The term “personal space” is relatively new—but that uneasy feeling you get when someone moves too close is ancient. “There really is such a thing” as personal space, says neuroscientist Michael Graziano, author of the new book The Spaces Between Us. “The brain computes a buffer zone around the body.” We have this “second skin” hardwired into our DNA. (Discover how your brain determines what you see.)

When National Geographic caught up with Graziano at Princeton University, he explained Donald Trump’s unusual sense of personal space, why we wouldn’t be able to use tools without this second skin, and how his own family discovered that being born without a buffer zone can have devastating consequences. (Meet