The standard explanation for why the skull of hominins – humans, great apes, and their evolutionary ancestors, more or less – changed shape was so that it was better able to chew tough foods such as nuts. But this peaceful view of our evolutionary history is being challenged by University of Utah professors David Carrier and Michael H. Morgan who argue in their paper Protective buttressing of the hominin face, just published in Biological Reviews, that our faces evolved to survive a fist fight.

Human skull

Human skull: Bone structure changed more in males than females

“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,” Carrier said in a statement. “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.”

The unspoken assumption here, of course, is that males were more likely to get into fights than females (or, more specifically, that males were more likely to be struck in the face). While that fits common gender stereotypes, interpreting million year old stereotypes through a specific cultural lens is an easy way to make mistakes, as Carrier believes other researchers have done.

Carrier believes the evolutionary role of violence is underplayed

Carrier and Morgan point out that vulnerable portions of the skull thickened at the same time that hand proportions changed, allowing hominins to make a fist, and that being a glassjaw suddenly became a major disadvantage. Carrier has previously done research on how great ape legs shortened and plans research on changing foot posture during the same period.

He argues that the idea of a noble savage corrupted by civilization affects the way that many archeologists interpret the fossil record, leading them to pacifistic conclusion such as the jaw changing according to diet. By investigating the role of violence in hominid evolution, Carrier wants to answer what he sees as open questions about why our musculoskeletal structure evolved in the way that it did.