I just got around to reading this fascinating New York Times article about a possible link between some genetic diseases among Ashkenazic Jews and higher intelligence. I’m sure a lot of interesting stuff has already been said about the study on the web. I just haven’t had time to see it. But I would offer a tiny observation. The Times article, presumably mirroring the explanations in the original study, puts a lot of emphasis on the role of Jews as money-lenders, bankers and the like. The argument is that medieval Jews — restricted as they were from traditional agriculture — naturally selected for smarter spouses. Diseases such as Tay-Sachs are the unfortunate by-product of this bias. From the Times:

He and two colleagues at the University of Utah, Gregory Cochran and Jason Hardy, see the pattern of genetic disease among the Ashkenazi Jewish population as reminiscent of blood disorders like sickle cell anemia that occur in populations exposed to malaria, a disease that is only 5,000 years old.
In both cases, the Utah researchers argue, evolution has had to counter a sudden threat by favoring any mutation that protected against it, whatever the side effects. Ashkenazic diseases like Tay-Sachs, they say, are a side effect of genes that promote intelligence.
The explanation that the Ashkenazic disease genes must have some hidden value has long been accepted by other researchers, but no one could find a convincing infectious disease or other threat to which the Ashkenazic genetic ailments might confer protection.
A second suggestion, wrote Dr. Jared Diamond of the University of California, Los Angeles, in a 1994 article, “is selection in Jews for the intelligence putatively required to survive recurrent persecution, and also to make a living by commerce, because Jews were barred from the agricultural jobs available to the non-Jewish population.”
The Utah researchers have built on this idea, arguing that for some 900 years Jews in Europe were restricted to managerial occupations, which were intellectually demanding, that those who were more successful also left more offspring, and that there was time in this period for the intelligence of the Ashkenazi population as a whole to become appreciably enhanced.

And:

Ashkenazi Jews occupied a different social niche from their European hosts, and that is where any selective effect must have operated, the Utah researchers say. From A.D. 800, when the Ashkenazi presence in Europe is first recorded, to about 1700, Ashkenazi Jews held a restricted range of occupations, which required considerable intellectual acumen. In France, most were moneylenders by A.D. 1100. Expelled from France in 1394, and from parts of Germany in the 15th century, they moved eastward and were employed by Polish rulers first as moneylenders and then as agents who paid a large tax to a noble and then tried to collect the amount, at a profit, from the peasantry. After 1700, the occupational restrictions on Jews were eased

Here’s my quibble, and I’m sure people who know more have an answer. But, the percentage of Jews in medieval moneylending alone has to be a very small number out of the total demographic pie. I mean most medieval Jews were in agriculture (or at least I’m pretty sure they were). Most of the Ashkenazi Jews I know are descended from the Shtetl not from long lines of bankers. It seems farfetched to me to imagine that this small stratum of financiers could be responsible for the widespread genetic effects described in the article.

But that doesn’t mean I disagree with the larger thrust of the piece. I do believe there was natural selection for intelligence among Ashkenazi Jews, I just think it was more widespread and had less to do with class and occupation than the Times article would suggest. In the Jewish community, at least as I understand it, it was always better to marry a rabbi than to marry, say, a butcher (though a butcher was an excellent catch). The competition to become a rabbi was considerable and the requirements for the job were intellectually formidible. Moreover, speaking broadly, Jews valued education, literacy etc for its own sake.

While it’s obviously the case that the Jews’ status as moneylenders owed a great deal to Christian theology, anti-Semitism and the like, it was also in a sense a natural consequence of the fact that Jews were well qualified for the jobs in the first place. There were other peoples, tribes and the like who could take the jobs. But last time I checked there weren’t that many famous Gypsy financiers. The Jewish emphasis on education made them the natural choice. The fact that this in turn only lead to even greater opportunities only proved to Jews that their instincts in favor of education were correct.

Anyway, if I’m wrong about this, I’d be glad to hear it.