Chewing may not be responsible for humans evolving chins, say scientists who suggest that a dip in hormone levels as we became more societally domesticated may have caused the feature to emerge.
"In some way, it seems trivial, but a reason why chins are so interesting is we're the only ones who have them," said Nathan Holton, who studies craniofacial features and mechanics at the University of Iowa.
New research led by Holton and colleagues posits that 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 societally domesticated.
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Using advanced facial and cranial biomechanical analyses with nearly 40 people whose measurements were plotted from toddlers to adults, 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, the chin became a bony prominence, the adapted, pointy emblem at the bottom of our face.
"In short, we do not find any evidence that chins are tied to mechanical function and in some cases we find that chins are worse at resisting mechanical forces as we grow," said Holton.
"Overall, this suggests that chins are unlikely related to the need to dissipate stresses and strains and that other explanations are more likely to be correct," Holton said.
UI anthropologists led by Robert Franciscus think the 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.
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.
The research was published in the Journal of Anatomy.
