What are buttcheeks for?

[Mister Obvious]

The answer is that most animals use another method to maintain balance: a tail. Humans don't have tails, and so compensate with abnormally large glutes.

Aha, that kinda makes sense. Maybe bigger hips means better balance, and maybe those kinda chicks are supposed to dance and do other weird kinda shit, maybe that's what they call a 'secondary sex characteristic'.