A study from the University of Utah on Wednesday suggested that the size and shape of human hands evolved not only to manipulate tools, but also so that men could form fists and fight.

The study explored two facets of the fist — one, that it causes more harm to opponents, and, two, that a clenched fist buttresses hands from damage to fragile bones, muscles and tendons.

According to University of Utah biology professor David Carrier, this finding could be an answer to evolutionary questions concerning humans and innate violence.

"The role aggression has played in our evolution has not been adequately appreciated," he said.

Delicate destructive hands

Compared to our simian ancestors, humans have delicate yet destructive hands with smaller palms and fingers, and longer, stronger, more flexible thumbs. That structure enables the formation of a fist, which gives humans, particularly males with their stronger bone structure, an obvious evolutionary advantage among the great apes.

"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," said Carrier.

Forming a close-handed battering ram allowed early human males to protect their mates and property by hammering opponents with a fist, which acted as an effective weapon in the hand-to-hand combat arsenal.

"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," said Carrier.

"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."

Fists pack more punch

In an effort to record the impact of a punch, Carrier had 10 men with martial arts training hit a punching bag with slaps, shoves and punches.

Carrier found that a strike with a fist contained 1.7 to three times more force than an open-handed slap.

Also, in order to determine how human fists provide strength and stability, in a way that apes with their bigger palms and longer fingers can't, Carrier measured how much pressure a hand can take when it is clenched and unclenched.

"Because the experiments show the proportions of the human hand provide a performance advantage when striking with a fist, we suggest that the proportion of our hands resulted, in part, from selection to improve fighting performance," said Carrier.

The report also argued that fists are used as displays of threats. Carrier said that the reflexive response to anger is to form a fist to cause intimidation.

"More than any other part of our anatomy, the hand represents the identity of Homo sapiens. Ultimately, the evolutionary significance of the human hand may lie in its remarkable ability to serve two seemingly incompatible but intrinsically human functions," said the report.