Five million years of slugging it out with fists has left its mark on the human face, scientists believe. Evidence suggests it evolved to minimise damage from altercations after our ancient ancestors learned how to throw a punch.

Researchers studied the bone structure of australopiths, ape-like bipeds living 4m to 5m years ago which predated the modern human primate family Homo. They found that australopith faces and jaws were strongest in just those areas most likely to receive a blow from a fist.

US lead researcher Dr David Carrier, from the University of Utah, said the australopiths had hand proportions that allowed the formation of a fist, in effect turning the hand into a club.

"If indeed the evolution of our hand proportions was 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."

The study, published in the journal Biological Reviews, builds on previous work indicating that violence played a greater role in human evolution than many experts would like to admit.

Carrier, a biologist, has investigated the short legs of great apes, the bipedal posture of humans and the hand proportions of hominins, or early human species. He argues that these traits evolved, to a large extent, around the need to fight.

An artist's impression of how human faces may have evolved to minimise injury from punches. Photograph: University Of Utah

"When modern humans fight hand to hand, the face is usually the primary target," said Carrier. "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. These bones also show the greatest difference between males and females in 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."The debate over the dark side of human nature can be traced back to the French philosopher Jean-Jacques Rousseau, who argued that before civilisation humans were "noble savages".

This idea, that civilisation corrupted the human race and made us violent, remains strong in social science, said Dr Carrier. However, the facts did not fit the theory.

Dr Carrier added: "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.

"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."

Co-author Dr Michael Morgan, a University of Utah physician, said: "I think our science is sound and fills some long-standing gaps in the existing theories of why the musculoskeletal structures of our faces developed the way they did.

"Our research is about peace. 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."