Why do black women have such great behinds?

I guess I might be a little bias, but I have always wondered why they have such perfect behinds.(Halle Berry, Rihanna, Alicia Keys, Lauren London, Iman, Tyra Banks) I am not into, big booties, but I love nice and round ones. I am trying not to come of as a pig, because I am far from that, I am just wondering why they have the nicest behinds. Don't get me wrong other races do to, but not quite like that. Is this just a gift from god?