natural history of ashkenazi intelligence - Henry C Harpending ...

Ashkenazi intelligence 13
Societies reward different behavioural traits. In some times and places successful
warriors and soldiers have had high status, in others merchants, in still others
bureaucrats as in ancient China. There were societies in pre-modern Europe in
which merchants and businessmen ranked near the top, but this was atypical. To the
extent that status and wealth were inherited rather than earned, the correlation
between cognitive traits and reproductive success in elite groups may have been quite
weak.
In almost every case elite groups experienced substantial gene flow with other,
much larger groups that were not subject to the same selective pressures. This means
that the selective pressures experienced by such groups were diluted, and spread out
into the general population. Christian merchants in London or Rotterdam may have
experienced selective pressures similar to those of the Ashkenazi Jews, but they
intermarried: there was extensive gene flow with the general population, the majority
of whom were farmers. The selection pressures experienced by farmers were probably
quite different: most likely cognitive skills did not have as high a correlation with
income among farmers that they did among individuals whose occupations required
extensive symbol manipulation, such as moneylenders, tax-farmers and estate
managers.
The Ashkenazi occupational pattern was different from that of the Jews living
in the Islamic world. The Jews of Islam, although reproductively isolated, did not
have the concentration of occupations with high IQ elasticity. Some had such jobs
in some of the Arab world, in some periods, but it seems it was never the case that
most did. In part this was because other minority groups competed successfully for
these jobs: Greek Christians, Armenians, etc., in part because Moslems, at least some
of the time, took many of those jobs themselves, valuing non-warrior occupations
more highly than did medieval Christians. In fact, to a large extent, and especially
during the last six or seven hundred years of relative Moslem decline, the Jews of
Islam tended to have ‘dirty’ jobs (Lewis, 1984). These included such tasks as cleaning
cesspools and drying the contents for use as fuel, a common Jewish occupation in
Morocco, Yemen, Iraq, Iran and Central Asia. Jews were also found as tanners,
butchers, hangmen and other disagreeable or despised occupations. Such jobs must
have had low IQ elasticity; brilliant tanners and hangmen almost certainly did not
become rich.
The suggested selective process explains the pattern of mental abilities in
Ashkenazi Jews: high verbal and mathematical ability but relatively low spatio-visual
ability. Verbal and mathematical talent helped medieval businessmen succeed, while
spatio-visual abilities were irrelevant.
Genetic evidence about Ashkenazi history and the bottleneck hypothesis
Evidence from polymorphic gene frequencies
The prevalence of several inherited diseases among Ashkenazim is often attributed
to one or more population size bottlenecks in the past. Since the only evidence for
such a bottleneck is the mutations themselves, it is important to look at other genetic
markers for signs of any bottleneck. Episodes of small effective size could have