But they had to be free to wander to follow nomadic food sources, and they were limited by access to food that the human body could use to create Docosahexaenoic acid, which is a fatty acid required for human brain development. Originally humans got this from fish living in the lakes and rivers of central Africa. However, about 80,000 years ago, we developed a gene that let us synthesise the same acid from other sources, freeing humanity to migrate away from the wet areas, past the dry northern part, and out into the fertile crescent.

So your point is that the expressed IQ was DHA-bound for those living away from the shore, thus making them not smart enough to develop civilization where the conditions were ripe, right? Why the DHA specifically? Wouldn't there be workarounds goven that "IQ is polygenic", if the evolutionary pressure was toward higher IQ? I'm wondering if this is but one of a multitude of possible explanations, and how one would attempt to falsify it.