Ow, My Head

Unlike the widespread reporting of the credulous media, the human skull is not specifically evolved to take a punch from other humans. Brian Switek explains the many problems with this hypothesis at National Geographic’s Phenomena. I admit that I thought, throughout my rugby career, that my head, and only my head, had evolved to be punched. It turns out that the way I played rugby had evolved to make people want to punch me in the head¹. I was a particularly annoying person to play rugby against².

Fortunately, human skulls are pretty robust in some key ways. It is just very unlikely that they got that way due to the evolutionary pressure of hominids punching each other in the noodle. One of the key problems with the punching hypothesis is that it is pure conjecture (and unreasonable conjecture, at that) without supporting experimental evidence. What would it take to really test the punching hypothesis?

WARNING: This post may contain a Game of Thrones spoiler “below the fold”. 

Me with ironic signage at the aftermatch after-stomping social (Photo Credit: Dan Totman, taken on ~2008 cellphone, Used with permission) – this photo was shown at my thesis defense

There are good reasons to protect your brain throughout evolutionary time, like predators and falling down, even if your ancestors were not regularly exposed to left hooks³. Bone is a pretty good building material. According to the experts, not even someone as improbably large as The Mountain in Game of Thrones could not crush a human skull, even by stepping on it. I found this very reassuring, as I have been the victim of a head stomping from a large and deranged individual.

Let us for a moment ignore plausibility with the élan of non-Bayesian, amateur statistical enthusiasts and ponder the “faces are made for punching” hypothesis more empirically. We need to start by taking a stab at defining a hypothesis:

Bone morphology of hominid skulls was significantly influenced by selective pressure of punching by other hominids.

This, I admit, is a pretty mediocre hypothesis, and, like any mediocre hypothesis, it carries within several other hypotheses that go unstated⁴. There are significant questions related to fitness and what “taking a punch” actually means.

While having one’s skull caved in is bad for fitness, we’ve excluded that risk. Realistically, being knocked out/concussed may be the most serious, frequently occurring result of a punch - it makes it very easy for the leopards to eat you. Concussions are less about skull structure and more about getting your head whipped around, which is controlled primarily by neck muscles. You don’t need to be punched to get a concussion. Mitigating concussion risk, however, would not just be an adaptation to being punched by your fellow humans. You could get smacked with a bear paw, get roundhouse kicked by Chuck Norris, fall, or be clubbed.

Other injuries that commonly occur from a punch are unpleasant, but less likely to immediately lead to a failure to produce viable offspring. Noses, orbits of the eye, teeth, and lower jaws break relatively easily. Punched skin is susceptible to cuts. In the absence of hard data, it is difficult to say that these injuries hurt fitness. Clichés suggest that these injuries might even increase fitness:

Chicks dig scars (sexual selection)

You should see the other guy… (relative fitness)

It is improbable that there are punch-specific fitness benefits to the structure of our faces, it does not mean that there are not individual facial feature variants that are better at taking a punch than others.

Photo Credit: Dnalor_01; Source: Wikimedia Commons; CC-BY-SA 3.0)

To test this we will need a disturbing number of skulls – maybe we could collaborate with the Capuchin friars. The features of those skulls would need to be measured in exacting detail to establish the quantitative variations in the skull bones.

We could also use a robot that can consistently simulates a punch with a specific force to a specific location. This could be as simple as a device that applies a specific forces to specific locations. A punching robot would be better, because the force of a fist can be distributed across the face.

It would be useful to have not just skulls, but heads with skin, muscle, and fat to provide realistic absorption and distribution of the punch force. That would, however, introduce additional variation, which will have to be measured and which will require larger sample sizes. We would also have to convince an Institutional Review Board (IRB) to approving of a robot punching lots of humans in the face to study an implausible hypothesis. And, if imaging cannot measure the bones in enough detail, we’ll have to decapitate those humans and let flesh-eating beetles remove all the soft tissue. Tough sledding, that.

Finally, we need a metric for “taking a punch” – a “Balboa Scale”. This could be as simple as asking if specific bones fracture at certain levels of force or it could complexly capture both bone damage and the absorption of force to reduce acceleration of the brain case.

If we got all those elements in place, we could then correlate variation in Balboa scores with variation in bone measurements between skulls to identify features that explain variation in Balboa scores with statistical significance. We could then look for trends in those features among our hominid ancestors. Are they more robust in hominid lineages compared to other primates or mammals? Have they become more robust or less over time? Once we have established the existence of the phenomena of punchable facial features, we can start asking why the phenomena exists. To speculate wildly, but plausibly, maybe features that are good for chewing tough food are also good for absorbing damage.

Ironically, the features that were proposed, but not tested, for being “good at taking a punch” were more robust in our ancestors than in Homo sapiens. We may be getting worse at being punched.

At least, that is the Nature side of the equation. There is also Nurture. In my experience, one of the best ways to develop your ability to take a punch is to have been hit in the face a few times. Getting hit in the face with intent is pretty damn shocking the first time, but you get used to it. You can get used to almost anything.

NOTES
1. Rugby has a reputation as a sport whose violence extends beyond the rules. In my experience, the level of “dirty play” decreases dramatically as the players become more skillful and the referees are more experienced. The stereotypes primarily exist at the lower end of amateur rugby.
2. In the context of a rugby match, this is a pretty solid strategy, provided you can avoid injury. Not only is the other team distracted by wanting to punish you (which is worth zero points on the scoreboard), but punching is illegal and can get you carded, leaving your team down a player.
2. I was eye gouged, once, briefly. The misbegotten soul who tried to gouge my left eye (my only left eye) over a dispute about legal possession of the rugby ball (I was right, he was wrong) didn’t really have his heart in it. Warrior metaphors to one side, rugby is not battle. It is not, literally, a life-and-death struggle. Gouging an eye is going to be gross. He got a broken nose for his trouble. I like my eyes, astigmatized and short-sighted as they are.
3. Our hominid ancestors who could not form a tight fist for punching probably did not evolve skulls for absorbing tight-fisted punches from other members of their species.
4. This, I admit, is a pretty mediocre sentence, and, like any mediocre sentence, this one carries within it way too many commas.