Washington:
Human faces have evolved to minimise injury from punches, according to a new study.
University of Utah biologist David Carrier and Michael H Morgan, a University of Utah physician, studied the bone structure of australopiths, ape-like bipeds which predated the modern human primate family Homo.
They found that australopith faces and jaws were strongest in those areas most likely to receive a punch.
The findings present an alternative to the previous long-held hypothesis that the evolution of the robust faces of our early ancestors resulted largely from the need to chew hard-to-crush foods such as nuts.
"The australopiths were characterised 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," said Carrier, lead author of the study.
"If indeed the evolution of our hand proportions were associated with selection for fighting behaviour you might expect the primary target, the face, to have undergone evolution to better protect it from injury when punched," Carrier said.
The rationale for the research conclusions came from determining a number of different elements, said Carrier.
"When modern humans fight hand-to-hand the face is usually the primary target. What we found was that the bones that suffer the highest rates of fracture in fights are the same parts of the skull that exhibited the greatest increase in robusticity during the evolution of basal hominins.
"These bones are also the parts of the skull that show the greatest difference between males and females in both australopiths and humans.
"In other words, male and female faces are different because the parts of the skull that break in fights are bigger in males," said Carrier.
"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.
"Together these observations suggest that many of the facial features that characterise early hominins may have evolved to protect the face from injury during fighting with fists," he said.
The latest study by Carrier and Morgan builds on their previous work, which indicated that violence played a greater role in human evolution than is generally accepted by many anthropologists.
The study was published in the journal Biological Reviews.