its tail and acquires in their place lungs and four legs (Fig. 2),
so as now to be fitted for life on dry land. From what we otherwise know
of the structure of the frog and the animals to which it is allied, we
are justified in concluding that the tadpole is a recapitulative phase
of development, and represents to us more or less closely an ancestor of
the frog which was provided with gills and tail in the adult state, and
possessed neither legs nor lungs.

[Illustration: FIG. 3.—Adult shrimp of the genus Peneus.]

A less familiar case is that of a certain kind of shrimp, which is
illustrated in the wood-cuts (Fig. 3 and right lower corner of Fig.
4). The little creature which issues from the egg of this shrimp is
known as the “Nauplius form.” Many animals very different in appearance
from this shrimp make their first appearance in the world as Nauplii;
and it appears probable that the Nauplius-phase is the recapitulative
re-presentation of an ancestor common to all this set of animals,
an ancestor which was not _exactly_ like the Nauplius, but not very
different from it.

[Illustration: FIG. 4.—Nauplius larval-form of various Crustacea
(Shrimps, Water-fleas, Barnacles, &c.).]

The Nauplius of our shrimp gradually elongates. At first it has but
three pair of limbs, but it soon acquires additional pairs, and a jointed
body, and thus by gradually adding to its complexity of structure as seen
in Figs. 5 and 6, it approximates more and more to the adult form from
the egg of which it originated.

[Illustration: FIG. 5.—Larva of the Shrimp Peneus.]

[Illustration: FIG. 6.—More advanced larva of the Shrimp Peneus.]

And now we are approaching the main point to which I wish to draw the
reader’s attention. In attempting to reconstruct the pedigree of the
animal kingdom and so to exhibit correctly the genetic relationships of
all existing forms of animals, naturalists have hitherto assumed that the
process of natural selection and survival of the fittest has invariably
acted so as either to improve and elaborate the structure of _all_ the
organisms subject to it, or else has left them unchanged, exactly fitted
to their conditions, maintained as it were in a state of _balance_. It
has been held that there have been some six or seven great lines of
descent—main branches of the pedigree—such as that of the Vertebrates,
that of the Molluscs, that of the Insects, that of the Starfish, and
so on; and that along each of these lines there has been always and
continuously a progress—a change in the direction of greater elaboration.

Each of these great branches of the family-tree is held to be
independent—they all branch off nearly simultaneously from the main
trunk like the leading branches of an oak. The animal forms constituting
the series in each of these branches are supposed to gradually increase
in elaboration of structure as we pass upwards from the main trunk of
origin and climb further and further towards the youngest, most recent
twigs. New organs have, it is supposed, been gradually developed in each
series, giving their possessors greater powers, enabling them to cope
more successfully with others in that struggle for existence in virtue
of which these new organs have been little by little called into being.
At the same time _here and there_ along the line of march, certain forms
have been supposed to have “fallen out,” to have ceased to improve,
and being happily fitted to the conditions of life in which they were
long ago existing, have continued down to the present day to exist in
the same low, imperfect condition. It is in this way that the lowest
forms of animal life at present existing are usually explained, such
as the microscopic animalcules, Amœbæ and Infusoria. It is in this way
that the lower or more simply-made families of higher groups have been
generally regarded. The simpler living Mollusca or shellfish have been
supposed necessarily to represent the original forms of the great race
of Mollusca. The simpler Vertebrates have been supposed necessarily to
represent the original Vertebrates. The simpler Worms have been supposed
necessarily to be the stereotyped representatives of very ancient Worms.

That this is, to a certain extent, a true explanation of the existence
at the present day of _low_ forms of animals is proved by the fact that
we find in very ancient strata fossil remains of animals which differ,
ever so little, from particular animals existing at the present day;
for instance, the Brachiopods (lamp-shells), Lingula and Terebratula,
the King-crabs, and the Pearly Nautilus are found living at the present
day, and are also found with no appreciable difference in very ancient
strata of the earth’s crust; strata deposited so long ago that most of
the forms of life at present inhabiting the earth’s surface had not then
been brought into existence, whilst other most strange and varied forms
occupied their place, and have now for long ages been extinct.

Whilst we are thus justified by the direct testimony of fossil remains in
accounting for _some_ living forms on the hypothesis that their peculiar
conditions of life have been such as to maintain them for an immense
period of time _in statu quo_ unchanged, _we have no reason for applying
this hypothesis, and this only_, to the explanation of all the more
imperfectly organised forms of animal or plant-life.

It is clearly enough possible for a set of forces such as we sum up under
the head “natural selection” to so act on the structure of an organism
as to produce one of three results, namely these; to keep it _in statu
quo_; to increase the complexity of its structure; or lastly, to diminish
the complexity of its structure. We have as possibilities either BALANCE,
or ELABORATION, or DEGENERATION.

Owing, as it seems, to the predisposing influence of the systems of
classification in ascending series proceeding steadily upwards from the
“lower” or simplest forms to the “higher” or more complex forms,—systems
which were prevalent before the doctrine of transformism had taken firm
root in the minds of naturalists, there has been up to the present day
an endeavour to explain every existing form of life on the hypothesis
that it has been maintained for long ages in a state of Balance; or
else on the hypothesis that it has been Elaborated, and is an advance,
an improvement, upon its ancestors. Only one naturalist—Dr. Dohrn, of
Naples—has put forward the hypothesis of Degeneration as capable of wide
application to the explanation of existing forms of life;[4] and his
arguments in favour of a general application of this hypothesis have
not, I think, met with the consideration which they merit.

