Produced by Sankar Viswanathan, Robert Cicconetti, and the
Online Distributed Proofreading Team at http://www.pgdp.net







                         Transcriber's Note:

    This etext was produced from the March 1953 issue of Galaxy. Extensive
    research did not uncover any evidence that the U.S. copyright on this
    publication was renewed.


                             STUDENT BODY


                           By F. L. WALLACE


                        Illustrated by ASHMAN


     _When a really infallible scientific bureau makes a
      drastically serious error, the data must be wrong ... but
      wrong in what way?_

       *       *       *       *       *




The first morning that they were fully committed to the planet, the
executive officer stepped out of the ship. It was not quite dawn.
Executive Hafner squinted in the early light; his eyes opened wider,
and he promptly went back inside. Three minutes later, he reappeared
with the biologist in tow.

"Last night you said there was nothing dangerous," said the executive.
"Do you still think it's so?"

Dano Marin stared. "I do." What his voice lacked in conviction, it
made up in embarrassment. He laughed uncertainly.

"This is no laughing matter. I'll talk to you later."

The biologist stood by the ship and watched as the executive walked to
the row of sleeping colonists.

"Mrs. Athyl," said the executive as he stopped beside the sleeping
figure.

She yawned, rubbed her eyes, rolled over, and stood up. The covering
that should have been there, however, wasn't. Neither was the garment
she had on when she had gone to sleep. She assumed the conventional
position of a woman who is astonished to find herself unclad without
her knowledge or consent.

[Illustration]

"It's all right, Mrs. Athyl. I'm not a voyeur myself. Still, I think
you should get some clothing on." Most of the colonists were awake
now. Executive Hafner turned to them. "If you haven't any suitable
clothing in the ship, the commissary will issue you some. Explanations
will be given later."

The colonists scattered. There was no compulsive modesty among them,
for it couldn't have survived a year and a half in crowded spaceships.
Nevertheless, it was a shock to awaken with no clothing on and not
know who or what had removed it during the night. It was surprise more
than anything else that disconcerted them.

On his way back to the spaceship, Executive Hafner paused. "Any ideas
about it?"

Dano Marin shrugged. "How could I have? The planet is as new to me as
it is to you."

"Sure. But you're the biologist."

As the only scientist in a crew of rough-and-ready colonists and
builders, Marin was going to be called on to answer a lot of questions
that weren't in his field.

"Nocturnal insects, most likely," he suggested. That was pretty weak,
though he knew that in ancient times locusts had stripped fields in a
matter of hours. Could they do the same with the clothing of humans
and not awaken them? "I'll look into the matter. As soon as I find
anything, I'll let you know."

"Good." Hafner nodded and went into the spaceship.

       *       *       *       *       *

Dano Marin walked to the grove in which the colonists had been
sleeping. It had been a mistake to let them bed down there, but at the
time the request had been made, there had seemed no reason not to
grant it. After eighteen months in crowded ships everyone naturally
wanted fresh air and the rustle of leaves overhead.

Marin looked out through the grove. It was empty now; the colonists,
both men and women, had disappeared inside the ship, dressing,
probably.

The trees were not tall and the leaves were dark bottle-green.
Occasional huge white flowers caught sunlight that made them seem
larger than they were. It wasn't Earth and therefore the trees
couldn't be magnolias. But they reminded Marin of magnolia trees and
thereafter he always thought of them as that.

The problem of the missing clothing was ironic. Biological Survey
never made a mistake--yet obviously they had. They listed the planet
as the most suitable for Man of any so far discovered. Few insects, no
dangerous animals, a most equitable climate. They had named it Glade
because that was the word which fitted best. The whole land mass
seemed to be one vast and pleasant meadow.

Evidently there were things about the planet that Biological Survey
had missed.

Marin dropped to his knees and began to look for clues. If insects had
been responsible, there ought to be a few dead ones, crushed, perhaps,
as the colonists rolled over in their sleep. There were no insects,
either live or dead.

He stood up in disappointment and walked slowly through the grove. It
might be the trees. At night they could exude a vapor which was
capable of dissolving the material from which the clothing had been
made. Far-fetched, but not impossible. He crumbled a leaf in his hand
and rubbed it against his sleeve. A pungent smell, but nothing
happened. That didn't disprove the theory, of course.

He looked out through the trees at the blue sun. It was bigger than
Sol, but farther away. At Glade, it was about equal to the Sun on
Earth.

He almost missed the bright eyes that regarded him from the
underbrush. Almost, but didn't--the domain of biology begins at the
edge of the atmosphere; it includes the brush and the small creatures
that live in it.

He swooped down on it. The creature fled squealing. He ran it down in
the grass outside the grove. It collapsed into quaking flesh as he
picked it up. He talked to it gently and the terror subsided.

