Once he woke in the night shivering, his muscles involuntarily burning energy to keep him alive.

The sleeping world was full of light: the Moon was high and full and the forest glowed blue white and black. Long, sharp shadows striped the littered floor, and the vertical trunks of the leafless trees gave the scene an eerie geometrical precision. But the tangled branches higher up were a more complex and dismal sight, bone bare and glimmering with frost, a harsh contrast to the warm green glow of the leaves of high summer.

In its way it was a beautiful scene, and Noth's wide archaic eyes served him well, revealing to him detail and subtle colorations that would have been invisible to any human. But all Noth perceived was a lack lack: a lack of light, of warmth, of food- and a lack of kin in this group of strangers, save for his sister, whose still-growing body was buried somewhere in the huddling troop. And he knew on a deep cellular level that the true winter had yet to begin, long, drawn-out months of a kind of slow agony as his body consumed itself in order to keep him alive.

He squirmed across the branch, trying to force his way deeper into the group. Each of the adults knew that it was in everybody's long-term interests that she should take her turn at the edge of the group, briefly suffering the cold in order to shelter the rest; it wouldn't help to have outliers die of frostbite. But still Noth's lowly rank worked against him, and when the other males picked up his scent they sleepily combined to push him back out of the huddle, so he finished up almost as exposed as when he had started.

He lifted his muzzle and puffed out a breath, hooting mournfully.

These primates could draw no comfort from those around them. Noth found pleasure in grooming- but only in his own physical sensations, and in the effect it had on others' behavior toward him, not in how others felt. The other notharctus were simply a part of his environment, like the conifer trees and podocarps, the foragers and predators and prey: nothing to do with him. him.

These huddling notharctus, despite their physical closeness, were each lonelier than any human would ever be. Noth was forever locked inside the prison of his head, forced to endure his miseries and fears alone.

The morning dawned clear, but a freezing mist lay over the forest. Even though the sun grew bright there was little heat to be had from its rays.

The notharctus stretched limbs stiff with cold and long hours of immobility. Cautiously, watchfully, they headed down to the ground. On the forest floor they scattered slowly. The senior females moved around the edge of this loose clearing, using their wrists, armpits, and genitals to renew scent markers.

Noth picked through the frozen mulch. The dead leaves were of no use to him, but he had learned to burrow under places where the leaf litter was particularly thick. The mulching leaves could trap moisture and keep the frost away; here there was dew to lap up, and unfrozen ground to dig in search of tubers, roots, or even the rhizomes of hardy ferns.

A series of hooting cries broke out, startlingly loud, echoing through the forest. Noth looked up, whiskers twitching.

There was a commotion around a stand of podocarp. Noth saw that a group of notharctus, strange females with a scattering of pups, had come out of the forest. They were approaching the podocarp.

Biggest and some of the other females dashed forward. The troop's big dominant male- who Noth thought of as something like the Emperor the Emperor- joined in the females' charge. Soon they were all displaying ferociously, hooting and scraping musk over their long tails. The strange females cowered back, but they responded in kind. The forest briefly filled up with the cacophony of the argument.

The female clans, the heart of the notharctus' society, were fiercely territorial. These strange females had ignored the scent markers left by Big and the others, bright warning signs in a notharctus' sensorium. At this time of year food was becoming short; in the final scramble to stoke up their bodies' stores for the rigors of winter, a rich stand of podocarp was worth fighting for.

The females, with babies clinging to their fur, went further in their wars than their males were prepared to. They quickly escalated the confrontation to lunges and feints and even slashes with canine teeth. The females fought like knife fighters.

But it wasn't going to work. Though not one notharctus laid a paw on another, the display by Biggest and the rest overwhelmed the newcomers. They backed off toward the long gray-brown shadows of the deeper forest- though not before one older pup had lunged forward, cheekily sunk his teeth into a cold-wizened fruit, and run off with his bounty before he could be stopped.

Suddenly aware of the vulnerability of their treasure, the females closed around the podocarp now, munching greedily at the fruit. Some of the older, more powerful males, including the Emperor, were soon feeding alongside Biggest and the rest. Noth, with the other young males, circled the feeding group, waiting his turn at whatever would be left.

He dared not challenge the Emperor.

Male notharctus had their own complex and different social structure, overlaying that of the females. And it was all about mating, which was the most important thing- the only only thing. The Emperor had a large territory, including the ranges of many female groups. He would aim to mate with all the females in his territory, and so maximize his chances of propagating his genes. He would scent mark females to repel other suitors. And he would fight fiercely to keep other strong males away from his wide empire, just as Noth's father had fought to exclude Solo. thing. The Emperor had a large territory, including the ranges of many female groups. He would aim to mate with all the females in his territory, and so maximize his chances of propagating his genes. He would scent mark females to repel other suitors. And he would fight fiercely to keep other strong males away from his wide empire, just as Noth's father had fought to exclude Solo.

