“I see,” I said, and let the subject drop. No need asking her about selective female infanticide. I could see that it was being practiced simply by counting the children.

Women were a liability in this rugged hunting life. They were necessary for procreation, of course, but too many women meant too many babies, too many mouths to feed. So female children were weeded out at birth. Conversely, once a woman was no longer capable of bearing children, her usefulness to the clan was finished and they apparently got rid of her. Not that the men lived much longer: disease and accidents took their toll, and if they were not enough, there was always war. Long before human beings learned to tame the wild ponies that they hunted for food, the Four Horsemen of the Apocalypse kept human numbers in balance with the rigors of the Neolithic landscape.

Without consciously deciding to do so, I was changing that balance. It took me many weeks to realize that it was so. But as I taught the clan how to make bows and arrows, how to dig pits and camouflage them so that animals would fall into them, I began to realize that I was altering — ever so slightly — the ecological balance of this era. For it was not preordained that humans should live in small, scattered hunting groups and survive on the ragged edge of starvation. Only their lack of knowledge, their lack of proper tools, kept these hunters weak and vulnerable. Given more knowledge, better tools, they would become the masters of this world.

And eventually build nuclear bombs and vast cities choking in their own filth, I knew. Yet, as I woke up each morning in this dawn of human history and watched these people get ready to work another day with little more than their bare hands, I realized that my choice was the only one I could make. They were part of me, I knew, as human as I was. For me to refuse to help them would be the same as for me to refuse to breathe. No matter what the consequences, I had to choose life over death, knowledge over ignorance, humankind over all the other forms of life in the world.

And then I would see Ava walking gracefully among her people, sipping water from a gourd, tending to a crying infant, and I realized that all my fine thoughts were merely excuses. I did what I did to help this clan because she was here, and I could not face the idea that one day, when she grew too slow to stay up with them, her clansmen would open her veins and let her spirit leave her body.

My own knowledge of Neolithic technology was shadowy, at best, but I remembered seeing pictures of spear-throwers, long, grooved handles that effectively extended the length of the throwing arm and allowed one to fling a spear twice the distance that he could unaided. I experimented for the better part of a week and finally taught myself how to make one and use it.

Dal’s suspicions of me almost vanished when I showed him how to throw a spear farther than any man had before. The bow and arrow he had regarded with misgivings, mainly because I was far from expert at feathering the arrows and they were consequently far from accurate. But the spear-thrower fit into his experience and expectations beautifully. The first day he used it he brought down a gazelle that fed the whole clan for two nights. I was instantly besieged with requests for more of them. I made three, under the watchful eyes of the men and boys. Then they started making them, and within a week they were building better ones than I could.

Each night I gazed up at the stars longingly, searching their eternal patterns for some sign of where on Earth I might be. Most of the constellations looked familiar. I recognized Boцtes, Andromeda, Perseus and the Little Dipper. Clearly, I was in the Northern Hemisphere. The Big Dipper looked strange, lopsided, its stars rearranged. If instinct had not done so already, that would have convinced me that I had moved many millennia through time.

The double-peaked volcano that loomed ahead of us seemed strangely familiar, but I could not place it. When I asked Dal what its name was, he gave me a strange stare. Either this clan did not name mountains or the name was too sacred to be spoken casually.

The landscape was rising now, and we climbed grassy slopes that grew steeper with each passing day. After almost a week of that, the land flattened out into a broad plateau covered by a dark and gloomy forest. Huge boles of pine and spruce alternated with groves of birch trees and mighty oaks. Beneath the trees the undergrowth was sparse, but it grew thick and tangled wherever the green canopy overhead thinned enough to let sunlight filter through to the ground. Dal kept us on a trail that meandered through the shadows of the trees — bare ground, softened by fallen pine needles. Easy hiking.

The forest was rich with game. Every morning the men and older boys went out to hunt boar, deer, and whatever else they could find. Often a few of the women went with them. The other women and younger boys stayed at the campsite, some of them trapping smaller game. I became expert at the sling and could usually kill a couple of rabbits or squirrels in an hour or so. The clan ate well in the forest. I wondered why they ever left it.

I asked Ava, one afternoon when she had stayed in camp instead of going off with the hunters.

“We go to the valley, to our camping place for the summer,” she told me. “There we will meet other clans. There will be marriages and feasting.”

I sat with my back against the bole of a huge oak, while she knelt on the thin grass, sorting out the roots and herbs she had spent all morning collecting.

“Why don’t the clans meet here in the forest?” I asked. “There’s more game here than anywhere else I’ve seen.”

She gave me the kind of patient smile that a teacher might offer a struggling student. “The valley is better. There is plenty of game there. And other kinds of food as well. Here in the forest…” She looked around the gloomy shadows cast by the trees, highlighted here and there by shafts of ghostly sunlight filtering through the leaves overhead. “Here there are dark spirits, dangerous and foul.”

I knew of a dark spirit that was very real. I wondered if Ahriman was lurking in these dreary woods.

“And enemies who can ambush us,” Dal’s strong voice broke into our conversation. “The forest is an easy place for enemies to trap us.”

He strode up to us, strong and confident and smiling through his coppery red beard. Over one shoulder he had slung a young boar, its hind legs tied together by a thong.

Ava jumped to her feet, so obviously happy to see him that I felt instantly jealous and resentful. “Why are you back so soon?”

Letting his catch drop to the ground, Dal pointed and said, “We found a new watering place, further up the hill. All the animals go there to drink. It wasn’t there last year; something has dammed the stream to make a big pool. At sundown we can take enough game to carry us through the rest of the way to the valley!”

By sundown the whole clan was staked out by the watering spot, a large, still pool fed by a tiny stream that trickled through the woods from far above, where the snows still lay on the mountainside. Only the two elders, the babies, and the four oldest women had been left behind. Dal brought everyone else and carefully supervised our placement around the pool and on either side of the trail that led to it.

He was confident enough of himself to direct even me to a hiding place. I accepted his orders with a smile; Dal no longer feared me, and I felt good about that. I had been accepted.

We waited, hunkered down into the ground, covered with leaves and foliage, hoping that the wind would not change and give away our hiding positions to the animals that would come to the pool for their evening drink.

The afternoon light faded. Birds chattered and swooped through the trees. A procession of ants marched two inches in front of my eyes as I lay on the ground, itching and sweating despite the coolness of the forest shadows. Three spears lay beside me. A leafy oak branch lay over me. On either side of me I could see other clan members, similarly hiding and camouflaged. We were all to wait until Dal made the first move.