Bro science” refers to theories chalking human evolution up to our basic urge to fistfight. In a new study published in the Journal of Experimental Biology, researchers hoped to find evidence that the human hand had evolved to form a tight fist to help males fight over females. Because that’s what human evolution is all about, brah!

But it’s hard to assess the effectiveness of a punch without incurring a few broken bones, so the team used arms from nine male cadavers to do the punching for them. Shaping the corpse hands into “buttressed” (thumb curled around index and middle fingers) and “unbuttressed” (thumb outward) fists, University of Utah researchers used the cadaver hands to throw various punches and open-palm slaps at padded dumbbells meant to approximate the firmness of a human face. They hoped to find evidence that our fist-making ability allowed ancient males to throw harder punches at their neighbors without sustaining too many injuries.

Their cadaver-boxing experiment, which involved hundreds of punches, succeeded in providing the evidence they were looking for: A buttressed punch is 55 percent more forceful than an unbuttressed one and twice as powerful as an open-hand slap. Without having evolved the right-hand proportions, forming such an effective buttressed fist wouldn’t have been possible.

These photos of a living person's hands punching or slapping a padded dumbbell weight show the positions of cadaver arms and hands in a University of Utah study.

Critics of bro science argue that fist formation is just a happy coincidence of human fingers evolving for dexterity. We’re built to use tools, and if humans had really evolved to punch each other in the face, then our faces would also have evolved to withstand the blows.

Lead author David Carrier and his team aren’t having any of it. They suggest that the hand proportions that evolved are optimized for punching and manual dexterity. They’ve already argued that our evolutionary forebears, the Australopiths, did have facial structures meant to withstand blows from angry neighbors, and the only reason ours are more delicate is because we as a species eventually weaned ourselves off physical brutality.

If we are truly products of brutal male ancestors, outfitted with anatomy adapted for fighting, it’s possible our emotions and reflexes might be, too, Carrier suggests. He doesn’t disagree that humans are, by nature, cooperative and peaceful, but he also doesn’t believe that aggression didn’t play a big part of our evolution.

Whether or not his fistfighting theory is right, there’s no shortage of evidence that bromotions are still running high, millennia after our forebears first brawled.


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