 This is our question. Specifically, do male beards, which cover some of the most vulnerable parts of the face, provide protection when males punch each other? Well, where did this question come from? First, we know that males do, on occasion, punch each other. We also know that in fistfights, the primary target is usually the face. We know that when males punch, they usually punch other males, not always, but usually. Finally, facial hair is expressed very different in males and females, and this turns out to be important. Charles Darwin was the first biologist to wonder about human beards. And he was very interested in these differences between males and females, what we call sexual dimorphism, which are anatomical, physiological, and behavioral differences between male and female animals. Darwin realized that the males of a number of species of mammals grow thick manes of fur around their faces and necks. For example, lions, sea lions, bobcats, and elk. He also observed that these manes first begin to grow at the time males become sexually mature and start competing with other males for access to females. He suggested that manes provide protection during male-male fighting. Darwin also pointed out that the beards of humans first appear, first begin to grow, when males become sexually mature. Additionally, Darwin realized that the facial hair of the other great apes is not different between males and females. These photos compare a male and female chimpanzee, and as you can see, there's no difference in their facial hair. But compared to the other great apes, human males have a lot more facial hair, and human females have a lot less. When it came to explaining the beards of human males, Darwin suggested that male facial hair was the result of female preference. In other words, he thought human males have facial hair, have beards, because females prefer males with a full beard. Well, he had a full beard and was certainly an attractive guy, and he had a reputation for not being particularly pugnacious, so we can see how it made sense to Darwin that human beards were not about fighting, but about attracting females. However, recent studies indicate that human females, on average, do not find full beards to be particularly attractive. In fact, women in affluent societies are actually more often repelled by full beards than attracted to them. So we decided to test Darwin's lion-main hypothesis, that human beards provide physical protection when one is punched in the face. So because of the nature of this study, there were some obvious ethical implications for how we test this hypothesis. We can't exactly go around punching a man with and without beards, and measuring our results there. So that was kind of the beginning of this project, just figuring out how to model it. And the solution that we came up with was we're modeling beard with sheet fleece, and our bone tissue was modeled using a short fiber epoxy composite that has similar strength and stiffness to the bone. So we overlaid the sheet skin over that bone tissue epoxy, and we measured these sheet fleece in three different conditions. So the first one is the composite covered with skin that's been completely plucked, meaning you're plucking out the follicles, all the hair fibers, everything. And then the composite covered with the sheared fleece, so shearing down to just a certain length, but also leaving that follicle intact. And then a composite that's completely covered with the fleece, so entirely the fleece has not been modified at all. And the way that we measured impacts, we had this machine, it's an Instron Dynatup. So what it is, it has this device, it's an impact head that you would drop directly on the sheet skin sample. And it's measuring the amount of force that each sample absorbs prior to breaking. So then this kind of drops on it just like a hammer, breaks that composite, and then you're measuring how much energy it's absorbing in jewels. And results you can see here, so the graph plots the peak energy absorbed by the different test samples, fully furred, completely plucked, and sheared to a few millimeters in length. And our findings, so the total energy was absorbed was 37% greater in the furred samples compared to the plucked and the sheared samples. So statistically very significant. So there you have it, are beards a type of armor? This man who had a beard thought the beards were not armor. Our results suggest that they may be. So what is the broader significance of this study? If human beards did evolve to protect male faces, many of us have to face the darker side of human nature every time we look in the mirror. But there are two sides to the human nature coin. There's no doubt that humans are the most empathetic and cooperative species on the planet. We also love peace and safety. Given that reducing violence in the future is a goal we all share, we think it is important to keep in mind that our anatomy reminds us that in certain circumstances we can and sometimes do respond with aggression.