What disguised them from researchers for so long was the fact that these diseases were passed along in the womb, across the placenta, mostly by disease agents composed of proteins smaller than DNA. Some were passed along in the ovum. So we had no way to compare a clean, healthy organism with an infected one until we finished mapping the human genetic code and realized that these diseases weren't there. When we finally tracked them down as loose proteins in the cells, we--"

"We?" I asked.

"I speak of our forebears, of course," said Father. "Our predecessors."

"You aren't in medical research."

"Our colleagues in science," said Father. "We've come a long way to have you quibble about my choice of pronouns. And anthropology is the science of which medicine is merely a subset."

I had a snappy retort about how nobody ever asks if there's an anthropologist in the house, but I kept it to myself, mostly because I didn't want to win points here, I wanted to hear the story.

"How do you inoculate an organism against in utero infection?" asked Mother rhetorically. "How do you cleanse an ovum that has already been infected?"

"What we developed," Father began, then interrupted himself. "What was developed."

"What emerged from the development process," said Mother helpfully.

"Was," said Father, "an elegant little counterinfection. Learning from the way these protein bits worked, the researchers came up with a protein complex that hijacked the cell's DNA just the way these infectious agents did. Only, instead of destroying the host cell, our little counterinfection caused the human DNA to check aggressively inside the cell for proteins that didn't belong there. There are already mechanisms that do bits and parts of that, but this one worked damn near perfectly. Nothing was in that cell that didn't belong there. It even detected and threw out the wrong-handed proteins that caused spongiform encephalopathies."