Their reasoning is straightforward enough: If the gene mutations responsible for diseases in Ashkenazim didn’t confer some evolutionary selective advantage, they wouldn’t persist. Cochran and Harpending liken these defective genes to the genes in Africans that often deform hemoglobin. Carrying one copy of the gene, most research suggests, helps ward off malaria—surely an adaptive advantage. Two copies, however, cause sickle-cell anemia.
Cochran and Harpending reasoned the same must be true of the genes that cause illness among Ashkenazi Jews, particularly the four that cause mutations in the enzymes responsible for breaking down fats: Tay-Sachs, Niemann-Pick, Gaucher disease, and mucolipidosis type IV. Two copies cause devastating illness, but one, they speculate, mutely aids the carrier.
How? By enhancing intelligence. Without this extra edge, they hypothesize, the Ashkenazim would never have survived. The Jews “experienced unusual selective pressures that were likely to have favored increased intelligence,” they say. “Their jobs were cognitively demanding, since they were essentially restricted to entrepreneurial and managerial roles as financiers, estate managers, tax farmers, and merchants. These are jobs that people with an IQ below 100 essentially cannot do.”
“I have a stack of books, like four feet high, on all metabolic diseases,” Cochran tells me. “And the four sphingolipid diseases affecting Ashkenazi Jews”—the ones he and Harpending believe enhance intelligence—“are all in the same chapter. That’s like one in 100,000 odds. People could say it’s chance, I suppose—in the same way it’s chance that 27 percent of all of those guys go to Stockholm every year.”
There’s scant physical evidence for this assumption. But what the authors found was intriguing. Among the papers they unearthed were studies by Steven Walkley, a neuroscientist at Albert Einstein College of Medicine, that showed growth of additional dendrites in the tissues of humans and cats with Tay-Sachs and Niemann-Pick. They also cite a 1995 study in the Journal of Biological Chemistry that shows increased neural growth in the brains of rats with Gaucher disease. The authors decided to contact Ari Zimran, the head of the Gaucher Clinic at the Shaare Zedek Medical Center in Jerusalem. It turns out that 81 of his 255 working-age patients have jobs that require, by the author’s estimates, an IQ of at least 120. Twenty-three are engineers, and fourteen are scientists—a number that, if it were consistent with the Israeli workforce, should be just six.
Yet there are many who’d find a very different way of explaining the intelligence of these patients. They wouldn’t invoke their extra dendrites. They’d invoke their mothers.
To say that the Jews have a history of emphasizing scholarship is not just the fantasy of ethnic chauvinists and Woody Allen fans. To look at a single page of the Talmud is to understand this, with its main text at the center, its generations of rabbis arguing around the rim. The dialectic and critical reasoning are at its core.
Growing up, most children in Jewish households are at least vaguely aware of their intellectual aristocracy—who do you think was counting all those Nobel Prize winners? The Swedes?—and if it’s not the intellectuals they’re aware of, it’s the high-achieving Jews, the ones who killed on Dick Cavett, played lead guitar, helmed the Starship Enterprise. (The one season I attended Sunday school, one of my first assignments was to find the name of a Jewish celebrity; when I returned the following week with the name of Beverly Sills, rather than Gene Simmons, my teacher didn’t find it the least bit strange.) All minorities have their private halls of fame, of course, but it was a Jew, Adam Sandler, who took this obsessive curatorial tendency and set it to music. “David Lee Roth lights the menorah / So do James Caan, Kirk Douglas, and the late Dinah Shore-ah . . . ”
It’s staggering what an emphasis on scholarship, both secular and religious, combined with a history of relentless displacement will do. One could argue it’s a near-certain recipe for achievement. Just last month, Sherwin Nuland, author of How We Die, wrote a meticulous, almost pointillist essay for The New Republic explaining why Jewish doctors have been held in high esteem for centuries. (The title of the article: “My Son, the Doctor.”) He notes that physical healing has always been privileged by Jewish scripture, and therefore became the province of learned rabbis, the apotheosis of whom was Maimonides. If the Jews were expelled from a particular country, as they so often were, they could take their profession with them—medicine was divinely portable.
From there, Nuland draws on the work of John Efron, a historian at the University of California at Berkeley, pointing out that once universities opened their doors to Jews, much of the Jewish emphasis on scholarship shifted from the religious to the secular, partly as a result of their tremendous desire for social respectability. At the fin de siècle, for example, Jews made up a mere 1 percent of the German population, but they made up 50 percent of all the doctors in Berlin and 60 percent of all the doctors in Vienna. “It had to do with emerging from the ghetto,” says Efron, author of Medicine and the German Jews: A History. “There were enormous social pressures to succeed—part of the emancipation process was to show that Jews were good Europeans, good Austrians, and medicine was a universal, non-parochial science, where the barriers to entry were low but the prestige was enormously high. It’s the same pattern you’re seeing in the United States today, if you have a look at medical-school acceptances: There are much larger numbers of Asian and Indian students.” Numbers from the American Association of Medical Colleges bear this out: Today, 18 percent of all med students are Asian, as opposed to 6 percent just a dozen years ago.