I get the impression that one difference between Africa and the rest is the shit in Africa evolved to deal with people. Stuff of a certain size survived that wouldn't have anywhere else in the world. And I don't think it's due to African incompetence at primitive hunting. The American megafauna were taken down with spears. I think it's that the stuff in Africa are survivors that have been around people for a long time. The ones that were vulnerable got eaten, but there's still large game in Africa. In a way that there isn't in Europe or America.