At work, you glance with suspicion at the person who neglects to wash his filthy hands after a trip to the toilet. At home, you change your child’s diaper, unclog the shower drain, empty your cat’s litter box, pop a zit, throw out the fuzzy leftovers in the fridge. If you manage to complete a single day without experiencing any form of disgust, you are either a baby or in a coma.

Disgust shapes our behavior, our technology, our relationships. It is the reason we wear deodorant, use the bathroom in private and wield forks instead of eating with our bare hands. I floss my teeth as an adult because a dentist once told me as a teenager that “Brushing your teeth without flossing is like taking a shower without removing your shoes.” (Do they teach that line in dentistry school, or did he come up with it on his own? Either way, 14 words accomplished what a decade of parental nagging hadn’t.) Unpeel most etiquette guidelines, and you’ll find a web of disgust-avoidance techniques. Rules governing the emotion have existed in every culture at every time in history. And although the “input” of disgust — that is, what exactly is considered disgusting — varies from place to place, its “output” is narrow, with a characteristic facial expression (called the “gape face”) that includes a lowered jaw and often an extended tongue; sometimes it’s a wrinkled nose and a retraction of the upper lip (Jerry does it about once per episode of “Seinfeld”). The gape face is often accompanied by nausea and a desire to run away or otherwise gain distance from the offensive thing, as well as the urge to clean oneself.

The more you read about the history of the emotion, the more convinced you might be that disgust is the energy powering a whole host of seemingly unrelated phenomena, from our never-ending culture wars to the existence of kosher laws to 4chan to mermaids. Disgust is a bodily experience that creeps into every corner of our social lives, a piece of evolutionary hardware designed to protect our stomachs that expanded into a system for protecting our souls.