"But how could the counteragent cause us to revert to an earlier stage of evolution?" I asked.

"You weren't listening," said Father.

I thought for a moment. "Homo neanderthalensis isn't an earlier stage," I said. "There was no more evolution after that."

"Only a disease," said Father.

It seemed too incredible to me, as an eleven-year-old who prided himself on understanding the world. "Human intelligence is an infection?"

"Passed from mother to child through the ovum," said Mother. "By a disease agent that alters the DNA in order to replicate itself. We should have realized it from the fact that in utero development recapitulates evolution, but there is no stage in which the fetus passes through a habiline form. We did not evolve past it. The DNA is hijacked and we are born prematurely, grossly deformed by the disease. Neotenic, erectstanding, language-mad, lacking in sense of smell, too feeble to survive on our own even as adults, in need of clothing and shelter and community to a degree that the Neanderthals never were. But ... smart."

"So now," said Father, "do you understand why medical science has to rely on inoculation to fight off cancer, so that a small percentage-far smaller than ever before in human history, but not zero-a small percentage dies? Elizio died because the only alternative we've found is for this race of perfectly healthy, immortal, dim-wilted beings to inherit the Earth."

I stood there for a long time in silence, watching the Neanderthals, trying to see how their behavior was different from ours. In the years since then, I have come to realize that there was no important difference. Being smarter hasn't made us act any differently from the Neanderthals. We make better tools. We have a longer, more thorough collective memory in the form of libraries. We can talk much more fluently about the things we do. But we still do basically the same things. We are Neanderthals, at heart.