Tay-Sachs disease. Canavan disease. More than a dozen more.
It offended Cochran's sense of logic. Natural selection, the self-taught genetics buff knew, should flush dangerous DNA from the gene pool. Perhaps the mutations causing these diseases had some other, beneficial purpose. But what?
At 3:17 one morning, after a long night searching a database of scientific journals from his disheveled home office in Albuquerque, Cochran fired off an e-mail to his collaborator Henry Harpending, a distinguished professor of anthropology at the University of Utah in Salt Lake City and a member of the National Academy of Sciences.
"I've figured it out, I think," Cochran typed. "Pardon my crazed excitement."
The "faulty" genes, Cochran concluded, make Jews smarter.
That provocative -- some would say inflammatory -- hypothesis has landed Cochran and Harpending in the middle of a charged debate about the link between IQ and DNA.
They have been sneered at by colleagues and excoriated on Internet forums. They have been welcomed to speak at a synagogue and a Jewish medical society. They were asked to write a book; that effort, "The 10,000 Year Explosion," was published early this year.
Scientists are increasingly finding that propensities for human behaviors -- for addiction, aggression, risk-taking and more -- are written in our genes. But the idea that some groups of people are inherently smarter is troubling to many. Some scientists say it has such racist implications it's unworthy of consideration.
"What are their theories about those on the opposite end of the spectrum?" asked Neil Risch, director of the Institute for Human Genetics at UC San Francisco, who finds the matter so offensive he can barely discuss it without raising his voice. "Do they have genetic theories about why Latinos and African Americans perform worse academically?"
The biological basis for intelligence can be a thankless arena of inquiry. The authors of "The Bell Curve" were vilified 15 years ago for suggesting genes played a role in IQ differences among racial groups.
But Cochran, 55, and Harpending, 65, say there's no question that as a whole, Ashkenazi Jews -- those of European descent -- have an abundance of brain power. (Neither man is Jewish.)
Psychologists and educational researchers have pegged their average IQ at 107.5 to 115. That's only modestly higher than the overall European average of 100, but the gap is large enough to produce a huge difference in the proportion of geniuses. When a group's average IQ is 100, the percentage of people above 140 is 0.4%; when the average is 110, the genius rate is 2.3%.
Though Jews make up less than 3% of the U.S. population, they have won more than 25% of the Nobel Prizes awarded to American scientists since 1950, account for 20% of this country's chief executives and make up 22% of Ivy League students, the pair write.
"People are perfectly willing to admit that some people are taller or some people are shorter," Cochran said. "But no one wants to say 'This group is smarter.' "
Once Cochran gets talking, it's hard to get him to stop. He jumps from idea to idea, beginning new sentences before finishing old ones. In e-mail discussion groups, where he befriended Harpending, he thrives on debating people and proving them wrong.
A PhD physicist, he started out in El Segundo, developing satellite imaging systems and other optics hardware for Hughes Aircraft in the 1980s. As the Cold War ended and defense budgets shrank, Cochran moved his family to Albuquerque and became an optics consultant while indulging his amateur interest in biology.
He worked for a while with evolutionary biologist Paul Ewald on theories that germs cause common disorders like heart disease and Alzheimer's. The pair courted controversy by postulating that some unidentified pathogen prompts a hormonal imbalance that makes babies more likely to become gay.