It turns out that human hands aren’t just for using tools or playing instruments. New research, reported by the University of Utah, reveals that human hands evolved so men could make fists and fight like Rocky Balboa.
Compared with apes, humans have shorter palms and fingers and longer, stronger, flexible thumbs. These are features that scientists have long thought evolved so our ancestors could create and use tools.
“The role aggression has played in our evolution has not been adequately appreciated,” says senior author David Carrier, a professor of biology at the University of Utah. “There are people who do not like this idea, but it is clear that compared with other mammals, great apes are a relatively aggressive group, with lots of fighting and violence, and that includes us. We’re the poster children for violence.”
This study may finally put to rest the debate about whether humans are, by nature, aggressive animals.
“Our anatomy holds clues to that question,” Mr. Carrier posits. “If we can understand what our anatomy has evolved to do, we’ll have a clearer picture of who we were in the beginning, and whether aggression is part of who we are.”
While the way human hands evolved helped our manual dexterity, the study’s senior author argues that the proportions of our hands help us make a fist, shielding delicate hand bones, muscles and ligaments during a fight.
As human hands evolved, a person who could hit with a clenched fist had a better chance of winning a mate. Mr. Carrier also notes that our ancestors fought for food, water, land and shelter as well as pride, reputation and revenge.
“If a fist posture does provide a performance advantage for punching, the proportions of our hands also may have evolved in response to selection for fighting ability, in addition to selection for dexterity,” Mr. Carrier contends.
To determine what, if any, advantages a human fist has in a fight, Mr. Carrier and his colleagues conducted three experiments. The first experiment tested whether humans can hit hard with a fist. The researchers found that the peak force was the same whether the punching bag was hit with a fist or slapped with an open hand. They did find, however, that a fist hits with the same force with one-third of the surface area as the palm and fingers.
“Because you have higher pressure when hitting with a fist, you are more likely to cause injury,” Mr. Carrier says.
The second and third experiments tested the idea that a fist protects the hand during a fight. The researchers discovered that the buttressing provided by the human fist increased the stiffness of the knuckle joint fourfold and doubled the ability of the fingers to transmit punching force.
“Because the experiments show the proportions of the human hand provide a performance advantage when striking with a fist, we suggest that the proportions of our hands resulted, in part, from selection to improve fighting performance,” Mr. Carrier says.
Mr. Carrier argues that if manual dexterity was the only reason human hands evolved, humans could have evolved manual dexterity with longer thumbs without the fingers and palms getting shorter.
“There is only one way you can have a buttressed, clenched fist: the palms and fingers got shorter at the same time the thumb got longer,” Mr. Carrier posits.
To bolster their argument, the researchers pointed out several other arguments that human hands evolved for fighting, including the fact that no ape hits with a clenched first other than humans and that humans use fists as threat displays.
The study’s findings are described in detail in a recent issue of the Journal of Experimental Biology.