That the most intelligent of the population would continue to choose priesthood event after celibacy was made mandatory by the Roman Catholic Church.
Perhaps the most intelligent of the population did not continue to choose the path of celibacy over and over again for 25-50 generations.
There would probably be more startups in the Arab population if they weren't so discriminated against in the country.
I can't believe someone down-voted my previous comment. Is it now anti-Semitic to say that the Jews aren't genetically superior to everyone else?
Can there really be evidence that the genetically similar brothers and relatives of Christian priests weren't helped by their siblings status? Can we show that priests had a disproportionate amount of the intelligence genes of the Christian population to begin with? Can we show that converted Jews (like my ancestors) didn't skew the results? Can we show, even, that priest didn't actually reproduce quite freely through the behind-the-scenes-hanky-panky they were famous for? The list could go on and on. Jeesh!
Historically (e.g. medieval times) the priesthood drew many of most intelligent/academic segment the population, as a compelling alternative to manual labor.
Beginning in the 4th century, Christian priesthood adopted celibacy, which later was made mandatory by the Roman Catholic Church, which sought to prevent inheritance from draining its coffers. http://en.wikipedia.org/wiki/Celibate#Christianity
Meanwhile, Jewish Rabbis have been encouraged to marry and bring up children throughout this history.
Over centuries, you get a selective drift which results in a different distribution of intelligence among the populations. This explains in part the statistical incidence of academic achievement in the jewish population: http://en.wikipedia.org/wiki/Ashkenazi_Jews#Achievements
Note that I'm speaking here of statistical measures. There are plenty of dumb jews, just as non-jews. But thousands of years of policy from the Catholic church has led to a population shift which has excluded many of the historically most academic in nature from procreating over 25 - 50 generations.
An explanation I first came across in Nozick's http://en.wikipedia.org/wiki/Anarchy,_State,_and_Utopia