Compared with apes, humans have shorter palms and fingers and longer, stronger, flexible thumbs - features that have been long thought to have evolved so our ancestors could make and use tools, a new study has found.
For a University of Utah study, men whacked punching bags, suggesting human hands evolved not only for the manual dexterity needed to use tools, play a violin or paint a work of art, but so men could make fists and fight.
"The role aggression has played in our evolution has not been adequately appreciated," said University of Utah biology Professor David Carrier, senior author of the study.
"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," Carrier said.
"We are the poster children for violence". Humans have debated for centuries "about whether we are, by nature, aggressive animals," he added.
As our ancestors evolved, "an individual who could strike with a clenched fist could hit harder without injuring themselves, so they were better able to fight for mates and thus more likely to reproduce," he said.
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Fights also were for food, water, land and shelter to support a family, and "over pride, reputation and for revenge," he added.
"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," Carrier says.
Carrier and co-author Michael H Morgan conducted their study to identify any performance advantages a human fist may provide during fighting.
The first experiment involved 10 male students and non-students