Jews first came to Europe in the eighth and ninth centuries. They worked as traders before taking financial jobs made available by Christians who were religiously forbidden from charging interest. By 1100, local registries listed most Ashkenazi as lenders. That set the stage for natural selection to do its work, Cochran and Harpending theorise. According to the theory, the smartest individuals made the most money, and the wealthiest families had the most surviving children. The genes of the most intelligent Jews spread most, slowly raising the average IQ of the group. Over 40 generations—roughly 1,000 years—an increase of just three-tenths of an IQ point per generation would add up to a cumulative advantage of 12 IQ points, Cochran and Harpending conclude.
_Karen Kaplan, LATWP