Two University of Utah researchers proposed on Monday that the
face of the ancestors of modern humans evolved millions of years ago
in a way that would limit injuries from punches during fist fights
Their theory, published in the journal Biological Reviews, is
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 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,
These are also the bones that show the greatest difference between
women and men in early human ancestors and modern humans, Carrier
In both apes and humans, males are much more violent than females,
and most male violence is directed at other males, Carrier said. The
violence underpinning the need for a more robust facial structure
may have involved fist fights over females, resources and other
Australopithecus was a lineage that preceded our genus, Homo, and it
emerged more than 4 million years ago in Africa. Australopithecus
was bipedal, smaller than modern people and 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.
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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, 4 million to 5 million years ago, at about the same
time as the bipedal posture appeared, Carrier added.
Carrier said anthropologists have thought 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 can explain
many of these features. But he said recent analyses of wear patterns
in teeth suggest most of these creatures did not eat hard objects.
The study by Carrier and Michael Morgan, a University of Utah
physician, builds on their previous research highlighting the role
they contend violence played in driving human evolution.
"I think our science is sound and fills some longstanding gaps in
the existing theories of why the musculoskeletal structures of our
faces developed the way they did," Morgan added.
(Reporting by Will Dunham. Editing by Andre Grenon)
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