It's worth noting that the Ashkenazi theory remains unproven. No one has actually found any variants which would increase intelligence markedly. At some point t

It's worth noting that the Ashkenazi theory remains unproven. No one has actually found any variants which would increase intelligence markedly. At some point that starts to look suspicious - maybe they don't exist after all. Based on all the GWASes and additional studies which have been done since 2007 and a continued absence of confirmed examples of IQ-boosting variants with negative pleiotropic effects, I now would explain the lack of optimization of intelligence as being an example of 'too complex for evolution because too many little changes to do simultaneously', that is, mutation load: essentially, there are too many little effects (which sum up to make us far stupider than we have to be), which have been created & maintained by too many demographic bottlenecks and genetic drift and other effects, too much background selection, and too much selection on other traits (plus some level of dysgenics), for the various harmful variants to have been meaningfully selected against over the past 50kya. And that's why we could boost intelligence a lot with few harmful and many beneficial side effects.