Human hands built the Taj Mahal and adorned the ceiling of the Sistine Chapel with glorious art - but they also evolved for fighting, according to a new theory.
Compared with apes, humans have shorter palms and fingers and longer, stronger flexible thumbs.
Experts have long assumed these features evolved to help our ancestors make and use tools.
But new evidence from the US suggests it was not just dexterity that shaped the human hand, but violence also. Hands largely evolved through natural selection to form a punching fist, it is claimed.
Professor David Carrier, from the University of Utah, said: "The role aggression has played in our evolution has not been adequately appreciated. 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."
The forces of natural selection that drove hands to become nimble-fingered also turned them into weapons, Prof Carrier believes. To test the theory Prof Carrier conducted experiments with volunteers aged 22 to 50 who had boxing or martial arts experience. In one, participants were asked to hit a punchbag as hard as possible from different directions with their hands in a range of shapes, from open palms to closed fists.
The results, published in the Journal of Experimental Biology, show that tightly clenched fists are much more efficient weapons than open or loosely curled hands. A punch delivers up for three times more force to the same amount of surface area as a slap. And the buttressing provided by a clenched fist increases the stiffness of the knuckles fourfold, while doubling the ability of the fingers to deliver a 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," said Prof Carrier.
In their paper, Prof Carrier and colleague Michael Morgan, a University of Utah medical student, ponder on the paradoxical nature of the human hand.
They conclude: "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."