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Evolved Fists or the Best Weapons at Hand?

Posted February 27, 2013

My most memorable punch in the face was a beaut. Back during my first year of studying karate, some classmates and I had met up for a little unsupervised sparring practice—never a good idea for novices. After an hour or so of this, my friend Eric and I were easing out of it with what was supposed to be an easy cool-down round when he, with a surge of enthusiasm, threw a left jab that popped me front and center across the chin, teeth, and tip of the nose. (So nicely placed.)

My eyes rolled up into my skull and a warm red blanket of numbness closed in from every side of my field of vision. My knees slowly folded, all resolve to support my worthless body gone. Fight over! My concerned friends looked on while I, on the floor, gingerly felt out whether there was any actual damage (there wasn’t… that time). The punch hadn’t been so much painful as deeply stunning, and it was probably a good ten minutes before I stopped feeling its disorienting effects.

Experiences like that one, not to mention the far more powerful punches in prize fights or even board-breaking demonstrations by martial artists, can inspire considerable respect for the prowess of the human hand as a weapon. They also inspired a widely publicized recent study by evolutionary biologists Michael H. Morgan and David R. Carrier at the University of Utah, who have suggested that while evolution was reshaping our hands to improve our ability to use tools, it was also shaping them to throw more effective punches.

It’s a clever speculation, and its authors don’t really offer it as much more than that. Perhaps it contains a kernel of truth worth further investigation. Personally, though, I find it unpersuasive on evolutionary grounds—and what the heck, on fighting grounds, too.

Ancient hands, questionable fists

The great apes and the tree-dwelling ancestors we shared with them had hands that excelled at prehensile power grips, which were essential for holding tightly to branches. Only humans, however, have hands with the dexterity for precision grips that can manipulate small objects between the tips of the thumb and opposing fingers. Grab a hammer: power grip; grab a pencil: precision grip.

Comparison of the external (A) and skeletal (B) proportions of the hands of chimpanzees (at left) and humans. From Morgan and Carrier, J.Exp.Bio. (2013).

What makes our precision gripping possible is that our hands have much boxier proportions than do those of the chimps and apes. Our thumbs are longer, more flexible, and proportionally stronger, while our fingers are shorter. Those dimensions started to emerge more than three million years ago, roughly around the time that our australopith ancestors started to walk on two legs. Given the huge survival advantages that came with tool use, biologists have long surmised that dexterity was the primary factor that drove evolutionary changes in our hands.

But in their paper in the January 15 issue of The Journal of Experimental Biology, Morgan and Carrier point out that our hand’s shape also allows us to do something else that the apes can’t: make a true fist. Only humans can curl their fingertips tightly into the center of the palm without leaving a space, and only humans can then buttress (fold and lock) the thumb across the first two fingers—an arrangement that turns our fists into hard, unyielding clubs.

Diagram of a fist.

This is no coincidence, according to Morgan and Carrier. In all the known species of great apes, males fight with one another for the opportunity to mate. Among gorillas and chimps this conflict can be brutal, and even the relatively peaceful bonobo males mix it up over females. That conflict should exert evolutionary pressure to make males better fighters. In the case of humans, the researchers posit, it could have meant that natural selection found a hand design that makes us simultaneously great tool users and punchers.

The fight is on

Carrier’s interest in the role of fighting on human evolution isn’t new. In 2011 he published a paper in PLoS ONE that argued male-male aggression in our ancestors might have created sexual selection pressure favoring taller men (and not necessarily taller women), because their height would have enabled them to strike downward more powerfully during fights. This new set of experiments, however, seems to have been inspired by a heated discussion with their biomechanics colleague Frank Fish, as noted in what is now one of my all-time favorite acknowledgments in a research paper:

We thank Professor Frank Fish for suggesting the null hypothesis with a wave of his fist and the exclamation ‘I can hit you in the face with this, but it did not evolve for that!’

Morgan and Carrier seem to have taken that as a challenge.

