And they are perfectly likely to be appropriately laughed at or sneered at. This whole thread is based upon a deliberate fallacy. First, the assertion that race and heredity are necessarily correlative. It ignores the vast wealth of scientific data that contradicts the postulates to pursue a narrow, unscientific premise. I'm not at all sure it isn't just a troll thread, the veneer of "science" and "thought" being so incredibly thin; its "heritage" in eugenics so apparent.
I will, however, give it the consideration it deserves, which is little. Asking the question itself is not inappropriate, but the suppositions upon which it is based have been so thoroughly debunked as to not be considered serious. Because of that, I'll not be citing the vast catalogue of contradictory studies, and leave that to others, if they care.
The postulate begins and ends with the idea that heredity is immutable, which is, of course, ridiculous. Were that so, smart people (or cats) would never have deficient children, and all mental (and other hereditary) defects would only yield idiot/defective children. Genetics and basic empirical knowledge refutes that most thoroughly. Nor does it gain credibility by extrapolating individual hereditary chains to societies, civilizations or races. Humans adapt to their conditions. It is the genius of our species in particular. That applies to hunting, farming, urban and rural conditions. Environmental factors are infinitely more predictive (as has been pointed out) than "breeding". A child who is malnourished is more likely to falter than one who is well-nourished. Exposure to academics also has greater influence. Economic circumstances yield far higher correlations. Genius exists in all civilizations. Consider mathematics, language and chemistry. Who invented our alphabet, mathematical concepts, gunpowder? The statement of the premise ultimately demonstrates its vacuity.