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Fighting shaped human hands

December 19, 2012
The Company of Biologists
We're all used to the idea that humans evolved their distinctive hand proportions for enhanced dexterity, but now researchers have come up with an alternative theory: that human hands evolved for combat. The duo provide evidence that the long thumb that wraps across the fingers in a fist packs the curled digits tightly together to make a compact club for use in combat.

The human hand is a finely tuned piece of equipment that is capable of remarkable dexterity: creating art, performing music and manipulating tools. Yet David Carrier from the University of Utah suggests that the human hand may have also evolved its distinctive proportions for a less enlightened reason: for use as a weapon. In a new study, Carrier and colleague Michael Morgan publish their theory that human hands evolved their square palms and long thumb to stabilise the fist and produce a compact club for use in combat.

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The study appears in in The Journal of Experimental Biology at http://jeb.biologists.org.

Carrier recalls that the idea occurred to him during an impassioned discussion with fellow biomechanic Frank Fish about sperm whales. Explaining that he had published a paper suggesting that the whales might use their spermaceti organs as battering rams, Carrier says 'Frank didn't buy the argument and at one point he raised his fist and said, "I can hit you in the face with this, but that is not what it evolved for."' A light went on in Carrier's head. Sure, the human hand evolved for dexterity, but he adds, 'You could manipulate the proportions of a chimp hand in ways that would enhance manual dexterity, but they would not necessarily end up with the proportions that we have.' Maybe there was more to Fish's challenge than met the eye.

According to Carrier and Morgan, modern chimpanzees have long palms and fingers with a short thumb, while the human palm and fingers are much shorter and the thumb longer and stronger. Carrier explains that this squat arrangement allows us to clench our hand into a fist when we fold the thumb across the fingertips however, chimp fingers form an open doughnut shape when curled. Could the tightly packed human fist provide internal support -- buttressing -- to the digits to protect them from damage during combat? In addition, Carrier wondered whether curling the fingers into a fist could allow punching men to deliver a more powerful blow (increase the peak force of an impact) than slapping with the open hand. Carrier and Morgan decided to find out whether hands are more effective when balled into a fist or wielded in a slap.

'Fortunately, Michael had a lot of experience with martial arts and he knew people who were willing to serve as subjects', Carrier recalls. Asking the athletes to thump a punchbag with their hands in a range of shapes (from open-handed slaps to closed fists) using various delivery styles (over arm, sideways and head on), Morgan and Carrier measured the force of each impact. However, they were surprised to see that 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', Carrier says.

Next the duo tested whether buttressing the hand by curling the fingers and thumb stiffens the structure. They asked the martial arts experts to roll their hands into variations of the fist shape -- two with the thumb extended sideways -- and then push the first joint of the index finger against a force transducer to measure the rigidity of the knuckle joint in the presence and absence of the buttressing thumb. Impressively, the knuckle joint was four times more rigid when supported by the thumb. And when the duo measured the amount of force that the athletes could deliver through the fist surface of the index and middle fingers, they found that the presence of the buttressing thumb doubled the delivered force by transmitting it to the wrist through the metacarpals (palm bones) of the thumb and the index finger.

So our short, square hands are perfectly proportioned to stiffen our fists for use as weapons and allow us -- well, males predominantly -- to deliver powerful punches without incurring injuries.

Story Source:

The above story is based on materials provided by The Company of Biologists. The original article was written by Kathryn Knight. Note: Materials may be edited for content and length.

Journal Reference:

  1. M. H. Morgan, D. R. Carrier. Protective buttressing of the human fist and the evolution of hominin hands. Journal of Experimental Biology, 2012; 216 (2): 236 DOI: 10.1242/jeb.075713

Cite This Page:

The Company of Biologists. "Fighting shaped human hands." ScienceDaily. ScienceDaily, 19 December 2012. <www.sciencedaily.com/releases/2012/12/121219223446.htm>.
The Company of Biologists. (2012, December 19). Fighting shaped human hands. ScienceDaily. Retrieved March 31, 2015 from www.sciencedaily.com/releases/2012/12/121219223446.htm
The Company of Biologists. "Fighting shaped human hands." ScienceDaily. www.sciencedaily.com/releases/2012/12/121219223446.htm (accessed March 31, 2015).

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Fine Hands, Fists of Fury: Our Hands Evolved for Punching, Not Just Dexterity

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