Ashkenazi intelligence

The intelligence of Ashkenazi Jews has been the subject of study and speculation within the fields of psychometry and evolutionary biology. Psychometric studies have reported a higher than average intelligence quotient among Ashkenazi Jews than among the general population. There has been a broad range of speculation about the possible causes of these findings, as well as a measure of controversy, as they touch upon several sensitive subjects such as the possible relationship between race and intelligence, as well as issues of racialism, philo-semitism and anti-semitism.
One highly publicised proposal by Gregory Cochran, Jason Hardy and Henry Harpending, suggests that the Ashkenazi had jobs in which increased IQ strongly favoured economic success, in contrast with other populations, who were mostly peasant farmers.
Psychometric findings
Cochran et al. write that according to some studies from the 1970s Ashkenazi Jews score 0.75 to 1.0 standard deviations above the general European average. This corresponds to an IQ 112-115. They have high verbal and mathematical scores, while their visuospatial abilities are typically somewhat lower, by about one half a standard deviation, than the European average. Lynn and Longley in a 2006 review write that the best reading of Jews in Britain is 110 and in the US is 109.5. Brian Ferguson writes that 90% of US Jews are Ashkenazi and that US data usually do not discriminate origin.
The study argues that European Jews were forbidden to work in many of the common jobs of the Middle Ages from 800 to 1700 CE, such as agriculture, and subsequently worked in high proportion in professions such as finance and trade, some of which were forbidden to non-Jews by the Church. Those who performed better are known to have raised more children to adulthood, according to Cochran et al. passing on their genes in greater proportion than those who performed less successfully. Another selection may have been that those with low IQ were unable to perform such professions and drifted away from the Jewish community. Jews rarely married outside of their faith, creating a reproductively isolated population in which this pressure, the authors argue, would be able to influence gene frequency. The authors write that before this time period Jews likely did not have unusual occupations and there is no evidence of high cognitive ability. Some of these diseases (especially torsion dystonia) have been associated with high intelligence. In an unpublished critique of the paper, Brian Ferguson writes that all of the basic assumptions of Cochran et al.'s theory are unsupported. For example, he observes that Torah study developed while most Jews were still farmers and that by the second half of the first millennium most Jews were literate in stark contrast to other farming populations. This was an important reason for why Jews could move into more skilled professions. He argues that an environment-only explanation emphasizing that Jews partake of cultural tradition of scholarship and abstract thought can well explain the IQ differences. Ferguson also notes that the paper is not the first to propose that Jews evolved higher intelligence. Steven Pinker has commented that he believes that the core of the hypothesis could be assessed beyond reasonable doubt by a suitable study.
The New York Times described a mixed reaction to the Cochran et al. paper. Steven Pinker said "it's certainly a thorough and well-argued paper, not one that can easily be dismissed outright." Dr. Andrew Clark said that the authors "make pretty much all of the classic mistakes in interpreting heritability". In addition, several raised the possibility of a "founder effect" rather than natural selection being the rationale for the genetic diseases (in disagreement with the paper which dismissed that possibility as statistically unlikely.) Regarding the interpretation of Jewish medieval history, professor of Jewish studies Paul Rose said "I think that some of their conclusions may be right though they still need a lot of work to be persuasive to historians and others."
Other studies
Lynn in his 2006 book Race Differences in Intelligence writes that Israel has an average IQ of only about 95. Lynn explains this by breaking down the Israeli population into three components: 40 percent Ashkenazi Jews with an average IQ of 103; 40 percent Sephardi Jews (Oriental Jewish) with an average IQ of 91; and 20 percent Arab with an average IQ of 86. Lynn suggests these differences could have arisen from selective migration (more intelligent Jews emigrated to Britain and the USA), intermarriage with neighboring populations with different average IQs, selective survival through persecution (European Jews were the most persecuted), and the presence of ethnic non-Jews among the Ashkenazim in Israel as a result of the immigration of people from the former Soviet Bloc countries who posed as Jews.
David and Lynn in a 2007 literature review examined the average IQ of European (largely Ashkenazi) and Sephardic Jews in Israel and found a 14 point lower average score for the Sephardic Jews. The authors argue that this can be explained by the hypothesis of Cochran et al. since Sephardic Jews were allowed to work in a much wider range of occupations and therefore did not come under the evolutionary pressure described in the Cochran et al. study.
A 2010 study by Bray et al. genotyped 471 unrelated Azkhenazi individuals and write that most of the diseases are not under strong positive selection, but rather rose to their current frequency through genetic drift after a population bottleneck. They also write that the Azkhenazi population are less isolated than previously thought with between 35 and 55 percent of the modern Ashkenazi genome coming from European descent.
Other proposed explanations
* A long cultural history encouraging scholarship and learning. Botticini and Eckstein argue that from the end of the second century, Judaism enforced a religious norm requiring Jewish fathers to educate their sons. The high cost of this in subsistence farming communities caused voluntary conversions, explaining a large part of a reduction in the size of the Jewish population from 4.5 million to 1.2 million. As the Jews invested in education, they could then enter skilled occupations. Cochran et al. argue that this is unlikely since there are no similar outcome in other groups such as Romani who have faced frequent persecution.
* A variant of the above is that selective migration and survival before and during the Holocaust selected for high IQ.<ref name="anti"/>

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