It nibbled contentedly on his jacket as he carried it back to the
ship.

       *       *       *       *       *

Executive Hafner stared unhappily into the cage. It was an
undistinguished animal, small and something like an undeveloped
rodent. Its fur was sparse and stringy, unglamorous; it would never be
an item in the fur export trade.

"Can we exterminate it?" asked Hafner. "Locally, that is."

"Hardly. It's ecologically basic."

[Illustration]

The executive looked blank. Dano Marin added the explanation: "You
know how Biological Control works. As soon as a planet has been
discovered that looks suitable, they send out a survey ship loaded
with equipment. The ship flies low over a good part of the planet and
the instruments in the ship record the neural currents of the animals
below. The instruments can distinguish the characteristic neural
patterns of anything that has a brain, including insects.

"Anyway, they have a pretty good idea of the kinds of animals on the
planet and their relative distribution. Naturally, the survey party
takes a few specimens. They have to in order to correlate the pattern
with the actual animal, otherwise the neural pattern would be merely a
meaningless squiggle on a microfilm.

"The survey shows that this animal is one of only four species of
mammals on the planet. It is also the most numerous."

Hafner grunted. "So if we kill them off here, others will swarm in
from surrounding areas?"

"That's about it. There are probably millions of them on this
peninsula. Of course, if you want to put a barrier across the narrow
connection to the mainland, you might be able to wipe them out
locally."

The executive scowled. A barrier was possible, but it would involve
more work than he cared to expend.

"What do they eat?" he asked truculently.

"A little bit of everything, apparently. Insects, fruits, berries,
nuts, succulents, and grain." Dano Marin smiled. "I guess it could be
called an omnivore--now that our clothing is handy, it eats that,
too."

Hafner didn't smile. "I thought our clothing was supposed to be
verminproof."

Marin shrugged. "It is, on twenty-seven planets. On the twenty-eighth,
we meet up with a little fella that has better digestive fluids,
that's all."

Hafner looked pained. "Are they likely to bother the crops we plant?"

"Offhand, I would say they aren't. But then I would have said the same
about our clothing."

Hafner made up his mind. "All right. You worry about the crops. Find
some way to keep them out of the fields. Meanwhile, everyone sleeps in
the ship until we can build dormitories."

Individual dwelling units would have been more appropriate in the
colony at this stage, thought Marin. But it wasn't for him to decide.
The executive was a man who regarded a schedule as something to be
exceeded.

"The omnivore--" began Marin.

Hafner nodded impatiently. "Work on it," he said, and walked away.

The biologist sighed. The omnivore really was a queer little
creature, but it was by no means the most important thing on Glade.
For instance, why were there so few species of land animals on the
planet? No reptiles, numerous birds, and only four kinds of mammals.

Every comparable planet teemed with a wild variety of life. Glade, in
spite of seemingly ideal conditions, hadn't developed. Why?

He had asked Biological Controls for this assignment because it had
seemed an interesting problem. Now, apparently, he was being pressed
into service as an exterminator.

He reached in the cage and picked up the omnivore. Mammals on Glade
were not unexpected. Parallel development took care of that. Given
roughly the same kind of environment, similar animals would usually
evolve.

In the Late Carboniferous forest on Earth, there had been creatures
like the omnivore, the primitive mammal from which all others had
evolved. On Glade, that kind of evolution just hadn't taken place.
What had kept nature from exploiting its evolutionary potentialities?
There was the real problem, not how to wipe them out.

Marin stuck a needle in the omnivore. It squealed and then relaxed. He
drew out the blood and set it back in the cage. He could learn a lot
about the animal from trying to kill it.

       *       *       *       *       *

The quartermaster was shouting, though his normal voice carried quite
well.

"How do you know it's mice?" the biologist asked him.

"Look," said the quartermaster angrily.

Marin looked. The evidence did indicate mice.

Before he could speak, the quartermaster snapped, "Don't tell me
they're only mice-like creatures. I know that. The question is: how
can I get rid of them?"

"Have you tried poison?"

"Tell me what poison to use and I'll use it."

It wasn't the easiest question to answer. What was poisonous to an
animal he had never seen and knew nothing about? According to
Biological Survey, the animal didn't exist.

It was unexpectedly serious. The colony could live off the land, and
was expected to. But another group of colonists was due in three
years. The colony was supposed to accumulate a surplus of food to feed
the increased numbers. If they couldn't store the food they grew any
better than the concentrates, that surplus was going to be scanty.

Marin went over the warehouse thoroughly. It was the usual early
construction on a colonial world. Not esthetic, it was sturdy enough.
Fused dirt floor, reinforced foot-thick walls, a ceiling slab of the
same. The whole was bound together with a molecular cement that made
it practically airtight. It had no windows; there were two doors.
Certainly it should keep out rodents.

