@mathlover Well,'we can certainly debate over what a "race" is. The way I look at it today is it's a low-res layman's term for ethic and cultural groups.

Migratory patterns brought different evolutionary pressures on the migrants. In turn, that produced phenotypic differences in skin colour, stamina, tolerance to things like milk, etc. And of course, it would affect the most expensive organ in the body, the brain.

I am going to be doing a lot of research on this shortly for a matter I need to deal with, and I might share some of what I find here.

For some regions today, like the US and South America, you have the "mutt effect" where a lot of mixing took place between the European and African stock. Even more so in South America than the US.

Other areas of the world have remained more or less genetically isolated, like Africa, Iceland, etc.

@lordalveric From what I have heard from my father (medical doctor) the brain part is more affected by the variations within populations (and even more so by environmental factors) than by racial differences, and the effects of the latter two are so large that racial differences in neurology are negligible.

You are correct about the matter of what "race" is.