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Gwern has written an essay on why. https://www.gwern.net/Drug-heuristics https://www.gwern.net/Drug-heuristics Here’s a brief snippet > the intervention may

Gwern has written an essay on why. https://www.gwern.net/Drug-heuristics https://www.gwern.net/Drug-heuristics Here’s a brief snippet > the intervention may be simple, give major enhancements, but result in a net loss of reproductive fitness The famous Ashkenazi theory of intelligence comes to mind. According to this theory, the Ashkenazi were forced into occupations demanding intelligence, and micro-selected for high intelligence. Except the high IQ genes were not previously prevalent among either Jews or gentiles because - like sickle-cell anemia - when they became too prevalent, they result in horrible diseases like Tay-Sachs. In 2007, a unique mutation in a Scottish family was found to increase verbal IQ in afflicted family members vs non by something like 25 points; this would be great for them - except for how that mutation starts causing blindness in one’s 20s or later. (In general, it’s much easier to find mutations or other genetic changes breaking intelligence than helping in cases of retardation26 and autism27.)

gwern 8y ago
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.

gwern 8y ago

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.