Human face shaped by violence, US researchers suggest
US researchers suggest male skull in particular evolved the way it did so it could take a punch
Reuters in Washington
Current theory about the shape of the human face just got a big punch in the mouth.
Two University of Utah researchers have proposed that the face of the ancestors of modern humans evolved millions of years ago in a way that would limit injuries from punches during fistfights between males.
Their theory, published in the journal Biological Reviews on Monday, was presented as an alternative to a long-standing notion that changes in the shape of the face were driven more by diet - the need for a jaw that could chew hard-to-crush foods such as nuts.
"Studies of injuries resulting from fights show that when modern humans fight, the face is the primary target," biologist Professor David Carrier said. "The bones of the face that suffer the highest rates of fracture from fights are the bones that show the greatest increase in robusticity during the evolution of early bipedal apes, the australopiths."
These were also the bones that showed the greatest difference between women and men in early human ancestors and modern humans, Carrier added.
In both apes and humans, males were much more violent than females, and most male violence was directed at other males, Carrier said.
The violence underpinning the need for a more robust facial structure may have involved fistfights over females, resources and other disputes.
Australopithecus was a lineage that preceded our genus, Homo, and it emerged more than four million years ago in Africa.
Australopithecus was bipedal and somewhat smaller than modern people, and the genus possessed a combination of ape and human characteristics.
"Comparing great apes such as chimps and gorillas to australopiths, what changed in the face was a reduction in the length of the jaws, a great increase in the robustness and strength of the jaws, molar teeth and jaw muscles, a substantial increase in the size and strength of the cheek bones, and an increase in the part of the face that surrounds the eyes," Carrier said.
The proportions of the hand that allowed for the formation of a fist and the great increases in the robustness of the face occurred early in our lineage, four to five million years ago, at about the same time as the bipedal posture appeared, Carrier added.
Carrier said anthropologists had thought that the new facial traits in the first bipedal apes were the result of a diet that included very hard objects, and the biomechanics of eating such food could in fact explain many of these features.
But he said recent analyses of wear patterns in teeth suggested that most of these creatures did not eat hard objects.
The study by Carrier and Dr Michael Morgan, a University of Utah physician, builds on their previous research highlighting the role that they contend violence has played in driving human evolution.