Modern industrialized societies are plagued by crowded, ill-aligned teeth, a condition that the dental profession refers to as “malocclusion”—which translates literally to “bad bite.” Survey data from 1998 suggests that as much as a fifth of the U.S. population has significant malocclusion, over half of which require at least some degree of orthodontic intervention. Braces, tooth extractions, and retainers are the bread and butter for all the dentists and orthodontists tasked with setting straight our dental deviations. Having braces as a child has become so common in the Western world that it can seem a rite of passage—today, an estimated 50 to 70 percent of U.S. children will wear braces before adulthood. But what did humans do to fix their teeth before modern dentistry, before Novocain, gauze, and rubber spacers?

As it turns out, our ancestors did not suffer from crooked teeth to the same extent that we do today. Our species’ fossil record reveals a telling story: the epidemic of crooked teeth developed in humans over time.

So what’s happening to our mouths? Why do we today face an epidemic of crowded, unruly, crooked teeth? The answer, as it turns out, has been lying right under our noses the whole time: the problem is our jaws.

A key precipitating factor for malocclusion relates to the size of our jaws. For healthy development, jaws must be able to provide sufficient room for all of the thirty-two teeth that grow in the mouth. Over time, our teeth have grown crooked because our jaws have grown smaller. Why? The epidemic’s roots lie in cultural shifts in important daily actions we seldom think about; things like chewing, breathing, or the position of our jaws at rest, and these changes have in turn been brought about by much bigger sociohistorical developments—namely, industrialization.