A closer examination revealed an unexpected flaw. The floor was as
hard as glass; no animal could gnaw through it, but, like glass, it
was also brittle. The crew that had built the warehouse had evidently
been in such a hurry to get back to Earth that they hadn't been as
careful as they should have been, for here and there the floor was
thin. Somewhere under the heavy equipment piled on it, the floor had
cracked. There a burrowing animal had means of entry.

Short of building another warehouse, it was too late to do anything
about that. Mice-like animals were inside and had to be controlled
where they were.

The biologist straightened up. "Catch me a few of them alive and I'll
see what I can do."

       *       *       *       *       *

In the morning, a dozen live specimens were delivered to the lab. They
actually did resemble mice.

Their reactions were puzzling. No two of them were affected by the
same poison. A compound that stiffened one in a matter of minutes left
the others hale and hearty, and the poison he had developed to control
the omnivores was completely ineffective.

The depredations in the warehouse went on. Black mice, white ones,
gray and brown, short-tailed and long-eared, or the reverse, they
continued to eat the concentrates and spoil what they didn't eat.

Marin conferred with the executive, outlined the problem as he saw it
and his ideas on what could be done to combat the nuisance.

"But we can't build another warehouse," argued Hafner. "Not until the
atomic generator is set up, at any rate. And then we'll have other
uses for the power." The executive rested his head in his hands. "I
like the other solution better. Build one and see how it works."

"I was thinking of three," said the biologist.

"One," Hafner insisted. "We can't spare the equipment until we know
how it works."

At that he was probably right. They had equipment, as much as three
ships could bring. But the more they brought, the more was expected of
the colony. The net effect was that equipment was always in short
supply.

Marin took the authorization to the engineer. On the way, he privately
revised his specifications upward. If he couldn't get as many as he
wanted, he might as well get a better one.

In two days, the machine was ready.

It was delivered in a small crate to the warehouse. The crate was
opened and the machine leaped out and stood there, poised.

"A cat!" exclaimed the quartermaster, pleased. He stretched out his
hand toward the black fuzzy robot.

"If you've touched anything a mouse may have, get your hand away,"
warned the biologist. "It reacts to smell as well as sight and sound."

Hastily, the quartermaster withdrew his hand. The robot disappeared
silently into the maze of stored material.

In one week, though there were still some mice in the warehouse, they
were no longer a danger.

       *       *       *       *       *

The executive called Marin into his office, a small sturdy building
located in the center of the settlement. The colony was growing,
assuming an aspect of permanency. Hafner sat in his chair and looked
out over that growth with satisfaction.

"A good job on the mouse plague," he said.

The biologist nodded. "Not bad, except there shouldn't be any mice
here. Biological Survey--"

"Forget it," said the exec. "Everybody makes mistakes, even B. S." He
leaned back and looked seriously at the biologist. "I have a job I
need done. Just now I'm short of men. If you have no objections...."

[Illustration]

The exec was always short of men, would be until the planet was
overcrowded, and he would try to find someone to do the work his own
men should have done. Dano Marin was not directly responsible to
Hafner; he was on loan to the expedition from Biological Controls.
Still, it was a good idea to cooperate with the executive. He sighed.

"It's not as bad as you think," said Hafner, interpreting the sound
correctly. He smiled. "We've got the digger together. I want you to
run it."

Since it tied right in with his investigations, Dano Marin looked
relieved and showed it.

"Except for food, we have to import most of our supplies," Hafner
explained. "It's a long haul, and we've got to make use of everything
on the planet we can. We need oil. There are going to be a lot of
wheels turning, and every one of them will have to have oil. In time
we'll set up a synthetic plant, but if we can locate a productive
field now, it's to our advantage."

"You're assuming the geology of Glade is similar to Earth?"

Hafner waggled his hand. "Why not? It's a nicer twin of Earth."

Why not? Because you couldn't always tell from the surface, thought
Marin. It seemed like Earth, but was it? Here was a good chance to
find out the history of Glade.

Hafner stood up. "Any time you're ready, a technician will check you
out on the digger. Let me know before you go."

       *       *       *       *       *

Actually, the digger wasn't a digger. It didn't move or otherwise
displace a gram of dirt or rock. It was a means of looking down below
the surface, to any practical depth. A large crawler, it was big
enough for a man to live in without discomfort for a week.

It carried an outsize ultrasonic generator and a device for directing
the beam into the planet. That was the sending apparatus. The
receiving end began with a large sonic lens which picked up sound
beams reflected from any desired depth, converted it into electrical
energy and thence into an image which was flashed onto a screen.

