Actually, whawha, the Southern Black kids you refer to are genetically West African or a mix of that with European. They do not dominate running at any event 1500m or longer. Nor would they if they decided to. This post will get a bunch of negative votes for the period of time prior to it's deletion. That is a given.
Still the same, the physical characteristics that allow a particular athlete (regardless of race) to be successful at sports such as basketball, football, and hockey are contradictory to the characteristics necessary for success in any endurance sport. LeBron James would not hold the AR at the marathon if he had been convinced starting at the age of 11 to care about it. He does not have a small, light bone structure nor 90+% slow-twitch fibers.
One cannot be both 6'11" and 145 lbs. One cannot have both 90% slow-twitch and 90% fast-twitch. Although the presence and success of individuals with West African ancestry in sprints (and other sports where high fast-twitch %s are beneficial) is so obvious as to not need mention here, even the most athletic members of the genotype in question do not appear in all-time results at any T&F distance event.