Evolution

If she had been older, more integrated into the group, her decision might have been different. But as it was she slid down the tree’s rough bark toward the ground, her small mouth already moist with anticipation. It was this moment of decision that caused a great divergence in her own life — and the destiny of the greater family of primates in the future.

She had dropped the remains of her nut kernel. Behind her the little crowder, its patient wait over, fell on the sweet fragments. But in an instant more of its fellows came swarming over the branch to steal its prize.

As she climbed down the tree Roamer disturbed a troop of screechers. These primates were very small, with manes of fine silky hair and bizarre white moustaches. Startled by her passing they chattered and scurried away into the deeper recesses of the foliage, almost birdlike in the speed of their movements and the brightness of their furry "plumage."

Screechers made a living by digging into tree bark with their bottom teeth to make the gum flow. When they were done with a hole, they urinated into it to deter others from feeding there. There were many species of these little creatures, each specializing in the gum of one particular tree, and they were differentiated by their hairstyles. With their extravagant fur and trilling calls they made the forest canopy a place of color, life, and noise.

On the ground was still another form of primate. This was a potbelly, a solitary male. He was four times Roamer’s size, his bulky body coated in thick black fur. He sat squat, steadily pulling leaves off a bush and cramming them between his powerful jaws. His muzzle was stained black: he had been chewing charcoal from a lightning-struck stump, a supplement which neutralized the toxins in his leafy diet.

As Roamer dropped lightly to the floor he glared at her, his mouth a ferocious downturn, and let out a roar. She glanced around nervously, fearing his call might have attracted the attention of the careless mother bird.

Roamer was under no threat from the potbelly. He had an enormous stomach with an enlarged lower intestine within which his low-nutrition food could be partially fermented. To let this mighty organic factory work effectively, he had to remain motionless for three-quarters of his time. This close she could hear the endless rumbling of his huge ungainly stomach. He was remarkably clean, though; given his lifestyle, he had to be sanitary, like a sewer rat. As she moved away from his precious patch of forest floor the potbelly subsided into a sulky silence.

The forest clearing was cluttered. Grasslands were still rare. In the absence of grass, the ground cover was rarely less than a meter tall, a clutter of low shrubs and bushes including aloe, cactus, and succulents. Most spectacular of all were giant thistlelike plants strewn, in their season, with psychedelically colored flowers. Such spectacles graced most of Earth’s landmasses in this era, but it was an assemblage that would be unusual in human times; it was something like the fynbos flora of southern Africa.

To reach the bird’s nest, Roamer would have to leave the cover of the trees. But the open sky today seemed very bright — bright and washed-out white — and there was a peculiar electric stink to the air. She would be exposed out there; she hesitated, uneasy.

Clinging to the edge of the forest, she tried to work her way closer to the eggs.

She skirted a marshy area, part of the mighty river’s floodplain. She could see the water: Clogged with scummy vegetation, it glimmered, utterly flat, under a high sun. But there was a smell of salt in the air. Here, not far upstream of the river’s delta, she was close to the ocean, and occasional floods and high tides had laden the soils with brine, making the vegetation sparse.

Animals moved through the clearing, seeking the open water. In low scrub a group of gazellelike stenomylus cropped, moving in a tight, nervous cluster and peering about anxiously as they chewed. They were trailed by a smaller herd of cainotheres, like small, long-eared antelope. Other deerlike browsers worked through the forest itself. But the stenomylus were not gazelles but a kind of camel — as were the cainotheres, with their oddly rabbitlike heads.

Close to the shore clustered a family of bulky herbivores reminiscent of rhinos. These were not true rhinos, and the sad curve of their upper lips gave a clue to their ancestry: They were actually arsinoetheres, creatures related to elephants. In the water itself wallowed a mating pair of metamynodons, very like hippos; wading birds stepped cautiously away from their clumsy passion. The metamynodons were actually more closely related to rhinos than were the arsinoetheres.