Most DNA sequences don't do anything, as far as we know. The longer a population has been in a particular area, the more variation such DNA will show, because it has has been accumulating random mutations for longer. This is different from variation that results from evolutionary selection pressures. Prof. Fatimah Jackson has in fact argued that the transport of Africans across the Atlantic, and their settlement as slaves in the New World, produced just such selection pressures for variability. But Gladwell is wrong to say that within groups of Africans, there will be more variability in any genetic trait.
Natural selection is all about favouring some variants over others.
And that would do more to demolish racial stereotypes than finding a white Michael Jordan. Scientific racists like to claim that they aren't racist because they don't actually hate other races. M. Le Pen says - blacks are better endowed for sports and dance than whites. Brains, Genes and New Guineans Jared Diamond doesn't believe that Europeans conquered Americans and Africans because Europeans are innately cleverer than other peoples. This book is intended to be a major statement against racial science.