The last few years had been times of plenty, and the troop’s numbers had expanded. There had been a baby boom, of which Roamer was a part. But growth brought problems. There was too much competition for food, for one thing. Every day there were squabbles.

And then there was the grooming. In a small group there was time to groom everybody. It all helped to maintain relationships and cement alliances. When a group got too big, there just wasn’t the time to do that. So cliques were forming, subgroups fragmenting out whose members groomed each other exclusively, ignoring the rest. Already some of the cliques were traveling separately during the day, although they would still come together to sleep.

Eventually all of this would become too intense. The grooming cliques would fission off, and the group would split up. But the new, smaller groups each had to be large enough to offer protection against predators — the main purpose of these daytime bands in the first place — so it would be a long time yet, perhaps even years, before any fission was permanent. It happened all the time, an inevitable consequence of the growing sizes of primate communities. But it meant there was a lot of squabbling to be done.

So Roamer was happy to get away from all the bickering for a while.

The bug thoroughly masticated, Roamer inspected her palm nut. She knew that the kernel was delicious to eat, but her hands and teeth were not strong enough to break open the shell. So she began to pound the shell against the branch.

She became aware of two bright eyes watching her, and a slim, rust-colored body clinging to a branch. She was not alarmed. This was a crowder, a type of primate closely related to Roamer’s kind but smaller, more slender — and a lot less smart. Beyond its slim form Roamer made out many more of its kind, clinging to the branches of this tree and the next, arrayed through the forest’s green-lit world. The crowder was not competing for Roamer’s nut, and was certainly not threatening her; all the little primate wanted was Roamer’s leavings.

Roamer was mostly a fruit eater. But the crowders, like their common adapid ancestors, relied heavily on the caterpillars and grubs they snatched from the branches, and they had sharp, narrow teeth to process their insect prey. They lived in great crowded mobile colonies of fifty or more. This gave them a defense against predators and other primates. Even a troop of anthros would have had trouble driving off one of these agile, coordinated mobs.

But Roamer was a lot smarter than any crowder.

It would be tens of millions of years before any primate used anything that could be called a true tool. Much of Roamer’s intelligence was of a specialized kind, designed to enable her to cope with the fast-shifting intricacies of her social life. But Roamer was clever at understanding the natural environment around her and manipulating it to get what she wanted. Smashing a nut against a tree trunk was hardly advanced engineering, but it required her to plan one or two steps ahead, a precursor of much greater inventiveness in ages to come. And such nut smashing was a cognitive leap beyond the grasp of any crowder, which was why the crowders were hanging around now.

Roamer heard a rustling far below. She clung to her branch, peering down into the green gloom.

She could see the litter of the forest floor, and a shadowy shape moving through the trees with a rustle of feathers, tentative pecks at the ground. It was a flightless bird, something like a cassowary. And when she tracked back the way the bird had come to the middle of the clearing, Roamer made out a rounded, polished gleam.

Eggs. There were ten of them, nestling in the bird’s crude nest, each of them a reservoir of yolk as big as Roamer’s head. In the stillness of noon, with her mate away, the bird had left her nest briefly unguarded, taking the chance that no harm would come to it while she briefly assuaged her hunger. She was unfortunate that Roamer’s sharp eyes had detected the nest so quickly.

Roamer hesitated for a heartbeat. If she went after the eggs she would be taking a risk. Her nut cracking had already delayed her long enough for the troop to move away, and it would be bad to get lost. And the bird itself was a menace. A stalking monster, it was one of the last representatives of a twenty-million-year dynasty. After the comet, around the world, the land mammals had at first remained small, crammed into the dense forests — but some birds had grown large, and flightless monsters like this had briefly contested the role of top predator. Released from the weight limitations of flight they had become heavily built, muscular, and monstrously powerful, with beaks that could snap a backbone. But they had been out of time: When the mammalian herbivores grew large, so did mammal carnivores, and the birds could not compete.

The eggs were there, right below Roamer. She could take them easily.

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.