At the depth of ten miles, the image was fuzzy, though good enough to
distinguish the main features of the strata. At three miles, it was
better. It could pick up the sound reflection of a buried coin and
convert it into a picture on which the date could be seen.

It was to a geologist as a microscope is to a biologist. Being a
biologist, Dano Marin could appreciate the analogy.

He started at the tip of the peninsula and zigzagged across, heading
toward the isthmus. Methodically, he covered the territory, sleeping
at night in the digger. On the morning of the third day, he discovered
oil traces, and by that afternoon he had located the main field.

He should probably have turned back at once, but now that he had found
oil, he investigated more deliberately. Starting at the top, he let
the image range downward below the top strata.

It was the reverse of what it should have been. In the top few feet,
there were plentiful fossil remains, mostly of the four species of
mammals. The squirrel-like creature and the far larger grazing animal
were the forest dwellers. Of the plains animals, there were only two,
in size fitting neatly between the extremes of the forest dwellers.

After the first few feet, which corresponded to approximately twenty
thousand years, he found virtually no fossils. Not until he reached a
depth which he could correlate to the Late Carboniferous age on Earth
did fossils reappear. Then they were of animals appropriate to the
epoch. At that depth and below, the history of Glade was quite similar
to Earth's.

Puzzled, he checked again in a dozen widely scattered localities. The
results were always the same--fossil history for the first twenty
thousand years, then none for roughly a hundred million. Beyond that,
it was easy to trace the thread of biological development.

In that period of approximately one hundred million years, something
unique had happened to Glade. What was it?

On the fifth day his investigations were interrupted by the sound of
the keyed-on radio.

"Marin."

"Yes?" He flipped on the sending switch.

"How soon can you get back?"

He looked at the photo-map. "Three hours. Two if I hurry."

"Make it two. Never mind the oil."

"I've found oil. But what's the matter?"

"You can see it better than I can describe it. We'll discuss it when
you get back."

       *       *       *       *       *

Reluctantly, Marin retracted the instruments into the digger. He
turned it around and, with not too much regard for the terrain, let it
roar. The treads tossed dirt high in the air. Animals fled squealing
from in front of him. If the grove was small enough, he went around
it, otherwise he went through and left matchsticks behind.

He skidded the crawler ponderously to halt near the edge of the
settlement. The center of activity was the warehouse. Pickups wheeled
in and out, transferring supplies to a cleared area outside. He found
Hafner in a corner of the warehouse, talking to the engineer.

Hafner turned around when he came up. "Your mice have grown, Marin."

Marin looked down. The robot cat lay on the floor. He knelt and
examined it. The steel skeleton hadn't broken; it had been bent,
badly. The tough plastic skin had been torn off and, inside, the
delicate mechanism had been chewed into an unrecognizable mass.

Around the cat were rats, twenty or thirty of them, huge by any
standards. The cat had fought; the dead animals were headless or
disemboweled, unbelievably battered. But the robot had been
outnumbered.

Biological Survey had said there weren't any rats on Glade. They had
also said that about mice. What was the key to their error?

[Illustration]

The biologist stood up. "What are you going to do about it?"

"Build another warehouse, two-foot-thick fused dirt floors, monolithic
construction. Transfer all perishables to it."

Marin nodded. That would do it. It would take time, of course, and
power, all they could draw out of the recently set up atomic
generator. All other construction would have to be suspended. No
wonder Hafner was disturbed.

"Why not build more cats?" Marin suggested.

The executive smiled nastily. "You weren't here when we opened the
doors. The warehouse was swarming with rats. How many robot cats would
we need--five, fifteen? I don't know. Anyway the engineer tells me we
have enough parts to build three more cats. The one lying there can't
be salvaged."

It didn't take an engineer to see that, thought Marin.

Hafner continued, "If we need more, we'll have to rob the computer in
the spaceship. I refuse to permit that."

Obviously he would. The spaceship was the only link with Earth until
the next expedition brought more colonists. No exec in his right mind
would permit the ship to be crippled.

But why had Hafner called him back? Merely to keep him informed of the
situation?

       *       *       *       *       *

Hafner seemed to guess his thoughts. "At night we'll floodlight the
supplies we remove from the warehouse. We'll post a guard armed with
decharged rifles until we can move the food into the new warehouse.
That'll take about ten days. Meanwhile, our fast crops are ripening.
It's my guess the rats will turn to them for food. In order to protect
our future food supply, you'll have to activate your animals."

The biologist started. "But it's against regulations to loose any
animal on a planet until a complete investigation of the possible ill
effects is made."

"That takes ten or twenty years. This is an emergency and I'll be
responsible--in writing, if you want."

The biologist was effectively countermanded. Another rabbit-infested
Australia or the planet that the snails took over might be in the
making, but there was nothing he could do about it.

"I hardly think they'll be of any use against rats this size," he
protested.

