Evolving Less Punchable Faces

By Julie Beck

A subset of our early bipedal ancestors, the australopiths, had “distinctly robust” faces. They looked like this—wide flat cheekbones, broad jaws, and thick orbital bones around the eyes. A new study published in Biological Review suggests that these features developed as a defense to early hominids’ preferred weapon—their fists.

The researchers, David Carrier and Michael Morgan of the University of Utah, theorized in a previous paper that humans’ ability to clench their hands into fists was natural selection’s way of making hands into better weapons. (Slap fights just weren’t cutting it anymore.) And if early humans had similar punching preferences as current humans do, the face was a prime target—a 1998 study of male assault victims found that 68.5 percent of injuries were facial.

A model of the male Australopithecus afarensis at the
Smithsonian Natural History museum (Tim Evanson/flickr)

Interestingly, the face bones that are most likely to fracture in homo sapiens—including cheekbones, mandibles, noses, and orbital bones—“tend to exhibit disproportionally large dimensions in australopiths, often equal to or exceeding values reported in much larger-bodied male gorillas,” the study reads. “Regardless of the evolutionary reasons for these features, the facial skeleton of australopiths was well proportioned to withstand strikes.”

Previous theories of why the face developed this way focused on chewing, and the ability to crush hard foods and grasses. But the researchers point out that some studies suggest australopiths may not have had that many hard foods in their diets after all, and that these facial features didn’t experience much strain during chewing. Perhaps, they think, since males exhibited these characteristics significantly more than females, “the proportions of these parts of face may be a result of sexual selection on fighting performance.”

Once we get into the homo genus, the robustness of the australopiths is reduced. Cheekbones are thinner, and faces are just smaller overall. The evolution toward a more vertical face, which we still see in humans “reduced the rotational moment on the skull from a blow” to the mandible, so we’ve still got that going for us. But the researchers posit that we may not need the facial structures of australopiths as much anymore because there has been a “more-or-less continuous reduction in upper body strength” throughout the evolution of the homo genus.

Still, the study notes that wide faces in human males are still associated with violence and fighting ability. So if you’re engaging in fisticuffs with a guy who looks a little prehistoric, it might be safer to aim for his stomach.

This article available online at:

http://www.theatlantic.com/health/archive/2014/06/evolving-less-punchable-faces/372461/