Evolution (25 page)

As the Tethys died there was a great drying, right across the belly of the world. Once there had been mangrove forests in the Sahara. Now a great belt of semiarid scrub spread around the old track of the Tethys, across North America, southern Eurasia, and northern Africa.

Meanwhile, the huge land bridge that had closed off the northern Atlantic, spanning from North America to northern Europe via Greenland and Britain, was being severed, and the Atlantic reached up to the Arctic Ocean. As the ancient east-west ocean passage was being closed, so a new channel from south to north was opening.

Thus ocean currents were reshaped.

The oceans were great reservoirs of energy, restless, unstable, mobile. And all the oceans were laced with currents, great invisible Niles that dwarfed any river on land. The currents were driven by the sun’s heat and the Earth’s rotation; the top few meters of the oceans stored as much energy as the whole of the atmosphere.

Now the huge equatorial currents that had once rolled around the Tethys belt were disrupted. But already the great flows that would dominate the widening Atlantic were in place: A precursor of the Gulf Stream flowed, a mighty river sixty kilometers across, running south to north with the force of three hundred Amazons.

But this change in circulation patterns would reconstruct the planet’s climate. For while equatorial currents promoted warming, north-south interpolar currents provoked a vast refrigeration.

To make matters worse, Antarctica had settled over the Earth’s southern pole. Now its great ice cap had begun to gather, for the first time in two hundred million years. Vast, cold circumpolar ocean currents gathered in the southern seas, feeding the great northward currents of the Atlantic.

It was a crucial change: the start of a mighty planetary cooling, a downturn of the graph, that would persist to human times and well beyond.

All over the planet, the old climate belts shrank toward the equator. Tropical vegetation types survived only in the equatorial latitudes. In the north, a new kind of ecology appeared, a temperate woodland of mixed conifers and deciduous trees. Vast swaths of it covered the northern lands, stretching across North America, Europe, and Asia from the tropic to the Arctic.

This climatic collapse triggered a new dying— what paleobiologists would later call the Great Cut. It was a drawn-out, multiple event. In the ocean the plankton population crashed repeatedly. Many species of gastropods and bivalves disappeared.

And on the land, after thirty million years of comfortable success, the mammals suffered their first mass extinction ever. Mammalian history was cut in half. The exotic assemblages of Noth’s times finally succumbed. But new, larger herbivores began to evolve, with heavy-duty ridged teeth able to cope with the new, coarser vegetation typical of seasonal woodland. By Roamer’s time the first proboscideans, properly equipped with trunks and tusks, were already walking the African plains. The trunk, unparalleled for muscular flexibility save for an octopus’s arm, was used for stuffing the animal’s mouth with the vast quantity of food it needed. These deinotheres had stubby trunks, and odd, downward-curving tusks that they used for stripping the bark from trees. But, unlike their moeritherium ancestors, they
looked
like elephants, and some already grew as tall as the African elephants of later times.

And this was a time of success for the horses. The descendants of the timid creatures of Noth’s forest world had diversified into many woodland browser types— some of them as large as gazelles, but with tougher teeth than their ancestors had had to take leaves rather than soft fruit— along with longer-legged plains animals slowly adapting to a diet of grass. Most of the horses now had three toes on both their front and back feet, but some plains-living runners were starting to lose their side toes, and were putting all their weight on their central toes. But as the forests shrank this diversity was already falling; soon many of the forest species would disappear. The rodents, too, were diversifying, with the appearance of the first gophers, beavers, dormice and hamsters, a great diversity of squirrels— and the first rats.

But the new conditions were not kind to the primates. Their natural habitat, the tropical forests, had shriveled back to the southern tropics. Many of the primate families had gone extinct. Fruit eaters like Roamer lingered only in the tropical woodlands of Africa and southern Asia, clinging to the year-long food supply these forests still provided. By the time Roamer was born there were no primates left north of the tropics, and— since the rise of the rodents— none in the Americas at all: not a single species.

But that was soon to change.

