“People are perfectly willing to admit that some people are taller or some people are shorter,” Gregory Cochran said. “But no one wants to say This group is smarter“:
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.
Cochran’s an interesting fellow, a Ph.D. physicist who started in aerospace before becoming interested 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.Cochran read more than 15 genetics textbooks and became intrigued by the deadly diseases that disproportionately afflict Ashkenazi Jews: Tay-Sachs, a neurological disorder that debilitates children before killing them, usually by age 4. Canavan disease, which turns the brain into spongy tissue and typically claims its victims before they can start kindergarten. Niemann-Pick disease Type A, in which babies accumulate dangerous amounts of fats in various organs and suffer profound brain damage and death before their second birthday.
He was struck by the fact that so many of the diseases involved problems with processing sphingolipids, the fat molecules that transmit nerve signals.
This seemed an unlikely coincidence. Genetically isolated groups often have higher rates of certain diseases. But of the more than 20,000 human genes, only 108 are known to be involved in sphingolipid metabolism. The odds of Ashkenazi Jews having four sphingolipid storage disorders by random chance are less than 1 in 100,000, he calculated.
He talked it over with Harpending, an expert in human population genetics. They came to believe this was an example of heterozygote advantage — where having two copies of a mutated gene can mean disaster but one copy is helpful.