The statement that the hypothesis of Degeneration has not been recognised
by naturalists generally as an explanation of animal forms, requires
to be corrected by the exception of certain kinds of animals, namely,
those that are parasitic or quasi-parasitic. With regard to parasites,
naturalists have long recognized what is called _retrogressive
metamorphosis_; and parasitic animals are as a rule admitted to be
instances of Degeneration. It is the more remarkable whilst the
possibility of a degeneration—a loss of organisation making the
descendant far _simpler_ or _lower_ in structure than its ancestor—has
been admitted for a few exceptional animals, that the same hypothesis
should not have been applied to the explanation of other simple forms
of animals. The hypothesis of Degeneration will, I believe, be found to
render most valuable service in pointing out the true relationships of
animals which are a puzzle and a mystery when we use only and exclusively
the hypothesis of Balance, or the hypothesis of Elaboration. It will, as
a true scientific hypothesis, help us to discover causes.

We may now examine a few examples of undeniably degenerate animals, and
first, I may call to mind the very remarkable series of lizard-like
animals which exist in the south of Europe and in other countries, which
exhibit in closely related genera a gradual loss of the limbs—a local or
limited Degeneration. We have the common Lizard (_Lacerta_), with five
toes on each of its well-grown fore and hind limbs; then we have side by
side with this a lizard-like creature, _Seps_, in which both pairs of
limbs have become ridiculously small, and are evidently ceasing to be
useful in the way in which those of _Lacerta_ are useful; and lastly,
we have _Bipes_, in which the anterior pair of limbs has altogether
vanished, and only a pair of stumps, representing the hinder limbs,
remain.

No naturalist doubts that Seps and Bipes represent two stages of
Degeneration, or atrophy of the limbs; that they have, in fact, been
derived from the five-toed four-legged form, and have _lost_ the
locomotor organs once possessed by their ancestors. This very partial
or local atrophy is not however that to which I refer when using the
word Degeneration. Let us imagine this atrophy to extend to a variety
of important organs, so that not only the legs, but the organs of
sense, the nervous system, and even the mouth and digestive organs are
obliterated—then we shall have pictured a thorough-going instance of
Degeneration.

Degeneration may be defined as a gradual change of the structure in
which the organism becomes adapted to _less_ varied and _less_ complex
conditions of life; whilst Elaboration is a gradual change of structure
in which the organism becomes adapted to more and more varied and complex
conditions of existence. In Elaboration there is a new _expression_ of
form, corresponding to new perfection of work in the animal machine.
In Degeneration there is _suppression_ of form, corresponding to the
cessation of work. Elaboration of some one organ _may_ be a necessary
accompaniment of Degeneration in all the others; in fact, this is
very generally the case; and it is only when the total result of the
Elaboration of some organs, and the Degeneration of others, is such as to
leave the whole animal in a _lower_ condition, that is, fitted to less
complex action and reaction in regard to its surroundings, than was the
ancestral form with which we are comparing it (either actually or in
imagination) that we speak of that animal as an instance of Degeneration.

Any new set of conditions occurring to an animal which render its food
and safety very easily attained, seem to lead as a rule to Degeneration;
just as an active healthy man sometimes degenerates when he becomes
suddenly possessed of a fortune; or as Rome degenerated when possessed
of the riches of the ancient world. The habit of parasitism clearly
acts upon animal organisation in this way. Let the parasitic life
once be secured, and away go legs, jaws, eyes, and ears; the active,
highly-gifted crab, insect, or annelid may become a mere sac, absorbing
nourishment and laying eggs.

Reference was made above to the larval stage of a certain shrimp (Figs.
4, 5, 6). Let us now compare these with the young stages of a number
of shrimp-like animals, viz., Sacculina, Lernæocera, Lepas, Cyclops,
Limnetis, (all drawn in Fig. 4), some of which lead a parasitic life.
All start equally with the recapitulative phase known as the Nauplius;
but whilst the Nauplius of the free-living shrimp grows more and more
elaborate, observe what happens to the parasites—they degenerate
into comparatively simple bodies; and this is true of their internal
structure as well as of their external appearance. The most utterly
reduced of these parasites is the curious Sacculina (Fig. 7) which
infests Hermit-crabs, and is a mere sac filled with eggs, and absorbing
nourishment from the juices of its host by root-like processes.

[Illustration: FIG. 7.—Adult Sacculina (female).]

Lernæocera again, which in the adult condition is found attached to
the gills of fishes, has lost the well-developed legs of its Nauplius
childhood and become an elongated worm-like creature (Fig. 8), fitted
only to suck in nourishment and carry eggs.

[Illustration: FIG. 8.—Adult female Lernæocera.]

Amongst these Nauplii—all belonging to the great group Crustacea, which
includes crabs and shrimps—is one which gives rise to an animal decidedly
degenerate, but not precisely parasitic in its habits. This Nauplius is
the young of the ship’s Barnacle, a curious stalked body, inclosed in a
shell of many pieces (Fig. 9). The egg of the Barnacle gives rise to an
actively swimming Nauplius, the history of which is very astonishing.
After swimming about for a time the Barnacle’s Nauplius fixes its head
against a piece of wood, and takes to a perfectly fixed, immobile state
of life (Fig. 10). The upper figures represent the Nauplius stage of
animals closely resembling the Barnacle: the lower figures show the
transformation of the Nauplius into the young Barnacle. Its organs of
touch and of sight atrophy, its legs lose their locomotor function, and
are simply used for bringing floating particles to the orifice of the
stomach; so that an eminent naturalist has compared one of these animals
to a man standing on his head and kicking his food into his mouth.

[Illustration: FIG. 9.—Adult Barnacle or Lepas (one of the Cirrhipedes).
Natural size.]

[Illustration: FIG. 10.—Development of Cirrhipedes (Barnacle and
Sea-acorn). After Huxley.]

