"There was a quarantine of sorts," said Father. "The participants accepted the rules-no physical contact with anyone outside the city during the two years of the stud: In exchange, nobody dies of any kind of disease. They jumped at it."

"The counterinfection got loose!" I said.

"No. Everybody kept to the rules. This was science, not the movies," said Father. "But in the Manhattan Project, as we inevitably called it, for the first time the test included infants, newborns, children born after the study began, children conceived after the study began. We were so interested in the result with the aging population that it had never crossed our minds that ... well, it did cure aging. The people who have it would never die of old age. The trouble was, the children were born--"

"As Neanderthals," I said, making the obvious guess.

"And over time," said Father, "as cells were replaced, the adult bodies also tried to reshape themselves. It was fatal for them. You can't take an existing body and make it into something else like that. You had a few years of perfect health, and then your bones destroyed themselves in the frantic effort to grow into new shapes. The little ones, the ones who were changed in the womb, only they survived."

"And that's who I'm seeing out there," I said.

Father nodded. "It took fifteen years to find a way to sterilize them all without our counterinfection undoing the sterilization. By then there were so many, of them that to keep them all in their natural habitat required a vast reserve. It really wasn't all that hard to get the citizens of this area to evacuate. Nobody wanted to be anywhere near Manhattan, Kansas. So once again, Homo neanderthalensis has a plot of ground here on Earth. Homo neanderthalensis, the most intelligent toolmaking species ever to evolve naturally."