It was a question of the DNA. As time had worn away, the molecular software that controlled the development of creatures had itself evolved, becoming tighter, more robust, more controlled. It was as if each genome had been redrafted over and over, each time junk and defects were combed out, each time the coherence of the whole was improved- but each time the possibility for major change was reduced. Extraordinarily ancient, made conservative by the inward-looking complexity of the genomes themselves, life was no longer capable of a great innovation. Even DNA had grown old.

This epochal failure to innovate was an opportunity lost. And life could not take many more hammer blows.

The light in the sky was strange. But, Remembrance's instinctive calculus quickly computed, it was no threat. In this she was wrong. Purga, who had watched the Devil's Tail similarly slide silently overhead, might have told her that.

Before the sun had touched the horizon she at last reached her forest in the lee of the volcanic hills, her target for many days. Remembrance peered up at the tall trees before her, the canopy that strained up toward the sky. She thought she saw slim shapes climbing there, and perhaps those dull clots of darkness were nests.

They were not her people. But they were people, and perhaps they would be like her.

She pulled herself off the ground and clambered upward into the comforting green of the canopy.

Something fluttered past her head. It was a flying fish, coming from the sea. As she watched, it sailed into the forest canopy, flapping its fin-wings earnestly, and settled clumsily onto a nest, air wheezing into primitive lungs.

CHAPTER 19.

A Far Distant Futurity Montana, Central New Pangaea. Circa 500 million years after present.

I.

Ultimate dug listlessly in the dirt, hoping to find a scorpion or beetle. She was a mound of orange-colored fur on the rust-tinged ground.

This was a flat, dry plain of crimson red rock and sand. It was as if the land had been scraped bare by some vast blade, and the bedrock wind-burnished to a copper sheen. Once there had been mountains to the west, purple-gray cones bringing relief to eyes wearied by flatness. But long ago the wind had torn all the mountains down, leaving great fans of scattered rocks over the plains, rocks that had themselves eroded to dust, leaving no trace.

Half a billion years after the death of the last true human, a new supercontinent had assembled itself. Dominated by desert, as red as the ancient heart of Australia, it was like a vast shield fixed to the blue face of the Earth. On this New Pangaea, there were no barriers, no lakes or mountain ranges. Nowadays it didn't matter where you went, from pole to equator, from east to west. Everywhere was the same. And there was dust everywhere. Even the air was full of red dust, suspended there by the habitual sandstorms, making the sky a butterscotch-colored dome. It was more like Mars than Earth.

But the sun was a ferocious disk, pumping out heat and light, much brighter than in the past. Any human observer would have cowered from that great fire in the sky.

Under that tremendous glare the heat lay heavy on the land, by day and by night. There was no sound save for the wind and the scratching of the few living things, no sense that things had ever been different on this red planet. The land felt felt empty, a huge place of resonant silence, a stage from which the actors had departed. empty, a huge place of resonant silence, a stage from which the actors had departed.

As it happened, far beneath the dust where Ultimate dug- buried under half a billion years of deposits, under the salt and the sandstone of New Pangaea- was the place that had been known as Montana. Ultimate was not far above Hell Creek, where the bones of Joan Useb's mother had at last joined those of dinosaurs and archaic mammals in the strata she had searched so assiduously.

Ultimate had no way of knowing her peculiar place in history, still less of understanding. But she was among the last of her kind.

Ultimate went home. Home was a pit carved in the harder rock. It offered some shelter from the wind. This was where Ultimate and her kind eked out their lives.

The pit looked artificial. Its floor was smooth, its terraced walls steep. The pit was in fact a quarry, made half a billion years earlier by human beings, dug deep into the bedrock. Even after all this time, even as mountains had come and gone, the quarry had survived almost intact, a mute memorial to the workings of man.

Trees grew on the floor of the pit, standing stately and alone, like sentinels, with their satellite termite colonies towering all around. They were stubby, ugly trees with perennial needlelike leaves, defiant of time. Little else lived here save the people, and other symbiotes of the trees, and many, many tiny creatures that toiled in the dust.

As Ultimate clambered down the pit's walls, the wind changed and began to blow from the west, from the direction of the inland ocean. Gradually the humidity rose. At last, over the ruined mountains to the west, heavy black clouds began to gather.

Ultimate peered into the western sky. It had never rained here, in Ultimate's lifetime. Most clouds coming from the distant ocean dumped their rainfall long before they reached a place like this, deep in the supercontinent's interior. It took a mighty storm indeed to breach those immense defenses of arid plain, a once-in-a-lifetime monster. But that was what was approaching now. You could feel it in the air, feel that something was wrong.

