“If you’re looking across all of the hominids, which is the family tree after the split with chimpanzees, there are not really that many traits that we can point to that we can say are exclusively human,” Duke University’s James Pampush told NPR. “Those animals all walked on two legs. The one thing that really sticks out is the chin.” While other animals have jaws, no others besides humans have the little section of bone on the lower jaw that juts past the teeth.
The chin isn’t just the lower part of your face: It’s a specific term for that little piece of bone extending from the jaw. While it may seem odd, humans are in fact the only animals that have one. Even chimpanzees and gorillas, our closest genetic cousins, lack chins. Instead of poking forward, their lower jaws slope down and back from their front teeth. Even other ancient hominids, like the Neanderthals, didn’t have chins —their faces simply ended in a flat plane. Over the last century, scientists have proposed many ideas to explain why humans evolved chins, from helping us chew food to speaking.
Pampush argues that many of these theories don’t hold up under further scrutiny. He published this idea recently in the journal Evolutionary Anthropology. “The chin is one of these rare phenomena in evolutionary biology that really exposes the deep philosophical differences between researchers in the field,” Pampush tells Yong. One of the most popular ideas is that our ancestors evolved chins to strengthen our lower jaws to withstand the stresses of chewing. But according to Pampush, the chin is in the wrong place to reinforce the jaw. As for helping us speak, he doubts that the tongue generates enough force to make this necessary. A third idea is that the chin could help people choose mates, but sexually selective features like this typically only develop in one gender, Pampush tells Siegel.