Why do black girls have such big butts?

Obviously not *all* black girls, but a very large portion of them, I think most of them, have very round, full bottoms.

On white girls it's fairly rare to find that, and on Asians/Indians it's almost non-existent, I've found.
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Update: Another thing I notice on black girls is that a lot of them also have extremely tiny waists in addition to the butt thing. Huge, plump lips as well.
Why do black girls have such big butts?
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