The hand is a complicated, potentially fragile part of the human skeleton. It contains some of the smallest bones in the body, and the level of articulation between the joints makes it the most dexterous natural tool at our disposal.
A new study in the USA suggests part of the evolution of the human hand was shaped by fighting, and points to aggression and violence being a part of out genetic makeup.
The original study by the University of Utah was to determine the difference in force and acceleration of punches thrown by martial artists, with an open hand (palm strike) and a closed hand (a typical punch with a fist).
BBC News has more on the study:
"We asked the question: 'can you strike harder with a fist than with an open palm?'," co-author David Carrier told BBC News.
"We were surprised because 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," said Prof Carrier.
"There is a performance advantage in that regard. But the real focus of the study was whether the proportions of the human hand allow buttressing (support)."
As it turns out, the forming of a closed fist does indeed improve mechanical support in the hand for impact, and its natural design evolved for this purpose. In particular it is the MCP joints -- the visible knuckles you punch with when forming a fist -- that become 'stiffer' by approximately 4 times.
Having said that, we do still see in Mixed Martial Arts and Boxing fractures or breaks to the hand, even ones that are well wrapped beforehand. Some of that may be down to poor form in the technique, some of it may be down to attempting to deliver more force than the hand is structurally capable of withstanding. Or in some cases it's just an incidence of bad luck.
Interestingly we're the only animals that can form a fist to this extent; not even primates we're closely related to can close their hand in such a way:
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.
"There may, however, 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," the researchers write.
"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.
What this has brought up is debate on the nature of humans being aggressive and violent, a notion that for some is uncomfortable to discuss due to the general perception that we've evolved socially where such tendencies are kept in check:
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."
Sport as an outlet for violence and aggression in a controlled and regulated environment is often an argument used to defend combat and full contact sports, and if academics are forced to consider the nature of humans as suggested above, they may well endorse the idea of safely venting these behaviours as opposed to dangerously restricting and repressing them.
The full research paper titled 'Protective buttressing of the human fist and the evolution of hominin hands' can be read at The Journal of Experimental Biology website.