The Emperor had done well to hold on to his wide-ranging fiefdom for more than two years. But like all of his short-lived kind, he was aging quickly. Even Noth, the lowliest newcomer, made endless automatic computations of the Emperor's strength and fitness; the drive to mate, to produce offspring, to see his own line go on, was as strong in Noth as in any of the males here. Soon the Emperor would surely meet a challenge he could not withstand.

But for now, Noth was in no position to challenge the Emperor or any of the stronger males in the loose pecking order above him. And he could see that the supply of podocarp fruit was dwindling rapidly.

With a frustrated hoot he hurried over the forest floor and scampered briskly into a tree. The branches, slippery with residual frost, dew, and lichen, were all but bare of leaves and fruit. But it might still be possible to find caches of nuts or seeds, stashed away by providential forest creatures.

He came to a hollow in an aging tree trunk. In its dank, rotting interior, he saw the gleam of nutshells. He reached in with his small, agile hands and hauled out one of the nuts. The shell was round, seamless, complete. When he rattled it he could hear the kernel inside, and saliva spurted into his mouth. But when he bit into the shell his teeth slid over the smooth, hard surface. Irritated, he tried again.

There was an almighty hissing. He hooted, dropped the nut, and scuttled to a higher branch.

A creature the size of a large domestic cat came scrambling clumsily toward the nut cache. It raised its head to Noth and hissed again, showing a pink mouth with powerful upper and lower incisors. Satisfied that it had driven off the raider, it dug out one of its stored nuts and, with a clench of its powerful jaws, cracked the shell. Soon it was nibbling purposefully, widening the hole it had made. At last it reached the nut's kernel- Noth, tucked behind the tree trunk, was almost overwhelmed by the sudden sweet aroma- and fed noisily.

This ailuravus looked something like a rudimentary squirrel, with a mouselike face. It had a long bushy tail, the purpose of which was to slow its fall, parachute-like, every time it tumbled out of a tree, as it frequently did. Although it was clumsier than the notharctus as it moved about in the trees, lacking a primate's grasping hands and feet, it was more than big enough to have fought off Noth.

The ailuravus was one of the first rodents. That vast, enduring family had emerged a few million years earlier in Asia, and had since migrated around the world. This small encounter was a skirmish at the start of an epochal conflict for resources between the primates and the rodents.

And the rodents were already winning.

They were beating primates to the food, for one thing. Noth would have needed a nutcracker to eat hazelnuts or brazil nuts, and a millstone to process grains like wheat and barley. But the rodents, with their ferocious, ever-growing incisors, could break through the toughest nut and grain seed coats. Soon they would begin to consume the fruits of the best trees before they were even ripe.

Not only that, the rodents outbred the primates by a large factor. This ailu could produce several litters within a single year. Many of its young would fall to starvation, competition with their siblings, or predation by birds and carnivores. But it was enough that some should survive to continue the line, and for the ailu each of its young represented little investment- unlike the notharctus who bred just once a year and for whom the loss of a single pup was a significant disaster. And the rodents' vast litters incidentally offered up much raw material to the blind sculptors of natural selection; their evolutionary rate was ferocious.

Even though primates like Noth were much smarter than rodents like the ailu, his kind could not compete.

It wasn't just the plesiadapids that were becoming rare in North America. It was no coincidence that Noth's kind had been pushed up into this marginal polar forest. In the future Noth's line would migrate further, passing over the roof of the world to Europe and thence to Asia and Africa, adapting and reshaping as they went. But in North America the rodent victory would, within another few million years, be complete. A new ecology would arise, populated by gophers, squirrels, pack rats, marmots, field mice, and chipmunks. There would be no no primates in North America: none at all, not for another fifty-one million years, not until human hunters, very distant descendants of the notharctus, came walking over the Bering Strait from Asia. primates in North America: none at all, not for another fifty-one million years, not until human hunters, very distant descendants of the notharctus, came walking over the Bering Strait from Asia.

When the rodent was done feeding, Noth crept cautiously out of his hiding place. With his agile hands he sought out the scraps of kernel the ailu had dropped, and crammed them into his mouth without shame.

For a few hours a day the southern sky still grew bright. But the sun made its cycles beneath the horizon now. Almost all of the lakes were frozen over, and the trees were laden with frost, some of it gleaming in thick lacy shards where mist had frozen out on spiderwebs. The notharctus' movements through the trees and over the silent forest floor were sluggish and dull. But it didn't matter; the forest could offer them little more food this autumn.

