>>11385153Because population bottlenecking, simple as that. Take 100 Africans with a IQ of 120, leave them on a isolated island for a couple of centuries. Assuming they don't die from inbreeding their population IQ average will be +100 IQ. This is despite being from an ancestral population with 75-80 IQ average.
The reason why is because by removing a sub-set of them from the greater population you reduce the likelihood of assorted mating. Thus lower genetic diversity but increase proliferation of high IQ genes within the mating pool that's left. But this goes both ways of course, a population that hits bottleneck but with a lower IQ will increase proliferation of those genes. Which explains how humans migrating out of Africa (which itself is a population bottleneck) dispersed into groups with varied IQ differences. Otherwise populations like the Australian Aboriginals, Indians, Oceania and non-inuit Amerindians with IQ range of 65-87 wouldn't exist.
