A handsome chin is a feature only seen in humans, so scientists set out to tackle the evolutionary mystery behind it.
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," says Nathan Holton, who studies craniofacial features and mechanics at the University of Iowa. "It's unique to us."
The researchers believe our chins are not linked to mechanical features like chewing, but rather changes in hormonal levels that occurred as we became social beings. They looked at advanced facial and cranial biomechanical analyses involving over 40 individuals whose measurements were tracked from toddlers to adulthood. The findings suggest mechanical forces were incapable of producing the resistance needed to create new bones in the lower mandible.
The team concluded the chin arose from "simple geometry, and as our faces became smaller the defining feature emerged. Humans' lifestyle started to change 80,000 years ago, and the development accelerated when we migrated from Africa about 20,000 years later. During this period of evolution, humans became more communicative and artistically inclined; men became less territorial, and more likely to exchange goods and idea with each other. This attitude change is believed to have caused a reduction in hormone levels, especially testosterone. This led to shifts in craniofacial region, such as a reduction in face size.
The examination of the periodic measurements showed children have extremely undefined chins, but they become more prominent with age. Chin "growth" appeared to rely on how each feature in the face adapted to head size.
"What we're arguing is that modern humans had an advantage at some point to have a well-connected social network, they can exchange information, and mates, more readily, there's innovation," said UI anthropologists led by Robert Franciscus, "And for that to happen, males have to tolerate each other. There had to be more curiosity and inquisitiveness than aggression, and the evidence of that lies in facial architecture."
The findings were published in a recent edition of the Journal of Anatomy.