The sea around Roamer was a sheet of gunmetal gray across which waves rippled, languid as mercury. Roamer was in an utterly baffling place: a sketchy, elemental two-dimensional environment, static yet full of mysterious churning motion, that could not have been more different from the forest.

She felt nervous climbing around on top of the vegetation. She expected some ferocious aerial predator to bite into her skull at any moment. And as she moved she could feel the uneasy raft shift under her, its loosely tangled components rustling with the slow breathing of the sea. It felt as if the whole thing might disintegrate at any moment.

There were just six anthros: three males, two females— including Roamer— and the infant who still clung sleepily to the fur of its mother. These were the only survivors of Whiteblood’s troop.

The anthros sat on a tangle of branches, eyeing one another. It was time to form provisional hierarchies.

For the two females the priorities were clear enough.

The other female, the mother, was a burly individual more than a decade old. This child was her fourth and— though she could not know it— now her only surviving offspring. Her most noticeable characteristic was a fur-free patch of scar tissue on one shoulder where she had once been burned in a forest fire. The infant, clinging to Patch’s chest, was tiny, small even for its age, just a scrap of fur. Patch, the mother, studied Roamer dismissively. Roamer was small, young, and a stranger, not even remote kin. And, as a nursing mother, Patch would always have priority. So she turned her broad back on Roamer and began to stroke her infant, Scrap.

Roamer knew what she had to do. She scuttled over the branches to Patch, and dug her fingers into fur that was still moist and began to comb out tangles and bits of debris. When she probed at Patch’s skin, she found knots of muscle, and places which made Patch wince to be touched.

As Roamer’s strong fingers worked, Patch relaxed slowly. Patch, like all of them, had been battered by her precipitate removal from the forest, and was stressed by her sudden dumping into this extraordinary emptiness and the loss of her family. It was as if she could, for a moment, under the magic of the other’s touch, forget where she was. Even the infant, Scrap, seemed soothed by the contact between the two females.

Roamer herself was calmed by the simple, repetitive actions of the grooming, and by the subtle social bond she was building up with Patch.

The males’ negotiations were more dramatic.

Whiteblood found himself facing two younger males, brothers, in fact. One had a peculiar crest of snow-white hair that stuck up around his eyes, making him look permanently surprised, and the other had a habit of using his left arm predominantly over his right, so much so that the muscles on his left side were much more heavily developed than those on the right, like those of a left-handed tennis player.

Both Crest and Left were smaller and weaker than Whiteblood, and, younger, they had not outranked him back in the forest. But now Whiteblood had lost all of his allies, and together these two might defeat him.

So, without hesitation, he launched into a display. He stood upright, shakily, hooted and shrieked, and threw handfuls of leaves. Then he turned around, spread his backside and blew shit through moist fur.

Left was immediately intimidated. He shrank back, arms folded around himself.

Crest was more defiant, and answered Whiteblood’s display with a shrieking tantrum of his own. But he was outsized by Whiteblood and, without the support of his brother, could not hope to best the older male. When Whiteblood began to cuff him about the head and neck, Crest quickly backed down, tumbling onto his back and spreading his arms and legs like an infant, showing his submission. All of this was halted only when an incautious stamp plunged Whiteblood’s leg through the foliage and into the cold water. He yelped, pulled back his leg, and sat with legs folded beneath him, subdued.

But he had done enough. The brothers approached him now, their heads bent and postures humble. A brief interval of frantic mutual grooming ensured the new hierarchy was reinforced, and the three males started to pick bits of shit out of each other’s fur.

The rough-and-ready communities of Noth had been like street gangs, held together by not much more than brute force and dominance, with each individual aware of little more than her own place in the pecking order. But by now the advantages of social living had driven primate societies to baroque intricacy, and had spurred the development of new types of mind.

Group living required a lot of social knowledge: knowing who was doing what to whom, how your own actions fit in with this, who you had to groom and when, to make your life easier. The larger the group, the greater the number of relationships you had to keep track of, and as those relationships changed constantly, you needed still more computational capacity to handle it all. By allowing their group living to develop to such extremes of complexity, primates continued to get relentlessly smarter.

Not all primates, though.

