Thanks for a thoughtful response. I still wonder though, since if you compare say, blacks to whites, blacks have or tend to have different noses, different lips, different hair, etc. so it seems possible, perhaps probable, that their brains work a little differently too.
I haven’t read “The Bell Curve” and I wonder if they tried to vary the testing methods in order to overcome what could be an unintended bias.
First of all, you need to grasp the fact that DNA studies show far more variations among various African populations than between any two non-African populations.
IOW, Europeans are more closely related to Asians than either is to Africans, and many Africans are more distantly related to other Africans than they are to Euro-Asians.
Point is: you can't say, "Africans this, or Africans that", any more than you would lump together Europeans & Asians.
Second, most African-Americans are of mixed Afro-European ancestry, somewhat similar to, for example, Egyptians.
Third, African-Americans score higher on IQ tests than any others of African descent in the world, and those scores continue to rise anywhere they are not destroyed by cultural pathologies like drug abuse, single parent families, anti-"white" attitudes, etc..
Finally, think of human brains the same way we think of computers: there's hardware (DNA design) and software (culture) each effecting the other profoundly.
But unlike computers, no two humans have exactly the same mix of hardware & software, and especially diverse groups such as African-Americans will necessarily be more diverse amongst themselves than are, for example, different European populations.
Does that make sense?