Your Beard May Protect Your Brain If You Take It on the Chin

Evolutionary pressure related to pugilism helped push facial hair to the fore.

Posted Apr 19, 2020

Quarantine and lockdowns around the globe have given rise to some significant changes in personal grooming. If social media is any metric, there have been mixed results on the haircare front for many. Front and center for facial hair, a recent study suggests an unexpected beneficial bit about beards that may answer a conundrum in evolution.

Physical characteristics like facial hair in humans cluster across biological sex based on relative balance in the neuroendocrine system. Sexual dimorphism has been used as an explanation for differences in many phenotypes across species in the animal kingdom. Although not the focus here, it must be stated that the reality is far more complex than this historical binary classification since sex refers to biological attributes on a distribution distinguishing organisms as male, female, intersex, and hermaphrodite.

Regardless of how it's categorized, one phenotype that has remained a bit of a puzzle is the differential prevalence of facial hair at the extreme ends of characteristics of biological sex distribution between males and females. Why do males as contrasted with female humans tend to more commonly display facial hair? That is, beyond hormonal regulation, what evolutionary pressures would such differentiation serve?

Researchers Ethan Beseris, Steven Naleway, and David Carrier at the University of Utah looked at this problem from the perspective of evolution in a study published in Integrative Organismal Biology. The answer in their paper, "Impact Protection Potential of Mammalian Hair: Testing the Pugilism Hypothesis for the Evolution of Human Facial Hair" may surprise you. The authors proposed three things that led to their study:

  • Most of the physical aggression exhibited in the great apes, including us humans, is male-on-male violence;
  • Bare-hand human fighting involves a predominant focus on facial attack;
  • Sexual differences in evolution may be greatest in phenotypes that enhance protection in violent encounters.

All of which brings us to facial hair and its potential mechanical role in taking a punch. Beserin, Naleway, and Carrier tested the idea that beards might disperse and absorb blunt impact (like that from a fist) energy and protect human skin and facial bones. (This is an area of controversy in MMA and boxing.) They created three tissue composites that stood in for bone and then covered it with skin from sheep that was either "shorn" or hairy. The hairy samples (of which there were three levels of "fur" covering) were then subjected to impact.

Fully furred samples absorbed more energy and altered peak forces than those less furred. Mostly this had to do with dispersion over the forces over time (a change in impulse). Their results clearly show a mechanically protective function of hair mitigating against violent impact. This suggested to the authors that an evolutionary advantage might exist that gave rise to sex-based ranges in the phenotypical expression of facial hair in humans.

These scientists wrote that their results are "consistent with the hypothesis that beards evolved to enhance fighting performance by providing protection to vulnerable aspects of the face." How much this may or may not translate into protection against brain injury related to concussive impacts remains to be seen. The extent to which facial hair might offer some minor protection against incidental and accidental contact with the face is also unclear.

I reached out to the senior author, David Carrier, for additional comments, especially related to motivation and context. Despite the surprising fact that no one involved with this study were martial artists or combat sports athletes, they are "considering another study on the effect that full beards have on the accuracy of punching." He further told me that:

"We wound up following a similar path to this question as Darwin did, not realizing he had traveled the path first. Darwin pointed out that in mammals sexual dimorphism is often a result of sexual selection acting to improve fighting ability in males. He also recognized that facial hair is one of the most sexually dimorphic feature of humans and that this type of sexual dimorphism distinguishes us from the other great apes. We had the additional observation that the part of the face that is primarily covered by the beard, the lower jaw, is one of the things that most often breaks when males fight. Interestingly, Darwin argued that manes in lions, sea lions, and elk provided protection when males fight, but when it came to humans he argued that beards are a result of female preference, not male contest competition."

As with other animals, facial hair may form a protective barrier for humans. Whether we have more or less in common with those quadrupedal cats and our other evolutionary cousins remains for further study.

Regardless, if you have facial hair and your current quarantine, lockdown, or physical isolation has you neglecting the occasional trim, you may be doing yourself a protective favor to be maintained against mishap when we are all eventually out and about.

(c) E. Paul Zehr (2020)