In the Dark

I found out today that this year an IgNobel Prize has been awarded for a paper on Impact Protection Potential of Mammalian Hair: Testing the Pugilism Hypothesis for the Evolution of Human Facial Hair which was actually published last April in the journal Integrative Organismal Biology. This seems to be a bona fide academic journal, though apparently not one that has very high standards.

Anyway, the abstract reads:

Because facial hair is one of the most sexually dimorphic features of humans (Homo sapiens) and is often perceived as an indicator of masculinity and social dominance, human facial hair has been suggested to play a role in male contest competition. Some authors have proposed that the beard may function similar to the long hair of a lion’s mane, serving to protect vital areas like the throat and jaw from lethal attacks. This is consistent with the observation that the mandible, which is superficially covered by the beard, is one of the most commonly fractured facial bones in interpersonal violence. We hypothesized that beards protect the skin and bones of the face when human males fight by absorbing and dispersing the energy of a blunt impact. We tested this hypothesis by measuring impact force and energy absorbed by a fiber epoxy composite, which served as a bone analog, when it was covered with skin that had thick hair (referred to here as “furred”) versus skin with no hair (referred to here as “sheared” and “plucked”). We covered the epoxy composite with segments of skin dissected from domestic sheep (Ovis aries), and used a drop weight impact tester affixed with a load cell to collect force versus time data. Tissue samples were prepared in three conditions: furred (n = 20), plucked (n = 20), and sheared (n = 20). We found that fully furred samples were capable of absorbing more energy than plucked and sheared samples. For example, peak force was 16% greater and total energy absorbed was 37% greater in the furred compared to the plucked samples. These differences were due in part to a longer time frame of force delivery in the furred samples. These data support the hypothesis that human beards protect vulnerable regions of the facial skeleton from damaging strikes.

E A Beseris, S E Naleway, D R Carrier
Integrative Organismal Biology, Volume 2, Issue 1, 2020

This study has attracted a number of silly headlines such as “Big manly beards evolved so we could take punches to the head, study says” and a rebuke from the Beard Liberation Front.

My main problem with the article are (i) that the study itself is very flawed and, worse, (ii) that the claims made of a link to evolution are clearly bullshit; the latter is especially disappointing because the connection to evolution was explicitly caimed by biologists, who really ought to know better.

On point (i) I’ll just point out that the experiment didn’t involve beards or punching. The team built models – sixty of them – made of fibres and epoxy resin to represent human bone, covered in sheepskin to mimic facial hair. Those models were either ‘furred’ (‘full beard’ with 8cm-long hairs), ‘sheared’ (0.5cm length ‘trimmed beard’) or ‘plucked’ (‘hairless’ shaven face). Human hair follicles are four times as thick as those from sheep, but five times less densely packed, so a fleece roughly approximates a beard. The biologists then used a mechanical striker to repeatedly drop a 4.7kg weight onto each model to measure the impact and record the damage.

The results showed that furred models were better than both sheared and plucked models at taking the ‘punch’: a beard will absorb 37% more energy than a shaven face, for example, partly because springy hairs serve as suspension to slow down and soften the blow. As the researchers explain, “the greatest advantage offered by the hair is that it distributes the force of impact over a longer time frame”.

The problem is that this experiment isn’t at all realistic. Dropping a load onto a solid object would simulate hitting a dummy rather than a person; the latter can roll with a punch, the former cannot. In addition, many punches thrown in fights – as opposed to the boxing ring – are not straight to the chin but some variation of the hook that hits the side of the head causing it to rotate. Now allowing the models to rotate is a significant flaw in the experiment.

But the bigger problem with the study is (ii), that its results are interpreted as evidence for evolution on the grounds that facial hair represents a form of ‘sexual dimorphism’ leading to the suggestion that certain facial features evolved as a result of competitive fighting between human males .There is then the idea is that, just as a lion’s thick mane covers vital regions such as the jugular vein, beards help protect against potentially lethal punches to the throat and jaw. This is the so-called ‘pugilism hypothesis’ (from the Latin pugil, pugilis meaning a boxer) and this study says nothing at all about whether or not this is true. Even if you think the experiment is realistic, its results shed no light on the pugilism hypothesis. That is not a matter that can be settled by biomechanics but has to involve evolutionary biology, and specifically how the trait in question might have evolved through natural selection.

Charles Darwin’s 1871 book The Descent of Man discusses hair in great detail but didn’t make the mistake of equating the lion’s mane with human hair: although he argued that the thick hair of various mammals might provide protection in fights between competing males, he believed that human facial hair is a ‘secondary sexual character’ that evolved as a result of female preferences, and rightly pointed out that human populations differ in their ability to grow thick beards — not something you would expect if facial hair has a protective function. Not every biological feature is the result of natural selection either: a given characteristic could be an adaptation that evolved for a specific function, but it could also have no “purpose:

Anyway in reading this silly article I became interested in beards in boxing, given that boxers are generally clean-shaven. A ban on beards in boxing has been in place in many forms of the sport and still is in, for example, the Olympics. There has been recent discussion about a beard ban being a form of discrimination against, say, Sikh boxers and the amateur sport. I think beards are only allowed in professional boxing if both sides agree.

So why would anyone forbid a boxer to wear a beard? I don’t buy the argument about a beard cushioning a punch, for the reasons outlined above and for the fact that the gloves play the role of “distributing the force of impact” far more effectively than a beard would. Some have argued that a full beard may make it difficult for an opponent to locate the line of the jaw and hence strike the wearer’s chin. Another suggestion is that a beard would conceal cuts and bleeding and possible hinder medical attention.

I’m not sufficiently expert to say whether any of these are reasonable, but reading an article like this one by promoter Frank Warren convinces me that the major factor in the beard ban is just an irrational aversion to beards among the boxing hierarchy. In other words, pogonophobia.