But more of the hunters came boiling out of the cover of the rock bluffs and trees. Men and women together, all armed with spears and axes; they were dirt-crusted, lean, hard-eyed. They had come hunting Pebble and his group, as if they were a herd of unwary antelope.

Pebble could see desperation in the eyes of the others. These newcomers were not nomads, not invaders by instinct, any more than Pebble’s people would have been. Only a dire catastrophe of their own could have forced them to this plight, to make them come into a new and strange land, to wage this sudden war. But now that they were here, they would fight to the death, for they had no choice.

There was a howl. The hunter who had taken on his uncle was standing now. One arm dangled, bloody and broken. But he was grinning, his mouth a mass of blood and broken teeth. Pebble’s uncle lay at his feet, his chest split open.

Already Pebble’s folk had lost two of their three adult men, Flatnose and his brother. They had no chance of resisting.

The survivors ran. There was no time to grab anything, no tools or food — not even the children. And the hunters fell on them as they fled, using the butts of their spears to fell and disable. The third man was cut down. The hunters caught two of the women, and the girl younger than Pebble. The women were thrown to the ground, face first, and the young men pulled their legs apart, jostling for the right to be first.

The others ran, on and on, until the pursuers gave up.

Pebble looked back the way they had come. The hunters were pawing through the settlement, the ground that had been Pebble’s ancestors’ for time out of memory.

There were five of them left from the village, Pebble realized. Two women, including his mother, Pebble himself and a smaller girl, and one of the infants — not Pebble’s sister. Just five.

Her face hard, Dust turned to Pebble. She laid a hand on his shoulder. “Man,” she said gravely. “You.”

It was true, he saw with horror. He was the oldest male left: of the five, only the squalling infant in the dirt at his feet was male.

Dust scooped up the motherless infant and held him close. Then she turned resolutely away from her settlement and began to stomp away to the north, her lame gait leaving uneven tracks in the dirt. She didn’t look back, not once.

Bewildered, terrified, Pebble followed.

The Pleistocene, this era of ice, was an age of brutal climatic turbulence. Droughts and floods and storms were commonplace: in this age a “once-in-a-century” climatic disaster came around every decade. It was a time of intense variations, a noisy time.

This created an environment that was intensely challenging for all the animals who inhabited it. To cope with the changes many creatures got smarter — not just hominids, but carnivores, ungulates, and others. The average mammalian brain size would double across the two million years of the Pleistocene.

The great family of hominid species to which Pebble belonged had been born in Africa, as had so many others, far to the south of here. Smarter, stronger than Far’s folk, they had pushed in a great arc out of Africa into Europe, south of the ice, and into Asia, as far as India. They had adapted their technology, their ways, and, over enough time, even their bodies to the disparate conditions they encountered.

And they had displaced the older forms of people. Elegant, skinny walkers like Far still survived in eastern Asia, but they clung on in Africa only in pockets. In Europe they were extinct altogether. As for the pithecine types, the last of them had succumbed long ago, squeezed out between the chimps and the new savannah folk. Still, the hominid range was narrow. There were still no people in the cold northern lands, none in Australia, and none in the Americas, none at all. But the Old World felt ever more full of them.

Meanwhile the land was growing poorer.

Once more there had been extinctions. And this time the people had had a lot to do with it. Under climate pressure, many of the larger, slow-breeding species of animals had found themselves increasingly tied to the water sources. They therefore became an easier target for increasingly clever hominid hunters, who, looking for the lowest-risk kills, selectively picked off the old, the weak — and, crucially, the very young.

The largest and least versatile species had been taken out first. In Africa, of the wide and ancient elephantid family, only the true elephants remained. Many varieties of giraffe, pig, and hippo had followed.

And then there was fire.

The harnessing of fire, not so many generations before Pebble’s time, had been one of the most significant events in hominid evolution. Fire offered many advantages: warmth, light, protection from carnivores. It could be used to harden wood, and its heat could be used to make many plant and animal foods digestible. There was still no organized large-scale firing and ground clearing; that would come later. But already the daily use of fire had had, little by little, a profound impact on the vegetation, as those plants able to withstand fire were favored at the expense of less hardy cousins. And meanwhile, though true agriculture lay far in the future, hominids had begun to select those plant species they favored for their own purposes — just as Pebble had cleared grass from the yam stand.

Such small actions, repeated every day across hundreds of thousands of years, had an immense impact. Once the landscape had been shaped by the trampling of elephants: Far and her kind had been marginal. Not so now. This landscape had been made by people.

By now it was as if this bare landscape of fire-resistant trees and sparse grass-eaters were somehow natural, and had been here forever, for all time. It had been this way so long that no mind on Earth could remember how things might have been different.

Seal had caught a spider on the beach. He scampered over the sand and brought it to Pebble, grinning. “Spider web spider fish.” Pebble tapped Seal on the head, warming to his infectious energy, and wishing he shared some of it.

Seal ran back to the clump of dune grass where he had found the spider. The web was built on a fan of strong radial lines, over which the spider had laid a spiral of continuous sticky web. Now — delicately, delicately, holding a small stick in his wide fingers — the boy lifted the spiral off its nonsticky guide ropes. He moved the rod spoke by spoke, twirling it so that the sticky stuff formed a dangling mass at the end of the rod. Then he hurried to a tidal pool, sheltered by lumpy, eroded rocks. He put his stick in the water, letting the sticky mass dance on the water’s surface.

A tiny fish came to nibble the enticing lure. But with every bite its jaws got stuck more firmly in the web. At last it was glued to the stick and was easily scooped out of the water. Seal popped it straight into his mouth with a grin of triumph. Then he dipped his makeshift rod into the dead spider’s glue sac and settled it back into the water.

Seal, brought out of the abandoned settlement in the arms of Dust eleven years back, was twelve years old now — seven years younger than Pebble himself. His early years had been quite different from Pebble’s: They had been years on the move. But Seal didn’t seem disturbed by his experiences. Perhaps he had got used to migrating, like one of the big grass-chewers that followed the seasons. And he had taken to the ocean. He was too heavy to swim — they all were — but whenever Pebble saw him in the shallow water close to the shore, he was reminded of a playful mammal of the sea.

But, eleven years after the trauma of the attack that had killed his father, Pebble had nothing in common with Seal’s inventive playfulness.

At nineteen Pebble was fully mature, his frame as squat and powerful as his father’s had been. But he was battered. His body bore old scars from ferocious, desperate hunting incidents. In a collision with a wild horse he had suffered a cracked rib that had never healed properly, and for the rest of his life he would suffer a diffuse pain every time he took a breath. And he bore the marks of wounds inflicted by people; too often he had had to fight.