The people hurried back to their Tree, and clambered into its welcoming branches. Hurried, yes- but still they moved with a languid slowness, as if they were swimming through the air's dense heat.

At ten years old, Ultimate looked something like a small monkey. She was long-limbed, with a narrow torso, narrow shoulders: Even now, in these distant descendants of mankind, the basic body plan of the primates persisted. Her slim body was coated in thick fur, bright red, red as the sand. She had a small head with a large brow and a mobile, expressive face- a very human face, in fact. Small flaps of skin, rather like eyelids, could cover her ears, nose, anus, vagina to trap precious moisture. Her brow was swollen, almost as if her kind had re-evolved the big forebrains of the human age, but behind that brow there was only spongy bone, a great system of sinuses that worked as a refrigeration system to keep her brain cool.

And, though she was fully grown, her body was childlike. Ultimate was functionally female- people still gave birth- but there were no males any more, and gender was meaningless. She had no breasts, not even vestigial nipples. Nowadays there was no need for mother's milk, just as there was no need for the elaborate superstructure of a large brain. The Tree took care of all of that for you.

And she was not bipedal. That was obvious as she made her way back to the Tree: her arms and legs were made for swinging and climbing, her feet for grasping, not walking upright. That particular locomotive experiment had been thoroughly buried long ago. Compared to her ancestors, she was slow-moving, lethargic, like all her kind.

At the Tree, Ultimate looked for her daughter.

The infant's leafy cocoon nestled in the crook of a low branch. Threads of orange hair littered over her swollen brow, the little girl was safely enfolded in soft white down. As the Tree's sap passed along the pale thread of the belly-root that wormed into her stomach, the child stirred and murmured, her tiny thumb clamped firmly in her mouth, dreaming vegetable dreams.

Something was wrong. Ultimate was not capable of much in the way of analysis, but her instinct was unmistakable. She prodded at the tangled red fur on the child's little belly, and smoothed out the fluffy cottonlike lining of the cocoon. The little girl mewled, turning blindly in her sleep. Nothing Ultimate did made that feeling of wrongness go away. Uncertain, she patted the walls of the cocoon back into place.

The wind rose, like a great breath.

Ultimate clambered higher into the Tree's welcoming branches. Hastily she pulled her own cocoon into place around her body, sealing up the leaves. The leaves were thick and tough, like plates of leathery armor. The others were doing the same, people huddling on the branches, so that it looked as if the Tree were suddenly sprouting huge black fruits.

The clouds streamed overhead, blotting out the intense heat of a too hot sun. Ultimate stared. Curiosity wasn't much use now, when there was so little difference in the world across great stretches of time and space. But today was was different. She had never felt air as moist and heavy and oppressive as this, never seen black clouds that boiled and bubbled like that. different. She had never felt air as moist and heavy and oppressive as this, never seen black clouds that boiled and bubbled like that.

And in the last moment before the storm hit, she glimpsed something new.

Settled on the timeworn plain, it was a sphere. It was twice as tall as she was. It was not blue like the evening sky, nor rust red like the ground, nor the color of sand and dirt like most of the creatures in the world. Instead, it was a shimmering mixture of purple and black, the colors of the night.

On this day of strangeness, here was something extraordinary. She gaped, unable to comprehend. But she sensed that this new thing was not of her world. In that she was right.

But now lightning cracked, and she buried her face in the green, mewling. The leaves closed around her, sealing themselves up seamlessly. In the warm darkness the air grew moist and comforting. But when the belly-root came probing for the valvelike orifice on her stomach, just below her navel, she pushed it away. She was here for shelter; she had nothing to give the Tree today.

And then the storm hit.

Wind and dust came out of the west like a red wall. Dried plants were shattered. Even the scattered, stately Trees were shaken, branches ripped away. People and other symbiotes were wrenched from their cocoons, utterly terrified.

The first few raindrops, landing like bullets, heralded an immense downpour. The rain was so heavy it even began to erode the rock-hard surfaces of the ancient termite mounds. There was nothing to absorb the water, no grass to consolidate the loose soil. Within minutes water was running down every dried-out gully and streambed. A great muddy wave came cascading into the quarry. The water seethed around the roots of the trees, turbulent, tinged red by mud.

But the rain dissipated as quickly as it had begun. The clouds cleared, racing deeper into the heart of the supercontinent. The flood quickly subsided, sinking into the parched sand.

