Why do we have crooked teeth when our ancestors didn’t? - G. Richard Scott

All these ancient skulls have perfectly straight teeth, despite almost certainly never sporting braces. And this isn't some strange sample. According to the fossil record, ancient humans usually had straight teeth, complete with third molars—or wisdom teeth. In fact, the dental dilemmas that fuel the demand for braces and wisdom teeth extractions today appear to be recent developments.

So what happened? While it’s nearly impossible to know for sure, scientists have a hypothesis. A couple million years ago, the ancestors of modern humans lived a subsistence lifestyle. Their teeth and jaws had to work hard to make the food they ate digestible. Indeed, the surfaces of many of their teeth show extensive wear and flattening. They also had larger jaws and teeth overall. At some point, they began using tools and fire to cook and prepare food, which helped break it down.

A lot more time passed and, around 12,000 years ago, some humans started farming and domesticating animals and plants. Over the course of several thousand years, it became more common for people to process and refine their food. Milling technologies helped remove the tougher parts of grains, like the germ and bran from rice and wheat. Fast forward to the industrial Revolution, and technological innovations dramatically accelerated these processes.

In a relatively short time, many human mouths were relieved of a great deal of their grinding, crushing, and pulverizing duties. And interestingly, it was around this time that tooth crookedness appears to have become more common. Examining fossils spanning millions of years of evolution, researchers have observed a gradual decrease in tooth and jaw size in humans and our ancestors.

Many think that, for most of human history, dietary shifts—like the introduction of meat and the advent of cooking—were gradual, and that changes in tooth and jaw size basically kept pace with one another. But with the more recent revolutions in agricultural and culinary habits, that relationship changed. As the theory goes, over a relatively short period, some human populations saw a decrease in jawbone size, while teeth stayed roughly the same size, meaning they're left vying for limited space.

When they do grow in, they may displace others and get jostled into some eccentric positions. And then wisdom teeth, which are usually the last to make their debut, seem to only complicate things further. In many cases, they have little or no space to emerge. This can lead to impacted wisdom teeth, which may cause discomfort and infections if not surgically removed.

So larger jaws appear to be associated with greater chewing demands. And many scientists think that as people's diets have become less chewy, their jaws have gotten smaller—and that this has led to dental crowding, resulting in dental crookedness and impacted wisdom teeth. This hypothesis has been supported by some preliminary experimental data.

In a 1983 study, researchers raised 43 squirrel monkeys on diets of either naturally tough or artificially soft food. Those fed softer food had more crowded premolars, rotated or displaced teeth, and narrower dental arches. And a 2004 study similarly observed that hyraxes raised on cooked foods experienced roughly 10% less growth in facial areas involved in chewing compared to those given raw and dried foods.

In other words, the issue at large seems to be environmental—or one of lifestyle—instead of a genetic one, though heritable factors may be at play in some instances. It’s estimated that somewhere between 30 to 60% of people today experience some level of tooth crowding. But this trend varies across global populations. Some people naturally never have wisdom teeth. And some don’t experience tooth crowding or crookedness and still get their wisdom teeth without a hitch.

This seems to coincide with diets that are less processed. So how can we prevent tooth crowding early, using lifestyle changes and orthodontics? Well, it’s certainly something to chew over.