Through all this the big potbelly had sat on the comfortable branch she had found, methodically stripping it of leaves. She had no interest in the peculiar displays and hairy fiddling of the anthros.

Even among her own kind the potbelly knew little of the society of others. She ignored other females and let herself be bothered by males only when she felt the urge to mate— which, in fact, was on her now. When they were in season anthros like Patch and Roamer showed sexual swellings on their rumps. That would have been of little use to a creature who spent most of her time sitting on her backside, so on the potbelly’s chest pinkish blisters had swollen brightly in an unmistakable hourglass shape. But as there was no male potbelly around, nobody was doing anything about it.

Not that the potbelly cared much. She didn’t understand where she was and what had become of her any more than the anthros did, but it didn’t trouble her. She could see there were plenty of leaves on this fallen tree to last her through the day. She had no real idea that there could be such a thing as a tomorrow different from today, that it might not find her in an endless forest full of nutritious leaves.

Already the anthros were starting to feel hungry; their low-nutrition diet worked through their systems quickly. They broke up their grooming circles and spread out over the branches of the fallen mango. The tree had lost much of its fruit, along with most of its inhabitants, when it fell from the bank. But Crest, one of the brothers, quickly turned up a cluster of fruit that had gotten lodged in an angle of branch and trunk. He hooted to summon the others.

The new miniature society worked efficiently. Though Crest managed to grab one piece of fruit for himself, he was quickly pushed away by Whiteblood. But Whiteblood was in turn usurped by Patch. Though she was not much more than two-thirds of Whiteblood’s size, the infant clinging to her chest was like a badge of authority. Whiteblood took one fruit and, grumbling, moved back, giving way to Patch.

While this was going on Roamer, like the brothers, knew that she would get no nearer to the fruit until the dominant ones had taken what they wanted.

Alone, she walked carefully, all four limbs grasping, toward the edge of the raft, where the tangle of branches was a little looser. The two terrified crowders, huddled together, skittered away as she approached. Through the foliage she could see murky brown water, littered with bits of wood and leaf, rippling languidly. The sun glimmered in a hundred places, shining through gaps in the cover of the fallen tree, and the dancing light was entrancing, distracting.

Roamer was hungry, but she was also thirsty. She dipped her hand cautiously into the water— it was cool— and scooped up a mouthful. The water was mildly salty— not bitterly so, for even so far from land the river’s powerful outflow diluted the ocean’s brine. But as she drank the taste of salt began to build up in her mouth, and she spat out her last mouthful.

Hungry, bored, the brothers came to inspect her as she drank, head bent down into the foliage, arm outstretched, buttocks raised. They sniffed her curiously, but they could smell how young she was, too young to mate.

When the older ones were done, Roamer and the others fell on the fruit.

With their bellies full for now, the anthros were calming down. But already the haphazard raft had drifted out of sight of the land, already the anthros had eaten much of the fruit from the drowned mango tree. And already the potbelly, complacently munching, had stripped half the branches of their leaves.

And none of them had seen the pale gray triangle that slid silently through the water, not meters away.

The shark circled the crude, disintegrating raft. Alerted by the feeding frenzy as the drowned inhabitants of the riverbank forest were washed out to the waiting mouths of the ocean, the shark had been attracted by the scent of stale blood that leaked from the indricothere carcass. But now it sensed motion on the tangled foliage that floated overhead. It circled, calculating, patient.

The shark was not as intelligent as its parallels on land. But then it was not much like an animal at all. The bones of its back were not bone, but tough cartilage that gave the shark better flexibility than more advanced fish. Its jaw was cartilage too, in which were loosely attached teeth, serrated like steak knives, perfect for shearing flesh. Its projecting snout looked crude, but it cut through the water with the precision of a submarine’s engineering, and it was equipped with nostrils that could detect minute traces of blood. Beneath the snout was a special organ with extraordinary sensitivity to vibration, enabling it to sense the struggles of a frightened animal across immense distances. Behind its small head, the shark’s entire body was made of muscle, designed for power, for forward drive. It was like a battering ram.