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According to H. Harpending & G. Cochran Ashkenazi IQ is not derived but evolved under selective pressures during the Middle Ages.
They suggest more intelligent Jews had more surviving children than less intelligent Jews and the average IQ was gradually increasing.
Check:
"The 10,000 Year Explosion - How Civilization Accelerated Human Evolution":
https://lesacreduprintemps19.files.w...harpending.pdf
"Natural History of Ashkenazi Intelligence":
http://web.mit.edu/fustflum/document...jbiosocsci.pdf
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That was the case not only with Jews but also with other European Medieval populations, only perhaps to a lesser degree.
Studies on Medieval family size show that wealthy people had more surviving children than poor people throughout most of Europe.
In Poland-Lithuania of the 15th - 16th centuries wealthy peasants had 1,6 - 2 surviving sons per father, while peasants of average wealth had 1,1 - 1,5 (where replacement fertility = 1,05 sons per father = 2,1 children per father). Poor peasants probably had sub-replacement fertility. That was more related to wealth than to class, because medium nobles had 2 - 2,1 (the same as wealthy peasants) and magnates (very rich nobles) had 2,9. Poor nobles probably had less than 2.
In 16th - 17th centuries in England fathers with assets at death lower than 25 pounds had sub-replacement fertility (less than 2,1 surviving children).
By surviving I mean surviving to adulthood, so that they could have their own children.
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From Nicholas Wade, "A Troublesome Inheritance...", New York 2014:
(...) Clark has uncovered the simple genetic mechanism through which the Malthusian economy wrought these changes on the English population: the rich had more surviving children than did the poor. From a study of wills made between 1585 and 1638, he finds that will makers with Ł9 or less to leave their heirs had, on average, just under two children. The number of heirs rose steadily with assets, such that men with more than Ł1,000 in their gift, who formed the wealthiest asset class, left just over four children. The English population was fairly stable in size from 1200 to 1760. In this context, the fact that the rich were having more children than the poor led to the interesting phenomenon of unremitting social descent. Most children of the rich had to sink in the social scale, given that there were too many of them to remain in the upper class. Their social descent had the far-reaching genetic consequence that they carried with them inheritance for the same behaviors that had made their parents rich. The values of the upper middle class - nonviolence, literacy, thrift and patience - were thus infused into lower economic classes and throughout society. Generation after generation, they gradually became the values of the society as a whole. This explains the steady decrease in violence and increase in literacy that Clark has documented for the English population. Moreover, the behaviors emerged gradually over several centuries, a time course more typical of an evolutionary change than a cultural change. (...)
And here the data for Poland-Lithuania:
http://homoeconomicus.uwb.edu.pl/pdf...ograficzne.pdf
From page 21 (number of sons per father who lived to their adulthood):
^ Note that English graph shows children per family (couple), while Polish graph shows sons per father.
So in case of English graph replacement fertility is 2,1 while in case of Polish graph it is 1,05.
4 surviving children in English graph, is equivalent to 2 sons living to adulthood in Polish graph.
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