Human facial structure evolved to tolerate punches to the head, according to new research that suggests our ancestors spent a lot of time fighting.
The study, published in the latest issue of the journal Biological Reviews, presents an alternative to the long-held theory that human faces look the way they do primarily because of a past evolved need among our ancestors to chew hard foods, like nuts.
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Such ancestors likely included the australopiths, which lived 4 to 2 million years ago in Africa.
"The australopiths were characterized by a suite of traits that may have improved fighting ability, including hand proportions that allow formation of a fist; effectively turning the delicate musculoskeletal system of the hand into a club effective for striking," David Carrier, lead author of the study, said in a press release.
"If indeed the evolution of our hand proportions were associated with selection for fighting behavior you might expect the primary target, the face, to have undergone evolution to better protect it from injury when punched," added Carrier, who is a University of Utah biologist.
With that in mind, Carrier and colleague Michael Morgan, a University of Utah physician, studied both modern skulls and those of australopiths. They compared differences between males and females, and noted how facial bones respond to impacts.
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The researchers found that bones that suffer the highest rates of fractures in fights are the same parts of the skull that exhibited the greatest increase in sturdiness during the evolution of our early human relatives. These bones are also the parts of the skull that show the greatest difference between males and females in both australopiths and humans today.
"In other words," Carrier said, "male and female faces are different because the parts of the skull that break in fights are bigger in males. Importantly, these facial features appear in the fossil record at approximately the same time that our ancestors evolved hand proportions that allow the formation of a fist."
He continued, "Together, these observations suggest that many of the facial features that characterize early hominins may have evolved to protect the face from injury during fighting with fists."
What were our prehistoric ancestors fighting about? Based on human behavior today and other primate behavior, it's likely that they often fought over mates, territory and other resources. They also might have just gotten on each other's nerves. After all, some were often cooped up for periods of time in caves and rock shelters.
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If the latest theory holds true, then other ideas about human evolution go out the window. For example, French philosopher Rousseau argued that, before civilization, humans were noble savages and that civilization corrupted us, making us more violent.
Our distant past probably wasn't very tranquil, though.
"The hypothesis that our early ancestors were aggressive could be falsified if we found that the anatomical characters that distinguish us from other primates did not improve fighting ability," Carrier said. "What our research has been showing is that many of the anatomical characters of great apes and our ancestors, the early hominins (such as bipedal posture, the proportions of our hands and the shape of our faces) do, in fact, improve fighting performance."
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The researchers hope their findings could one day help to resolve problems associated with human aggression, inborn or not.
"Our research is about peace," Morgan explained. "We seek to explore, understand, and confront humankind's violent and aggressive tendencies."
"Peace begins with ourselves and is ultimately achieved through disciplined self-analysis and an understanding of where we've come from as a species. Through our research we hope to look ourselves in the mirror and begin the difficult work of changing ourselves for the better."
Photo: Big Show performing a knockout punch on Randy Orton. Credit: Wikimedia Commons.