All humans have an inherent desire to control the unpredictable twists of everyday life. The global (but mainly American) community of “preppers” takes the instinct further: They believe they can ready themselves for the apocalypse. Also known as survivalists, preppers hunker down in remote bunkers and surround themselves with weapons and supplies in the expectation that, come doomsday, society will break down into a Hobbesian state of nature—where life will be solitary, poor, nasty, brutish and short, and it’ll be every man (they’re usually men) for himself.

The attitude of preppers is merely an extreme version of how we all think about external threats. “We just can’t bear the idea that disaster is completely random,” says seismologist Lucy Jones, author of the book Th...