Study: Cadaver arms suggest human fists evolved for punching, too

SALT LAKE CITY, Oct. 22 (UPI) -- Most researchers agree the human hand evolved for tool creation and manipulation, but some scientists say violence played a role too.

To test the hypothesis that human fists are uniquely designed for fist fighting, researchers at the University of Utah tested the mechanics of punching using human cadaver arms.

After rigging the arms with fishing wire and guitar tuning tabs to control the arms' muscles and tendons, researchers installed stress sensors on the hand bones and tested various types of punching motions.

The results suggest a clinched and buttressed fist -- easily formed thanks to humans' shorter palms and fingers and longer, stronger, flexible thumbs -- can safely withstand a greater amount of force than an open palm or a looser, straight-fingered, non-buttressed fist.

Researchers shared their results in the Journal of Experimental Biology.

"We tested the hypothesis that a clenched fist protects the metacarpal [palm or hand] bones from injury [and fracture] by reducing the level of strain during striking," lead study author David Carrier wrote in the new paper. "Our results suggest that humans can safely strike with 55 percent more force with a fully buttressed fist than with an unbuttressed fist, and with twofold more force with a buttressed fist than with an open hand slap."

Carrier and his research partners aren't arguing that fist-fighting was a primary driver of human evolution, only that it was one factor among many.

Researchers admit they can't necessarily disprove the idea that humans' punch-prone fist was simply a coincidence of evolution -- an idea offered by most evolutionary scientists. Still, Carrier says his work lends credence to the "aggressive ape" theory of evolution and offers a corollary storyline to the dexterity hypothesis.

"As an alternative, we suggest that the hand proportions that allow the formation of a fist may tell us something important about our evolutionary history and who we are as a species," Carrier, a biology professor at Utah, said in a press release. "If our anatomy is adapted for fighting, we need to be aware we always may be haunted by basic emotions and reflexive behaviors that often don't make sense -- and are very dangerous -- in the modern world."

In an effort to quell critics, Carrier says early human faces evolved to withstand and deflect blows. Species such as Homo australopithecus had a more triangular face and flatter nose. It was only after punching gave way to different types of weapons that faces become more delicate and humans lost some of their punching power with diminished upper body strength.

Some have called Carrier's logic "bro science," questioning the motivations of his emphasis on male-on-male violence. But Carrier says he believes human propensity for empathy and cooperation are equally important evolutionary drivers; he says his critics misinterpret his aims.

"There's a fear that if there is evidence that we are anatomically specialized for aggressive behavior, that might in some way justify violence, might justify aggression, might justify bad behavior," Carrier told the Los Angeles Times. "And the way I respond to that is by saying understanding is not justification."