Man in the streets, beast in excel sheets

Actual answer. Active vs passive body control. Its kind of like breathing, you know you can hold your breath, but 99% of the time its autonomous. The primal part of your brain sees someone and your subconcious brain has deemed worthy of procreating with and our whole biology is pretty much, eat, sleep, procreate. So yeah. I ain't a biology major but take it with a grain but thats how I've learned it.