There came a last clear day, when layers of red-tinged cloud stacked up against a violet southern sky, and the purple-green aurora rolled like a vast curtain over the stars.

The notharctus hurried to the ground and began to dig in places where the soil had been kept unfrozen by layers of leaves or under the roots of trees. Tonight would be the hardest frost of the winter so far, and they all knew it was time to get under cover. So the primates dug, building burrows in which Purga would have felt comfortable. It was as if the brief interval in the trees had been nothing but a dream of freedom.

In the deepest dark, Noth pushed his way through tunnels quickly worn smooth by the passage of primate bodies and over a floor littered with loose fur. At last his powerful nose guided him to Right.

Gently Noth sniffed his sister. She was already dormant, curled tightly up with her tail wrapped around her, close to the belly of Big. She had grown during their months with Biggest's troop, but Right would always be small, always retain traces of the runt who had been bullied by her now-dead twin. Still her winter fur seemed sleek, healthy, and free of knots and dirt, and her tail was fat with the store that should sustain her through the winter.

Noth felt a kind of satisfaction. Given their dreadful start to the summer, they had both beaten the survival odds better than expected. With no pups of his own, this was still the only kin Noth had- his entire genetic future depended on Right- but for now there was nothing more he could do for her.

In darkness, immersed in the scents and subtle noises of his kind, Noth snuggled as close as he could to his sister. He shut his eyes, and was soon asleep.

Briefly he dreamed, of fragments of summer light, of long shadows, of his mother's fall from the trees. And then, as his body shut down, his mind dissolved.

IV.

The sun's rays, almost horizontal, shone like searchlights into the forest. Above the slowly melting ponds a chill mist hovered, shining in elaborate pink-gray swirls, pointlessly beautiful. From the gaunt tree trunks immense black shadows stretched north. But the first leaves were budding on the bare branches, tiny green plates hanging almost vertically to catch the sun's light. The leaves were already at work: The days of spring and summer were so short that these hardy vegetable servants had to gather every droplet of light they could.

It was just a glimpse, a dawn that would last no more than a few minutes. But it was the first time for several months that the disk of the sun had shown.

The forest was quiet. The great herbivorous migrants were still hundreds of kilometers to the south; it was weeks yet before they would come back, seeking their summer feeding grounds, and even the birds had yet to arrive. But Noth was already awake, already out, working.

Fresh from his burrow he was gaunt, his tail flaccid and drained of fat. His fur, ragged and stained yellow by urine, hung around him in a cloud, lit up by the sun, making him look twice his true size. There was still little fodder to be had in the trees, so he had to scurry over the littered, frosty ground. After the winter's chill, it was as if nobody had ever lived here, and everywhere he moved he marked rocks and tree trunks with his musk.

All around him, in grim competition, the males of the troop were foraging. They were all adults: Even those born less than a year ago were approaching their full size, while relative veterans like the Emperor himself, approaching his third birthday, moved more stiffly than last year. After their winter of starving sleep, all of them looked sick, and the lingering cold bit hard through their loose fur and into their fat-deprived bodies.

There were risks in moving around so early. In the burrows, the females still slept, consuming the last of their winter stores. The predators were already active- and as food was still scarce, early-bird primates made a tempting target. If one of the males did find an unexpected cache of food he was quickly surrounded by snapping, jealous rivals, making the empty forest echo to their hoots and yips.

But Noth had no choice but to risk the cold. The days of breeding were approaching, a time of ferocious competition for the males. Noth's body knew that the sooner it laid down a store of strength and energy for the battles to come, the better chance he would have of finding a mate. He had to accept the risks.

Navigating with a blurred recollection of the landscape map he had built up last season, Noth made his way to the largest of the nearby lakes.

The lake was still mostly frozen, covered by a lid of gray ice littered with loose, hard-grained snow. A pair of ducklike birds, early immigrants, padded over the ice, pecking hopefully at its surface. Beneath the gray Noth could see the chill blue of older ice, a lens of deep-frozen material that had failed to melt through last summer, and would likewise fail to melt this year.

Close to the water's edge he passed a gray-white bundle. It was a mesonychid. Like the Arctic fox of later times, it endured the winter above ground. But in a sudden cold spell during the winter this meso had become lost in a blizzard, and, succumbing to exposure, had died, here at the shore of the lake. Its body had quickly frozen, and for now appeared perfectly preserved. But as it thawed the bacteria and insects had begun feasting: Noth could detect the sweet stench of decay. Saliva spurted into his mouth. The half-frozen meat would be good, and maggots were a salty treat. But his thirst outweighed his hunger.