Were it not for the recapitulative phases in the development of the
Barnacle, we may doubt whether naturalists would _ever_ have guessed that
it was a degenerate Crustacean. It was in fact for a long time regarded
as quite remote from them, and placed among the snails and oysters; its
true nature was only admitted when the young form was discovered.

Other parasitic organisms, which exhibit extreme degeneration as
compared with their free-living relatives, might be cited and figured
in profusion, did our limits permit. Very noteworthy are the degenerate
Spiders—the mites, leading to still more degenerate forms, the Linguatulæ.

We have two of these represented in Figs. 11 and 12. The one (Fig. 11),
as compared with a spider is seen still to possess the eight walking
legs, small, it is true, whilst the palps and daggers of the spider have
dwindled to a beak projecting from the front of the globular unjointed
body. In the other the eight legs have become mere stumps, and the body
is elongated like that of a worm.

[Illustration: FIG. 11.—Acarus equi. A degenerate Spider or mite
parasitic on the skin of the horse.]

[Illustration: FIG. 12.—Degenerate Spider (Demodex foliculorum) found in
the skin of the human face.]

The instances of degeneration which we have so far examined are due to
parasitism, except in the example of the Barnacle, where we have an
instance of degeneration due to sessile and immobile habit of life. We
may now proceed to look at some sessile or immobile animals which are not
usually regarded as degenerate, but which, I think, there is every reason
to believe are the degenerate descendants of very much higher and more
elaborate ancestors. These are certain marine animals, the Ascidians, or
sea-squirts. These animals are found encrusting rocks, stones, and weeds
on the sea bottom. Sometimes they are solitary (Fig. 13), but many of
them produce buds, like plants, and so form compound masses or sheets of
individuals all connected and continuous with one another, like the buds
on a creeping plant (Fig. 14).

[Illustration: FIG. 13.—Two adult Ascidians: to the left Phallusia—to
the right Cynthia: the incurrent and excurrent orifices are seen as two
prominences. Half the natural size.]

We will examine one of the simple forms—a tough mass like a leather
bottle with two openings; water is continually passing in at the one
and out at the other of these apertures. If we remove the leathery
outer-case (Fig. 15), we find that there is a soft creature within which
has the following parts:—Leading from the mouth a great throat, followed
by an intestine. The throat is perforated by innumerable slits, through
which the water passes into a chamber—the cloaca: in passing, the water
aërates the blood which circulates in the framework of the slits. The
intestine takes a sharp bend, which causes it to open also into the
cloaca. Between the orifice of the mouth and of the cloaca there is a
nerve-ganglion.

[Illustration: FIG. 14.—A colony of compound Ascidians (Botryllus)
growing on a piece of sea-weed (Fucus). Each star corresponds to eight or
more conjoined Ascidians. Natural size.]

My object in the next place is to show that the structure and
life-history of these Ascidians may be best explained on the hypothesis
that they are instances of degeneration; that they are the modified
descendants of animals of higher, that is more elaborate structure,
and in fact are degenerate Vertebrata, standing in the same relation
to fishes, frogs, and men, as do the barnacles to shrimps, crabs, and
lobsters.

[Illustration: FIG. 15.—Anatomy of an Ascidian (Phallusia). At the top
is the mouth, to the right the orifice of the cloaca. In the cloaca
lies an egg, and above it the oblong nerve ganglion. The perforated
pharynx follows the mouth and leads to the bent intestine which is seen
to open into the cloaca. The space around the curved intestine is the
body-cavity; in it are seen oval bodies, the eggs, and quite at the lower
end the curved heart. The root-like processes at the base serve to fix
the Ascidian to stones, shells, or weed.]

The young of some, but by no means of all these Ascidians, have a form
totally different from that of their parents. The egg of Phallusia
gives rise to a tadpole, a drawing of which placed side by side with
the somewhat larger tadpole of the common frog is seen in the adjoining
figure (Fig. 16). The young Ascidian has the same general shape as the
young frog, but not only this; the resemblance extends into details,
the internal organs agreeing closely in the two cases. Further still as
shown by the beautiful researches of the Russian naturalist, Kowalewsky,
the resemblance reaches absolute identity when we examine the way in
which the various organs arise from the primitive egg-cell. Tail, body,
spiracle, eye, and mouth, agree in the two tadpoles, the only important
difference being in the position of the two mouths and in the fact that
the Ascidian has one eye while the frog has two.

[Illustration: FIG. 16.—Tadpole of Frog and of Ascidian. Surface view.]

[Illustration: FIG. 17.—Tadpole of Frog and of Ascidian. Diagrams
representing the chief internal organs.]

Now let us look at the internal organs (Fig. 17). There are four
structures, which are _all four_ possessed at some time of their lives
by all those animals which we call the Vertebrata, the great branch of
the pedigree to which fishes, reptiles, birds, beasts, and men belong.
And the combination of these marks or structural peculiarities is an
overwhelming piece of evidence in favour of the supposition that the
creatures which possess this combination are derived from one common
ancestor. Just as one would conclude that a man whom one might meet,
say on Salisbury Plain, _must_ belong to the New Zealand race, if it
were found not only that he had the colour, and the hair, and the shape
of head of a New Zealander, but also that he was tattooed like a New
Zealander, carried the weapons of a New Zealander, and, over and above
in addition to these proofs, that he talked the Maori language and none
other; so here, in the case of the vertebrate race, there are certain
qualities and possessions, the accumulation of which cannot be conceived
of as occurring in any animal but one belonging to that race. These four
great structural features are—first, the primitive backbone or notochord;
second, the throat perforated by gill-slits; third, the tubular
nerve-centre or spinal cord and brain placed along the back; and lastly,
and perhaps most distinctive and clinching as an evidence of affinity,
the myelonic or cerebral eye.

