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So Why Do We Have Chins? Experts Have the Answer

Apr 15, 2015 12:33 AM EDT
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The next time you're at a museum peering at early primate and Neanderthal skulls - even those from wild apes today - look closely for the one thing human skulls exclusively have. No, it's not a larger brain-case or a handsome jaw line... it's a chin. Now researchers think they know why it is that modern humans developed this unique, protruding characteristic when no other primates did.

"In some way, it seems trivial, but a reason why chins are so interesting is we're the only ones who have them," Nathan Holton, who studies craniofacial features and mechanics at the University of Iowa, reiterated in a statement.

A chin that protrudes past our teeth is in-fact more unique than other "human traits," such as opposable thumbs or hips and vertebrate adapted for bipedal walking.

And what may be most intriguing is that experts are fairly certain that the chin didn't arise from jaw-related actions such as chewing. Holton explained that a chin is certainly not of any use in buffering the mechanical forces of chewing.

That's why the researcher and his colleagues used advanced facial and cranial biomechanical analyses on nearly 40 volunteers whose structural measurements had been plotted from when they were toddlers, all the way into their adult years. (Scroll to read on...)

(Photo : Nathan Holton lab, University of Iowa) University of Iowa researchers find that we develop chins as our head size increases, from childhood to adulthood. At about 4 years of age (left), we have little indication of a chin, but by our 20s, we have a prominent point at the bottom of our faces.

According to the analytical results, which were published in the Journal of Anatomy, the chin was likely a simple geometric happenstance. That is, chin "growth" has more to do with how each feature in our face adapts as our head size increases - much like how you'd fit individual pieces together in an ever changing and expanding puzzle. Simply due to the structure of the chin, it less readily changes than other facial features.

This led the team to conclude that as the human face became smaller in our evolution from early humans and other primates (our faces are about 12 percent shorter than those of Neanderthals), the chin simply became a constant bony prominence.

But why did the face shrink anyways? A lot of it has to do with a single hormone.  Anthropologists and evolutionary biologists have long theorized that between 80,000 and 20,000 years ago, humanity's ancestors started forming stronger alliances between groups, as opposed to constant in-fighting. As a consequence, humans started seeing reduced levels of testosterone in their youth.

Contrary to popular belief, testosterone actually is a consequence of anger, not a cause for it, even if the hormone does aid males in furious and violent behavior. This led to noticeable changes to the male craniofacial region - namely a shrinking face and more prominent chin.

"What we're arguing is that modern humans had an advantage at some point to have a well-connected social network, they can exchanged information, and mates, more readily, " added anthropologist Robert Franciscus.

In this way, diplomatic males with prominent chins wound up reproducing more frequently than shallow-chinned and quick-to-anger males. This flooded the human genome pool with prominent chin traits - traits which carried over to humans today.

"There had to be more curiosity and inquisitiveness than aggression," said Franciscus, "and the evidence of that lies in facial architecture."

So raise that chin high with pride! Not only is it a characteristic unique to us humans, but it is a badge for how far humanity's civility has come.

For more great nature science stories and general news, please visit our sister site, Headlines and Global News (HNGN).

- follow Brian on Twitter @BS_ButNoBS.

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