Human Hands Evolved for Punching

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. For this latest study, he and co-author Michael Morgan, a medical student, conducted three experiments. First, they analyzed what happened when men, aged from 22 to 50, hit a punching bag as hard as they could. The peak stress delivered to the bag -- the force per area -- was 1.7 to 3 times greater with a fist strike compared with a slap. "Because you have higher pressure when hitting with a fist, you are more likely to cause injury to tissue, bones, teeth, eyes and the jaw," Carrier said. The second and third experiments determined that buttressing provided by the human fist increases the stiffness of the knuckle joint fourfold. It also doubles the ability of the fingers to transmit punching force, mainly due to the force transferred from the fingers to the thumb when the fist is clenched. In terms of the size and shape of hand anatomy, the scientists point out that humans could have evolved manual dexterity with longer thumbs, but without the fingers and palms getting shorter. The researchers additionally point out that humans use fists during threat displays. There is also a difference in body size between males and females, particularly evident with hands and arms. This, Carrier said, is "consistent with the hand being a weapon." Defending children may even help to explain human hand anatomy, since both men and women are often driven to protect their offspring, in addition to fighting with others over territory, resources and for other reasons...more