Parents had to stick together, for the sake of their children: it was not monogamy, but it was close. Fathers had learned it was essential to stay around if their genetic inheritance was to go on to further generations. But women’s ovulation was concealed, and they were almost continually sexually receptive. It was a lure: If a man was going to invest in raising a kid, he needed to be confident the kid really was his — and if he didn’t know when his partner was fertile, the only way to ensure that was to stay around.

But it wasn’t all compulsion. Couples preferred sex in private — or as much as was possible in such a close, small community. Sex had become a social cement that bound couples together. Relentless Pleistocene selection was shaping everything that would make up humanity. Even love was a by-product of evolution. Love, and the pain of loss.

But the shaping was not complete. The desultory talk in this crude hut was not much more than gossip. Toolmaking, food gathering, and other activities were still walled off from consciousness, in compartmented, if roomy, minds. And they still groomed like apes.

They were not human.

Pebble felt irritable, restless, confined. Gruffly he grabbed a slice of rhino belly from Seal, who protested loudly: “Mine, mine!” Then he went to sit, alone, in the doorway, facing the sea.

Close by, he could see the scrubby land where the people cleared away weeds from peas and beans and yams. But beyond that, looking north and west, a sunset towered into the sky, its purple-pink light painting the planes of his face. It was a magnificent Ice Age sunset. The glaciers, scouring across the northern continents, had thrown vast amounts of dust into the air; the sun’s light was refracted through great clouds of ground-up rock.

Pebble felt stuck, like one of Seal’s little fish glued to his blobs of spiderweb.

Barely conscious of what he was doing, he felt around on the ground for a sliver of rock. When he had found one sharp enough he lifted it to his right arm — he had to look for a patch that wasn’t already scarred — and he pressed the stone to his flesh, relishing the delicious prickling pain.

He wished his father were here, so they could cut together. But the stone remained, the pain almost comforting as it pushed through his epidermis. He ran the stone blade down his arm, feeling the warmth of his own blood. He shuddered with the pain, but relished its cold certainty, knowing he could stop at any moment, yet knowing he would not.

Isolated, depressed, his life blocked, Pebble had turned in on himself, and a behavior that had once served to enable young men to compare their strength in a reasonably harmless way had become solitary and destructive. Pebble’s kind were not human. And yet they knew love, and loss — and addiction.

In the darkness behind him, his mother watched, her bone-hooded eyes clouded.

Pebble was woken in the gray of the predawn — but not by the light or the cold.

A tongue lapped at his bare foot. It was almost comforting, and it penetrated his uneasy dreams. Then he woke enough to wonder what was doing the licking. His eyes snapped open.

A shaggy, muscular wolf stood on all fours before him, silhouetted against the dawn sky.

He yelped and dragged his legs back. The wolf whined, startled. Then it scampered away a few paces, turned and growled.

But a person stood beside the wolf.

She was at least a handbreadth taller than he was. Her body was slender, her shoulders narrow, her long legs elegant, like a stork’s. She had narrow hips and shoulders, small high breasts, and a long neck. Her body was all stringy muscle: He could see the firm bulges of her arms and legs. She looked almost like a child, a great stretched-out child, her features unformed. But she was no child — he could tell that from the breasts, the thatches of hair under her arms, and from the fine lines that had gathered around her eyes and mouth.

The skinny folk on the island were just like this, from the neck down, anyhow. But from the neck up, Pebble had never seen anything like her.

Her chin stuck out into a kind of point. Her teeth were pale and regular — and unworn, like a child’s, as if she had never used them to treat animal skin. Her face seemed flattened, her nose small and squashed back. Her hair was frizzy and black but hacked short. And the ridge over her eyes — well, there was no ridge. Her brow rose smoothly and straight up, and then her skull swept back into a great bulging shape like a rock, quite different from the turtle-shell shape of his own cranium.

She was a human — anatomically, a fully modern human. She might have stepped out of a tunnel through time from Joan Useb’s chattering crowd in Darwin Airport. She could not have been a greater shock to heavy-browed Pebble if she had.

Her eyes flickered as she glanced from Pebble to the people — Hands, Cry, others — who had come out to see what was going on. She said something incomprehensible, and held out the harpoon at Pebble, point first.

Pebble stared, fascinated.

The harpoon’s shaft was notched at the end, and in the notch, attached by resin and sinew thread, there was a carved point. It was a slim cylinder, not more than a finger’s-width wide at the center. On one side fine barbs had been carved into the surface, pointing away from the direction in which the harpoon would be thrust. Its surface wasn’t roughly finished like his own tools; it looked smooth as skin.

Her harpoon wasn’t her only artifact, he saw now. She wore a scrap of some treated hide around her waist. A thing like a net, woven of vines, perhaps, was slung around her neck. Inside it nestled a collection of worked stones. They looked like flint. Flint was a fine stone, easy to shape, and he had encountered it several times during his trek out of Africa. But there was no flint to be found anywhere near this beach. So how had it got here? His confusion deepened.

But his attention was drawn back to that harpoon point. It was made of bone.

Pebble’s people used bits of broken bone as scrapers or as hammers to finish the fine edges of their stone tools, but they did not try to shape it. Bone was difficult stuff, awkward to handle, liable to split in ways you didn’t anticipate. He had never seen anything like this regularity, this finishing, this ingenuity.

In the future he would always associate her with this marvelous artifact. He would think of her as Harpoon. Unthinking, helplessly curious, he reached out with his long, broad fingers to touch the harpoon’s point.

“Ya!” The woman backed off, grasping the harpoon. At her side, the wolf bared its teeth and growled at him.

Tension immediately rose. Hands had picked up heavy cobbles from the beach.

Pebble raised his arms. “No no no…” He had to work hard, gesturing and jabbering, to persuade Hands not to hurl his stones. He wasn’t even sure why he did this. He ought to be joining Hands in driving her off. Strangers were nothing but trouble. But the dog, and the woman, had done him no harm.

And she was staring at his crotch.

He glanced down. An impressive erection thrust out. Suddenly he was aware of the pulse that beat in his throat, the hotness of his face, the moistness of his palms. Sex was a commonplace with Green or Cry, and it was usually pleasurable. But with this child-woman, with her flattened, ugly face and her harpoonlike body? If he were to lie on her, he would probably crush her.

But he had not felt like this since his first time, when Green had come to straddle him in the night.

The wolf growled. The woman, Harpoon, scratched the creature’s ruff. “Ya, ya,” she said gently. She was still looking at Pebble, her teeth showing. She was grinning at him.

Suddenly he felt ashamed, as if he were a boy who could not control his body. He turned and ran into the sea. When the water was deep enough to cover him he plunged forward face first. There, his mouth clamped closed, he grabbed at his erection and tugged it. He ejaculated quickly, the stringy white stuff looping in the water.