I forgot to mention that it also noted that Tay-Sachs, a neurological genetic disorder for which Ashkenazi Jews are routinely tested before marriage, is theorized to be the bad side of brain overclocking achieved through selective breeding. It's really a pretty cool idea.

This is an old internet meme; here is a 2003 version:

http://www.jerrypournelle.com/archives2/archives2mail/mail264.html#smarts

This formulation is much more developed and a lot more interesting. One version: Jews got their smarts by running a 5,000 year breeding experiment. Girls were encouraged to marry guys who excelled in mastering the intricacies of Jewish law - in essence, a life-long intelligence/reasoning test. People who weren't smart enough were not encouraged to stay in.