Evolution

The oxy flinched at the unexpected aggression of this tiny creature. But she is no threat. The oxy, angered, quickly recovered his composure, and prepared to call Plesi’s bluff.

But Plesi had vanished into the undergrowth. She had never meant to attack the oxy, only to gain a precious second of time. And she had left Strong behind.

The young carpolestid, transfixed by the carnivore’s stare, flattened herself against the ground. The oxy crushed Strong with his paw, snapping the little primate’s spine. Strong, flooded with pain, turned on her attacker, seeking to gouge his flesh with her teeth. In her final moments Strong discovered something like courage. But it did her no good.

The oxy played with the crippled animal for a while. Then he began to feed.

As the world recovered, so its changing conditions shaped its living inhabitants.

The mammals were beginning to experiment with new roles. The ancestors of the true carnivores, which would eventually include the dogs and cats, were still small, ferretlike animals, busy, opportunistic general feeders. But the oxyclaenus had begun to develop the specializations of mammalian predators to follow: vertical legs for sustained speed, strong permanent teeth anchored by double roots and with interlocking cusps designed to shred meat.

It was all part of an ancient pattern. All living things worked to stay alive. They took in nourishment, repaired themselves, grew, avoided predators.

No organism lived forever. The only way to counter the dreadful annihilation of death was reproduction. Through reproduction, genetic information about oneself was passed on to one’s offspring.

But no offspring was identical to its parents. At any moment each species contained the potential for much variation. But all organisms had to exist within a frame of habitability set by their environment — an environment, of weather, land, and living things, which they shaped in turn. As survival was sought with ruthless ferocity, the frame of the environment was filled up; every viable variation of a species that could find room to survive was expressed.

But room was at a premium. And competition for that room was relentless and unending. Many more offspring were born than could possibly survive. The struggle to exist was relentless. The losers were culled by starvation, predation, disease. Those slightly better adapted to their corner of the environment inevitably had a slightly better chance of winning the battle for survival than others — and therefore of passing on genetic information about themselves to subsequent generations.

But the environment could change, as climates adjusted, or as continents collided and species, mixed by migrations over land bridges, found themselves with novel neighbors. As the environment, of climate and of living things, changed, so the requirements of adaptation changed. But the principle of selection continued to operate.

Thus, generation by generation, the populations of organisms tracked the changes in the world. All the variations of a species that worked in the new frame were selected for, and those that were no longer viable disappeared, sinking into the fossil record, or into oblivion altogether. Such turnovers were unending, a perpetual churn. As long as the "required" variation lay within the available genetic spectrum, the changes in the population could be rapid — as rapid as human breeders of domesticated animals and plants would find as they strove for their own ideas of perfection in the creatures in their power. But when the available variation ran out, the changes would stall, until a new mutation came along, a chance event caused, perhaps, by radiation effects, that opened up new possibilities for variation.

This was evolution. That was all there was to it: It was a simple principle, based on simple, obvious laws. But it would shape every species that ever inhabited the Earth, from the birth of life to the last extinction of all, which would take place under a glowering sun, far in the future.

And it was working now.

It was hard.

It was life.

Plesi had made an unspoken bargain with the oxy: Take my child. Spare me. Even as she clambered back through layers of green and into the safety of the trees, seeking her surviving daughter, that dreadful stratagem still echoed in her mind.

That, and a feeling that came from deep within her cells, a thought she might have expressed as: I always knew it was too good to be true. The teeth and claws weren’t gone. They were just hiding. I always knew they’d come back.

Her instinct was right. Two million years after the uneasy truce imposed by the dinosaurs’ death, the mammals had started to prey on each other.

That night Weak, bewildered, terrified herself, watched her mother twitch and growl in her sleep.