Fighting may have shaped the evolution of the human hand, according to a new study by a University of Utah research team. Details have been published in the Journal of Experimental Biology. This article is from a variety of news sources and includes some of my own comments.
The researchers used instruments to measure the forces and acceleration when martial artists hit a punch bag. They found that the structure of the fist provides support that increases the ability of the knuckles to transmit "punching" force.
"We asked the question: 'can you strike harder with a fist than with an open palm?'," co-author David Carrier said. The fist strikes were not more forceful than the strikes with the palm. In terms of the work on the bag there is really no difference." Of course, the surface that strikes the target with a fist is smaller, so there is more stress from a fist strike. "The force per area is higher in a fist strike and that is what causes localised tissue damage,and thus there is a performance advantage in that regard.Surprisingly, both methods produced the same level of maximum force. But the clenched fist delivered that same force to a smaller surface area, meaning it could inflict more tissue damage and be likelier to break bones.That suggested people use a clenched fist for punching in order to maximize bodily damage to their opponents, not to maximize the force they can produce.
Next, the researchers measured the force generated as participants pushed their hands against a surface in different configurations — one in which the fist was clenched and two others with the thumb sticking out. The clenched fist could support much more of each participant's body weight without causing the index and third finger to overextend. The clenched fist, it turns out, "locks the index finger and the middle finger into place, and that's what makes the fist so stiff," Carrier said. The configuration prevents people from injuring their hands while dealing deadly blows, he said.
But the real focus of the study was whether the proportions of the human hand allow buttressing (support)." The team found that making a clenched fist did indeed provide protective buttressing for the delicate bones of the hand. Making a fist increased the stiffness of the second meta-carpo-phalangeal, or MCP, joint (these joints are the knuckles visible when the hand is clenched as a fist) by a factor of four. It also doubled the ability of the proximal phalanges (the bones of the fingers that articulate with the MCP joints) to transmit a punching force.
There may be only one set of skeletal proportions that allows the hand to function both as a mechanism for precise manipulation and as a club for striking.In their paper, Prof Carrier and Michael H Morgan from the University of Utah's school of medicine, point out that the human hand has also been shaped by the need for manual dexterity. But they say that a number of different hand proportions are compatible with an enhanced ability to manipulate objects. The bones of the hand line up into a strong, buttressed structure in a fist.
"Once hands are no longer used in locomotion there could have been many different ways to manipulate and many different ways to punch," said Milford Wolpoff, a paleo-anthropologist at the University of Michigan, who was not involved in the study. "A hand that does both is really limited in its morphology." "Ultimately, the evolutionary significance of the human hand may lie in its remarkable ability to serve two seemingly incompatible, but intrinsically human, functions." Our closest relatives, chimpanzees and bonobos do not generally form fists, and the researchers think they are unable to: when a chimp curls up its fingers it forms a doughnut shape.
Prof Carrier commented: "The question for me is 'why wasn't this discussed 30, 40 years ago.' As far as I know it isn't in the literature." Asked whether the idea that aggression may have played a key role in shaping the human body might previously have been unpalatable to researchers, Prof Carrier explained: "I think we're more in that situation now than we were in the past. "I think there is a lot of resistance, maybe more so among academics than people in general - resistance to the idea that, at some level humans are by nature aggressive animals. I actually think that attitude, and the people who have tried to make the case that we don't have a nature - those people have not served us well. "I think we would be better off if we faced the reality that we have these strong emotions and sometimes they prime us to behave in violent ways. I think if we acknowledged that we'd be better able to prevent violence in future." He also noted that no other apes other than humans hit with a clenched fist and that human beings use fists instictively as threat displays.
The fighting hands, in turn, may have led to even more fighting. "Once that selection for climbing went away, there may also have been this selection for physical fighting — particularly in males. And these proportions would have increased how dangerous an individual was in those fights," Carrier said. As a follow-up, the team wants to study whether differences in women and men's hands (women in general have a longer index finger) potentially make women more dexterous and men more dangerous. Sexual dimorphism also plays a role as difference in body shape seems to be greater in primates, as there is more competition between males. In humans the difference is in the upper body and arms, which is consitent with the hand being a weapon.
This isn't the first time Carrier has argued that humans evolved to fight. Last year he published research suggesting that humans became bipedal to better land crushing blows.
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