Why are our hands shaped the way they are? Compared with those of other apes, the thumb is long and the palms and fingers are short. Scientists have a variety of theories as to why they evolved to be that way - perhaps it was the comparatively longer thumb that permitted us to make tools, or the proportions of the hand may be the indirect consequence of natural selection for a foot with a long toe, so handy for keeping balance while walking on two feet. Researchers at the University of Utah now have another suggestion: the hand is the shape that it is because it allows us to make a nice fist for punching that protects key parts of the hand from harm. The proposal, made by student Michael Morgan and biologist David Carrier, was published in the Journal of Experimental Biology . The duo tested their fighting fist hypothesis in a series of experiments in which men pounded punching bags, squeezed pressure sensors or performed one-handed push-ups on top of pressure sensors. From this, the scientists learned that force meted out by the hand is about the same when a bag is punched by a fist versus slapped, but nearly twice as great when you consider that the fist delivers its force to a smaller surface area. The study also found that the knuckle joint of the index finger is rendered stiffer and more stable, transferring force more effectively and protecting the hand, when a tight fist is made. In other words, the fist is a great fighting tool. And, they write: "There appears to be a paradox in the evolution of the human hand. It is arguably our most important anatomical weapon, used to threaten, beat and sometimes kill to resolve a conflict. Yet it is also the part of our musculoskeletal system that crafts and uses delicate tools, plays musical instruments, produces art, and conveys emotions."