andrewducker: (Default)
andrewducker ([personal profile] andrewducker) wrote2012-03-06 11:00 am

[identity profile] gwern branwen (from livejournal.com) 2012-03-07 02:47 am (UTC)(link)
The defects *have* to be relatively rare for heterozygote advantage to be fitness-improving in the postulated Ashkenazi historical context. If half your infants die of genetic diseases, you need the other half to be basically Supermen who bed Lois Lanes every other day to make up for your losses. At a rate like 1% or whatever the real rate is, then it becomes more possible for a small increase in IQ to have enough of an expected-value to pay for the genetic defects.

In any case, it's just one example.