The human face evolved over millions of years, and many factors went into its final design. One of the aspects of our history that helped shape faces was violence, based on a new study.

Researchers believe significant changes occurred in faces of our ancestors because of violence. This is believed to be especially true of Australopithecus, a species that lived between 3.9 and 2.9 million years ago.

University of Utah investigators studied the factors that contributed to the development of the human race. They found our ancestors with faces best able to withstand punches left the greatest number of offspring.

"When humans fight hand-to-hand the face is usually the primary target and the bones that suffer the highest rates of fracture are the parts of the skull that exhibit the greatest [prominence]," the researchers wrote in an article announcing their findings.

Over the course of their one million years on the planet, Australopiths evolved more efficient - and damaging - methods of fighting, including punching fists. This turned hands into effective clubs. When fists strike faces, they can break bones and cartilage, lowering the chances for the victim to attract members of the opposite sex.

"What we found was that the bones that suffer the highest rates of fracture in fights are the same 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," David Carrier, one of the leaders of the study, said.

The ability to make a fist and faces better able to take punches, evolved at nearly the same time, lending support to the main conclusion of the study.

Anthropologists and other investigators traditionally held the belief that the evolution of human faces was guided largely by the need to eat new foods, including nuts. This study builds upon previous research by the team, showing conclusive ties to violent acts.

"Our research is about peace. We seek to explore, understand, and confront humankind's violent and aggressive tendencies," Carrier told the press.

Investigation of the role violent acts played in the evolution of human faces was published in the journal Biological Reviews.