"You've got hormones. Apply them." The executive turned and began
discussing construction with the engineer.

       *       *       *       *       *

Marin had the dead rats gathered up and placed in the freezer for
further study.

After that, he retired to the laboratory and worked out a course of
treatment for the domesticated animals that the colonists had brought
with them. He gave them the first injections and watched them
carefully until they were safely through the initial shock phase of
growth. As soon as he saw they were going to survive, he bred them.

Next he turned to the rats. Of note was the wide variation in size.
Internally, the same thing was true. They had the usual organs, but
the proportions of each varied greatly, more than is normal. Nor were
their teeth uniform. Some carried huge fangs set in delicate jaws;
others had tiny teeth that didn't match the massive bone structure. As
a species, they were the most scrambled the biologist had ever
encountered.

He turned the microscope on their tissues and tabulated the results.
There was less difference here between individual specimens, but it
was enough to set him pondering. The reproductive cells were
especially baffling.

Late in the day, he felt rather than heard the soundless whoosh of the
construction machinery. He looked out of the laboratory and saw smoke
rolling upward. As soon as the vegetation was charred, the smoke
ceased and heat waves danced into the sky.

They were building on a hill. The little creatures that crept and
crawled in the brush attacked in the most vulnerable spot, the food
supply. There was no brush, not a blade of grass, on the hill when the
colonists finished.

       *       *       *       *       *

Terriers. In the past, they were the hunting dogs of the agricultural
era. What they lacked in size they made up in ferocity toward rodents.
They had earned their keep originally in granaries and fields, and,
for a brief time, they were doing it again on colonial worlds where
conditions were repeated.

The dogs the colonists brought had been terriers. They were still as
fast, still with the same anti-rodent disposition, but they were no
longer small. It had been a difficult job, yet Marin had done it well,
for the dogs had lost none of their skill and speed in growing to the
size of a great dane.

The rats moved in on the fields of fast crops. Fast crops were made to
order for a colonial world. They could be planted, grown, and
harvested in a matter of weeks. After four such plantings, the
fertility of the soil was destroyed, but that meant nothing in the
early years of a colonial planet, for land was plentiful.

The rat tide grew in the fast crops, and the dogs were loosed on the
rats. They ranged through the fields, hunting. A rush, a snap of their
jaws, the shake of a head, and the rat was tossed aside, its back
broken. The dogs went on to the next.

Until they could not see, the dogs prowled and slaughtered. At night
they came in bloody, most of it not their own, and exhausted. Marin
pumped them full of antibiotics, bandaged their wounds, fed them
through their veins, and shot them into sleep. In the morning he
awakened them with an injection of stimulant and sent them tingling
into battle.

It took the rats two days to learn they could not feed during the day.
Not so numerous, they came at night. They climbed on the vines and
nibbled the fruit. They gnawed growing grain and ravaged vegetables.

The next day the colonists set up lights. The dogs were with them,
discouraging the few rats who were still foolish enough to forage
while the sun was overhead.

An hour before dusk, Marin called the dogs in and gave them an
enforced rest. He brought them out of it after dark and took them to
the fields, staggering. The scent of rats revived them; they were as
eager as ever, if not quite so fast.

The rats came from the surrounding meadows, not singly, or in twos and
threes, as they had before; this time they came together. Squealing
and rustling the grass, they moved toward the fields. It was dark, and
though he could not see them, Marin could hear them. He ordered the
great lights turned on in the area of the fields.

The rats stopped under the glare, milling around uneasily. The dogs
quivered and whined. Marin held them back. The rats resumed their
march, and Marin released the dogs.

The dogs charged in to attack, but didn't dare brave the main mass.
They picked off the stragglers and forced the rats into a tighter
formation. After that the rats were virtually unassailable.

The colonists could have burned the bunched-up rats with the right
equipment, but they didn't have it and couldn't get it for years. Even
if they'd had it, the use of such equipment would endanger the crops,
which they had to save if they could. It was up to the dogs.

The rat formation came to the edge of the fields, and broke. They
could face a common enemy and remain united, but in the presence of
food, they forgot that unity and scattered--hunger was the great
divisor. The dogs leaped joyously in pursuit. They hunted down the
starved rodents, one by one, and killed them as they ate.

When daylight came, the rat menace had ended.

The next week the colonists harvested and processed the food for
storage and immediately planted another crop.

[Illustration]

Marin sat in the lab and tried to analyze the situation. The colony
was moving from crisis to crisis, all of them involving food. In
itself, each critical situation was minor, but lumped together they
could add up to failure. No matter how he looked at it, they just
didn't have the equipment they needed to colonize Glade.