There hadn't been such a storm since Ultimate's mother had first opened her eyes. Nothing in Ultimate's experience had prepared her for such a catastrophic downpour. But the Tree, in its slow vegetable way, understood.

Even as Ultimate cowered, shocked, in her cocoon, she felt the leathery skin pulse around her. She longed to stay here in the moist dark rather than face whatever lay beyond these enclosing walls. But she was made to feel uneasy, restless. The Tree wanted her to leave, to go to work.

She set her back against the cocoon wall and pushed. The leaves came free of one another with a moist, sucking noise. She tumbled out of the Tree, and landed in mud.

All around her people were falling out of the Tree. They took experimental steps and knuckle-walks. The mud felt strange: It was heavy, clinging, crimson stuff that stuck to their legs and feet and hands.

The ferocious sun was shining once more, and the mud was already drying, the water escaping into the air, the ground baking hard. But for these rare minutes the ground was a cacophonous swarm of noise and motion. With visible speed, tendrils, leaves, and even flowers were pushing out of the mud. They had come from seeds that had lain dormant for a century. Soon sacs began to pop. Like tiny artillery pieces, they shot new seeds through the air. Entire reproductive cycles were being completed in minutes.

Insects emerged from their own encysted hiding places to dance and mate over the transient pools. On the ground there were more insects- ants, scorpions, cockroaches, beetles, and their much morphed descendant species. Many of the ants were leaf eaters, and Ultimate could see great chains of them trooping back and forth from the burgeoning plants bearing bits of greenery for their nests.

And there were many, many small lizards. They were hard to see, so well did their reddish skin match the color of the ground. Everywhere they hunted. Some of them had no smarter strategy than to sit with their mouths open by the ant columns, waiting for clumsy insects to stumble in.

One small, sturdy cactuslike plant, a ball of leathery skin and defensive spikes, dragged its upper roots from the soil, abandoning a deep, extensive root system. On roots that quivered like clumsy legs, it tottered toward the still-running water. When it got there, the walking plant subsided into the mud, as if with a sigh. Immediately the inefficient vegetable muscles that had powered its short journey began to dissolve, and new roots began to work their way into the moist ground.

All over the pit people were feeding on the sudden plants, reptiles, amphibians, insects. They were mostly adults: Children were rare in these straitened times; the Tree saw to that.

Ultimate, a rainstorm virgin, stared at all this, gaping.

A froglike creature erupted from the ground. It hopped and stumbled to the nearest of the temporary ponds, where it leapt into the water and began to croak noisily, guiding the emerging females who followed to it. Soon the pond was a splashing frenzy of amphibian mating. Ultimate grabbed one of the frogs. It was like a slimy sac of water. She popped it into her mouth. Briefly she felt its coldness, its heart hammering against her tongue, as if in disappointment that its century-long wait in a cocoon of hardened mud was going to end in such ignominy. Then she bit down, and delicious water and salty blood gushed into her mouth.

But already the pools were drying, the water hissing into the parched earth. The frogs' spawn had hatched, and tadpoles, fast metamorphosing, were feeding on algae, tiny shrimps, and each other. They swarmed out of the water after their parents- and were snapped up by a mass of tiny lizards in a quivering feeding frenzy. But already the young frogs were digging their way into the mud, constructing for themselves mucus-lined chambers in which they would wait out the decades until the next storm, their skins hardened, their shriveled metabolisms slowing into suspended animation.

People were stumbling away from the feeding grounds now. Some were carrying the heavy seeds of the Tree, huge pods as large as their own heads. Like the frogs, this strange day was the Tree's once-a-century opportunity to have the seeds of its next generation buried for it by its armies of symbiotes.

Ultimate saw Cactus chasing a small, scuttling lizard with a plump tail full of stored fat.

Cactus had been born about the same time as Ultimate, and as they had grown up they had learned about the world together, sharing, competing, fighting. Cactus was small and round. This was unusual for her people, who were generally skinny and long limbed, the better to lose their body's heat- and she was prickly tempered, indeed like a cactus. Cactus was a kind of companion, even a sister, but she wasn't Ultimate's friend. You had to be able to see somebody else's point of view to call them a friend, and that ability had long been given up. People didn't have friends these days- no friends apart from the Tree.

