From Yahoo News:

Scientists have found the reason why blacks dominate on the running track and whites in the swimming pool: it's in their belly-buttons, a study published Monday shows.

What's important is not whether an athlete has an innie or an outie but where his or her navel is in relation to the rest of the body, says the study published in the International Journal of Design and Nature and Ecodynamics.

The navel is the center of gravity of the body, and given two runners or swimmers of the same height, one black and one white, "what matters is not total height but the position of the belly-button, or center of gravity," Duke University professor Andre Bejan, the lead author of the study, told AFP.

"It so happens that in the architecture of the human body of West African-origin runners, the center of gravity is significantly higher than in runners of European origin," which puts them at an advantage in sprints on the track, he said.

Individuals of West African-origin have longer legs than European-origin athletes, which means their belly-buttons are three centimeters (1.18 inches) higher than whites', said Bejan.

That means the black athletes have a "hidden height" that is three percent greater than whites', which gives them a significant speed advantage on the track.

For example, I'm about the same height as Michael Jordan, but not exactly the same shape. But I am a better swimmer than Michael Jordan, in that I can swim. (Despite spending many years around luxurious swimming pools, Jordan is said to have never learned how to swim because he finds it unpleasant to immediately sink to the bottom of the pool.) In proportions, I'm closer to Michael Phelps, the Human Surfboard swimmer, who is tall but has relatively short legs.

All this is not exactly new news. O.J. Simpson gave a more detailed explanation of black and white physiological differences to Time Magazine in 1977.