Not sure what the point of this article is supposed to be... for 2000 years, Jewish communities around the world (especially Orthodox) have been closely interbreeding, and with a much smaller pool to start from.
Excellent point!
I think the difference is one breeds within the community, the other breeds within the family.
See also post #21, in that society if you marry your daughter off to a non-relative you have no control what-so-ever over how badly he mistreats her, you have some slight control (via familial pressure) over a brother.
The Jews were mostly engaged in money-lending, trading, and crafts -- occupations where smart people are more likely to earn enough to keep their families fed. The stupid men either didn't earn enough to attract a wife, or their families starved.