Humans are designed to compartmentalize objects, ideas, and experiences. It’s how we survive. Our early ancestors’ ability to instantaneously decide a whether a situation was safe or dangerous was imperative if they wanted to keep their weak, hairless little bodies alive long enough to pass along their genes.
As societies developed, understanding our place within that structure, as well as everyone else’s, became just as important. We wanted to look at somebody and immediately know certain things about them (namely, were they trying to have sex with us, and were we trying to have sex with them). We would use visual cues to gather information about a person and tailor our behavior accordingly.