The fault seemed to lie with Biological Survey; they hadn't reported
the presence of pests that were endangering the food supply.
Regardless of what the exec thought about them, Survey knew their
business. If they said there were no mice or rats on Glade, then there
hadn't been any--_when the survey was made_.

The question was: when did they come and how did they get here?

Marin sat and stared at the wall, turning over hypotheses in his mind,
discarding them when they failed to make sense.

His gaze shifted from the wall to the cage of the omnivores, the
squirrel-size forest creature. The most numerous animal on Glade, it
was a commonplace sight to the colonists.

And yet it was a remarkable animal, more than he had realized. Plain,
insignificant in appearance, it might be the most important of any
animal Man had encountered on the many worlds he had settled on. The
longer he watched, the more Marin became convinced of it.

He sat silent, observing the creature, not daring to move. He sat
until it was dark and the omnivore resumed its normal activity.

_Normal?_ The word didn't apply on Glade.

The interlude with the omnivore provided him with one answer. He
needed another one; he thought he knew what it was, but he had to have
more data, additional observations.

He set up his equipment carefully on the fringes of the settlement.
There and in no other place existed the information he wanted.

He spent time in the digger, checking his original investigations. It
added up to a complete picture.

When he was certain of his facts, he called on Hafner.

The executive was congenial; it was a reflection of the smoothness
with which the objectives of the colony were being achieved.

"Sit down," he said affably. "Smoke?"

The biologist sat down and took a cigarette.

"I thought you'd like to know where the mice came from," he began.

Hafner smiled. "They don't bother us any more."

"I've also determined the origin of the rats."

"They're under control. We're doing nicely."

       *       *       *       *       *

On the contrary, thought Marin. He searched for the proper beginning.

"Glade has an Earth-type climate and topography," he said. "Has had
for the past twenty thousand years. Before that, about a hundred
million years ago, it was also like Earth of the comparable period."

He watched the look of polite interest settle on the executive's face
as he stated the obvious. Well, it _was_ obvious, up to a point. The
conclusions weren't, though.

"Between a hundred million years and twenty thousand years ago,
something happened to Glade," Marin went on. "I don't know the cause;
it belongs to cosmic history and we may never find out. Anyway,
whatever the cause--fluctuations in the sun, unstable equilibrium of
forces within the planet, or perhaps an encounter with an interstellar
dust cloud of variable density--the climate on Glade changed.

"It changed with inconceivable violence and it kept on changing. A
hundred million years ago, plus or minus, there was carboniferous
forest on Glade. Giant reptiles resembling dinosaurs and tiny mammals
roamed through it. The first great change wiped out the dinosaurs, as
it did on Earth. It didn't wipe out the still more primitive ancestor
of the omnivore, because it could adapt to changing conditions.

"Let me give you an idea how the conditions changed. For a few years a
given area would be a desert; after that it would turn into a jungle.
Still later a glacier would begin to form. And then the cycle would be
repeated, with wild variations. All this might happen--did
happen--within a span covered by the lifetime of a single omnivore.
This occurred many times. For roughly a hundred million years, it was
the norm of existence on Glade. This condition was hardly conducive to
the preservation of fossils."

Hafner saw the significance and was concerned. "You mean these
climatic fluctuations suddenly stopped, twenty thousand years ago? Are
they likely to begin again?"

"I don't know," confessed the biologist. "We can probably determine it
if we're interested."

The exec nodded grimly. "We're interested, all right."

Maybe we are, thought the biologist. He said, "The point is that
survival was difficult. Birds could and did fly to more suitable
climates; quite a few of them survived. Only one species of mammals
managed to come through."

"Your facts are not straight," observed Hafner. "There are four
species, ranging in size from a squirrel to a water buffalo."

"One species," Marin repeated doggedly. "They're the same. If the food
supply for the largest animal increases, some of the smaller so-called
species grow up. Conversely, if food becomes scarce in any category,
the next generation, which apparently can be produced almost
instantly, switches to a form which does have an adequate food
supply."

"The mice," Hafner said slowly.

       *       *       *       *       *

Marin finished the thought for him. "The mice weren't here when we got
here. They were born of the squirrel-size omnivore."

Hafner nodded. "And the rats?"

"Born of the next larger size. After all, we're environment,
too--perhaps the harshest the beasts have yet faced."

Hafner was a practical man, trained to administer a colony. Concepts
were not his familiar ground. "Mutations, then? But I thought--"

The biologist smiled. It was thin and cracked at the edges of his
mouth. "On Earth, it would be mutation. Here it is merely normal
evolutionary adaptation." He shook his head. "I never told you, but
omnivores, though they could be mistaken for an animal from Earth,
have no genes or chromosomes. Obviously they do have heredity, but how
it is passed down, I don't know. However it functions, it responds to
external conditions far faster than anything we've ever encountered."

