Evolution Update

Evolution Update

What Truly Makes Us Human? Maybe the Chin…

Brandon Kieft April 18, 2015

New research from the University of Iowa challenges the notion that our chin evolved for chewing.

There are many features that we all share, as modern humans, that are unique to our species – even when compared to close relatives such chimpanzees and skeletons of early homonids such at Neanderthals. But there is one distinction that you may have never heard (or cared) about: humans are the only species on earth with a true chin.

Many anatomists and research scientists have long viewed our chin as a physical adaptation to chewing our food, a process termed mastication. A prominent hypothesis suggests that the bending stress of chewing diverse foods caused enough physical force on the body to select for the development of new bone mass.

Early last week, however, a paper published in the Journal of Anatomy by researchers at the University of Iowa presented a much different view on the origin of the human chin. The researchers used biomechanical analyses on the cranium and facial bones and muscles of human subjects ranging from 3 to 20+ years old.

The results showed that during development, there is not enough mechanical force exerted on muscles and bones to cause the stress thought to give rise to new bone structure. Instead, their hypothesis suggests that the chin became prominent only because of the slimming down of our facial features. They note that human faces are about 15% shorter than a Neanderthal’s, and that this “slimming down” likely caused our prominent chin to become exposed.

They conclude by explaining that there is no evidence that chins are connected to a mechanical function on the human face. In fact, in a few of their study subjects, the chin actually hindered mechanical forces and caused resistance to chewing muscles.

Even more interestingly, the researchers also note that changing hormonal levels in ancient humans, such as decreasing testosterone in males, may have played a role in chin formation. They suggest that the chin is actually the product of humans evolving to become more social and less aggressive, allowing for art and individuality to trickle into the lives of these groups.

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