"In some way, it seems trivial, but a reason why chins are so interesting is we're the only ones who have them," says Nathan Holton, who studies craniofacial features and mechanics at the University of Iowa. "It's unique to us."
We develop chins as our head size increases, from childhood to adulthood. At about 4 years of age (left), we have little indication of a chin, but by our 20s, we have a prominent point at the bottom of our faces. Credit: Nathan Holton lab, University of Iowa