While anthropologists and evolutionary biologists are quite good at figuring out how and when humans evolved, figuring out why we are the way we are is much more difficult and involves a fair bit of assuming about what was important in the life of our ancient ancestors. University of Utah biologist David Carrier has hit on one promising idea, though: he thinks intraspecies violence—one man fighting another—was an important driver of human evolution.
For the past few years, Carrier has been researching the ways in which hominid bodies may have changed to improve our combat skills. In his latest work, says the BBC, Carrier suggests that the faces of early human ancestors evolved to be better at taking punches. Males, Carrier thinks, developed stronger jaw muscles and bigger bones to help ward off blows.
This idea actually begins with human hands. Not long after our ancestors came down from the trees, their hands began to change form, and, back in 2012, Carrier and his colleague Michael Morgan published research suggesting that those changes helped human ancestors throw a knock-out punch. The study was controversial within anthropological circles, says Wired UK, and many scientists were unconvinced that human hands evolved for punching.
But, if you believe that hands did evolve for punching, then the pair's next project certainly makes sense. In their latest paper, Carrier and Morgan argue that, in human ancestors, guys' propensity for bare-knuckle boxing sparked an evolutionary arms race between their hands and their faces—which, in a bout of fisticuffs, make enticing targets.
The facial bones most likely to break during a bout today are also the ones that seem to show the most evolutionary strengthening in human ancestors, says the BBC:
The jaw, cheek, eye and nose structures that most commonly come to grief in modern fist fights were also the most protected by evolutionary changes seen in the australopiths.
Furthermore, these are the bones that show the most differences between men and women, as well as between our male and female forebears. That is how you would expect defensive armour to evolve, Prof Carrier points out.
"In humans and in great apes in general... it's males that are most likely to get into fights, and it's also males that are most likely to get injured," he told BBC News.
As Kadhim Shubber for Wired UK points out, the earlier research on hand evolution was controversial. Since this new line of research grows out of that same hypothesis—that fist fights were an important driver of human evolution—many of those same criticisms will be carried over to the new work.