Ultimate wanted to follow Cactus, but she was distracted. Suddenly she longed for salt. That was the Tree's message to her, imprinted in the organic chemistry it had fed her while in the cocoon. The Tree needed salt. The Tree needed salt. And it was up to her to find it. She remembered where a salt bed was, a few hundred meters away. She was helplessly drawn that way. And it was up to her to find it. She remembered where a salt bed was, a few hundred meters away. She was helplessly drawn that way.

But in that direction stood the sphere, that enigmatic ball of black and purple that lowered silently over the teeming landscape.

She hesitated, caught between conflicting impulses. She knew the sphere was wrong. wrong. The great tide of human intelligence had long withdrawn, but the people had retained a good understanding of the land, its geography, and resources: efficient foraging was an essential skill if you were to find food and water in this desperately arid landscape. So she understood very well that the sphere shouldn't be here. But that was the way to the salt. The great tide of human intelligence had long withdrawn, but the people had retained a good understanding of the land, its geography, and resources: efficient foraging was an essential skill if you were to find food and water in this desperately arid landscape. So she understood very well that the sphere shouldn't be here. But that was the way to the salt.

Despite her unease, she set off.

The salt lick was almost at the foot of the sphere. She saw how mud had lapped up against its oddly gleaming surface. She tried to ignore the sphere, and began to scrabble in the sticky dirt.

There was no shortage of salt. A hundred million years ago, as the continents had danced toward their spontaneous assembly of this New Pangaea, a great inland sea had formed over much of North America. It had become landlocked, leaving only scattered lakes of brine. But that vanishing sea had left behind a vast bed of salt deposits, a shining plain that had stretched for hundreds of kilometers. The salt bed had been covered by debris washed down from the ruins of the fast-eroding mountains, and now lay buried under meters of rust-red sand, but it was still there.

Before long she had made a hole as deep as her arm could reach, and she was bringing up handfuls of dirt laced with gray-white salt. She chewed on the dirt, letting the salt crystals melt in her mouth, and spitting out the sand. With the salt in her belly, stored for later transmission to the Tree, Ultimate was released from her compulsion.

And again she became aware of the sphere. It had moved from where she had first seen it. And it hovered above the ground; a finger's-width of light could be seen beneath it.

She approached the sphere, walking on her hind feet and her knuckles, a dim curiosity alight in her eyes. Her fear wasn't strong. There were few novelties in her desert world. But likewise there were few threats. In a landscape like a tabletop, predators had a difficult time sneaking up on even the slowest and dullest of victims.

With a tentative fingertip she stroked the sphere's surface. It was neither warm nor cold. It was smooth, smooth, smoother than anything she had felt before. The hairs on her hand prickled, as if charged. And she could smell something, a smell like the quintessence of the desert itself, an electric smell of scorching, of burning, of dryness. smoother than anything she had felt before. The hairs on her hand prickled, as if charged. And she could smell something, a smell like the quintessence of the desert itself, an electric smell of scorching, of burning, of dryness.

The burnt-metal smell was in fact the result of exposure to hard vacuum: a legacy of space.

Their foraging done, one by one the people returned to the Tree, climbed into its branches, and folded themselves securely inside its leaves.

Ultimate pulled leathery leaves around her body. The belly-root snaked out quickly, probing for the valve on her stomach, and nestled into her like a reattached umbilical. As her salt-laden fluids began to circulate into the Tree, so Ultimate was rewarded by a soothing sense of security, of peace, of rightness. This mood was induced by chemicals leaked into her body as she exchanged blood for Tree sap, but it was no less comforting for that. This was her immediate reward for feeding the Tree, just as her longer-term reward was life itself. The Tree did not take without giving. Posthuman and Tree were neither of them parasites on the other. This was a true symbiosis.

But there was something wrong. Ultimate felt uneasy, wordlessly disturbed.

Even though the warm sap filled her head with green sleepiness, she kept thinking of how the child had been lying in her cocoon, her thumb in her mouth, the belly-root curled before her. Something had been wrong. Something had been wrong. Every instinct told her so. Every instinct told her so.

The sap pulsed harder into her gut, and soporific chemicals washed through her. This drastic injection meant the Tree wanted her to stay here, where she was, safe in her cocoon. But still that nagging sense of wrongness pulled at her.

She pulled the belly-root out of her stomach, and pushed hard with her shoulder and legs. The cocoon popped open, and she tumbled to the ground.

Briefly she was overwhelmed by light and warmth. Though the day was still bright the sun was low. Inside the cocoon, time swam at a different pace from the world outside- a pace chosen by the Tree. But the ground was hard and dust-strewn. Save for a few raindrop stipples, it was as if the storm had never been.

