Researchers used cadavers to determine whether human hands evolved not only to perform dexterous tasks but also to fight.
Human hands have shorter fingers, longer and more flexible thumbs and smaller palms compared to other apes, but no one is sure how it came to be. Biologists from the University of Utah tested cadaver arms and hands to test the theory that these limbs have evolved so that males could engage and defend against fights; for example, fisticuffs over females.
"The idea that aggressive behavior played a role in the evolution of the human hand is controversial," said senior author David Carrier, a biology professor of the university. He said that many skeptics attribute the development of the human fist to mere coincidence that resulted from natural selection.
"That may be true, but if it is a coincidence, it is unfortunate," Carrier remarked, as he is one of the scientists who believe that the formation of the fist is actually part of human evolutionary history.
To test this theory, Carrier and his team bought the cadavers of nine males from a private supplier and the University of Utah's body donor program. Eight of these hands and arms were used to punch and slap on padded dumbbells.
The team's report suggested that human hands punching with a fully clenched fist has 55 percent more force than with a loosely clenched fist. They also determined that a buttressed fist can hit twice as strong as an open handed slap.
"This performance advantage of our hand proportions is consistent with our musculoskeletal anatomy being adapted for fighting," Carrier said.
While the results did not disprove the hypothesis, some critics were not as inclined to agree.
Mary Marzke of Arizona State University did not find the hypothesis behind the study as impressive. Professor Marzke pointed out that other monkeys are also able to do fist-like gestures, despite the absence of long thumbs and these gestures weren't used in fighting, but rather for handling food.
"It also is surprising that the authors compared fist-punching with palm-slapping, instead of with striking by the heel of the palm," Marzke said, adding that an open palm heel strike is just as effective in fighting and did not require human proportioned fingers to execute.
Another critic was Stony Brook University's Brigitte Demes, who said that the study did not provide any new and significant data to the table that confirms anything.
"The conclusions drawn are not based on evidence," Demes said, believing that even if punching is proven to be the superior form of hand-to-hand combat, there is no proof that human hands evolved for that specific purpose.
"There are many other behaviors that could be marshaled to explain the morphology of human hand bones," Demes explained.
As for what Carrier thinks about these criticisms, he said that it is a result of fear to the possibility that man was built to fight, a reasoning that could justify aggressive behaviors. But he argues that the fear is not necessarily valid.
"If our goal is to reduce violence in the future, we need to understand what this dark side of human nature is all about," Carrier concluded.
The findings of his study are published in the Journal of Experimental Biology.
