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The lower jaw of a chimpanzee or gorilla slopes backwards from the front teeth. So did the jaw of other hominids like Homo erectus. Even Neanderthal jaws ended in a flat vertical plane. Only in modern humans does the lower jaw end in a protruding strut of bone. A sticky-outy bit. A chin.
“It’s really strange that only humans have chins,” says James Pampush from Duke University. “When we’re looking at things that are uniquely human, we can’t look to big brains or bipedalism because our extinct relatives had those. But they didn’t have chins. That makes this immediately relevant to everyone.” Indeed, except in rare cases involving birth defects, everyone has chins. Sure, some people have less pronounced ones than others, perhaps because their lower jaws are small or they have more flesh around the area. But if you peeled back that flesh and exposed their jawbones — and maybe don’t do that — you’d still see a chin.
So, why do chins exist? There are no firm answers, which isn’t for lack of effort. Evolutionary biologists have been proposing hypotheses for more than a century, and Pampush hasrecently reviewed all the major ideas, together with David Daegling. “We kept showing, for one reason or another, that these hypotheses are not very good,” he says.
Read full, original post: We’re the Only Animals With Chins, and No One Knows Why