system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do people have butts?

Extremely random but I just need to know some please tell me. I don't understand what their evolutionary purpose is and would really like to know!
gpt
Well, one big reason that we have more prominent posteriors than other species, particularly those close to us, is bipedalism. You need way bigger gluts to walk on 2 legs than you do on 4. Additionally it clearly became a trait that was sexually selected for to at least some extent.