Hafner nodded to himself. "Then we'll never be free from pests." He
clasped and unclasped his hands. "Unless, of course, we rid the
planet of all animal life."

"Radioactive dust?" asked the biologist. "They have survived worse."

The exec considered alternatives. "Maybe we should leave the planet
and leave it to the animals."

"Too late," said the biologist. "They'll be on Earth, too, and all the
planets we've settled on."

Hafner looked at him. The same pictures formed in his mind that Marin
had thought of. Three ships had been sent to colonize Glade. One had
remained with the colonists, survival insurance in case anything
unforeseen happened. Two had gone back to Earth to carry the report
that all was well and that more supplies were needed. They had also
carried specimens from the planet.

The cages those creatures were kept in were secure. But a smaller
species could get out, must already be free, inhabiting, undetected,
the cargo spaces of the ships.

There was nothing they could do to intercept those ships. And once
they reached Earth, would the biologists suspect? Not for a long time.
First a new kind of rat would appear. A mutation could account for
that. Without specific knowledge, there would be nothing to connect it
with the specimens picked up from Glade.

[Illustration]

"We have to stay," said the biologist. "We have to study them and we
can do it best here."

He thought of the vast complex of buildings on Earth. There was too
much invested to tear them down and make them verminproof. Billions of
people could not be moved off the planet while the work was being
done.

They were committed to Glade not as a colony, but as a gigantic
laboratory. They had gained one planet and lost the equivalent of ten,
perhaps more when the destructive properties of the omnivores were
finally assessed.

A rasping animal cough interrupted the biologist's thoughts. Hafner
jerked his head and glanced out the window. Lips tight, he grabbed a
rifle off the wall and ran out. Marin followed him.

       *       *       *       *       *

The exec headed toward the fields where the second fast crop was
maturing. On top of a knoll, he stopped and knelt. He flipped the dial
to _extreme charge_, aimed, and fired. It was high; he missed the
animal in the field. A neat strip of smoking brown appeared in the
green vegetation.

He aimed more carefully and fired again. The charge screamed out of
the muzzle. It struck the animal on the forepaw. The beast leaped high
in the air and fell down, dead and broiled.

They stood over the animal Hafner had killed. Except for the lack of
markings, it was a good imitation of a tiger. The exec prodded it with
his toe.

"We chase the rats out of the warehouse and they go to the fields," he
muttered. "We hunt them down in the fields with dogs and they breed
tigers."

"Easier than rats," said Marin. "We can shoot tigers." He bent down
over the slain dog near which they had surprised the big cat.

The other dog came whining from the far corner of the field to which
he had fled in terror. He was a courageous dog, but he could not face
the great carnivore. He whimpered and licked the face of his mate.

The biologist picked up the mangled dog and headed toward the
laboratory.

"You can't save her," said Hafner morosely. "She's dead."

"But the pups aren't. We'll need them. The rats won't disappear merely
because tigers have showed up."

The head drooped limply over his arm and blood seeped into his
clothing as Hafner followed him up the hill.

"We've been here three months," the exec said suddenly. "The dogs have
been in the fields only two. And yet the tiger was mature. How do you
account for something like that?"

Marin bent under the weight of the dog. Hafner never would understand
his bewilderment. As a biologist, all his categories were upset. What
did evolution explain? It was a history of organic life on a
particular world. Beyond that world, it might not apply.

Even about himself there were many things Man didn't know, dark
patches in his knowledge which theory simply had to pass over. About
other creatures, his ignorance was sometimes limitless.

Birth was simple; it occurred on countless planets. Meek grazing
creatures, fierce carnivores--the most unlikely animals gave birth to
their young. It happened all the time. And the young grew up, became
mature and mated.

He remembered that evening in the laboratory. It was accidental--what
if he had been elsewhere and not witnessed it? They would not know
what little they did.

He explained it carefully to Hafner. "If the survival factor is high
and there's a great disparity in size, the young need not ever be
young. They may be born as fully functioning adults!"

       *       *       *       *       *

Although not at the rate it had initially set, the colony progressed.
The fast crops were slowed down and a more diversified selection was
planted. New buildings were constructed and the supplies that were
stored in them were spread out thin, for easy inspection.

The pups survived and within a year shot up to maturity. After proper
training, they were released to the fields where they joined the older
dogs. The battle against the rats went on; they were held in check,
though the damage they caused was considerable.

The original animal, unchanged in form, developed an appetite for
electrical insulation. There was no protection except to keep the
power on at all times. Even then there were unwelcome interruptions
until the short was located and the charred carcass was removed.
Vehicles were kept tightly closed or parked only in verminproof
buildings. While the plague didn't increase in numbers, it couldn't be
eliminated, either.

