One of the things you notice about African-American sprinters is that they tend to look like they are very African by ancestry, more so than the average African-American, even though track and field is traditionally something of a Talented Tenth pastime. Back in the Jim Crow era, Southern black colleges like Morehouse switched their main Spring sport from baseball to track so they could compete in the newspaper reports of times for Olympic team attention.
Allyson Felix, winning her fifth gold medal in her fourth Olympics, has the traditional middle-class African-American background: her father is a minister, her mother is a schoolteacher. Felix has what John Updike in The Coup called classic Negroid features, yet she’s the fairest of the four. Anchorwoman Tori Bowie from Mississippi is exceptionally dark for an African-American. She is darker than the Nigerian relay women.
These patterns within the African American population suggests that sprinting isn’t just socially associated with having at least one drop of African blood. Instead, in the 100 meters, the more drops the better.