Near the lake's shallow, muddy shore the ice was thin and cracked, and Noth could smell dank open water. The water was greenish, already full of life, and littered by grayish chunks of old ice cover. Noth dipped his muzzle into the water and drank, straining out the worst of the mucous slime between his teeth.

He could see that the open water bulged with clusters of small clear gray spheres: the spawn of the lake's amphibian inhabitants, laid down as early as possible. And closer by, in the shallows at his feet, Noth made out tiny wriggling black forms: the first tadpoles. He ran his hands through the water, letting the slime cling to his palms, and crammed the slippery harvest into his mouth.

With a flexing strain his bowels moved, and watery shit pooled beneath him.

But now the surface of the water broke, the ice cracking with sharp reports. Something huge was coming out of the lake. Noth scurried back to the cover of the nearest trees, eyes wide.

Like Noth, the crocodile had woken early, disturbed from its slumber by the brightness of the day. As it rose from the lake, bits of ice tumbled from its back. With a single graceful motion it clamped its jaws on the frozen meso: frost crackled, bones crunched. Then the croc slid backward into the water, dragging the carcass effortlessly, making barely a sound.

The crocodile was hungry.

Before the comet the largest animals in each of the world's ecologies had been reptilian: the plesiosaurs and ichthyosaurs in the oceans, the dinosaurs on land, and the crocodilians in fresh water. The disaster had wiped away these great families, and in their empty realms they would soon be replaced by functionally equivalent mammals- all save the crocodiles.

The freshwater environment had always been a difficult place to live. While the supply of plant material on land and in the sea was pretty reliable in space and time, freshwater environments were very variable. Erosion, abrasion, silting, flood, drought, and extremes of water quality were all hazards.

But the crocodiles- and other enduring freshwater species like turtles- were resilient. Some learned to walk overland in search of water. Others could take to the sea. Or they would just bury themselves eight or ten meters deep in the mud, and wait for the next cloudburst. And as for food, even during the worst of the killings on land and in the sea, they would subsist off the nutrients that continued to leach off the corpse-littered land, a "brown" food chain that persisted long after the green, growing things and the creatures that browsed them had died.

In this way the crocodiles had survived across a hundred and fifty million years, through extraterrestrial impacts, glaciation pulses, sea level changes, tectonic upheavals, and competition from successive dynasties of animals.

After all this time they were still capable of evolutionary novelty. Briefly, after the comet impact, the top predators around the water courses had been crocodile cousins with long legs and hooflike claws. They had been a nightmare, running predatory crocodiles capable of chasing down animals as large as small horses. Crocodiles had even adapted to survive here at the pole, where the sun didn't shine for months on end; they would simply wait out the winter months in deep hibernation.

Unlike the dinosaurs, unlike the plesiosaurs, the crocodiles would not be forced out of their freshwater niches by upstart mammals: not now, not ever.

Noth had lost the meso carcass, but some scraps of flesh and crushed maggots were smeared over the ground where it had lain. Hungrily he licked at the frozen ground.

At last the days of breeding arrived.

The females of the troop gathered in the branches of one tall conifer. They were feeding on ripe young fruit, cramming their bodies with the resources they would need to survive the drain of motherhood to come. The females were loosely marshaled by the more senior among them, including Big and Biggest. Right was among them. She had survived her first winter. She was filling out quickly, and when her scrappy winter fur had blown away she had emerged as a small but elegantly built adult, ready to mate.

The Emperor himself was among his female subjects. He moved from one to the other, heroically humping. Already he had been accepted by Biggest twice, and had deflowered an unprotesting Right. Now he was taking Big. She was bent over, clinging to a low branch, her head tucked between her knees, her tail uplifted. The Emperor was behind her, arms wrapped around her waist, hips thrusting with a rapidity born of exhaustion and urgency.

This was the day toward which the Emperor had worked all year, and now was the time for him to spend all of his authority and energy by covering as many of the females as possible.

But the Emperor was already tiring. And this female troop was only one of several in the wider territory he commanded.

In this ferociously seasonal place, baby rearing had to be squeezed into a drastically short period, so that offspring were produced when food was abundant and their new mothers could eat enough to produce plenty of milk. Any female who mated outside the breeding season was unlikely to see her offspring survive to adulthood. And any male who missed the chance to mate with a fertile female would have to endure a whole year of hardship, danger, and privation before getting another chance.

For the notharctus, the breeding season was just forty-eight hours forty-eight hours long. It was a frantic time. long. It was a frantic time.

