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The evolution of human chins – not what you’d think

21 April 2015

The evolution of human chins – not what you’d think

Image Credit: Tim Schoon, University of Iowa

Researchers from the University of Iowa have published research in the Journal of Anatomy on why exactly human beings have chins, and the results may not be what you think. Our very early ancestors didn’t have chins, no other species really have chins but modern humans do. It is not due to mechanical forces such as chewing that we developed chins – plenty of chinless species have to chew too! – but rather some curious facets of evolution that lead to their development. Nathan Holton, who studies craniofacial features and mechanics at the University of Iowa, said: “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.”

Holton and his colleagues found that our chins developed due to our faces and heads reducing in size as we evolved, quite possibly linked to changes in hormone levels as we became more societally domesticated. Using advanced facial and cranial biomechanical analyses with nearly 40 people whose measurements were plotted from toddlers to adulthood, the researchers conclude that forces, such as chewing, appear incapable of producing the resistance needed for new bone to be created in the lower mandible, or jaw area. As our faces got smaller, the chin became a bony prominence, an incidental feature of this size reduction.

Holton’s colleague, anthropologist Robert Franciscus, believes that our chin is a secondary consequence of us becoming more societal and interconnected beings. When humans, particularly males, began to live in communities rather than as isolated hunter gatherers, this reduced aggressive hormone levels. The reduction in testosterone for males resulted in notable changes in the craniofacial region. The face became smaller, marking a physiological departure that created a natural opportunity for our chins to emerge.

Franciscus commented: “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. 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 researchers conclude that human’s chin “growth” was more a result of how each feature of our head and faces adapted over time as opposed to our eating habits making it “grow” as a necessity. Holton concludes: “Our study suggests that chin prominence is unrelated to function and probably has more to do with spatial dynamics during development.”

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