This time Noth did not hesitate. He threw himself at Solo and began to pummel his back and shoulders with feet, hands, and muzzle. The Emperor joined in — and so did more of the males, until Solo was immersed beneath a blanket of hooting, jostling, inexperienced assailants. Any one of them Solo would have defeated — but not all of them together. Under the rain of inexpertly aimed blows, it was impossible even for him to rise.

At last he burrowed like a taeniodont through the forest floor detritus, out from under the clamoring pack. By the time the ragged army had noticed he was gone, that their punches and kicks were either landing in the dirt or on each other, Solo was limping away.

Aching, battered, Noth clambered back into the tree. When he got there he found the females grooming each other calmly, picking bits of dried semen out of their crotch hair, as if the combat beneath had never taken place. The Emperor was sitting quietly with the female Biggest. His flow of blood had stilled — but his copulatory campaign was suspended forever.

And here was Rival, vigorously covering Right. Noth saw his sister’s face buried in her own chest hair, low squeaks of pleasure emanating from her throat. Noth felt an oddly warm glow. He was not driven by jealousy of other males over his sister — even of this male whom he had bested, and who had apparently recovered very quickly. A deeper biochemical part of him recognized that with his sister pregnant, the line would go on: the shining unbroken molecular thread that stretched from Purga, through this moment lit by the low polar sun, on into unimaginable futures.

He heard a remote lowing. It was the call of a moeritherium, the matriarch of a migrant herd, walking slowly up from the south. With the return of the herds, summer had truly come again. And from all over the forest came a high keening: It was the song of the notharctus, a song of loneliness and wonder.

In just a few years Noth’s life would be over. Soon his kind would be gone too, their descendants transmuted into new forms; and soon, as Earth cooled from this midsummer peak, even the polar forest would shrivel and die. But for now — bloodied, panting, his fur covered with leaf mold — this was Noth’s moment, his day in the light.

The huge female Big approached him. He trilled gently. With a glance into his eyes, she turned her back and presented to him. Noth entered her quickly, and his world dissolved into unthinking pleasure.

Here, close to its final oceanic destination, the mighty river pushed sluggishly between walls of lush, moist forest. There were many meanders and oxbow lakes, which, cut off from the flow, had turned into stagnant marshes and ponds. It was as if the river were exhausted, its long journey done — but this river was draining the heart of a continent.

And this late summer there had been much rain. The river was high, and it spilled over onto land where the water table was already near the surface. The dense, muddy water contained fragments of eroded rock, mud, and living things. There were even rafts of tangled branches and bits of vegetation drifting like unruly schooners down the river’s tremendous length, relics that had already traveled thousands of kilometers from their point of origin.

High above the water, in the forest’s cacophonous upper story, the anthros were making their daily destructive procession.

They were like monkeys. Running along branches, using their powerful arms to swing from tree to tree, they stripped off fruit, ripped open palm fronds, and tore away great swaths of bark to get at insects. Crowds of females moved and worked together, occasionally stopping for a moment’s grooming. There were mothers with infants clinging to their backs and bellies, supported by clusters of aunts. Males, larger, wider-ranging, made loose alliances that merged and fragmented constantly as they competed for food, status, and access to the females.

More than thirty anthros worked here. They were clever, efficient foragers, and where they passed, they laid waste. It was a joyful, clamoring racket of feeding, cooperating, and challenging.

Temporarily alone, Roamer was swinging from one thick branch to the next. Though she was high above the ground, she had no fear of falling; she was in her element here, her body and mind exquisitely adapted for the conditions of this tangled forest canopy.

Bordering the sea, to the west, there were dense mangrove swamps. But here, inland, the ancient forest was rich and diverse, full of tall trees with flaring buttresses: papaws, cashews, fan palms. Most of the trees were fruit bearing and rich in resin and oils. It was a comfortable, rich place to live. But it was a relic of a world that was vanishing, for a great cooling had gripped the Earth since Noth’s time, and the once global and beneficent forests had shrunk back to scraps and fragments.

Roamer found a palm nut. She settled on a branch to inspect it. A caterpillar, fat and green, crawled over its surface. She licked off the caterpillar and chewed it slowly.

The troop moved noisily through the canopy around her. Alone or not, she knew exactly where everybody else was. In the long years since Noth’s time the primates had become still more intensely social: To the anthros, other anthros had become more interesting than mere things — the most interesting objects in the world. Roamer was as aware of the rest of her troop as if they were a series of Chinese lanterns stuck in the foliage, diminishing the rest of the world to a dull, mute grayness.

Roamer belonged to no species that would ever be labeled by humans. She looked something like a capuchin, the organ-grinder monkey that would one day roam the forests of South America, and was about that size. She weighed a couple of kilograms, and she was covered in dense black fur topped by white shoulders, neck, and face; she looked like she was wearing a nun’s wimple. Her arms and legs were lithe and symmetrical, much more so than Noth’s: It was a body plan typical of the inhabitant of an open forest canopy. Her nose was flat, her nostrils small and protruding sideways, more like the monkeys of a later South America than those of Africa.

She looked like a monkey, but she was no monkey. Remote descendants of Noth’s adapids, her kind was a type of primate called anthropoid — ancestral to both monkeys and apes, for that great schism in the family of primates had yet to occur.

Nearly twenty million years after the death of Noth, the grooming claws of notharctus feet had been replaced on Roamer’s body by nails. Her eyes were smaller than Noth’s, capable of a wide, three-dimensional field of view past her shorter muzzle, and each of her eyes was supported by a solid cup of bone; Noth’s had been protected by a mere ring of bone, and his vision could even be disturbed by his own cheek muscles when chewing. And Roamer had lost many of Noth’s ancestral relics of the times of night foraging. Her reliance on smell had diminished, to be replaced by a greater dependence on sight.

From Right’s grandchildren had sprung a great diffusing army. They had migrated down through the Old World to inhabit the dense tropical forests of Asia, and here in Africa. And as they had migrated, so they had flourished, diversified, and changed. But the line of Old World anthropoids would not continue through Roamer. Roamer could not know that she would never see her mother again — and her fate was to be far more strange than anything that had befallen her immediate ancestors.

The whiteness of Roamer’s fur made her face seem sketchy, unformed, and oddly wistful. But she had a youthful prettiness. In fact, she was three years old, still a year short of her menarche. A juvenile female independent of spirit, not yet fully absorbed into the troop’s hierarchies and alliances, she retained something of the solitary instincts of more distant ancestors. She liked to keep herself to herself. Besides, the group wasn’t a particularly happy bunch right now.