New research suggests having a chin is a unique physical feature that belongs to humans.

Compared with other human relatives like Neanderthals, modern Homo sapiens have particularly prominent chins. Nathan Holton, an anthropologist at the University of Iowa, said the modern human chin helps the jaw stand up to the forces generated by chewing.

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Primates and Neanderthals lack this human-defining feature, so a team of researchers looked at what caused it to develop, the University of Iowa reported.

"In some way, it seems trivial, but a reason why chins are so interesting is we're the only ones who have them. It's unique to us," added Holton.

Researchers believe our chins aren't linked to mechanical features like chewing, but rather changes in hormonal levels that occurred when we became social beings.

To find out whether chin prominence protects the jaw from bending while chewing, Holton and his colleagues examined X-ray images from the Iowa Facial Growth Study that tracked children's skull development from age 3 into adulthood.

Using 292 measurements from 18 females and 19 males, researchers tracked jaw development and bone distribution associated with protecting against various types of stresses.

The findings suggest mechanical forces were incapable of producing the resistance needed to create new bones in the lower mandible.

Chins become more prominent with age but the scientists found no consistent links between chin prominence and resistance. In fact, jaws are relatively better at resisting some types of forces at age three, when chins are not well developed, compared to adulthood, Holton said.

The new study appeared in the Journal of Anatomy.

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