The real reason we’re superstitious about broken mirrors, black cats, and the number 13

The rules of society say I’m an “adult” now. My hopscotch and jump rope days are long gone, but I still find myself reciting an adolescent rhyme as I walk the streets of New York City: “Don’t step on a crack or you’ll break your mama’s back.” Superstitions tend to latch on to our belief system early in life. And new scientific research might explain why distrust of black cats, broken mirrors, twitching eyes, and the number 13 tends to spread like wildfire.

In an analysis published in Proceedings of the National Academy of Sciences, a pair of theoretical biologists created a model based on game theory (a branch of mathematics that attempts to predict people’s actions and interactions) that answered the vital question: What are superstitions, and how do they become normalized in culture? They found that groups of individual that start with very different principals can mingle their way toward a shared belief system.

“What’s interesting here is that we show that, beginning in a system where no one has any particular belief system, a set of beliefs can emerge, and from those, a set of coordinated behaviors,” Erol Akçay, PhD, an assistant professor of biology at the University of Pennsylvania. Someone tells us that walking under a ladder is a recipe for disaster, and before we know it, we’re not just believing their warning. We’re actively dodging ladders.

“What’s interesting here is that we show that, beginning in a system where no one has any particular belief system, a set of beliefs can emerge, and from those, a set of coordinated behaviors.”

Our stock in superstitions only grows stronger as we gather “evidence” that steering clear of these amusing and innocuous threats enhances our lives. “[Someone] may say, ‘Okay, well I believe that when I observe this event I should behave this way because another person will behave that way.’ And over time, if they have success in using that kind of a strategy, the superstitions catch on and can become evolutionarily stable,” explains Bryce Morsky, PhD, a postdoctoral researcher. (These learned cues that influence how we interact in the world are known as “choreographers” in game theory.)

Feeling the need to knock on wood when you fear you might be jinxing yourself is typical if not irrational behavior, according to the researchers. Don’t hesitate to sage your apartment, and for the love of your mom, watch your step.

Because we’re feeling curious about why we do what we do, here’s why we should stop interrupting people and the fascinating reasons why you now love the foods you hated as a child.