Today, the start of the females' simultaneous estrus, the air was full of an invisible pheromone cloud, and there were males everywhere, helplessly drawn, erections poking out of their fur. Every male had prepared since the return of the sun, feeding to build up his strength, practicing spectacular tree swings and engaging in mock battles: They had been like athletes preparing for a contest. It was impossible for the Emperor to keep them all away, and there was intense competition. Today the hierarchy of males was stressed to the point of collapse.

The stress on the females would come later, during pregnancy and nursing, when the fast-growing fetus or newborn pup demanded the mother find a stream of high-energy food- and she must eat well at a time when almost every other adult female was nursing too. It was the heavy cost of reproduction that had led to the general dominance of females over males, and it was the reason why the females always got the best of the food.

It was the same all over the forest. Every notharctus troop was hitting its brief mating season simultaneously, the timing dictated by the invisible chemical scents that permeated the air for kilometers around. For today and tomorrow, the forest was filled with primate lust: a tremendous clamor of battling males, pheromone-laden females, and frantically thrusting hips.

Noth, pursuing another young male he thought of as Rival, hurled himself through a loose stand of conifers. He swung one-armed on spindly branches. On each dip the earth tipped up like a vast bowl, dead leaves and new green ferns and the dull forms of snuffling ground feeders fleeing under him.

He approached a gap between two tall trees. On the far side he saw Rival, standing upright, genitals pinkly visible, rubbing his scent markers on the bark. Rival barked a contemptuous challenge.

Without hesitating, Noth took a final huge swing. The branch flexed and hurled him on a smooth parabola high into the air. For a few heartbeats he flew, tail held high, hands and feet held out before him ready to grasp.

His head was filled with the stink of estrus. He had had an erection since he had woken this morning. Even now, as he sailed from tree to tree, his penis stuck out before him, pink and solid. He had yet to succeed in battling his way through the crowding males to get to a receptive female, and he felt as if his belly would burst if he didn't succeed soon. But even as he was consumed with inchoate lust, still he relished the power of his lithe body as he hurled it through the forest domain for which it was exquisitely adapted.

Noth had never felt so alive.

Noth landed in Rival's tree, just where he had aimed. He grasped the branches with faultless positioning of his hands and feet. But immediately Rival was on him.

Facing each other they stood upright, their spindly erections poking out. Noth, tail held erect, stalked toward Rival, vigorously rubbing his groin against the tree bark, chattering and barking. Rival responded in kind. It was a ritualized encounter, each of them responding to the other's movements in a kind of dance: tail waft followed by groin rub, wrist spread provoking a spitting glare.

Soon the air was filled with their angry stink. They came close enough for Noth to feel the tips of the other's bristling fur, and Rival's spittle sprayed his face.

Rival was about the same age as Noth, about the same size. He had joined the troop a little earlier than Noth and his sister. To him, Noth had invaded a troop that he had come to regard as "his." Noth and Rival were too similar, like brothers, too close to be anything but enemies.

Rival was marginally bigger and heavier than Noth, and if anything he had done better in the early-season feeding. But Noth's difficult year had forged an inner toughness, and he stood his ground.

Psychology won out. Rival subsided suddenly, his display collapsing. He turned his back on Noth and, briefly, symbolically, displayed his pink backside in a curt gesture of submission.

Noth hooted, relishing his moment. Briskly he rubbed his wrists over Rival's back, marking his victory with his scent, and released a stream of urine. Then he let Rival slink away along the branch toward a cluster of berries.

Rival would come to no harm. He would skulk alone in his tree for a time, perhaps feeding, withdrawing for a while from the fray. But his chances of mating were for a few hours reduced. Noth's urine would make him briefly sterile; it would even reduce his ability to make the special trilling calls used by the males to attract females.

For Noth it was a valid strategy. Today it was impossible for any male, however heroically he tried, to cover all the females. But he could reduce the number of competing males with such sensory intimidation.

With Rival defeated, Noth's penis throbbed anew; soon he would at last attain the satisfaction he craved. With fast, vigorous swings he hurled himself through the branches, across the forest toward the place the females clustered.

But he was not aware of the grim battle taking place there.

Still immersed in his females, the Emperor finished yet another mating. His penis raw and dangling, he stalked among the females, cuffing and snapping at any male he could reach.

And suddenly he found himself facing Solo.

The aging Emperor hauled himself upright, bared his teeth, and let his glands pump out still more of his potent musk. Hair bristling, muzzle working, he was a magnificent sight, enough to intimidate any other male.

Any but Solo.

Solo had spent a comfortable winter in a burrow with a female band not far from here. As soon as the light had returned he had joined in the early feeding, rapidly building his body to the peak of strength and power he had enjoyed last year.