Gregory Cochran has always been drawn to puzzles. This one had been gnawing at him for several years: Why are European Jews prone to so many deadly genetic diseases?
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 in his disheveled home office in Albuquerque, N.M., 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 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 in February.
Scientists increasingly are finding that propensities for human behavior — 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 that it’s unworthy of consideration.
“What are their theories about those on the opposite end of the spectrum?” said Neil Risch, director of the Institute for Human Genetics at the University of California, 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.
Psychologists and educational researchers have pegged their average IQ at between 107.5 and 115. That’s only modestly higher than the European average of 100, but it’s enough of a gap to produce a huge difference in geniuses. When a group’s average IQ is 100, the percentage of people above 140 is 0.4 percent; when the average is 110, the genius rate is 2.3 percent.
Although Jews make up less than 3 percent of the U.S. population, they have won more than 25 percent of the Nobel Prizes awarded to American scientists since 1950, account for 20 percent of the country’s CEOs, and fill 22 percent of the slots at Ivy League colleges, 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.’ “
Cochran, who has a doctorate in physics, developed satellite imaging systems and other optics hardware for Hughes Aircraft in El Segundo, Calif., in the 1980s. When the Cold War ended and defense budgets shrank, he 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 common disorders such as heart disease and Alzheimer’s are caused by germs. 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 Ashkenazi diseases: 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 Type A, in which babies accumulate dangerous amounts of fats in various organs and suffer profound brain damage and death before age 2.
He was struck by the fact that so many Jewish diseases involved problems with processing the same fat molecules, called sphingolipids, 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.
The most famous example of this is sickle cell anemia, which strikes people of African descent who have two defective copies of the hemoglobin B gene. As a result, they make red blood cells that are malformed and prone to clumping, which can lead to disability or death.
People who have only one bad copy of the gene make useful red blood cells that are deformed just enough to protect them from the malaria parasite. This protection against malaria, which is prevalent in Africa, has favored survival among carriers, allowing them to live long enough to procreate and pass the gene to future generations.
Instead of sickle cell anemia, Ashkenazi Jews contend with Tay-Sachs, Niemann-Pick and other diseases.
Instead of malaria resistance, the pair reasoned, Jews got an IQ boost.
The idea didn’t come out of nowhere. Researchers have been drawn to the question of Jewish intelligence and genetic diseases at least since the 1920s, when some of the disorders were first being studied. Many physicians remarked on the unusual intelligence of their patients.
One of the first to conduct a systematic study was Dr. Roswell Eldridge, a neurogeneticist at the National Institutes of Health. His study, published in 1970 in the medical journal Lancet, compared IQs of 14 children with a Jewish disease called torsion dystonia — a neurological disorder that causes uncontrollable muscle contractions that twist the body — along with 10 of their healthy siblings, and unrelated Jewish students matched by age, sex and school.
The patients had an average IQ score of 121, compared with 111 for the control students, Eldridge found. The patients’ siblings had an average IQ of 119, compared with 112 for their matched controls.
Dr. Ari Zimran, director of the Shaare Zedek Medical Center Gaucher Clinic in Jerusalem, thought he would get similar results by studying the very bright patients he treated for Gaucher’s disease, another Ashkenazi genetic disorder, in which excessive amounts of a fatty substance build up in certain organs, causing pain, fatigue and other symptoms.
His small study in the 1980s found no difference between IQs of patients and of unaffected relatives. A larger study might have done so, Zimran said. But he decided not to pursue it.
“There is enough anti-Semitism,” he said.
Cochran and Harpending are the first to make a broad case linking multiple Jewish genetic diseases to intelligence. Their theory draws on history, statistics, neurobiology and population genetics.
Jews first came to Europe in the eighth and ninth centuries. They worked as traders before taking financial jobs made available by Christians who were religiously forbidden from charging interest. By 1100, local registries listed most Ashkenazi as lenders.
That set the stage for natural selection to do its work, Cochran and Harpending theorize. Jews didn’t intermarry, keeping their gene pool closed. They were subjected to periodic persecution, which kept the population from outgrowing its white-collar niche.
According to the theory, the smartest individuals made the most money, and the wealthiest families had the most surviving children. The genes of the most intelligent Jews spread most, slowly raising the average IQ of the entire group.
Over 40 generations — roughly 1,000 years — an increase of just three-tenths of an IQ point per generation would add up to a cumulative advantage of 12 IQ points, Cochran and Harpending number-crunched. Some of their other models projected a benefit of 16 to 20 IQ points.
They wrote up their theory and sent it off to a journal. It was rejected.
Harpending said he gave it to an anthropologist friend, editor of another journal, who asked to publish it. That plan was called off, too.
The friend, who asked not to be identified because of the sensitive nature of the topic, said the paper was clearly controversial and its extraordinary claims required extraordinary evidence — which was lacking.
The paper found a home in 2005 in the Journal of Biosocial Science, a publication put out by Cambridge University.
Talk of the theory quickly spread among anthropologists and geneticists.
Within a few months, “every academic I came in contact with knew about this,” said R. Brian Ferguson, an anthropologist at Rutgers University in Newark, N.J. Many found it irresistible. A young colleague told Ferguson that the paper convinced him of the power of using genetics to study behavioral differences among people.
To Ferguson, that was a dangerous idea. There may indeed be versions of genes that are unique to Ashkenazi Jews, but it would be impossible, he said, to prove that those genes are responsible for higher IQs.
“This is not a legitimate area of research,” he said.
Others are more receptive to the theory, despite its thorny implications.
Dr. Melvin Konner, a biological anthropologist at Emory University in Atlanta, said he was impressed by the theory’s ability to explain why all the Ashkenazi diseases are clustered “on about five pages of a biochemistry textbook.” But, he added, Cochran and Harpending still have to show that the genes play a direct role in brain development.
“There’s evidence that some of them do,” he said. “It’s not a crazy idea; it’s just not nearly a proven idea.”
It would be easy to test the theory, said Steven Pinker, a Harvard cognition researcher: “See if carriers of the Ashkenazi-typical genetic mutations score higher on IQ tests than their non-carrier siblings.”
Cochran and Harpending readily acknowledge the need for such experiments. But they have no plans to do them. They say their role as theorists is to generate hypotheses that others can test.
“One criticism about our paper is, ‘It can’t mean anything, because they didn’t do any new experiments,’ ” Cochran said. “OK, then I guess Einstein’s papers didn’t mean anything either.”
Talk to us
> Give us your news tips.
> Send us a letter to the editor.
> More Herald contact information.
