As long as they met the basic constraint of numbers, even in this sparse landscape at the edge of the habitable world, Rood’s people ate well, enjoyed much leisure and, with their nonhierarchical, respectful society, were granted great health in body and mind. Rood inhabited a boggy, half-frozen Eden — even if a price had to be paid in countless small lives snuffed out in the cold and regretful dark.

But none of this grim calculus applied to Millo and Jahna.

They had both arrived at a time when their parents had been able to cope with supporting them. They had survived the hazards of early childhood. They were growing healthy and intelligent. Jahna had even been approaching her menarche, so that Rood had been anticipating his first grandchild. Now, thanks to a freak spring storm and his own unforgivable carelessness, all of that investment in energy and love had been taken away from him.

Preoccupied, Rood had walked out of the settlement. He was approaching the crude shantytown of the boneheads.

The boneheads looked up dully as he passed. Some of them were gorging on scraps of narwhal skin. One cow had an infant clamped to her scrawny breast; she turned away from him, cowering. The boneheads had no place in this land owned by human beings. Indeed the boneheads would have starved if not for the largesse, and waste, of the people. Neither animal nor person, nothing about the boneheads was worthy of respect. The boneheads didn’t even have names.

But they could be useful.

He came across one cow younger than the rest. In fact she was the cow whom Jahna had tormented not long before the disastrous expedition to the sea.

She looked up at him dully, her absurdly flat skull smeared with dirt. He knew this one was the same age as Jahna, but she was more advanced than his daughter; the boneheads grew up faster, lived harder, died younger. She sat in the dirt, dressed in an untied skin wrap, toying with a worn, broken pendant. The boneheads seemed to have enough mind to be fascinated by the artifacts of the people, yet not enough to make them for themselves: You could buy whatever you wanted from a bonehead for the sake of a mammoth-ivory bead or a carved bone harpoon.

On an impulse he didn’t fully understand, Rood reached down and pulled the wrap away from the cow’s body. If not for that pulled-forward face, that flattened head, her body wasn’t so bad, he thought; she had yet to develop the full, bearlike stockiness of the adults.

He found an erection pushing out of his own wrap.

He knelt down, grabbed the cow’s ankles, and twisted her onto her back. She complied easily, spreading her legs; evidently it wasn’t the first time she had been used like this. Probing at her warm flesh he found her crotch and anus were crusted with filth. He scraped her clean with his fingers.

And then, with a single, savage thrust, he entered her. For a brief, oceanic time, he was able to forget that disastrous moment when the storm closed in and he realized he had lost Jahna and Millo on the ice.

But it was quickly over. Pulling away from the girl he felt a deep, stomach-churning sense of revulsion. He used a corner of his wrap to clean himself.

The girl, still naked, rolled on her back and held up her hands, pleading silently.

Around his neck he wore a pendant, the tooth of a cave bear. He ripped it off his neck, breaking its deerskin thong, and threw it in the dirt. The bonehead girl scrabbled for the pendant and held it up before her face, turning it over and over, peering into its endless mysteries. A trickle of blood seeped from her bruised thighs.

Jahna and Millo continued to follow the coast, still hoping to come across the headland where they had last seen their father and his companions. At night they built snow houses, if there was snow, or slept under hastily constructed lean-tos. Jahna’s bow and Millo’s fast reflexes kept them provided with some food; small animals and birds.

They could keep themselves fed, even build shelter. But already Millo had spent one agonizing night after unwisely eating a fish that had not been properly gutted. Worst of all they had failed, night after night, to make a fire, no matter how earnestly they rubbed sticks or smashed bits of rock together. And that was costing them dearly. The uncooked meat was beginning to make Jahna’s teeth and stomach ache, and in the dead of night she imagined she would never be truly warm again.

The children plodded on; they had no choice. But they were losing weight, growing more tired every day, their clothing more ragged. They were slowly dying, Jahna knew. Though they were guided by the elder spirits within them, they did not yet know all they needed to know to keep themselves alive.

They came to a place where the tree line had strayed north, so they had to push through a scrap of forest. The trees, pines and spruce, grew sparse and tangled: gaunt and without leaves, they looked oddly frail. The path the children followed, worn by deer or goats, was soft with moss. It twisted through the trees, passing occasionally through more open glades.

As the light faded, ending another dismal day, the shadows of the trees striped over the ground, and the undergrowth turned black. Jahna and Millo were five million years removed from Capo, their last forest-dwelling ancestor, and to them the forest was a place well stocked with monsters and demons. They hurried forward anxiously.

At last they burst out of the trees. They found themselves on a scrap of snow-littered grassland where the yellow sward terminated in a ragged cliff edge. Beyond that blunt horizon the sea rolled, the pack ice distantly groaning and cracking, as it always did.

But the children faced a wall of flesh and antlers. It was a herd of megaloceros — creatures that would one day be called Irish elk. They walked massively, cropping at the new grass that poked hopefully through the scattered snow.

In the van was a huge male. He peered down his long nose at the children. His back bore a fleshy hump, a mound of fat to help sustain him through harsh times; in this early spring the hump was deflated. And his antlers, each twice as wide as a human was tall, were great heavy sculptures oddly like the open hands of a giant, with fingerlike tines branching off smooth palms.

There were thousands of deer in this herd alone, crowding out of the children’s sight. Like many giant herbivores in this paradoxically rich time, the megaloceros flourished in vast migrant crowds, wandering all across the Old World from Britain to Siberia and China. And this vast herd was bearing down on Jahna and Millo. It was a slow-moving barrier, immense antlers clattering, stomachs rumbling. The air was full of the overwhelming stink of musk and dung.

The children needed badly to get out of the way. Jahna saw immediately that they couldn’t evade the herd by running inland; it was too big, too widespread for that. The deer surely wouldn’t penetrate far into the forest, but they would force the children back into that deepening darkness, which was a place she really didn’t want to go back into.

On impulse she grabbed her brother’s hand. “Come on. The cliff!”

They ran across the frozen grass. The cliff edge sloped away sharply beneath a lip of turf. Hastily the children scrambled down. The bow on Jahna’s back caught on outcroppings of the rock, slowing her down. But they made it. They huddled on a narrow ledge, peering up at the ocean of black-brown fur that washed slowly along the cliff top.

The huge male looked on indifferently. Then he turned away, his burdened head dipping.

The antlers were heavy to carry, like weights held at arms’ length, and the buck’s neck had been redesigned to bear that load, with huge vertebrae and muscles like cables. The antlers were for sexual display — and for fighting; it was an awesome sight when two of these giant bucks clashed, heads down. But those great antlers would doom these animals. When the ice retreated and their habitat shriveled, there would be a selection pressure for smaller body sizes. While other species shrank to fit, the megaloceros would prove unable to give up their elaborate sexual displays. They had become overspecialized, their tremendous antlers over-expensive, and they would prove unable to cope with change.