Human hands evolved for punching, macabre experiment suggests
Published 22/10/2015 | 00:31
A macabre experiment involving animated cadaver arms, fishing line and guitar tuner knobs has lent support to the theory that human hands are designed for punching.
Scientists in the US set out to investigate the idea that one reason for the unusual shape of the human hand is that it evolved to facilitate fist fights between angry men.
They set up a bizarre series of tests in which arms from human corpses were placed in a pendulum-like apparatus that allowed them to swing punches at a padded force-detecting surface.
To make the dead fists clench, lengths of fishing line were attached to tendons controlling movements of the wrist, thumb and fingers.
And the guitar knobs? They were used to tighten or slacken the lines to switch between a "slapping" open hand, a hand formed into a fist with the thumb extended, or a "buttressed" fist with the thumb locked around the index and middle fingers.
After hundreds of punches and slaps using eight out of nine arms - one was too arthritic - the scientists concluded that human fists really did double as efficient clubs.
The team, led by Professor David Carrier, from the University of Utah, wrote in the Journal of Experimental Biology: "We tested the hypothesis that a clenched fist protects the metacarpal (palm or hand) bones from injury by reducing the level of strain during striking ...
"Our results suggest that humans can safely strike with 55% more force with a fully buttressed fist than with an unbuttressed fist, and with two-fold more force with a buttressed fist than with an open hand slap."
Compared with other great apes like chimpanzees, humans have shorter palms and longer, stronger and more flexible thumbs.
Such features are widely believed to have helped our ancestors make and use tools. But according to Prof Carrier, the pugilistic nature of early humans may have also had a hand in their evolution.
He points out that the faces of primitive hominids, such as the australopiths, had crude, lumpy faces armoured by strong bones that could resist punching.
As humans evolved and bare-knuckle boxing became a less common way to settle differences over mates and resources, their faces adopted the more delicate structure they have today.
The cadaver arms used in the experiment were obtained from the university's body donor programme and a private supply company.
Prof Carrier said: "Each one of these hands took about a week of work.
"First we had to dissect it to expose the muscles, apply one or more strain gauges, and then attach the lines to all the tendons so you can control the position of the wrist, thumb and fingers to create a buttressed fist, unbuttressed fist or open-palm posture.
"Everything had to be lined up just right - all the joints, tension in muscles, the orientation of bones."