Are Jews smarter? And non-Jews—not so much?

Ever since researcher Gary Cochran of the University of Utah sought to explain the apparent Ashkenazi intelligence edge as an easily-understood example of natural selection, the idea has attracted criticism from scholars of every persuasion. Here’s his thesis:
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In the Middle Ages, European Jews were subjected to legal discrimination, one effect of which was to drive them into money-related professions, such as banking and tax farming, which were often disdained by, or forbidden to, Christians. This, along with the low level of intermarriage with their non-Jewish neighbors (which modern genetic analysis confirms was the case), is Cochran’s starting point.

He argues that the professions occupied by European Jews were all ones that put a premium on intelligence. Of course, it is hard to prove that this intelligence premium existed in the Middle Ages, but it is certainly true that it exists in the modern versions of those occupations. Several studies have shown that intelligence, as measured by IQ tests, is highly correlated with income in jobs such as banking.

What can, however, be shown from the historical records is that European Jews at the top of their professions in the Middle Ages raised more children to adulthood than those at the bottom. Of course, that was true of successful non-Jews, as well. But in the Middle Ages, success in Christian society tended to be violently aristocratic (warfare and land), rather than peacefully meritocratic (banking and trade).

Put these two things together — a correlation of intelligence and success and a correlation of success and fecundity — and you have circumstances that favor the spread of genes that enhance intelligence. The questions are, do such genes exist and what are they if they do?
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I just came across another article here in the archives that includes a complementary propositon that Gentiles were self-selecting for traits other than mental agility during the very same time period:
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Rabbi Arthur Green, dean of the Rabbinical School at Boston’s Hebrew College, wondered whether the findings took into account all relevant factors in the development of Jewish intelligence. He noted that during the period in which the researchers believe the Jewish intelligence gene began to be selected, the majority Christian world was, in a sense, selecting against such a gene.

“In that same period of 1600 to 1800 years, Christian Europe was systematically destroying its best genetic stock through celibacy” of priests and monks, he said. “The Christian devotion to celibacy, particularly for the most learned and highest intellectual achievers, diminished the quality of genetic output and created a greater contrast with the Jewish minority.”
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That’s an angle that I never heard before, and I’ve been thinking about it since last night.

Any thoughts?

—Dennis Wilen