At thirty years old, Mother’s body was as lithe and upright as it had been in her youth. But her belly bore marks from the birth of her single child, her son, and her breasts sagged. Her buttocks were full; this was an adaptation to the long periods of drought, to help her store water in fat. Her limbs showed stringy muscles, and her belly showed none of the malnutritional swelling affecting many of the folk. She was evidently effective at the business of life.

But she couldn’t remember a time when she had been happy. Not even as a child, when she had been clumsy, slow to talk, slow to fit in. Not even when her son had been born, healthy and wailing.

She saw too much.

This drought, for instance. The clouds had gone away, which enabled the sun to beat down all day, which dried the land and made the water vanish, which made the animals die, which made the people go hungry. So the people went hungry because of the clouds. What she couldn’t figure out was what had made the clouds go away in the first place. Not yet.

This was what she had a talent for: seeing patterns and connections, networks of causes and effects that intrigued and baffled her. Her talent for spotting causal links brought her no comfort. It was more a kind of obsessive suspicion. But it did help her get through life sometimes — like today.

She came to a baobab tree, and studied its twisted branches. She knew what she wanted to make — a boomerang, a curved throwing weapon — and she inspected the branches and buttresses, looking for a place where the grain of the wood and its growth direction matched the weapon’s final shape, as she could see it in her mind.

She found one slender branch that might work. With a brisk snap she broke it off close to where it joined with the tree. Then she sat down in the baobab’s scrap of shade, took her stone tool, stripped off the bark, and began to carve the wood. She turned her stone blade over and over in her hand to bring favored edges into use. This tool — not quite an ax, or a knife, or a scraper — was her current favorite. Because any tool she couldn’t make on the spot had to be carried, she had manufactured this one tool to do many jobs, and she had retouched it several times.

Soon she had produced a smoothly curved stick some thirty centimeters long, flat on one side and rounded on the other. She hefted the boomerang in her hand, assessed its balance and weight with a judgment born of long practice, and quickly scraped away a little excess.

Then she walked out of the baobab’s shade and around the perimeter of the lake’s muddy fringe. She found the place where she had stashed a net of plaited bark fiber a few days before. The net was undisturbed. She shook it clear of dust, and the beetles that gnawed its dry fibers.

She hung the net across two gaunt, conveniently placed baobabs so that it faced the lake. She had chosen this site, in fact, because of the baobabs.

Now she walked back around the lake, until she was sideways when compared to the position of her net. She took her throwing stick. Her tongue protruding, she hefted it, rehearsing the throw she would make. She would get only one shot at this, and she had to get it right.

Pain pulsed at her temples, distant, like thunder in remote mountains.

She lost her balance, and grimaced, annoyed at the distraction. The pain itself was trivial, but it was a precursor of what was to come. Her migraine was a relentless punishment she endured frequently, and there was nothing to be done about it — it had no cure, of course, not even a name. But she knew she had to get on with her task before the pain made it impossible. Otherwise she would go hungry today, and so would her son.

Ignoring the throbbing in her head, she set herself once more, hefted the stick, and hurled it with strength and precision. The whirling stick followed a sweet curving arc high into the air over the lake, its wooden blades whirling with a subtle whoosh.

The roosting waterfowl rustled and cawed irritably, and when the stick turned in the air and fell on them they panicked. With a clatter of ungainly wings the birds took to the air and fled from the lake — and the flock’s low-flying outliers ran straight into Mother’s net. Grinning, she ran back around the lake to claim her prize.

Connections. Mother threw the boomerang, which scared the birds, which flew into the net, because Mother had placed it there. As examples of Mother’s causal-link thinking went, this had been elementary.

But with every step she took her headache worsened, as if her brain were rattling in her capacious skull, and her brief pleasure at her success was crowded out, as it always was.

Mother’s people lived in a camp close to a dry, eroded channel that ran into a gorge. Shelters had been set up among the rocky bluffs, just lean-tos, sheets of hide or woven rattan propped up on simple frames. There were no permanent huts here, unlike the structures in Pebble’s long-vanished encampment. The land wasn’t rich enough for that. This was the temporary home of nomadic hunter-gatherers, people forced to follow their food supply. The people had been here for a month.

The site had its advantages. There was a stream, the local rock was good for toolmaking, and there was a clump of forest nearby, a source of wood for fires, and bark, leaves, liana, and vines for cloth, netting, and other tools and artifacts. And the site was a good place to ambush animals that came wandering foolishly toward the gorge. But the produce of the area here had not been good. The camp was poor, the undernourished people listless. They would probably move on soon.

Mother stumbled home, three waterfowl slung on bits of leather rope over her shoulder. The pain in her head had grown sharp now, and every surface seemed overbright and tinged with strange colors. The ballooning of the human brain, in the millennia before the birth of Mother’s distant ancestor Harpoon, had been spectacular. This hasty rewiring brought unexpected benefits — like Mother’s pattern-making ability — but costs, like her plaguing migraine.

“Hey, hey! Spear danger spear!”

She looked around dimly.

Two of the younger men were staring at her. They wore wraparound hides tied in place with bits of sinew. They both held wooden spears, crudely finished, their tips hardened by charring. They had been hurling their spears at an ox hide they had draped over the branches of a tree. Mother, distracted by the pain and the strange lights, had almost blundered into their path.

She had to wait while the spear throwers completed their contest. Neither of the two young men was particularly skillful, and their hide wraps were shabby. Only one of their spears had pierced the hide to embed itself in the tree; the rest lay scattered in the dirt.

But one of the hunters was at least hurling his spears with more power, she saw. This boy held the spear unusually far back along its shaft, and used the length of his bony arms to get a little more leverage.

Tall for his age, whip thin, she thought of him as a sapling, drawn up by the sunlight. When Sapling threw the spear, it hissed through the air, oscillating slightly. The spear’s movement was intriguing. But as her eyes tracked it, her head hurt even more.

When the spear throwers were done she blundered on, seeking the dark of the hide she shared with her son.

Inside Mother’s hut was a stocky woman of thirty-five. She had ragged, graying hair and a habitually pinched, sour face. This woman, Sour, was using a pestle to grind a piece of root. She glared at Mother, her expression as hostile as usual. “Food, food?”

Mother waved a hand vaguely, caring nothing about Sour. “Birds,” she said.

Sour put down her pestle and root, and went outside to see the birds Mother had hung up.

Sour was Mother’s aunt. She had become embittered when she had lost her second child to some unknown illness a couple of days after childbirth. She would probably steal the birds, giving Mother and Silent a fraction of what Mother had brought home. But Mother, her head full of pain, felt too weary to care.