Most people have what’s called ‘personal space‘ — an amount of room that we’re comfortable having between us and other people. But have you ever wondered why?

Ralph Adolphs, a professor of psychology and neuroscience at the California Institute of Technology, says those “bubbles” are constructed and monitored by the amygdala — the brain region involved in fear.

Different cultures have varying amounts of socially-acceptable space, so we develop ours when we’re small children.

Back in the 1960s, anthropologist Edward Hall determined that Americans have four bubbles of different sizes. The first, deemed “intimate space,” is about 18 inches from us in all directions, and only families, pets and our closest friends are welcome within it. The next one out is what Hall called “personal space.” It extends 1.5 feet to 4 feet away, and while it’s okay to have friends and acquaintances there, we’re uncomfortable when strangers are.

The third zone, 4 to 12 feet away from us, is “social space,” is where we like conducting routine social interactions with new acquaintances or total strangers. And finally there’s “public space” — anything beyond 12 feet, where anyone is welcome.

Since most of us can’t always have as much room around us as we’d like, psychologist Robert Sommer thinks we cope by temporarily dehumanizing those around us, avoiding eye contact and pretending those other people are inanimate — which explains why everyone just stares up at the numbers in a crowded elevator.

[LiveScience]