There is large enough variance in Neanderthal ancestry among Europeans that we might actually be able to see differences within the European population (and then extrapolate those to guess how much of the European-African gap that explains). I seem to recall seeing some preliminary reports on this, but I can’t find them right now so I’m not confident they were evidence-driven instead of theory-driven.
It’s because Europeans are 4% Neanderthal and partake of the Neanderthals’ larger brains, and Africans aren’t.
There is large enough variance in Neanderthal ancestry among Europeans that we might actually be able to see differences within the European population (and then extrapolate those to guess how much of the European-African gap that explains). I seem to recall seeing some preliminary reports on this, but I can’t find them right now so I’m not confident they were evidence-driven instead of theory-driven.