University of Utah
Human faces may have evolved in response to being punched repeatedly.
In order to protect the jaw from breaking during punch-ups, an injury that could have proved fatal in our ancient past, humans evolved “protective buttressing”, claims a paper to be published on 9 June in Biological Reviews.
The research follows analysis of the human hand by the same University of Utah team that in 2012 published a controversial paper suggesting that our hands evolved to allow us to punch better.
“If indeed the evolution of our hand proportions were associated with selection for fighting behaviour,” said lead author David Carrier, “you might expect the primary target, the face, to have undergone evolution to better protect it from injury when punched”.
By examining the skulls of modern humans and australopiths, a human ancestor that became extinct two million years ago, the team detected strong evolutionary changes in the bones that are most likely to fracture during fights.
Additionally, the team says, the protective features in those same bones were markedly different between women and men.
“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.
The study contradicts previous research that suggested a diet of tough nuts and seeds helped drive evolution of our faces. Published in 2009, that study used CT scans to analyse the facial biomechanics of australopiths, finding that their jaws may have been adapted to crunching nuts.
Instead, argue Carrier and coauthor Michael Morgan, violence and conflict over resources, land and reproduction, changed the human face.
The idea that our skulls may be adapted to violence is part of a continuing line of research from Carrier and coauthor Michael Morgan on the influence of violence in early human societies.
Their 2012 study on human hands examined the forces exerted on the fists of martial artists when hitting a punchbag and argued that although our hands also evolved to be dexterous, violence was the leading influence on how they came to have the proportions they do today. In short, our hands are adapted to punching.
Not everyone was convinced, as this National Geographic blog post details, with critics variously arguing that ancient humans would not have fought like martial artists today, using their teeth as much as their hands, and that making a fist is not a natural position for the hand.
Carrier and Morgan’s latest paper is sure to attract similar debate, but if they’re right then understanding human evolution could be as simple as imagining a fist punching a human face — forever.