December 20, 2012

Did the human hand evolve for boxing (too)?

That is the intriguing conclusion of a new study:

Michael H. Morgan and David R. Carrier, Protective buttressing of the human fist and the evolution of hominin hands. The Journal of Experimental Biology, 2012. Freely accessibleLINK [doi: 10.1242/​jeb.075713 ]

Summary

The derived proportions of the human hand may provide supportive buttressing that protects the hand from injury when striking with a fist. Flexion of digits 2–5 results in buttressing of the pads of the distal phalanges against the central palm and the palmar pads of the proximal phalanges. Additionally, adduction of the thenar eminence to abut the dorsal surface of the distal phalanges of digits 2 and 3 locks these digits into a solid configuration that may allow a transfer of energy through the thenar eminence to the wrist. To test the hypothesis of a performance advantage, we measured: (1) the forces and rate of change of acceleration (jerk) from maximum effort strikes of subjects striking with a fist and an open hand; (2) the static stiffness of the second metacarpo-phalangeal (MCP) joint in buttressed and unbuttressed fist postures; and (3) static force transfer from digits 2 and 3 to digit 1 also in buttressed and unbuttressed fist postures. We found that peak forces, force impulses and peak jerk did not differ between the closed fist and open palm strikes. However, the structure of the human fist provides buttressing that increases the stiffness of the second MCP joint by fourfold and, as a result of force transfer through the thenar eminence, more than doubles the ability of the proximal phalanges to transmit ‘punching’ force. Thus, the proportions of the human hand provide a performance advantage when striking with a fist. We propose that the derived proportions of hominin hands reflect, in part, sexual selection to improve fighting performance.  

I wouldn't dare to comment much but for what I have read in the paper, it looks plausible, notably because it is indeed significantly efficient versus the open hand (as much as 3x) and because chimpanzees can't do it... but australopithecines could. 

However I can also imagine this development as a side-effect of other adaptive uses of the hand, such as grabbing a spear, which is no doubt a much more daunting weapon than a naked fist... in most cases at least.

Fig. 2

7 comments:

  1. The nice thing about fists, though, is that they're always at the ready. No need to reach for one, no chance of losing or forgetting one.

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    1. Of course... but in general, even the strongest humans, are much weaker than chimpanzees (who are not taller or generally bigger) or almost any other animal of comparable size, we have also lost most of our fangs, we really do rely on our wits almost one-sidedly, so it is a bit puzzling that we have developed anything at all to fight without weapons.

      It's not like we can beat a chimp in close unarmed combat and people in tribal societies do not generally box either (if there are fights they are either calmed, normally, or descend into uncontrolled violence with relative ease, as everyone is armed and knows how to kill).

      But well...

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  2. I find that there is a considerable amount of problems with the proposal: If we're talking sexual selection, then we're not necessarily talking about "a need for the most deadly weapon" (say, the one yu'll choose for pure survival in a live-or-death fight). When sexual selection is proposed as a cause, many other aspects of those natural "weapons" (than pure performance) must be taken into account. But the paper just deals on pure mechanical/physical/anatomical performance, and then it jumps into the sexual selection stuff and i think it is a too far too deep jump.

    I suggest that this substitution of a real & sexual-selection-related explanation with some experimentation based on pure physical optimization might be a response to another elemental problem of the proposal: the fact that it's enormously difficult to defend that a fist is:
    - a reasonably good natural weapon, compared to the natural weapons of other predators.
    - a reasonably good alternative to a real, built, weapon, even a really "primitive" one.
    - Not a by-product of another extremely useful adaptations of our hands and fingers and its grip and mobility.

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    1. Good points all, Millán. In truth the sexual selection argument looks feeble because, except maybe in some very specialized contexts, boxing is not how men get women to like them. Actually boxing is a modern English sport, it does not even exist in human nature as such: where all weapons at hand would be used.

      I'm therefore leaning towards an almost accidental evolution, possibly related to grabbing and carrying sticks and spears, which are much better weapons (and tools). I wonder if the australopithecines also used primitive weapons like batons, because if they walked upright and had hands like ours, then they could. And if they could, they probably did, even if their brain was like that of a chimp.

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    2. In truth the sexual selection argument looks feeble because, except maybe in some very specialized contexts, boxing is not how men get women to like them.

      Simply substitute, fist fighting, for all occurrences of, boxing, and your strained objections vanish, Maju, at least to a reasonable observer.

      Boys have been fighting over girls for as long as there have been girls to fight over. Not only is this a time-honored way of establishing mating fitness, it is not uncommon even today to find young girls instigating such fist fights among their suitors. As Kramer noted, it's the obvious reason why Inanna, a teen-aged girl, was a goddess of both warfare and sexual pleasure.

      And like so many comparable displays observed in other species, a fist fight is, outside of certain specialized contexts, a violent but non-lethal assertion of physical dominance over a sexual rival. So, the suggestion here is not necessarily far-fetched.

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    3. When does a fist fighting happen? Not in hunter-gatherer societies: fights unless regulated into sport are always dirty stuff and know no bounds (often they end up in killings) and also why to restrict ourselves to fists when we can kick, bite, use a club...?

      That's why I used "boxing" because there's no such thing as an spontaneous fist fight: it's cultural.

      "Boys have been fighting over girls for as long as there have been girls to fight over".

      I don't think that's correct at all. In most hunter-gatherer societies fighting is culturally and socially undesirable in all circumstances: it happens but not in such contexts. Also, unless it's rape (which is also systematically rejected), the girl is in the end who choses and not necessarily the strongest. Humans are not lions or bulls but more like bonobos or birds in these matters.

      "Inanna"...

      Neolithic stuff. Does not apply.

      If you want to really understand human nature you must forget of industrial age, metal age and farmer age altogether: 95% of the (pre-)history of Homo sapiens is hunter-gathering and that goes up to more than 99% if we count, as we must in this case, from Australopithecus sp.

      So you must look at hunter-gatherers: Pygmies, Bushmen, Hadza and many others documented in the anthropological literature. And there's no such thing as what you imagine so vehemently.

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    4. Maju: "...boxing is not how men get women to like them. Actually boxing is a modern English sport,"
      I think this resumes quite well the main problems of the hypothesis.

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