I'm not trying to knock what you are saying, because genetic makeup may very well have an influence on athletic performance. But, I think its much more a result of social and cultural influence than anything else. Kenyans make up .0005% of the world population, yet they win about 40% of international distance-running competitions. If they are so physically gifted in the department of endurance, why are they not dominating the Tour De France, Iron Man, etc.... If blacks are so good at jumping, why do they not dominate the high jump and pole vault? If they are so much stronger, where is their dominance in the shot-put, discus, javelin, and weight lifting events? If specific forms of music, art, dance, and comedy have emerged from the black subculture, is it wrong to assume that the representation of blacks in basketball is a result of the influence of culture and society as well? Additionally, take a sport like Judo. Japanese Americans make up .3% of the US population, yet they make up more than 1/5th of top competitors in Judo. Certainly a sport that requires speed, strength, and power such as a martial art would be dominated by blacks as well, right?
Take a look at the list of competitors in this video, you may recognize a name or two.....
http://www.youtube.com/watch?v=kuj-R9DFMmY