Linguists spend a lot of time thinking about all the strange ways humans can shape their mouths, and how that affects the sounds they can make. Anthropologists believe that since at least the Neolithic, humans have been born with overbites (in which the top teeth come down over the bottom teeth) and overjets (in which the top teeth are positioned more forward than the bottom teeth). If a person’s teeth are exposed to a lot of wear and tear over her lifetime, her jaws will shift to put her teeth in an edge-to-edge alignment instead. Extreme wear was common early in human history, when most of our ancestors were hunters and gatherers. In farming societies, on the other hand, people tend to put less strain on their teeth, and retain overbite and overjet for their whole life.

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John Lukacs, an anthropologist at the University of Oregon who was not involved in the new study, told me that agricultural diets are easier on the teeth in two main ways. First, they’re less diverse, made up mostly of staple grains such as corn, wheat, and rice. They’re also moderated by food-processing technologies such as grain mills and pickling jars. “It’s not just what you eat,” Lukacs said. “It’s how you prepare what you eat.”

Mouths with overbites and mouths with teeth lined up edge-to-edge are good at different things. F’s and v’s belong to a group of sounds called labiodentals because they’re made by touching the upper teeth to the lower lip, and the shape of a person’s mouth determines how easy they are to produce. If you’re reading this article, odds are you live in an agricultural, overbite-bearing society. When you say the word foot, you don’t have to move your mouth too much from its resting position, because your top teeth are already lined up with your bottom lip to make the labiodental f sound. If you move your teeth into an edge-to-edge position, roughly the way an adult hunter-gatherer’s jaws would be arranged, making an f sound involves a lot more movement. (Try it.) In fact, the authors of the Science study estimated that it’s nearly 30 percent easier for people with an overbite to make labiodental sounds than it is for people with edge-to-edge bites.

Because it’s so difficult for people with edge-to-edge bites to produce sounds like f and v, the study’s authors figured they would be unlikely to say them by accident, or to incorporate them into their languages. They checked to see whether they could find this pattern playing out in the real world by comparing the sound systems of languages across the world with the subsistence style of the people who speak those languages. About half of the world’s languages use labiodental sounds, but on average, languages spoken by hunter-gatherer societies turned out to use fewer than one-third the number of labiodental sounds as their agricultural counterparts.