New York – Ashkenazic Jewish Diseases Linked to Higher IQ

New York – The question had been gnawing at Gregory Cochran for years: Why are European Jews prone to so many deadly genetic diseases?

Natural selection, the self-taught genetics buff knew, should flush dangerous DNA from the gene pool. Could the mutations causing these diseases have some benefit?

After a long night of research in his Albuquerque office, it hit him: Those “bad” genes make Jews smarter.

That provocative – some would say inflammatory – hypothesis has landed Cochran and collaborator Henry Harpending, University of Utah professor of anthropology, in a charged debate about IQ and DNA. Their book describing the theory, The 10,000 Year Explosion, came out in February.

The Ashkenazi diseases include Tay-Sachs, a neurological disorder that debilitates children and usually kills them by age 4; and Canavan disease, which turns the brain into spongy tissue and typically claims its victims by age 5.

Many Jewish diseases involve problems with fat molecules called sphingolipids that transmit nerve signals. Of our more than 20,000 genes, only 108 are known to be involved in sphingolipid metabolism. Cochran calculated the odds of Ashkenazi Jews having four sphingolipid storage disorders by random chance are less than 1 in 100,000.

Cochran and Harpending came to believe that 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 too curvy to carry oxygen to critical organs.

People who have only one bad copy make useful red blood cells that are deformed just enough to protect them from the malaria parasite, insulating them against the disease.

Instead of sickle cell anemia, Ashkenazi Jews had to contend with diseases like Tay-Sachs. Instead of malaria resistance, the pair reasoned, Jews got an IQ boost.

Some scientists say the theory is 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 UC San Francisco. “Do they have genetic theories about why Latinos and African Americans perform worse academically?” But Cochran, 55, and Harpending, 65, say there’s no question Ashkenazi Jews have an abundance of brain power.

Researchers have pegged their average IQ at between 107.5 and 115. That’s only modestly higher than the European average of 100, but statistically, it’s enough to boost the number of geniuses nearly six-fold.