The surprising reason men may have evolved beards involves punches, violent fights and a scientific theory that has now earned an Ig Nobel Peace Prize

For something so ordinary, the human beard has an unusually complicated evolutionary history. It can signal age, masculinity or social dominance, but scientists have long debated why humans developed such conspicuous facial hair in the first place. One particularly unconventional theory suggests that the answer may lie not in attraction, but in combat.

In 2020, three researchers at the University of Utah set out to test whether a thick beard could have offered a physical advantage during male-to-male fights. Their study examined whether hair could absorb and redistribute the energy generated by a blunt impact, potentially reducing damage to the bones and tissues underneath it.

The research by Ethan A. Beseris, Steven E. Naleway and David R. Carrier, published in Integrative Organismal Biology, became a scientific test of what they called the “pugilism hypothesis” for the evolution of human facial hair.

The evolutionary mystery behind the beard

Human facial hair is one of the most pronounced differences between male and female humans. The researchers noted that beards are commonly associated with masculinity, social dominance and aggression, raising the possibility that facial hair could have played a role in competition between males.

The idea was not entirely new. Charles Darwin had previously suggested that the manes of some male animals might offer protection during fights. Lions, for example, have prominent hair around the head and neck. Some evolutionary researchers have consequently proposed that human beards could perform a somewhat comparable defensive function, particularly around the jaw.

There was another reason the scientists considered the theory worth testing. The mandible, or lower jawbone, is among the facial bones frequently fractured in interpersonal violence, according to research cited in their paper. Because much of the mandible is located beneath the area covered by a beard, the researchers wondered whether facial hair might have offered some protection during violent encounters.

They did not test the theory on human faces

The experiment did not involve people punching bearded volunteers. Instead, the researchers designed a laboratory model to isolate the mechanical effect of hair.

They used sections of domestic sheep skin, because sheep provide a convenient source of thick mammalian hair, and placed the tissue over a fiber-epoxy composite material designed to act as a bone analogue. The samples were divided into three groups: naturally furred, sheared and completely plucked.

Each sample was subjected to controlled impacts using a drop-weight impact tester equipped with a load cell, allowing the researchers to measure the force and energy involved in each strike. There were 20 samples in each of the three conditions.

The researchers were essentially asking a simple mechanical question: does a layer of hair change what happens when something strikes the tissue beneath it?

The hairy samples absorbed more energy

The results provided support for the protective hypothesis. The fully furred samples absorbed substantially more energy than the samples from which the hair had been removed. In one comparison, the furred material absorbed 37% more total energy than the plucked samples. The researchers also found differences in the way force was delivered, with the furred samples experiencing a longer period of loading.

In their broader analysis, the authors reported that furred samples absorbed nearly 30% more energy on average than sheared and plucked samples. They also experienced lower peak impact forces and were less likely to fail under the experimental conditions.

That does not mean a beard could make someone immune to a punch. The experiment demonstrated a mechanical effect in sheep skin mounted over a laboratory bone analogue, not protection during an actual human fight.

The researchers were careful about that distinction. Their conclusion was that the findings support the possibility that human facial hair could protect vulnerable facial structures from damaging impacts.

The beard as evolutionary armour

The researchers went further in discussing what a beard might theoretically do during an impact. Besides absorbing and dispersing some energy, they suggested that facial hair could potentially reduce skin injuries and bruising. They also proposed, without testing it directly, that hair might help deflect an oblique strike by reducing friction between the face and the object making contact.

The research was later recognized with the 2021 Ig Nobel Peace Prize, an award celebrating unusual research intended to make people laugh before making them think.