Africa has historically had much lower population density, well below Malthusian limits. Less population pressure from humans may have contributed to the survival of megafauna.
The lower population pressure in Africa is a reflection of parasites that evolved with humans there. By escaping from Malaria carried by African mosquitos and parasites carried by tsetse flies and the like humans lived longer, more fertile lives. The resulting population pressure outside Africa let humans kill the megafauna.
The lower population density in Africa wasn't some kind of harmony, it was a result of awful disease.
Now that many diseases are under control, Africa's population is exploding in a region where birth control was never relevant before. It is already overpopulated and still has birthrates that more than double population with each generation. Soon it will be the most overpopulated region in the world. The megafauna will require heroic efforts to save.
