Got a mouthful of metal and stack of orthodontic bills? You can thank your farmer ancestors for them.
That's according to an anthropologist who says the switch from chewing wild game to eating corn, rice and wheat could have shortened the human jaw so that teeth don't fit in it as well.
When agriculture took off in some parts of the world, it had a lot to offer people: Farmed foods are a more reliable source of calories, and are easier to chew and digest. But they also may have helped transform the jaw bone before the teeth could catch up.
To test this theory, Noreen von Cramon-Taubadel, a lecturer at the University of Kent in England, compared the shape of modern human jaws and skulls from 11 different cultures around the world. Included were places like Italy and Japan, with many centuries of agriculture as the primary food source, and Alaska and Australia, where people fed themselves by hunting and gathering.
While diet didn't affect the shapes of people's skulls, it had a big impact on their jawbones. The hunter-gatherers had longer, narrower jaws which left more room for adult teeth, while the farmers had shorter, wider jaws. That difference persisted independent of genetics, climate, and geography.
"The hunter-gatherer diet would have been very different, depending on where you lived in the world," says von Cramon-Taubadel. She's the author of the study published today in the Proceedings of the National Academy of Sciences. "What you're eating on a daily and annual basis is very variable."
But farmers tend to eat the same thing over and over, and easy-to-chomp cooked grains such as corn, wheat and rice make up the bulk of the diet.
People's teeth haven't changed much over the centuries, the anthropologist says. "It's interesting that there's this mismatch between teeth and bone." And these days, if you live in a country with dental care and the money to pay for it, that may mean orthodontia.
"Our behavior has such a dramatic effect on our biology," von Cramon-Taubadel concludes. "Some parts of our bodies are just more plastic. They're more prone to change."