Interesting. But don't those examples still appear to suggest more of a culturally-driven phenomenon?
It seems we'll always see ups and downs in the # and expression of great minds, depending on the circumstances in which men live.
I think you are suggesting the cart pulling the horse. Culture is created by brain power--the more complex and mentally stimulating the culture, the more brain power evidenced by those who created it.
Of course, through the generations, there is an ongoing interaction. And the culture will certainly influence how the individual develops. (That is only to recognize that both nature and nurture are factors in human development. However, based upon the studies of twins, nature accounts for from 2/3 to 3/4 of the ultimate result.)
A good practical example, is in the effect of the Welfare State in dumbing down the American population, by subsidizing the breeding habits at the bottom of the social structure, while causing a taxation burden, which makes many middle class couples limit their child bearing. Thus there has been a considerable fall off in average scholastic aptitudes since the middle of the past century, even though much more has been spent on cultural stimulation, etc., via various programs--admittedly not always well thought out.
William Flax Return Of The Gods Web Site