Making a fist of it: how hands evolved into a weapon
LONDON — The human hand evolved to be effective in fist fights, scientists have found, after they tested their theory using the arms of dead people.
Humans have shorter palms and fingers and longer, stronger, more flexible thumbs than apes, which some biologists believe evolved not just for manual dexterity but to form a punching fist. Now researchers from the University of Utah have tested that hypothesis by using eight arms from male corpses to perform hundreds of punches and slaps.
“The idea that aggressive behaviour played a role in the evolution of the human hand is controversial,” said professor David Carrier, senior author of the study. “Many skeptics suggest that the human fist is simply a coincidence of natural selection for improved manual dexterity. That may be true, but if it is a coincidence, it is unfortunate.”
The clenched fist is believed to protect the metacarpal bones of the palm by transferring part of the impact through the thumb to the wrist, allowing the hand to be used as a club.
“Metacarpals are bones in the hand that break most often — not finger bones, but bones of the palm,” Carrier said.
Researchers placed the arms in a pendulum-like piece of equipment to allow them to swing toward and punch a padded, force-detected dumbbell.
Strain gauges to measure bone deformation were glued to the side of the metacarpals on the back of the hand. The gauges measured stress on those hand bones during punches and slaps.
The study, published in the Journal of Experimental Biology, found that humans can safely strike with 55 per cent more force with a “fully buttressed fist” than with an “unbuttressed fist,” where the fingers are only loosely folded.