The subject is also explored in an episode of African American Lives.
In fact, because as a species we spent the most time in Africa, the greatest amount of genetic variations are currently found among people living on the African continent -- on a genetic level, an individual of East African ancestry may have more in common with a European than with a West African.
More reading on human evolution:
SURVEY: HUMAN EVOLUTION, The proper study of mankind
Guns, Germs and Steel
Darwin's Dangerous Idea