The human hand is a sophisticated work of art and science. Refined through centuries of evolution, hands enable us to perform unique functions which help us to not only survive but also to thrive as a species.
New research suggests the evolution of the modern human hand may be due to a very basic need: for use as a weapon.
In a study published in The Journal of Experimental Biology, University of Utah scientists theorize human hands evolved their unique square palms and long thumb in order to stabilize the fist, providing a built-in compact club early humans could use in combat.
An impassioned conversation with a colleague inspired David Carrier to pursue research on the matter.
In the course of their conversation, Frank Fish, an expert in biomechanics, formed a fist and said, “I can hit you in the face with this, but that is not what it evolved for.”
Fish’s proclamation made Carrier stop and think. While the human hand evolved to allow great dexterity, according to Carrier, a chimpanzee can also manipulate its hands in a way that would give it greater manual dexterity, but they still may not necessarily be able to form their hands like humans do.
Modern chimpanzees, according to Carrier, have long palms and fingers with a short thumb, while the human palm and fingers are much shorter and the thumb longer and stronger.
This difference brought on by evolution, allows us to clench our hand into a fist whenever we fold our thumb across the fingertips. A chimpanzee’s fingers, on the other hand, forms the shape of what he describes as an open doughnut shape when curled.
Carrier said that he wondered if the tightly-packed human fist provides some internal support to our fingers in order to protect them from being damaged during an altercation and if it also provides humans with the ability to deliver a more powerful blow against their opponents, as compared to the slap of an open hand.
Carrier and Morgan decided to find out whether hands are more effective when balled into a fist or used as an open-handed slap.
“Fortunately, Michael had a lot of experience with martial arts and he knew people who were willing to serve as subjects,” said Carrier.
First, the test subjects were asked to smack a punching bag with their hands formed into a wide variety shapes; from the open-handed slap to the tightly-clenched fist, using various styles to deliver the blows, such as over the arm, sideways and head on. As each of the fighters walloped their punching bag foe, the researchers would measure the force of each impact.
But after looking at the results of that experiment, the researchers were surprised to see the punch did not deliver more force per blow.
“In terms of the peak forces or the impulse, it did not matter whether the subjects were hitting with a clenched fist or open palm,” said Carrier.
Morgan and Carrier then wanted to find out whether supporting the hand, by curling the fingers and thumb, stiffens the structure of the hand. Asking their test subjects to form their hands into various fist shapes, the researchers measured the rigidity of the first knuckle joint of their subject’s index finger, first with the support of the thumb over the finger and then without the support of the thumb. They found the knuckle joint was four times more rigid when supported by the thumb.
Next, the researchers measured the amount of force that the fighters could deliver through the fist surface of their index and middle fingers. Again, they found that by using the thumb in forming a fist, the test subjects doubled the delivered force by transmitting it to the wrist through the palm bones of the thumb and the index finger.
The results of their experiments led Carrier and Morgan to conclude the square-shaped palms of today’s humans are perfectly proportioned to stiffen into a fist to be used as a weapon that delivers powerful punches without injuring ourselves.