There is no question that anatomy, physiology, and genetics has an effect on athletic potential. But so does opportunity and exposure. If you look at any sport you will observe that with increased access and opportunity, successful athletes emerge. Until there is equal access and opportunity for all, it will be difficult to determine who will succeed and who won't.
Why do so many Marathoners come from Ethiopia and Kenya not their neighbors, Tanzania, Sudan and Chad?
Why does France and Germany produce so many great cyclists and none from neighbor Poland?
Why so many good tennis players from Australia, Sweden, Russia but Italy just produced their first French Open champion?
Questions not easily answered.