An aggressive behavior such as punching may have played an important role in the human evolution, as biologists of the University of Utah used cadaver hands to punch and slap dumbbells in experiments to prove it.

Many experts support the idea that the human fist evolved in the actual shape in order to improve manual dexterity. So the theory that punching others with a clinched fist to reduce the injury risk, is at least controversial.

David Carrier, lead author of the study published in the Journal of Experimental Biology, suggests that our hands proportions could tells us about our evolutionary history, and who we are as a species: “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.”

Muhammad Ali overlooking the Chicago River and the city’s skyline. 1966 Photo: THOMAS HOEPKER/ Sport Magazine

When we compare to our ‘closest relatives’, we find that we have shorter palms and fingers, and our thumbs are longer, stronger and more flexible than the ones from apes. This allowed us to develop the manual dexterity to create tools that helped us get to where we stand now.

Putting dead arms to work

In order to test their hypothesis about the clenched fist that protects our bones from injuries and fractures, scientists used nine male cadaver arms (they ended up using only eight, one was too arthritic) to measure the level of strain during the strike.

This arms were placed in something similar to a pendulum, making them swing towards a padded, force-detecting dumbbell to punch it. Strain gauges were glued to the metacarpals to measure the bone deformation, its stretching and compression.

Carrier says that it is valid to extrapolate the results to the greater forces of a real punch, explaining that there is a linear relationship between the force applied and how much the bone can bend.

They found that humans can safely strike, using 55 percent more force, with a closed fist than with a open one, and with more force with an open fist than by slapping. Carrier and his team believe that, at the same time the hand evolved to perform manual chores, it also evolved to be used as “a club during fighting.”

The fisted punch protects our metacarpals – the fingers in our hands – that are the bones that break most often when someone punches a wall or someone else.

It’s not only about hands

This theory not only involves the evolution of our hands. The research team also says that the faces of human ancestors —such as the australopiths— also changed to become more resistant to punching. That could explain why our faces now are more fine and delicate, as the use of brute force have decreased —evolving in other ways of violence.

Also, the researchers say that natural selection wasn’t the only factor that influenced the hand’s development. They mention other possibilities, such as genetic drift, and genetic and developmental factors yet to discover. Carrier puts the example of the big toe, that got bigger than the rest of the toes so humans could run easily, saying that this same genes probably affected our hand proportions.

The bro-science

This theory has been criticized by many of experts in the field, giving it the nickname “bro science” — men hitting each other driving the human race towards evolution.

“I think some of that’s understandable. 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. And the way I respond to that is by saying understanding is not justification,” Carrier said to answer those allegations, according to the LA Times.

Source: EurekAlert