There was a flurry of tigers, but they were larger animals and were
promptly shot down. They prowled at night, so the colonists were
assigned to guard the settlement around the clock. Where lights failed
to reach, the infra-red 'scope did. As fast as they came, the tigers
died. Except for the first one, not a single dog was lost.

The tigers changed, though not in form. Externally, they were all big
and powerful killers. But as the slaughter went on, Marin noticed one
astonishing fact--the internal organic structure became progressively
more immature.

The last one that was brought to him for examination was the
equivalent of a newly born cub. That tiny stomach was suited more for
the digestion of milk than meat. How it had furnished energy to drive
those great muscles was something of a miracle. But drive it had, for
a murderous fifteen minutes before the animal was brought down. No
lives were lost, though sick bay was kept busy for a while.

That was the last tiger they shot. After that, the attacks ceased.

The seasons passed and nothing new occurred. A spaceship civilization
or even that fragment of it represented by the colony was too much for
the creature, which Marin by now had come to think of as the
"Omnimal." It had evolved out of a cataclysmic past, but it could not
meet the challenge of the harshest environment.

Or so it seemed.

       *       *       *       *       *

Three months before the next colonists were due, a new animal was
detected. Food was missing from the fields. It was not another tiger:
they were carnivorous. Nor rats, for vines were stripped in a manner
that no rodent could manage.

The food was not important. The colony had enough in storage. But if
the new animal signaled another plague, it was necessary to know how
to meet it. The sooner they knew what the animal was, the better
defense they could set up against it.

Dogs were useless. The animal roamed the field they were loose in, and
they did not attack nor even seem to know it was there.

The colonists were called upon for guard duty again, but it evaded
them. They patrolled for a week and they still did not catch sight of
it.

Hafner called them in and rigged up an alarm system in the field most
frequented by the animal. It detected that, too, and moved its sphere
of operations to a field in which the alarm system had not been
installed.

Hafner conferred with the engineer, who devised an alarm that would
react to body radiation. It was buried in the original field and the
old alarm was moved to another.

Two nights later, just before dawn, the alarm rang.

Marin met Hafner at the edge of the settlement. Both carried rifles.
They walked; the noise of any vehicle was likely to frighten the
animal. They circled around and approached the field from the rear.
The men in the camp had been alerted. If they needed help, it was
ready.

They crept silently through the underbrush. It was feeding in the
field, not noisily, yet they could hear it. The dogs hadn't barked.

They inched nearer. The blue sun of Glade came up and shone full on
their quarry. The gun dropped in Hafner's hand. He clenched his teeth
and raised it again.

Marin put out a restraining arm. "Don't shoot," he whispered.

"I'm the exec here. I say it's dangerous."

"Dangerous," agreed Marin, still in a whisper. "That's why you can't
shoot. It's more dangerous than you know."

Hafner hesitated and Marin went on. "The omnimal couldn't compete in
the changed environment and so it evolved mice. We stopped the mice
and it countered with rats. We turned back the rat and it provided the
tiger.

"The tiger was easiest of all for us and so it was apparently stopped
for a while. But it didn't really stop. Another animal was being
formed, the one you see there. It took the omnimal two years to create
it--how, I don't know. A million years were required to evolve it on
Earth."

Hafner hadn't lowered the rifle and he showed no signs of doing so.
He looked lovingly into the sights.

"Can't you see?" urged Marin. "We can't destroy the omnimal. It's on
Earth now, and on the other planets, down in the storage areas of our
big cities, masquerading as rats. And we've never been able to root
out even our own terrestrial rats, so how can we exterminate the
omnimal?"

"All the more reason to start now." Hafner's voice was flat.

Marin struck the rifle down. "Are their rats better than ours?" he
asked wearily. "Will their pests win or ours be stronger? Or will the
two make peace, unite and interbreed, make war on us? It's not
impossible; the omnimal could do it if interbreeding had a high
survival factor.

"Don't you still see? There is a progression. After the tiger, it bred
this. If this evolution fails, if we shoot it down, what will it
create next? This creature I think we can compete with. _It's the one
after this that I do not want to face._"

       *       *       *       *       *

It heard them. It raised its head and looked around. Slowly it edged
away and backed toward a nearby grove.

The biologist stood up and called softly. The creature scurried to the
trees and stopped just inside the shadows among them.

The two men laid down their rifles. Together they approached the
grove, hands spread open to show they carried no weapons.

It came out to meet them. Naked, it had had no time to learn about
clothing. Neither did it have weapons. It plucked a large white flower
from the tree and extended this mutely as a sign of peace.

"I wonder what it's like," said Marin. "It seems adult, but can it be,
all the way through? What's inside that body?"

"I wonder what's in his head," Hafner said worriedly.

It looked very much like a man.

--F. L. WALLACE

       *       *       *       *       *