As midday approached, the hominids moved away from the water, relaxed, satiated.

But Ax struck out on his own. Far trailed after him. He gazed back at her. She knew he was aware she was following him.

Ax came to a dried-up streambed laced with worn cobbles. He walked up and down the bed, examining the rocks, until he found what he wanted. It was a cobble about the size of his fist, flattened and rounded. He sat squat in the streambed and rummaged around until he found a suitable hammer-stone. He had brought some dried brush that he spread over his crossed legs for protection. Then he went to work, tapping at the core he had selected. Soon flakes flew away, briskly rattling off the cobble.

Far sat ten meters away, her legs folded before her, hugging her knees, fascinated by his toolmaking. It was like nothing she had seen before.

In fact, Ax and Far had grown up in toolmaking traditions separated by millennia.

Once they had put the trees behind them and moved definitively out onto the savannah, a new range of possibilities had opened up for the walkers. They were more than merely mobile. They migrated. But it wasn’t purposeful. For each individual, it was just a question of making a living. For people able to exploit new landscapes, it was often easier to walk to somewhere that looked a better place to live than to try to adapt to harsh conditions.

But as the generations ticked by the people covered thousands of kilometers. They even walked out of Africa, into lands where no hominid had set foot before. Before the great clamp of the glaciations tightened, equable conditions had spread well out of Africa into southern Europe, the Middle East, and southern Asia. Walking into these familiar surroundings the people followed the easy living of the coastlines, west around the Mediterranean and diffusing inland, at last colonizing Spain, France, Greece, Italy — as did animals later associated only with Africa, like elephants, giraffes, and antelope. To the east, they worked through India to the Far East, suffusing through what would become China, even working south to reach Indonesia.

It was not a conquest. Far’s kind had become far more widespread than any other ape species. But other animals, like the elephants, spread much further. And there were fewer of them. Their numbers in any given area were less than lions, say. Despite their tools the people were still just big animals in a landscape on which they had minimal impact.

And the great wandering was not purposeful. One of Far’s distant grandmothers had reached as far as Vietnam; now, in Far’s time, chance and the endless walking had brought her lineage back to East Africa, to home.

But here, in the ancient homelands, the returning migrants encountered new pressures.

Some hominid populations had elected not to move, despite the climate’s treacherous fluctuations. To survive they had been forced to become smarter. Better tools — crucially, the hand axes — had been the key to their survival. The ax’s secret was its teardrop shape. A flattened bi-faced shape gave a long cutting edge for minimal weight. Though they would still use simple pithecine-like flake tools if they needed to — the flakes, easy to make, were “cheap” and were actually better for some tasks, like tackling small prey — the hand axes were used not just for butchering meat, but for hacking sticks and clubs from branches, sharpening wooden spears, opening up beehives, digging into logs to get at larvae, peeling off bark, shredding pith, and opening the shells of tortoises and turtles. It was from a group of these stay-at-homes that Ax was descended.

Which was how Far, descendant of wanderers who had crossed southern Eurasia all the way to the Far East, now found herself confronted by the startlingly advanced technology of Ax and his kind.

Ax worked patiently. Her gaze wandering, Far noticed now that the dry bed here was littered with hand axes: many of the rocks she had assumed were just cobbles had actually been shaped. They all had the characteristic teardrop shape, and were all worked to a greater or lesser degree to give that fine edge all the way around the tool.

But these axes were strange. Some of the axes were tiny, the size of butterflies, while some were huge. Some of them were broken, some smeared with blood. But when she tried to pick up one of the larger axes, its edge cut into her fingers; it had hardly been used, if at all.

Someone walked up to her. She cowered back.

It was Scar-face, the man who had taught the children how to knap rock. He was looking at Far with a kind of hungry intensity. He had one of the huge axes in his hands. It was impractically large, too large to use to butcher. Still gazing at her he turned it over in his hands, and tapped at it with a hammer-stone, tidying up an edge. Then he scraped it over his leg, and removed a swath of the fine black hair that grew there. All through this he watched Far’s face and body, his half-covered eye gleaming.

She had absolutely no idea what he wanted — none, that is, until she saw the erection poking out of his tuft of pubic hair.

Ax had more or less finished the blade he was making: hand-sized, utilitarian, rough and ready, it was clearly a functional tool, manufactured in minutes. But when he saw what Scar-face was doing he threw down his ax angrily. He got up, scattering his spill of flakes, and punched the man’s shoulder. “Away! Away!”

Scar-face snarled back, his erection subsiding. At last Ax grabbed the huge gaudy ax out of his hands, and threw it to the ground. Part of its beautiful edge sheared off. Scar-face looked at the ax, at Far, and, with a final glare at Ax, walked away.

Far sat where she was, her knees tucked against her chest, fearful and baffled.

Ax stared at her. Then he stalked up and down the dry stream again, surveying the stones. At last he came across a big malformed volcanic block, so heavy it took two hands to lift it. He sat down again, picked up a few hammer-stones, scattered more brush over his legs.

He started to slam at the rock, displaying all his strength. Flakes and sheets of it began to fall away. But very quickly, thanks to his skill and strength, a crude hand ax teardrop shape emerged. Now he started to use a succession of smaller stones to shape the two lenticular surfaces, and to finish the edge to a fine blade.

Where his first effort had come easily, borne out of a rock that had already had the rough shape of the final ax, this rock was much more difficult. He couldn’t have picked a tougher challenge — and he had chosen it deliberately. And all through this he made sure Far was watching him.

The walking folk had already been making tools more or less like this for two hundred thousand years. Over such an immense span of time, the axes had become more than mere tools, more than functional.

To Ax, this feat of toolmaking was a kind of courtship. He was displaying his fitness as a mate to Far. By making the tool he was showing her in one clear demonstration the strength of his body, the precision of his working, the clarity of his mind, his ability to conceive and see through a design, his skill for locating raw materials, his coordination of hand and eye, his spatial skills, his understanding of the environment around him. All of these were traits he expected she would want to pass on to her offspring — and that was why such displays had acquired a logic of their own, divorced from the utility of the hand axes.

Driven by lust and longing, men and boys would make dozens of axes, over and over. They would labor for hours over a single ax, seeking perfect symmetry. They would make tiny axes the size of their thumbnails, or they would make huge unwieldy affairs that would have to be held in two hands like an open book. They would, as Ax had, seek out particularly difficult raw materials and go ahead and carve out axes anyhow. Sometimes they would even throw away their axes, deliberately, to show how rich they were in strength and skill.