Humans used to have straighter teeth—what changed?

How farming may have reshaped the human face

Ancient human skulls were strikingly different from our own. Early hunter-gatherers had large, powerful jaws built for the demanding work of chewing tough meats, fibrous vegetables, seeds, and nuts. But around 12,000 years ago, things began to change. As humans around the world traded hunting for farming, their diets changed too, incorporating more grains and cultivated produce into their diet.

These foods were softer, more processed, and required far less chewing.” We did not have ice cream or white bread back in the day,” says Sue Herring, professor emeritus in orthodontics at the University of Washington. “When you get your food straight from the environment, it’s probably a little [grittier] than stuff which has been cooked and processed.”

(Neanderthal teeth reveal intimate details of daily life.)

With softer diets came less mechanical strain on the jaw. Over generations, our mandibles began to shrink— a trend visible in the fossil record. That shrinkage is, at least in part, adaptive and the result of millennia of evolution, says Myra Laird, assistant professor of basic and translational sciences at the University of Pennsylvania School of Dental Medicine. “If you don’t need a huge mandible, it’s energetically costly to build that extra bone.”

But not all changes in jaw size and shape are evolutionary. Bone is highly responsive to physical stress—even within a single lifetime—and builds up around muscle attachment sites. In other words, less muscle usage results in less robust bones, Laird says, citing studies of craniofacial growth in non-human animals like hyraxes. “If you switch to a liquid diet, you will not use your muscles as much and see some shape changes in your face.”