Nobody was around. All the cocoons were closed- all but one. Cactus was gazing down at her, her small head protruding from her own half-sealed cocoon. With a look of playfulness, Cactus pushed her way out of her enclosing leaves and tumbled easily to the ground beside Ultimate.

Ultimate's sense of anxiety was still growing.

She hurried around the base of the Tree to find her baby's cocoon in the crook of the low branch. But it was sealed tight, and would not yield when she tried to open it. As if this were a game, Cactus joined her. The two of them dug their fingers into the seams between the sealed-up leaves, straining and pushing and grunting.

Once it would have occurred to a person to use a tool to open this pod. Not anymore. Toolmaking was gone, all the artifacts of man had long since rotted away save for a few pithecine nodules buried in lost strata. And Ultimate and Cactus weren't even very good at solving unusual problems, for in their flat world they encountered few novelties.

At last, however, the cocoon opened with a pop.

Here was Ultimate's baby, still swaddled in the white cottonlike material of the cocoon's interior. But, Ultimate saw immediately, the cottony stuff had grown thicker. It had closed around the baby's face, and tendrils of it were pushing into her mouth, nose, eyes, and ears.

Cactus flinched, an expression of revulsion on her face.

Both of them knew what this meant. They had seen it before. The Tree was killing Ultimate's baby.

A new Pangaea.

A hundred million years after Remembrance had gone to her unmarked grave, the Americas had begun to slide east once more. As the Atlantic closed, so Africa drifted north of the equator, in the process pushing Eurasia further north still. Meanwhile Antarctica sailed north to collide with Australia, and that new assemblage began to push into east Eurasia. So a new supercontinent had been born. Africa was the central plain of the new assemblage, with the Americas pressing to the west, Eurasia to the north, Australia and Antarctica to the east and south. In the interior, far from the mediating effect of oceans, severe conditions took hold- ferociously hot and arid summers, killingly cold winters.

All barriers to movement had been eliminated. There was a brutal free-for-all as plants and animals migrated in all directions. It was a chilling parallel to the great global mixing that humans had forced during their few thousand years of dominance of the planet- and, just as it had been before, a world united was a world reduced. There had been a rapid pulse of extinctions.

And as time wore away, things got worse.

The new supercontinent immediately began to age. The great tectonic collisions had thrown up new mountains, and as they eroded, their debris enriched the plains with chemical nutrients like phosphorus. But now there were no new mountain-building events, no new uplift. The last mountains wore away. Rainwater and groundwater, percolating through the soil, leached out the last nutrients- and when they were gone there was nothing to replace them.

New red sandstones were laid down, rust red, red as the lifeless Martian deserts had been- the signature of lifelessness, of erosion and wind, heat and cold. The supercontinent became a great crimson plain spanning thousands of kilometers and marked only by the worn stumps of the last mountains.

Meanwhile the reduction in sea levels exposed shallow continental shelves. As they dried out they quickly began to weather, drawing oxygen out of the air. On land many animals simply suffocated to death. And in the oceans, as the pole-to-equator temperature gradient flattened out, the circulation of the ocean slowed. The waters stagnated.

On land, in the sea, species fell away like leaves from an autumn tree.

In a desiccating world the familiar games of competition, of predator and prey, were not so effective anymore. The world didn't have the energy to sustain great complex food webs and pyramids.

Instead, life had fallen back on much more ancient strategies.

Sharing was as old as life itself. Even the cells of Ultimate's body were the result of mergers of more primitive forms. The most ancient bacteria had been simple creatures, living off the sulfur and heat of hellish early Earth. For them the emergence of cyanobacteria- the first photosynthesizers, which used sunlight to turn carbon dioxide into carbohydrates and oxygen- was a disaster, for reactive oxygen was a lethal poison.

The survivors won by cooperating. A sulfur eater merged with another primitive form, a free-living swimmer. Later an oxygen-breathing bacterium was incorporated into the mix. The three-part entity- swimmer, sulfur-lover, oxygen breather- became capable of reproduction by cell division and could engulf food particles. In a fourth absorption some of the growing complexes engulfed bright green photosynthetic bacteria. The result was swimming green algae, the ancestors of all plant cells. And so on.

Throughout the evolution of life there had been more sharing, even of genetic material. Human beings themselves- and their descendants, including Ultimate- were like colonies of cooperative beings, from the helpful bacteria in their guts which processed foods, to the mitochondria absorbed eons ago that powered their very cells.