Now let us convince ourselves that these four features exist not only
in the frog’s tadpole, as they do in all fishes, reptiles, birds, and
beasts, but that they also exist in the Ascidian tadpole, and, it may be
added, co-exist in no other animals at all.

The corresponding parts are named in Figs. 16 and 17, in such a way as to
render their agreement tolerably clear, whilst in Fig. 18 a more detailed
representation of the head of an Ascidian tadpole is given.

[Illustration: FIG. 18.—Ascidian Tadpole with a part only of the tail
_C_. _N_, nervous system with the enlarged brain in front and the narrow
spinal cord behind _n_; _N´_, is placed in the cavity of the brain:
_O_, the single cerebral eye lying in the brain; _a_, similarly placed
auditory organ; _K_, pharynx; _d_, intestine; _o_, rudiment of the mouth;
_ch_, notochord or primitive backbone. (From Gegenbaur’s “Elements of
Comparative Anatomy.”)]

It is clear then that the Ascidians must be admitted to be Vertebrates,
and must be classified in that great sub-kingdom or branch of the animal
pedigree. The Ascidian tadpole is very unlike its parent the Ascidian,
and has to go through a process of _degeneration_ in order to arrive
at the adult structure. The diagrams which are reproduced in Figs. 19
and 20, show how this degeneration proceeds. It will be observed, that
in somewhat the same manner as the young barnacle, the young Ascidian
fixes itself to a stone by its head: then the tail with its notochord
and nerve-chord atrophies. The body grows and gradually changes its
shape, whilst the cloacal chamber forms. The brain remains quite small
and undeveloped, and the remarkable myelonic eye (the eye in the brain)
disappears. The number of gill-slits increases as the animal grows in
size and its outer skin becomes tough and leather-like.

[Illustration: FIG. 19.—Degeneration of Ascidian Tadpole to form the
adult. The black pieces represent the rock or stone to which the Tadpole
has fixed its head.]

[Illustration: FIG. 20.—Very young Ascidian with only two gill-slits.
Compare with Fig 15; which is, however, seen from the other side, so that
left there corresponds to right here.]

[Illustration: FIG. 21.—Section through the eye (“surface-eye”) of a
Water-beetle’s larva. All the cells are seen to be in a row continuous
with _h_, the cells of the outermost skin or ectoderm. _p_, pigmented
cells; _r_, retinal cells connected at _o_ with the optic nerve; _g_,
transparent cells (forming a kind of “vitreous body”); _l_, cuticular
lens. (From Gegenbaur’s “Elements of Comparative Anatomy,” after
Grenacher.)]

Before saying anything further on the subject of degeneration, it seems
desirable once more to direct attention to the myelonic or cerebral eye
which the Ascidian tadpole possesses in common with all Vertebrates. All
other animals which have eyes develop the retina or sensitive part of
the eye from their _outer skin_ (See Figs. 21 and 22, and explanation.)
It is easy to understand that an organ which is to be affected by the
light should form on the _surface_ of the body where the light falls.
It has long been known as a very puzzling and unaccountable peculiarity
of Vertebrates, that the retina or sensitive part of the eye grows
out in the embryo as a bud or vesicle of the brain, and thus forms
_deeply_ below the surface and _away from the light_ (see Fig. 23,
and explanation). The Ascidian tadpole helps us to understand this,
for it is perfectly transparent and has its eye actually _inside_
its brain. The light passes through the transparent tissues and acts
on the pigmented eye, lying deep in the brain. We are thus led to the
conclusion—and I believe this inference to be now for the first time
put into so many words—that the original Vertebrate must have been a
transparent animal, and had an eye or pair of eyes _inside_ its brain,
like that of the Ascidian tadpole. As the tissues of this ancestral
Vertebrate grew denser and more opaque, the eye-bearing part of the brain
was forced by natural selection to grow outwards towards the surface,
in order that it might still be in a position to receive the influence
of the sun’s rays. Thus the very peculiar mode of development of the
Vertebrate eye from two parts, a brain-vesicle (Fig. 23, _A a_, and _B p
r_), and a skin-vesicle (Fig. 23, _B e, l_), is accounted for.

[Illustration: FIG. 22.—Section through the eye (“surface-eye”) of a
Marine Worm (Neophanta). _i_, integument spreading over the front of the
eye _c_; _l_, cuticular lens; _h_, cavity occupied by vitreous body; _p_,
retinal cells; _b_, pigment; _o_, optic nerve: _o´_, expansion of optic
nerve.]

[Illustration: FIG. 23.—_A._ Vertical section through the head of a very
young fish, showing in the centre the cavity of the brain _c_. On each
side is a hollow outgrowth (_a_) which will form the retina of the fish’s
eye (“cerebral eye”); _b_, will become the optic nerve connecting the
brain and the retina; _d_, integument.—_B._ Later condition of the hollow
outgrowth (_a_) of _A_. Its outer wall _r_ is pressed against its deeper
wall _p_ by an ingrowth (_l_) from the outer skin (ectoderm) _e_; _r_,
gives rise to the retinal cells, whilst only _l_, the cellular lens, is
derived from the surface of the skin.]

The cases of degeneration which I have up to this point brought forward,
are cases which admit of very little dispute or doubt. They are attested
by either the history of the individual development of the organisms in
question, as in Sacculina, in the Barnacle, and in the Ascidian, or they
are cases where the comparison of the degenerate animal, with others
like it in structure, but not degenerate, renders the hypothesis of
degeneration an unassailable one. Such cases are the Acarus or mite, and
the skin-worm (Demodex).

