[mnehring]

The difference is that the twin studies deal with unique family groups while the prior discussion was counteracting a blanket ‘racial’ judgment. The fact is that what we see in individual family groups don’t reflect what the whole of the represented race because the family group differences far outweigh the racial ones (ie, any racial group is so diverse in family differences, blanket statements cannot be made for a whole based on what we describe as ‘race’)

[secretagent]

Selection for IQ possibly genetic, with a correlation of heritable diseases:

Ashkenazim have the highest average IQ of any ethnic group, scoring 12 to 15 points above the European average. They are also strongly represented in fields and occupations requiring high cognitive ability. For instance, European-origin Jews account for 27 percent of U.S. Nobel science prize winners but make up only about 3 percent of the U.S. population.

But the group is also associated with neurological disorders, including Tay-Sachs, Gaucher's, and Niemann-Pick. Tay-Sachs is a fatal inherited disease of the central nervous system. Sufferers lack an enzyme needed to break down fatty substances in the brain and nerve cells. Gauchers and Niemann-Pick are similar, often fatal diseases.

http://news.nationalgeographic.com/news/2005/07/0718_050718_ashkenazim.html