Human chin came from evolution, not chewing

Our chins did not come from mechanical forces such as chewing but instead resulted from an evolutionary adaptation involving face size and shape - possibly linked to changes in hormone levels as we became more social, fascinating research indicates.

"Primates or the Neanderthals did not have chins. In some way, it seems trivial but a reason why chins are so interesting is we are the only ones who have them. It is unique to us," said Nathan Holton who studies craniofacial features and mechanics at University of Iowa.

Using advanced facial and cranial biomechanical analyses with nearly 40 people, the team concluded mechanical forces, including chewing, appear incapable of producing the resistance needed for new bone to be created in the lower mandible, or jaw area.

Rather, it appears the chin's emergence in modern humans arose from simple geometry.

"As our faces became smaller in our evolution from archaic humans to today - in fact, our faces are roughly 15 percent shorter than the Neanderthals - the chin became a bony prominence, the adapted, pointy emblem at the bottom of our face," Holton said.

Human chin is a secondary consequence of our lifestyle change, starting about 80,000 years ago and picking up great steam with modern humans' migration from Africa about 20,000 years later.

What happened was this.

Modern humans evolved from hunter-gatherer groups that were rather isolated from each other to increasingly cooperative groups that formed social networks across the landscape.

These more connected groups appear to have enhanced the degree to which they expressed themselves in art and other symbolic mediums.

Males in particular became more tranquil during this period, less likely to fight over territory and belongings, and more willing to make alliances, evidenced by exchanging goods and ideas, that benefited each and all.

The change in attitude was tied to reduced hormone levels, namely testosterone, resulting in noticeable changes to the male craniofacial region.

One big shift was the face became smaller - retrenching in effect - a physiological departure that created a natural opportunity for the human chin to emerge.

Children have flat, nearly imperceptible chins, much like what is seen in the Neanderthals.

That bony prominence only becomes visible as our heads and faces grow into adulthood.

"Our study suggests that chin prominence is unrelated to function and probably has more to do with spatial dynamics during development," the authors concluded in a paper published online in the Journal of Anatomy.