East Africans dominate distance racing every bit as much as West Africans dominate short races. Those who refuse to believe their own lying eyes will concoct all sorts of convoluted explanations to avoid the obvious - these groups simply have a genetic edge in these events. Other ethnic groups dominate in other arenas (Icelanders in "strong-men" competitions, Turks and other north-west-Asia-Minor groups in weightlifting, East Asians in gymnastics - the great Steve Sailer has a nice summary in this old article and in other spots on his blog). Of course the only reason people run away in horror from the obvious genetic explanation is that this invites the blood-curdling suggestion that genetics could be behind other observed differences in ethnic/racial groups as well. And that just can't - no, it couldn't possibly - no, never - it must be "stereotype threat" - yeah, that's the ticket!