We have seen that degeneration, or the simplification of the general
structure of an animal, may be due to the ancestors of that animal having
taken to one of two new habits of life, either the parasitic or the
immobile. Other new habits of life appear also to be such as to lead to
degeneration. Let us suppose a race of animals fitted and accustomed to
catch their food, and having a variety of organs to help them in this
chase—suppose such animals suddenly to acquire the power of feeding
on the carbonic acid dissolved in the water around them just as green
plants do. This would lead to a degeneration; they would cease to hunt
their food, and would bask in the sunlight, taking food in by the whole
surface, as plants do by their leaves. Certain small flat worms, by name
Convoluta, of a bright green colour, appear to be in this condition.
Their green colour is known to be the same substance as leaf-green; and
Mr. Patrick Geddes has recently shown that by the aid of this green
substance they feed on carbonic acid, making starch from it as plants
do. As a consequence we find that their stomachs and intestines as well
as their locomotive organs become simplified, since they are but little
wanted. These vegetating animals, as Mr. Geddes calls them, are the exact
complement of the carnivorous plants, and show how a degeneration of
animal forms may be caused by _vegetative nutrition_.

Another possible cause of degeneration appears to be the indirect one of
minute size. It cannot be doubted that natural selection has frequently
acted on a race of animals so as to reduce the size of the individuals.
The smallness of size has been favourable to their survival in the
struggle for existence, and in some cases they have been reduced to even
microscopic proportions. But this reduction of size has, when carried
to an extreme, resulted in the loss or suppression of some of the most
important organs of the body. The needs of a very minute creature are
limited as compared with those of a large one, and thus we may find
heart and blood-vessels, gills and kidneys, besides legs and muscles,
lost by the diminutive degenerate descendants of a larger race. That
this is a possible course of change all will, I think, admit. It is
actually exemplified in Appendicularia—the only adult representative
of the Ascidian tadpole—still tadpole-like in form and structure, but
curiously degenerate and simplified in its internal organs. This kind of
degeneration is also exemplified in the Rotifers, or wheel animalcules,
in the minute Crustacean water-fleas (Ostracoda), and in the Moss-polyps,
or Polyzoa. Roughly then we may sum up the immediate antecedents of
degenerative evolution as, 1, Parasitism; 2, Fixity or immobility;
3, Vegetative nutrition; 4, Excessive reduction of size. This is not
a logical enumeration, for each of these causes involves, or may be
inseparably connected with, one or more of the others. It will serve for
the present as well as a more exhaustive analysis. (See Note C.)

And now we have to note an important fact with regard to the _evidence_
which we can obtain of the occurrence of this process of degeneration. We
have seen that the most conclusive evidence is that of the recapitulative
development of the individual. The Ascidian Phallusia shows itself to
be a degenerate Vertebrate by beginning life as a tadpole. But such
recapitulative development is by no means the rule. Quite arbitrarily,
we find, it is exhibited in one animal and not in a nearly allied kind.
Thus very many animals belonging to the Ascidian group have no tadpole
young—just as some tree-frogs have no tadpoles. It is quite possible,
and often, more often than not, occurs, that _the most important part_
of the recapitulative phases are absent from the developmental history
of an animal. The egg proceeds very rapidly to produce the adult form,
and all the wonderful series of changes showing the animal’s ancestry are
absolutely and completely omitted; that is to say, all those stages which
are of importance for our present purpose. Just as certain bodies pass
from the solid to the liquid state at a bound, omitting all intermediate
phases of consistence, but giving evidence of “internal work” by the
suggestive phenomenon of latent heat—so do these embryos skip long tracts
in the historically continuous phases of form, and present to us only the
intangible correlative “internal work” in place of the tangible series of
embryonic changes of shape.

Now I want to put this case—a supposition—before the reader who has so
far followed me in these pages. Suppose, as might well have happened,
that the Barnacles, one and all, instead of recapitulating in their early
life, were to develop _directly from the egg to the adult form_, as so
many animals do; should we have ever made out that they were degenerate
Crustaceans? Possibly we should: their adult structure still bears
important marks of affinities with crabs and shrimps; but as a matter of
fact before their recapitulative development had been discovered they
were classed by the great Cuvier and other naturalists with the Molluscs,
the mussels and snails.

Suppose again that _all_ the existing Ascidians, as many of them actually
have, had long ago lost their recapitulative history in growth from the
egg: suppose that no such a thing as an Ascidian tadpole existed, but
that the Ascidian’s egg grew as directly as possible into an Ascidian, in
every living species of the group. This might easily be the case. Then
most assuredly we should not have the least notion that the Ascidians
were degenerate Vertebrates. We should still class them where they used
to be classed before the Russian naturalist Kowalewsky discovered the
true history and structure of the Ascidian tadpole. I believe that I
shall have the assent of every naturalist when I say that the vertebrate
character of the Ascidians and the history of their degeneration
would never have been suspected, or even dreamed of, had the Ascidian
tadpoles ceased to appear in the course of the Ascidian development at a
geological period anterior to the present epoch.

This being the case, it must be admitted that it is quite _possible_—I
do not say more than possible—that other groups of animals besides
parasites, Barnacles, and Ascidians, are degenerate. It is quite possible
that animals with considerable complexity of structure, at least as
complex as the Ascidians, may have been produced by degeneration from
still more highly-organized ancestors. Any group of animals to which we
can turn may possibly be the result of degeneration, and yet offer no
evidence of that degeneration in its growth from the egg.

