Human hands evolved so that men could make fists and fight, and not just for manual dexterity, new research finds.

The study, published in the Journal of Experimental Biology, adds to a growing body of evidence that humans are among the most aggressive and violent animals on the planet.

"With the notable exception of bonobos, great apes are a relatively aggressive group of mammals," lead author David Carrier told Discovery News. "Although some primatologists may argue that chimpanzees are the most aggressive apes, I think the evidence suggests that humans are substantially more violent."