Jon Entine has argued, most prominently in his book Taboo: Why Black Athletes Dominate Sports and Why we’re Afraid to Talk about It, that body type and physiology are shaped by evolution and can be correlated, somewhat loosely, to skin color. He claims that Africans from different parts of the continent have different body types and on average, excel in different sports. For example, Kenyans have won most of the cross-country races for the better part of thirty years, and East Africans who trace their ancestry to areas along the Rift Valley dominate endurance running. East Africans have a higher percentage of slow-twitch fibers in their muscles, a slightly longer body, longer legs, and larger lung capacities which help in endurance and long-distance running. Conversely, Western African-descended runners dominate in anaerobic sports, including sprinting. People with ancestral roots in this region of Africa have bigger, more visible muscles along with a higher number of fast-twitch fibers in their muscles. They also have less natural body fat, narrower hips, and higher levels of testosterone. Anthropologist Ian Kerr criticized Entine's hypothesis, stating that biological variation cannot be used to uphold claims of racial superiority in athletics.
Joseph L. Graves argues that Kenyans and East Africans who have done well in long distance running all have come from high-altitude areas, whereas East Africans from low-altitude areas do not perform particularly well. He also argues that Koreans and Ecuadorians from high-altitude areas compete well with Kenyans in long-distance races. This suggests that it is the fact of having trained in a high altitude, combined with possible local level physiological adaptations to high-altitude environments that is behind the success in long distance running, not race. Similarly, Graves argues that while it is superficially true that most of the world recordholders in 100-metre dash are of West African heritage, they also all have partial genetic heritage from Europe and Native America, they have also all trained outside of West Africa, and West African nations have not trained any top-level runners. Graves says these factors make it impossible to say to which degree the success is best attributed to genetic or to environmental factors.