All of this is part and parcel of the secular left not really believing in Darwinian evolution, just wanting it as a creation myth with which to displace Christianity.
If one really believes in Darwinian evolution, it is impossible to credit the notion that human populations living in vastly different environments (the African rainforest, the African savannah, Siberia, the Mediterranean basin, Scandinavia,...) for tens of thousands of years would not develop measurably different characteristics of a non-cosmetic nature, including cognitive characteristics. Of course, evolution being a slow process and almost all measurable human characteristics having some survival utility in almost all environments, one would expect the distributions of the measurable characteristics to overlap, but one would expect the means and standard deviations to vary in some way on the basis of the different selection pressures afforded by the radically different environments.
Which means, of course, that humans are presently in the process of evolutionary convergence due to interbreeding, not divergence.
Those populations are not isolated so much, anymore.
Also, Caucasians and East Asians contain measurable proportions of DNA from species of Homo other than sapiens.
Black Africans don’t.
I have no clue what that means, except that we aren’t “one race” other than metaphorically.
“Race” simply means breed, variety or sub-species, and is still used that way in other areas of biology.
Racists, of course, try to make race mean “species.” “Anti-racists” deny that humans are divided into races at all.