Accordingly, wherever we can note that a group of organisms is
characterized by habits likely to lead to degeneration, such as I have
enumerated, viz., parasitism or immobility, or certain special modes
of nutrition, or again, by minute size of its representatives—there
we are justified in applying the hypothesis of degeneration, even in
the absence of any confirmatory evidence from embryology. When we so
apply this hypothesis we find in not a few cases, in working over the
details of the organization of many different animals by the light
which it affords—that much becomes clear and assignable to cause which,
on the hypothesis either of “balance” or of “elaboration,” is quite
hopelessly obscure. As examples of groups of animals which can thus be
satisfactorily explained I may cite first of all the Sponges: as only
somewhat less degenerate, we have all the Polyps and Coral-animals, also
the Starfishes. Amongst the Mollusca—the group of headless bivalves, the
oysters, mussels and clams, known as the Lamellibranchs, are, when one
once looks at their structure in this light, clearly enough explained
as degenerated from a higher type of head-bearing active creatures like
the Cuttle-fish; whilst the Polyzoa or Moss-polyps stand in precisely
the same kind of relation to the higher Mollusca as do the Ascidians to
the higher Vertebrates: they have greatly degenerated, and become minute
encrusting organisms which, like some of the Ascidians, build up colonies
by plant-like budding growth. The Rotifers, or wheel animalcules, I have
already mentioned as best explained by the supposition that they are the
descendants of far larger and more fully-organized animals provided with
locomotive appendages or limbs: they have dwindled and degenerated to
their present minute size and curiously suggestive structure.

Besides these there are other very numerous cases of animal structure
which can best be explained by the hypothesis of degeneration. A
discussion of these, and a due exposition of the application of the
hypothesis of degeneration to the various groups just cited, would
involve a complete treatise on comparative anatomy and embryology, and
lead far beyond the limitations of this little volume.

All that has been, thus far, here said on the subject of Degeneration is
so much zoological specialism, and may appear but a narrow restriction of
the discussion to those who are not zoologists. Though we may establish
the hypothesis most satisfactorily by the study of animal organization
and development, it is abundantly clear that degenerative evolution
is by no means limited in its application to the field of zoology. It
clearly offers an explanation of many vegetable phenomena, and is already
admitted by botanists as the explanation of the curious facts connected
with the reproductive process in the higher plants. As a further example
of its application in this field, the yeast-plant may be adduced, which
is in all probability a degenerate floating form derived from a species
of mould (Mucor). In other fields, wherever in fact the great principle
of evolution has been recognised, degeneration plays an important part.
In tracing the development of languages, philologists have long made
use of the hypothesis of degeneration. Under certain conditions, in the
mouths and minds of this or that branch of a race, a highly elaborate
language has sometimes degenerated and become no longer fit to express
complex or subtle conceptions, but only such as are simpler and more
obvious. (See Note D.)

The traditional history of mankind furnishes us with notable examples of
degeneration. High states of civilisation have decayed and given place to
low and degenerate states. At one time it was a favourite doctrine that
the savage races of mankind were degenerate descendants of the higher and
civilised races. This general and sweeping application of the doctrine
of degeneration has been proved to be erroneous by careful study of the
habits, arts, and beliefs of savages; at the same time there is no doubt
that many savage races as we at present see them are actually degenerate
and are descended from ancestors possessed of a relatively elaborate
civilisation. As such we may cite some of the Indians of Central America,
the modern Egyptians, and even the heirs of the great oriental monarchies
of præ-Christian times. Whilst the hypothesis of universal degeneration
as an explanation of savage races has been justly discarded, it yet
appears that degeneration has a very large share in the explanation
of the condition of the most barbarous races, such as the Fuegians,
the Bushmen, and even the Australians. They exhibit evidence of being
descended from ancestors more cultivated than themselves.

With regard to ourselves, the white races of Europe, the possibility of
degeneration seems to be worth some consideration. In accordance with a
tacit assumption of universal progress—an unreasoning optimism—we are
accustomed to regard ourselves as necessarily progressing, as necessarily
having arrived at a higher and more elaborated condition than that which
our ancestors reached, and as destined to progress still further. On the
other hand, it is well to remember that we are subject to the general
laws of evolution, and are as likely to degenerate as to progress. As
compared with the immediate forefathers of our civilisation—the ancient
Greeks—we do not appear to have improved so far as our bodily structure
is concerned, nor assuredly so far as some of our mental capacities are
concerned. Our powers of perceiving and expressing beauty of form have
certainly _not_ increased since the days of the Parthenon and Aphrodite
of Melos. In matters of the reason, in the development of intellect, we
may seriously inquire how the case stands. Does the reason of the average
man of civilised Europe stand out clearly as an evidence of progress when
compared with that of the men of bygone ages? Are all the inventions and
figments of human superstition and folly, the self-inflicted torturing of
mind, the reiterated substitution of wrong for right, and of falsehood
for truth, which disfigure our modern civilisation—are these evidences of
progress? In such respects we have at least reason to fear that we may
be degenerate. Possibly we are all drifting, tending to the condition
of intellectual Barnacles or Ascidians. It is possible for us—just as
the Ascidian throws away its tail and its eye and sinks into a quiescent
state of inferiority—to reject the good gift of reason with which every
child is born, and to degenerate into a contented life of material
enjoyment accompanied by ignorance and superstition. The unprejudiced,
all-questioning spirit of childhood may not inaptly be compared to the
tadpole tail and eye of the young Ascidian: we have to fear lest the
prejudices, pre-occupations, and dogmatism of modern civilisation should
in any way lead to the atrophy and loss of the valuable mental qualities
inherited by our young forms from primæval man.