To test how much advantage the shape of the human fist gives fighters, Morgan and Carrier recruited 12 experienced fighters. They measured how much power the fighters could deliver with closed fist strikes versus open hand slaps from various angles, and how the force of a blow was distributed throughout the hand and wrist during impact. They also looked at what happened when the fighters struck with hands shaped into approximations of what primates’ fists look like. (If a chimp tries to make a fist, for example, its thumb juts out somewhat as shown in image C just below.)

The three hand postures studied by Morgan and Carrier: (A) a tight, fully buttressed fist, (B) a fist with tightly curled fingers but no support from a locked thumb, and (C) a fist without reinforcement from the fingers or thumb. From Morgan and Carrier, J.Exp.Bio. (2013).

How a fist changes shape during a punching impact (before: gray; after: black). A sturdy fist, as shown here, shows much greater stability than a more poorly shaped one does. From Morgan and Carrier, J.Exp.Bio (2013).

In brief, Morgan and Carrier documented that true fists do indeed make hand blows more formidable. Perhaps most notably, they showed that tucking the tips of the fingers directly into the palm doubled the stiffness of the middle finger’s knuckle during an impact—and reinforcing the fingers with the thumb doubled the stiffness again. That fourfold increase in stiffness not only makes the fist more clublike but could also reduce the tendency for the blow to hurt the puncher, because the reciprocal impact gets distributed throughout structures in the hand and wrist.

That general conclusion won’t come as a surprise to martial artists, who know from experience that a properly shaped fist can concentrate all the power of a punch into the small area across the top of the big knuckles of the index and middle fingers. (Japanese karateka refer to this hitting surface as seiken.) They also know that punching with an improperly shaped fist is an open invitation to injury. Nevertheless, it’s great that Morgan and Carrier have quantified some of these details, and I suspect that the findings about the effect of fist-shape on the stability of the joints will be one of the biggest lasting contributions of this paper.

Scoring the round

What, though, about their larger argument that natural selection was adapting our hands for pugilism at the same time it was making us dexterous? It’s not a preposterous idea, and I’d be interested in how further experiments by Morgan and Carrier (and more importantly, others) would explore it further. But the case seems weak and dubious to me for a variety of reasons.

A crucial test for Morgan and Carrier’s theory is precisely the argument that their colleague Frank Fish raised before their experiments began: can it distinguish fists specifically adapted for fighting from fists that we simply use when fighting because they are, well, handy. The late Stephen Jay Gould borrowed the term “spandrels” from architecture to account for features that look designed but are really happy accidents. Are our fists evolved weapons or just spandrels?

Without better knowledge about the constraints that might have influenced the shape of our hands, it is almost impossible to know. Evolutionary biologists often try to solve such problems by looking to the fossil record for signs that a feature’s function emerged over time. Morgan and Carrier haven’t done much of that kind of study yet, however: they discuss the shapes of apes’ hands and those of Australopithecus, but their work doesn’t report on the dimensions and fighting effectiveness of any ancestral species between them and us.

We also don’t yet know whether the modifications of fists would actually have provided enough of an advantage in practice to influence natural selection. Morgan and Carrier make the point that by striking with their seiken rather than their palm (shotei in karate), fighters can increase the stress on their opponent’s tissues by 1.7 to 3.0 times, thereby increasing the potential for injury at the point of contact. But the paper also acknowledges that open palm slaps exert about as much jerk (change in acceleration) on the target as punches do, and the level of jerk is what is most associated with traumatic brain and musculoskeletal injuries. So their argument depends on some assumptions about what kinds of inflicted injuries were most important in winning those fights for mating rights.

Remember, too, that even with their miserable fists, male gorillas and chimps can inflict devastating, even lethal injuries on their rivals. Yes, they are landing their blows with the immense strength of apes, but what they are hitting are other gorillas and chimps, which have a proportionate strength for taking a blow.

Nor is there much discussion in the paper about how apes, ancestral humans, and modern people actually fought. The paper mentions that punches are the most frequent blows thrown in mixed martial arts fights, and that babies innately raise their fists in anger, but those observations don’t really do anything to disprove Fish’s null hypothesis: that we use fists for aggression because it’s reasonably effective and easy for us to do.

