So it’s now a scientific fact. Or rather, it’s two of them: Jews, or at least Jews of Eastern-European ancestry, are smarter than most people – and being smart can be bad for your health. Actually, these claims haven’t been enshrined by science yet. They’ve merely been put forth as a theory by a team of three researchers from Utah University, in a newly published paper in the Journal of Biosocial Science. Integrating genetics with biochemistry, the three have proposed that Ashkenazi Jews were naturally selected for intelligence more than other people, which in turn led to the development among them of certain distinctive genetic diseases, such as Tay-Sachs, Niemann-Pick, and mucolipidosis type IV.

The Utah team has an explanation of why this is so. On the one hand, it argues, because Jews, for most of their European history, were mainly engaged in such mentally but not physically demanding occupations as commerce and money lending, their survival depended on intellectuality and quick-wittedness. Yet on the other hand, since one way of becoming mentally quicker is to produce more fatty chemicals of a type known as sphingolipids, which promote the growth of the axons and neurons on which brain activity depends, and since an overproduction of these same chemicals has been implicated in the genetic diseases that Ashkenazim are prone to, Jewish braininess and Jewish illnesses have gone together. In the world of evolution, nothing comes without its price tag.

Jews, of course, have always been convinced that (a) they’re smarter than others and (b) this hasn’t always been a great blessing. In Yiddish, the two expressions, a goyisher kop, “a gentile head,” and goyisher mazel, “a gentile’s luck,” complement each other ironically. The first refers to the belief that gentiles aren’t as bright as Jews; the second to the belief that they’re a lot luckier. It’s just that whereas in the past this was assumed by Jews to mean that too much thinking only got you into trouble, we’re now told that it’s a matter of sphingolipids.

Well, perhaps so. It’s certainly true that Jews have an unusual record both of intellectual accomplishment – although they account for only 3% of America’s population, the Utah study points out, they have won 27% of its Nobel prizes – and of misfortune. And just in case one seeks to put this intellectual accomplishment down to entirely environmental factors, such as parental attitudes toward education, the study also points out that while only four of every 1,000 northern Europeans have IQs of 140 and over, 23 of every 1,000 Jews do.

Yet there’s a better explanation of this than the Utah study offers. Historically, Ashkenazi Jews, more than benefiting from natural selection, bred for intelligence deliberately. You don’t have to be a genius, after all, to be a successful money-lender or a good businessman, and it’s doubtful whether generations of moneylenders would necessarily produce smarter offspring than generations of farmers – but you do have to be smart indeed to be a good Talmudist, and Ashkenazi marital patterns were geared to bringing as many good Talmudists as possible into the world.

This was done by the extremely common practice among Ashkenazim of rich Jews choosing sons-in-law on the basis, not of wealth or social standing, but of outstanding achievement in rabbinic studies. The well-off Ashkenazi businessman or money-lender didn’t insist that his daughter marry a young man who was rich like himself, the way wealthy Christians did; his prestige depended, rather, on her marrying someone brainy, whose intellectual pursuits he was willing to support. And inasmuch as the children of the rich in any society have a better chance for survival than the children of the poor, enjoying as they do superior nutrition, hygienic conditions, and medical care, this conscious alliance of wealth with intelligence, which was unique to European Jews, meant that from generation to generation, the percentage of intelligent Jewish children grew greater. Although sphingolipids may have had something to do with it, so did Jewish values.

The Utah study is of course only a hypothesis, and already it is under attack as much for social reasons as for scientific ones, it being highly politically incorrect in today’s scholarly world to assert that intelligence is distributed unequally among different peoples or races. After all, if some biological groups are naturally smarter than others, others must be naturally less smart – a claim that, when made by the social scientist Charles Murray some years back in his book “The Bell Curve,” led to his ostracism by the scientific community.

Before too many people, however, pounce on the Utah study for proclaiming Jewish “racial” superiority, one should keep in mind not only that the statistical differences involved are relatively minor (977 out of every 1,000 Jews do not have IQs over 140), and that other populations, such as Asians, may score even higher on tests, but that being smart, as folk wisdom everywhere knows, is not always the same as being wise.

Indeed, if “Jewish luck” has been bad over the centuries, this is not unrelated to the enormous blunders that Jews have made. Over and over in the course of their history, they have made the wrong friends and the wrong enemies, followed the wrong leaders, fought the wrong wars, quarreled foolishly and destructively among themselves, misread the political map of their times, deluded themselves with wishful thinking, and buried their heads in the sand rather than take a hard look at the dangers confronting them. Over and over, they have put their faith in unthinking beliefs rather than in critical analysis, and over and over, they have paid the price for not using the intelligence they supposedly have had so much of. Perhaps somewhere in the Jewish makeup, there is a gene for stupidity too. Its discovery would come as no more of a surprise than has that of the Utah study.

Mr. Halkin is a contributing editor of The New York Sun.