But still, Sapling now occasionally used sentences. He had picked up the habit from Mother. Each sentence was a genuine subject-verb-object compound. The people’s protolanguage was quickly developing around this seed of structure. Already the chattering people had had to invent pronouns — you, me, him, her — and different ways of expressing actions and their outcomes: I did kill, I am killing, I did not kill… They were able to express comparatives and negatives, explore alternatives. They could consider going to the lake today, or not going to the lake, all in a universe of words, where before they would have had to pick one path or another, or split into factions.

It wasn’t yet a full language. It wasn’t even as rich as a creole. But it was a start, and it was growing fast.

And in a sense Mother had discovered, not invented, that basic sentence structure. Its central logic reflected hominids’ deep apprehension of the world — a world of objects with properties — which reflected in turn a still deeper neural architecture common to most mammals. If a lion could have spoken, or an elephant, it would have spoken this way too. This central underpinning would be shared by almost all the myriad human languages that would follow in the ages to come, a universal template reflecting the essential causality of the world and the human perception of it. But it had taken Mother’s dark genius to give that deep architecture expression, and to inspire the linguistic superstructure that rapidly followed.

And now it was time for another step.

Sapling said something that grabbed her attention. “Spear kill bird,” he said excitedly. “Spear kill bird, spear kill bird…”

She frowned. “No, no.”

He stopped in midflow. Wrapped up in his performance he seemed to have forgotten she was there. “Spear kill bird.” He mimed the spear’s flight. He even picked up the ostrich’s ragged head and arced his outstretched hand toward it just as his spear had flown, straight and true.

“No!” she barked. She got up and grabbed his hand. “You lift hand.” She slapped the spear-thrower into his grip. “Hand push stick. Stick push spear. Spear kill bird.”

He pulled back, baffled. “Spear kill bird.” Isn’t that what I said?

Irritated, she went through it again. “You lift hand. Spear kill bird. You kill bird.” There was a causal chain, but the intention resided only in one place; in Sapling’s head. She could see it clearly. He had killed the bird, not the spear. She slapped his head. This is where the bird died, dummy. Inside your mind. The rest is detail. They argued for a while, but Sapling grew increasingly confused, his simple boyish pleasure in his kill waning now that his boasting had degenerated into this peculiar philosophical discussion.

Then a bolt of pain stabbed through Mother’s temples, as sharply and suddenly as Sapling’s spear of hardened wood must have slammed through the head of that hapless ostrich. She stumbled to her knees, her fists pressed to her temples.

But now, suddenly, in that instant of pain, she could see a new truth.

She imagined the spear arcing through the air, like the bright lightning in her head, piercing the bird’s skull and extinguishing its life. She knew that Sapling had thrown the spear. He had willed the bird dead, and everything else that followed was irrelevant.

But what if she hadn’t seen Sapling throw the spear? What if he had been hidden by a rock, a tree? Would she have believed that the spear was the ultimate cause — that the spear itself had intended to kill the bird? No, of course not. Even if she couldn’t see the whole causal chain, it must exist. If she saw the spear fly, she would know somebody must have thrown it.

Her peculiar vision of the world, the spiderweb of causes stretching across the world and from past to future, deepened further. If an ostrich fell, a hunter had willed it. And if a person died, another was to blame. As simple as that. She saw all this immediately, understood it on a deep intuitive level below words, as new connections opened in her complex, fast-developing consciousness.

The logic was clear, compelling. Appalling. Comforting.

And she knew how she had to act on this new insight.

She became aware that Sapling was kneeling before her, holding her shoulders. “Hurt? Head? Water. Sleep. Here…” He took her arm, trying to help her stand.

But that flash of pain had come and gone in an instant, a meteor leaving a trail of shattered and remade connections in her mind. She stood up and pushed past him, stalking back toward the settlement. There was only one person she needed now, one thing she had to do.

Sour was in her shelter, a rough lean-to of palm fronds, sleeping off the heat of the day.

Mother stood over her. In her arms she held a massive boulder, the largest she could carry; she cradled it as once she had cradled Silent.

Mother had never forgotten the day when Silent had first fallen ill. On that day everything had changed for her, as if the land had pivoted around her, as if the clouds and rocks had exchanged places. It had been the start of the pain. And she hadn’t forgotten Sour’s half smile. If I can’t have a kid of my own, she had been saying, I’m glad you will lose yours.

Now she saw everything clearly. Silent’s death had not been random. Nothing happened by chance in Mother’s universe: not anymore. Everything was connected; everything had meaning. She was the first conspiracy theorist.

And the first person she indicted was her closest surviving family member.

Mother didn’t know how Sour had committed her crime. It might have been a look, a word, a touch — some subtle way, an invisible weapon that had brought the boy down as surely as a spear of carved wood — but how didn’t matter. All that mattered was that Mother now knew who to blame.

She raised the rock.

In her last moment Sour woke, disturbed by Mother’s movement. And she saw the rock falling toward her head. Her world ended, as thoroughly and suddenly extinguished as Cretaceous Earth’s by the Devil’s Tail.

The hominid brain, fueled by the need for increasing smartness, fed by the people’s new fat-rich diet, had grown rapidly. It was more complex than any computer that humans would ever build. Inside Mother’s head were a hundred billion neurons — interacting biochemical switches — a number comparable to the number of stars in the Galaxy. But each of those switches was capable of taking a hundred thousand variable positions. And this whole suite of complexity was bathed in a fluid laced with more than a thousand chemicals that varied with time, season, stress, diet, age, and a hundred other influences, each of which could affect the functioning of the switches.

Before Mother, people’s minds were compartmented, with their subtle consciousness restricted to their social dealings while specialized modules dealt with such functions as toolmaking and environmental understanding, as well as more basic physiological functions such as breathing. The various functions of the brain had developed to some degree in isolation from one another, like separate subroutines not united into a master program.

It was all very jury-rigged, though. And this hugely complex biochemical computer was prone to mutation.

The physical difference between Mother’s brain and those of the people around her was tiny, the result of a minor mutation, a small change in the chemistry of the fat in her skull, a slight rewiring of the neuronal circuitry that underpinned her consciousness. But that was enough to give her a new flexibility of thinking, a breaking-through between the different compartments of her intelligence — and a hugely different perception.

But the rewiring of so immensely complicated an organic computer inevitably had side effects — not all of them desirable.