Fists aren’t clubs

To me, there’s also another unacknowledged problem with their hypothesis. Contrary to what one might be led to believe from Morgan and Carrier’s measurements and the terrifying blows thrown in boxing matches and other sporting events, human hands simply aren’t great as bludgeons.

Example of a boxer’s fracture, shown by the broken metatarsal of the ring finger (at arrow). [Photo: Yayay, via Wikimedia Commons]

There’s a reason that fighters wrap their hands before a fight and put on cushioned gloves, and it isn’t all intended to reduce the brutality unleashed on their opponents. If you throw a full-power punch with an unprotected fist into someone’s face or head, there’s a very good chance you will break a finger or metacarpal (one of bones in the palm of the hand). Bones of the hand are fragile compared to the more solid bones of the skull.

Yes, you can break someone’s nose or knock out teeth easily enough, but if your opponent ducks his chin and your fist slams into the hard dome of his temple instead, you may be hurt worse than he is. Fierce punches to the body are relatively safer for your hands, but even then there’s a chance of slamming into an elbow and suffering what’s known as a boxer’s fracture—a break that can shove your knuckle halfway to the center of your hand. Left untreated, a boxer’s fracture can permanently impair someone’s ability to fight and grip a tool, so it’s not an injury to dismiss casually among our prehistoric ancestors.

John L. Sullivan, aka the Boston Strong Boy, last of the heavyweight champions of bare-knuckle fighting. (via Wikipedia)

In the heyday of John L. Sullivan and bare-knuckle boxing matches in the 19th century, fighters mostly threw snapping punches to the face and hard punches to the body until an opponent was an easy target for a knockout, which is why they adopted a fighting stance that can look a bit comical to spectators of modern boxing. My understanding is that the use of boxing gloves was introduced precisely to enable fighters to punch one another with full abandon: promoters liked that it made the fights more exciting… and never mind the harm done to the fighters along the way. This is part of why the incidence of serious brain trauma among boxers may have increased after the introduction of gloves.

(Bare-knuckle boxing hasn’t disappeared as a sport, by the way, though many of the surviving competitions may be of questionable legality, to say the least. I won’t link to any specifically because these fights can still be bloody and nasty, but search YouTube and you’ll find plenty of clips from fights. Consider yourself warned, though!)

The limitations of fists are why martial arts fighters often use techniques that involve the palm heel (shotei), the open hand’s knife edge (shuto), and the hammer fist (tettsui) for power strikes—all of which have their own advantages and disadvantages. It’s also why combatants in hard-fighting styles like muay thai often favor using elbow and knee strikes, because those parts of the body are even more devastatingly clublike than the hand can be.

I can’t help but wonder whether the new study’s selection of experienced fighters as participants might not be a methodological weakness. Experienced fighters know how to make good fists. Every martial arts teacher knows that instructing beginners on how to make a sturdy fist is one of the first challenges: new students often routinely put their thumbs inside their fingers, they stick out thumbs, they bend their wrists—all mistakes that undermine the fist strength that Morgan and Carrier measured. Martial artists benefit from centuries if not thousands of years of tradition on how to make good fists.

Would our ancestors stretching back to Australopithecus naturally make fists more like boxers or like children? If their punches weren’t strong, why wouldn’t they simply rely more on other blows and kicks? If evolution adapted our hands for punching, I wonder why it didn’t do more to increase the density or stability of our punching knuckles and finger bones? Or maybe evolution really did all that it could without impairing the even more important dexterity of our hands.

The problem is that we don’t know enough about the relative importance of different hand features to understand the constraints on their evolution—which is why this study, for me, loses by TKO.

• • •

Morgan, M. H. and Carrier, D. R. (2013). Protective buttressing of the human fist and the evolution of hominin hands. J. Exp. Biol. 216:236-244. doi:10.1242/jeb.075713

Carrier DR (2011) The Advantage of Standing Up to Fight and the Evolution of Habitual Bipedalism in Hominins. PLoS ONE 6(5):e19630. doi:10.1371/journal.pone.0019630

Source: PLOS The Gleaming Retort, story by John Rennie

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