Natural History of Ashkenazi Intelligence

Abstract

This paper elaborates the hypothesis that the unique demography and sociology of Ashkenazim in medieval Europe selected for intelligence. Ashkenazi literacy, economic specialization, and closure to inward gene flow led to a social environment in which there was high fitness payoff to intelligence, specifically verbal and mathematical intelligence but not spatial ability. As with any regime of strong directional selection on a quantitative trait, genetic variants that were otherwise fitness reducing rose in frequency. In particular we propose that the well-known clusters of Ashkenazi genetic diseases, the sphingolipid cluster and the DNA repair cluster in particular, increase intelligence in heterozygotes. Other Ashkenazi disorders are known to increase intelligence. Although these disorders have been attributed to a bottleneck in Ashkenazi history and consequent genetic drift, there is no evidence of any bottleneck. Gene frequencies at a large number of autosomal loci show that if there was a bottleneck then subsequent gene flow from Europeans must have been very large, obliterating the effects of any bottleneck. The clustering of the disorders in only a few pathways and the presence at elevated frequency of more than one deleterious allele at many of them could not have been produced by drift. Instead these are signatures of strong and recent natural selection.

Cognitive Enhancement: Methods, Ethics, Regulatory Challenges

“…It is possible, however, that some alleles that are rare in the human population could have larger effects on intelligence, both negative and positive. 2 2 A possible example is suggested in (Cochran et al 2006), where it is predicted that heterozygoticity for Tay-Sachs' disease should increase IQ by about 5 points.…”

Evolutionary accounts of human behavioural diversity

“…However, some, perhaps most, anthropologists are highly uncomfortable with any role for genes in explaining variation between populations [78], with some exceptions (e.g. [79]). This reticence to include genetic variation as a source of diversity is likely to result, in part, from the racially discriminatory perspectives on human evolution that permeated the early part of the history of anthropology [3].…”

The Wisdom of Nature: An Evolutionary Heuristic for Human Enhancement

“…For instance, there is some indirect evidence that at least Type I Gaucher's Disease (and possibly other sphingolipid storage diseases) is linked to improved cognition, given the significantly higher proportion of sufferers in occupations correlated with high IQ.⁷⁴ This, and other circumstantial evidence, is used by the authors of the cited study to argue that heterozygote advantage can explain the high IQ test scores and the high prevalence of Type I Gaucher's Disease among Ashkenazi ⁷³ Allison 1954;Cavalli-Sforza andBodmer 1999. ⁷⁴ Cochran, Hardy andHarpending 2006. Jews. Should this prediction be borne out by finding an IQ advantage for heterozygote carriers of the diseases, it would suggest that screening to promote heterozygosity, or genetic interventions to induce it, would be viable forms of cognition enhancement that meet the EOC.…”