With all due respect, here's a simple question.
Why is is that men have nipples?
So they don’t look like aliens or mannequins...
You're asking me to explain part of God's plan and offer you some insights into His designs? Tall order and probably a fool's errand to boot. If you knew Him you would realize what a ridiculous question it is but since you apparently don't know Him, it appears reasonable to you. In any case, I'm not nearly as smart as He is so I don't have an answer for you right off the top of my head. Tell you what I'll do though. Next time I have a few minutes to spare I'll check in with Him to see if He would be willing to enlighten us. Or, you could ask Him yourself...
When YOU can produce a cat or a mouse from raw materials, you might have a bit more room to question God.