There is only one means of estimating our position, only one means of
so shaping our conduct that we may with certainty avoid degeneration
and keep an onward course. We are as a race more fortunate than our
ruined cousins—the degenerate Ascidians. For us it is possible to
ascertain what will conduce to our higher development, what will favour
our degeneration. To us has been given the power to _know the causes of
things_, and by the use of this power it is possible for us to control
our destinies. It is for us by ceaseless and ever hopeful labour to try
to gain a knowledge of man’s place in the order of nature. When we have
gained this fully and minutely, we shall be able by the light of the past
to guide ourselves in the future. In proportion as the whole of the past
evolution of civilised man, of which we at present perceive the outlines,
is assigned to its causes, we and our successors on the globe may expect
to be able duly to estimate that which makes for, and that which makes
against, the progress of the race. The full and earnest cultivation of
Science—the Knowledge of Causes—is that to which we have to look for the
protection of our race—even of this English branch of it—from relapse and
degeneration.




FOOTNOTES


[1] These pages formed a discourse delivered before the British
Association at Sheffield on the evening of August 22nd, 1879, under the
presidency of Professor Allman, LL.D., F.R.S.

[2] See Note A.

[3] See Note B.

[4] Der Ursprung der Wirbelthiere und das Princip des Functionswechsels.
Leipzig, 1875.




NOTES.




A.


“Die Phantasie ist ein unentbehrliches Gut; denn sie ist es, durch
welche neue Combinationen zur Veranlassung wichtiger Entdeckungen
gemacht werden. Die Kraft der Unterscheidung des isolirenden Verstandes
sowohl, als der erweiternden und zum allgemeinen strebenden Phantasie
sind dem Naturforscher in einem harmonischen Wechselwirken nothwendig.
Durch Störung dieses Gleichgewichts wird der Naturforscher von der
Phantasie zu Träumereien hingerissen, während diese Gabe den talentvollen
Naturforscher von hinreichender Verstandesstärke zu den wichtigsten
Entdeckungen führt.”—JOHANNES MÜLLER, _Archiv für Anatomie_, 1834.




B.


To many persons the conclusion that man is the naturally modified
descendant of ape-like ancestors appears to be destructive of the
belief in an immortal soul, and in the teachings of Christianity; and
accordingly they either reject Darwinism altogether, or claim for man a
special exemption from the mode of origin admitted for other animals.

It seems worth while, in order to secure a calm and unprejudiced
consideration for the teachings of Darwinism, to point out to such
persons that, as a matter of fact, whatever views we may hold with
regard to a soul and the Christian doctrines, they cannot be in the
smallest degree affected by the admission that man has been derived from
ape-like ancestors by a process of natural selection, so long as the
demonstrable fact, not denied by any sane person, is admitted, namely,
that every individual man grows by a process of natural modification
from a homogeneous egg-cell or corpuscle. Assuredly it cannot lower our
conception of man’s dignity if we have to regard him as “the flower of
all the ages,” bursting from the great stream of life which has flowed on
through countless epochs with one increasing purpose, rather than as an
isolated, miraculous being, put together abnormally from elemental clay,
and cut off by such portentous origin from his fellow animals, and from
that gracious Nature to whom he yearns with filial instinct, knowing her,
in spite of fables, to be his dear mother.

A certain number of thoughtful persons admit the development of man’s
body by natural processes from ape-like ancestry, but believe in the
non-natural intervention of a Creator at a certain _definite_ stage in
that development, in order to introduce into the animal which was at
that moment a man-like ape, something termed “a conscious soul,” in
virtue of which he became an ape-like man. It appears to me perfectly
legitimate and harmless for individuals to make such an assumption if
their particular form of philosophy or of religion requires it. Such an
assumption does not in any way traverse the inferences from facts to
which Darwinism leads us; at the same time zoological science does not,
and cannot be expected to, give any support to such an assumption. The
gratuitous and harmless nature of the assumption so far as zoological
science is concerned, and accordingly the baselessness of the hostility
to Darwinism of those who choose to make it, may be seen by the
consideration of a parallel series of facts and assumptions, which puts
the matter clearly enough in its true light.

No one ventures to deny, at the present day, that every human being
grows from the egg _in utero_, just as a dog or a monkey does; the
facts are before us and can be scrutinised in detail. We may ask of
those who refuse to admit the gradual and natural development of man’s
consciousness in the ancestral series, passing from ape-like forms into
indubitable man, “How do you propose to divide the series presented by
every individual man in his growth from the egg? At what particular phase
in the embryonic series is the soul with its potential consciousness
implanted? Is it in the egg? in the fœtus of this month or of that? in
the new-born infant? or at five years of age?” This, it is notorious,
is a point upon which Churches have never been able to agree; and it is
equally notorious that the unbroken series exists—that the egg becomes
the fœtus, the fœtus the child, and the child the man. On the other
hand we have the historical series—the series, the existence of which
is inferred by Darwin and his adherents. This is a series leading from
simple egg-like organisms to ape-like creatures, and from these to man.
Will those who cannot answer our previous inquiries undertake to assert
dogmatically in the present case at what point in the historical series
there is a break or division? At what step are we to be asked to suppose
that the order of nature was stopped, and a non-natural soul introduced?
The philosopher or theologian of this or that school may arbitrarily draw
an imaginary line here or there in either series, and the evolutionist
will not raise a finger to stop him. As long as truth in the statement of
fact, and logic in the inference from observed fact are respected, there
need be no hostility between evolutionist and theologian. The theologian
is content in the case of individual development from the egg to admit
the facts of individual evolution, and to make assumptions which lie
altogether outside the region of scientific inquiry. So, too, it would
seem only reasonable that he should deal with the historical series,
and frankly accept the natural evolution of man from lower animals,
declaring dogmatically, if he so please, but not as an inference of the
same order as are the inferences of science, that something called the
soul arrived at any point in the series which he may think suitable. At
the same time, it would appear to be sufficient, even for the purposes of
the theologian, to hold that whatever the two above-mentioned series of
living things contain or imply, they do so as the result of a natural and
uniform process of development, that there has been one “miracle” once
and for all time. It should not be a ground of offence to any school of
thinkers, that Darwinism, whilst leaving them free scope, cannot be made
actually contributory to the support of their particular tenets.

