system
A chat on subreddit /r/NoStupidQuestions
human
It's probably what biologists call a "spandrel" - a feature that isn't "for" anything but just happened as the collateral result of other adaptations - Same as male nipples.

Testosterone happens to influence hair growth, probably as part of its function in causing puberty, &amp; it also influences the skin in general (men &amp; women store fat slightly differently - women "save" more of it in case they have to breastfeed)

The difference isn't even that big naturally, you're used to seeing women who shave for cultural reasons.
gpt
I’m glad someone brought this up. I’m sure there are many reasons, but not everything in itself is an adaption. The same reason our guts are red — no real reason or adaptive advantage to having red guts. Just a result of how other parts of us developed.