Researchers have long debated the evolution of the human fist. There are two sides to the argument: One side says that the fist is a coincidence, a byproduct of our dextrous hands. The other side believes the fist evolved as a tool for punching.
Now a group at the University of Utah has tested the theory that human hands evolved for fighting in a unique and somewhat grotesque way–by using cadaver arms to punch dumbbells.
The study’s lead author, professor David Carrier, is in the fisticuffs camp. “Many skeptics suggest that the human fist is simply a coincidence of natural selection for improved manual dexterity,” he says in a statement. “That may be true, but if it is a coincidence, it is unfortunate.”
To test the theory, Carrier and his team procured nine cadaver arms and used them to strike a padded dumbbell. After discarding one arm as “too arthritic,” they proceeded to slap, whack and punch their way through hundreds of strikes, to test how much damage different techniques would cause the hands. Human hands have shorter palms and fingers, and longer thumbs, than other primates, so they can be better bunched into a fist.
“We tested the hypothesis that a clenched fist protects the metacarpal bones from injury by reducing the level of strain during striking,” said the study.
The metacarpals are the small bones in the palm of your hand and are the ones most likely to break upon landing a punch. Bunching your hand could protect these bones from damage.
The setup was macabre. Carrier’s team used nylon lines to yank on the tendons in the hand, allowing them to perform open-handed slaps, loose fisted whacks, and tightly bunched fists that used the thumb as a buttress. To tension the nylon lines, they used guitar tuning heads. Strain gauges were glued to the muscles in the backs of the hands.
The results showed that a buttressed fist can punch half as hard again before suffering damage and twice as hard as a slap.
But does this prove that we evolved thumbs just to mess up other cave-persons? Not necessarily. We evolved longer big toes to help us run, so Carrier speculates that “the same genes likely affected hand proportions as well.”
If we did evolve to have weapons as hands, then there are likely other, less physical, consequences to being Chuck Norris-like fighting machines.
“If our anatomy is adapted for fighting,” says Carrier, “we need to be aware we always may be haunted by basic emotions and reflexive behaviors that often don’t make sense–and are very dangerous–in the modern world.”