The difficulties which the theologian has to meet when he is called upon
to give some account of the origin and nature of the soul, certainly
cannot be said to have been increased by the establishment of the
Darwinian theory. For from the earliest days of the Church, ingenious
speculation has been lavished on the subject. As to the origin of
the individual soul, Tertullian tells us as follows:—_De Anima_, ch.
xix.—“Anima velut surculus quidam ex matrice Adami in propaginem deducta,
et genitalibus semine foveis commodata. Pullulabit tam intellectu quam et
sensu.”

Whilst St. Augustine says:—“Harum autem sententiarum quatuor de anima,
utrum de propagine veniant, an in singulis quibusque nascentibus
mox fiant, an in corpora nascentium jam alicubi existentes vel
mittantur divinitus, vel sua sponte labantur, _nullam temere affirmari
oporteret_: aut enim nondum ista quæstio a divinorum librorum catholicis
tractatoribus, pro merito suæ obscuritatis et perplexitatis, evoluta
atque illustrata est; aut si jam factum est, nondum in manus nostras
hujuscemodi litteræ provenerunt.”




C.


A very important form of degeneration, not touched on in the text,
is that exhibited in the Mexican axolotl, where the larval form of a
Salamander develops generative organs, and is arrested in its further
progress to the adult parental form. It is not possible to class this
with the other phenomena which I have enumerated as Degeneration, since
there is no modification of an adult structure, but simple arrest, and
retention of the larval structure in all its completeness. I should call
the phenomenon exhibited by axolotl “arrest” or “super-larvation” rather
than degeneration.

The result of super-larvation is in so far similar to that of those
changes to which it is desirable to restrict the term “degeneration,”
that it may be classed under “simplificative evolution” as opposed to
“elaborative evolution.” That there is a very real difference between
super-larvation and degeneration may best be seen by taking a case of
each process and instituting a comparison. Axolotl proceeds regularly
on its course of development from the egg, but instead of passing from
the aquatic gilled condition to the terrestrial gill-less adult form of
the Salamander, it remains arrested in the earlier condition, develops
its reproductive organs, and propagates itself. There is no loss or
atrophy in this case, but simply a dead stop in a progressive course.
On the other hand, as we have seen, the Ascidian loses, by a process of
atrophy and destruction, a powerful locomotive organ, a highly-developed
eye, a relatively large nervous system. The former may be compared to
a permanent childishness, the latter to the second childhood, which is
really atrophy and decay. It is highly probable that super-larvation
has taken place at various epochs and in various groups of the animal
kingdom, just as it does in axolotl, and yet we cannot hope for evidence
fitted to establish its occurrence in any one case, where it is no
longer possible by exceptional conditions to recover (as in the case of
axolotl, which can experimentally be made to advance to the Salamander
phase by proper treatment), the discarded, more developed adult form.
By super-larvation it would be possible for an embryonic form developed
in relation to special embryonic conditions and not recapitulative of
an ancestry, to become the adult form of the race, and thus to give to
the subsequent evolution of that race a totally and otherwise improbable
direction.

It seems also exceedingly probable that “super-larvation” does not occur
only as in axolotl through premature maturation of the reproductive
organs, but the phenomenon _may_ develop itself more slowly by a gradual
creeping forward, as it were, of larval features. Just as the adaptations
acquired in, and having relation to, later life tend to show themselves
in an early period of the development of the individual and out of
due season; so do characters acquired by the early embryo, and having
relation only to this early period of life tend to remain as permanent
structures, and by their invasion to perturb the adult organization. Such
perturbation may tend _either_ to simplification or elaboration.




D.


The term (degeneration of language) includes two very distinct things;
the one is degeneration of grammatical form, the other degeneration
of the language as an instrument of thought. The former is a far
commoner phenomenon than the latter, and, in fact, whilst actually
degenerating so far as grammatical complexity is concerned, a language
may be at the same time becoming more and more serviceable, or more and
more perfect as an organ having a particular function. The decay of
useless inflexions and the consequent simplification of language may
be compared to the specialization of the one toe of the primitively
five-toed foot of the horse, whilst the four others which existed
in archaic horses are, one by one, atrophied. Taken by itself, this
phenomenon may possibly be described as degeneration, but inasmuch as
the whole horse is not degenerate but, on the contrary, specialized and
elaborated, it is advisable to widely distinguish such local atrophy
from general degeneration. In the same way language cannot, in relation
to this question, be treated as a thing by itself—it must be regarded
as a possession of the human organism, and the simplification of its
structure merely means in most cases its more complete adaptation to the
requirements of the organism.

True degeneration of language is therefore only found as part and parcel
of a more general degeneration of mental activity. To some extent the
conclusion that this or that language, as compared with its earlier
condition, exhibits evidence of such degeneration, must be matter of
taste and open to discussion. For instance, the English of Johnson may
be regarded as degenerate when compared with that of Shakspeare. There
is less probability of a difference of opinion as to the degeneracy of
modern Greek as compared with “classical” Greek; or of some of the modern
languages of Hindustan as compared with Sanskrit, and I am informed that
the same kind of degeneration is exhibited by modern Irish as compared
with old Irish. Degeneration, in the proper sense of the word, so far as
it applies to language, would seem to mean simply a decay or diversion
of literary taste and of literary production in the race to which such
language may be appropriate.


LONDON: R. CLAY, SONS, AND TAYLOR, BREAD STREET HILL, E.C.