Genetics in sports aren't really discussed because of the taboo of "racism", but it's an interesting subject. People of west African descent have muscular builds and are the best at short burst sprints. However, their dense muscles come as a detriment for swimming. The slender, long legged (particularly calf-muscle) east Africans are best at long distance running. Swimming is dominated by whites because they are more buoyant and store more fat (perhaps due to evolving in a colder climate).