Prof. Gregory Cochran - The Evolution of Jewish IQ by Natural Selection

Cochran and Harpending's theory relegate the reason of Jewish high IQ to a mechanism of natural selection. Jews throughout history didn't intermarry thus keeping their gene pool closed. And since Jews were given the white collar and financial jobs made available by Christians who were forbidden by the Church from charging interest, this set the stage for natural selection to do its work. Since 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, thus slowly raising the average IQ of the entire group.

In this manner, over 40 generations -- roughly 1,000 years -- an increase of just 0.3 points per generation would have added up to a cumulative advantage of 12 points, Cochran and Harpending theorized. Some of their other models projected a benefit of 16 to 20 IQ points.