Podcast: How Men Evolved For Fighting

One of the things that makes humans, well, human is the ability to make a fist. Other primates canâ€™t do this.

The commonly accepted theory as to why humans developed the ability to make a fist is that they needed to do so in order to grasp tools.

But research conducted by my guests today have led them to posit a very different theory.

They argue that the reason we can make a fist is so we can give better knuckle sandwiches.

Their names are Dr. David Carrier and Dr. Michael Morgan. Dr. Carrier is a professor of evolutionary biology at the University of Utah and Dr. Morgan is an emergency room physician. When Dr. Morgan was an undergrad at the University of Utah, he worked with Dr. Carrier on two papers which explored the role physical aggression may have played in the development of the human fist. Today on the show, we discuss that idea and the theory that human bodies, especially male bodies, evolved for fighting.

Show Highlights

What led Carrier and Morgan to look into whether aggression contributed to the human ability to make a fist [03:00]
Whether human violence is biological, cultural, or a little bit of both [06:00]
Why men in particular are prone to violence and aggression [10:00]
The ritualistic pre-fight dance men take part in without even thinking about it [12:00]
Why the ability to make a fist may have evolved to make hand-striking more effective [14:30]
How punching with a fist increases the “force impulse” of a punch [17:00]
The critiques of Carrier and Morgan’s paper and their responses [20:00]
How the human head may have evolved to take a punch, but has gotten weaker over time [23:30]
The physiological differences between men and women that make men more adapted for fighting [29:30]
Why a man’s shoulders are like a stag’s antlers [32:00]
And much more!

Resources/Studies/People Mentioned in Podcast

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Read the Transcript

Brett McKay: Brett McKay here, and welcome to another addition of The Art of Manliness Podcast. One of the things that makes humans well, human, is the ability to make a fist. Other primates can’t do this and the commonly accepted theory as to why humans developed this ability, to make a fist, is they needed to do so in order to grasp tools. Research checked out by my guests today have led them to posit a very different theory. They argue that one of the reasons we can make a fist is so that we can give better knuckle sandwiches. That’s right, we have a fist so we can punch. They’re names are Dr. David Carrier and Dr. Michael Morgan. Dr. Carrier is a professor of evolutionary biology at the University of Utah, and Dr. Morgan is an emergency room physician. When Dr. Morgan was an undergraduate at the University of Utah, he worked with Dr. Carrier on two papers, which explored the role of physical aggression and what it may have played in the development of the human fist. Today on the show, we discuss that idea and the theory that human bodies, especially male human bodies, evolved for fighting.

Really great show. A lot of fascinating insights from links to resources that we mention throughout the show. Check out the show notes at AOM.is/aggression.

Dr. Dave Carrier and Dr. Mike Morgan, welcome to the show.

Dr. Morgan: Thanks for having us.

Dr. Carrier: Yes. Thanks very much.

Brett McKay: You two have worked together on research and published a paper that went out, I think it was last year, that caused some stir. Not only in academic circles but also in the popular press. I remember reading this research, I forgot where it was. It wasn’t in an academic journal it was on some website, about how aggression and violence in humans may have shaped the way the human body evolved. Before we get into the specifics of your research, I’m curious, how did you two get interested in this idea that there might be a connection between the physiology of our evolution and the emotions of our evolution, as well?

Dr. Morgan: Why don’t I start? I was an undergrad student with hopes and aspirations to go to medical school. I had been involved with some research with Dr. Carriers wife using live alligators. Dave was doing a lot of research on human locomotion and energy expenditure and he and I struck up a conversation one day. I think I had mentioned that I had some prior martial arts training. I have two black belts. Especially with Dave’s interest in aggression and violence, that things kind of spiraled from there. I’ve been lucky enough to have him as a great mentor and inquisitive mind … A great intellect. He asks, I think, some very important questions. Questions that interested me as well, with my background and experience in fighting and for me that was kind of where my interest began.

Dr. Carrier: Those conversations is really where our focus on the hand started. Going back a step farther, early on, this question about whether or not humans had specialized for aggressive behavior came out of some work we were doing with domestic dogs. We’ve been interested in whether or not they were functional trade offs, in terms of the anatomy that allows an animal to be a very efficient runner. For instance, the anatomy that allows an animal to be an effective fighter. We were using two breeds of dogs, Greyhounds and Pit bulls. Greyhound’s the runner, the Pit bull’s the fighter. Those two breeds share some anatomical similarities with the bipedal apes.

The early bipedal apes, we call the group, hominids, were built pretty much like chimpanzees but they were habitual bipeds. They love running around on their hind legs. They were relatively short and stout animals, like Pit bulls. Later, several million years later, you get the evolution of humans, this group we call homo, and that anatomy is very similar to modern human anatomy. That anatomy is appropriate, we think, for locomotor economy. It was that comparison with the two breeds of dogs to the early forms of the bipedal apes that got us thinking, maybe humans, particularly our early ancestors, were anatomically specialized for aggression.

Brett McKay: Side question is, there is a long standing debate and philosophy, and sociology, biology, about whether or not violence is part of human nature. Some have argued that humans, particularly males, are socially conditioned to be violent and aggressive. While, there’s another camp that argues that violence and aggression is just a natural part of being human. It seems like from the paper that I read, you’re coming from a school of thought that violence and aggression is maybe part of our biology. If that’s the case, I’m curious, what evolutionary benefit did our early human ancestors get from being violent and aggressive?

Dr. Morgan: I think this is a very interesting debate. For me, it’s hard to paint as just a black and white, nature verses nurture. You often times use the term, is this part of our biology or is this “instinctual” behavior versus social behavior? Is this behavior that we’re taught? I think those two ideas of socialization verse instinct when it comes to human behavior, is so ingrained that often times it’s impossible to separate the two. We always try to do that when we’re explaining these things.

The way I tend to look at it, Brett, is I think our behaviors ultimately, especially through the early development of man, we’re often times influenced by the environment and the pressures of those environments put on the social group. The social group, in turn, had to adapt and develop different behaviors and different behavior patterns to handle the stress the environment was putting on them. There certainly are situations where environmental stresses would probably lead to promoting or encouraging aggressive and violent behavior within any social structure, at any given time. It’s a blend of both of those things. I think environmental factors effect social behaviors, which in turn effect evolutionary behaviors, which ultimately effects the trajectory of our species.

Dr. Carrier: To add to that, those environmental factors influence all species and so there’s competition at different levels and basically all species. One of the things that’s unique to humans that might increase the stakes or increase the pressure, is that we have offspring that are incredibly dependent. We’re born in a very immature state and it takes years for parents to raise a young human to a stage where they can take care of themselves and make a contribution to the community. That investment in offspring has been shown to associate in a variety of different ways and different species. Associated with relatively high levels of aggression and high levels of competition.

One of the reasons humans may be so relatively violent in comparison to animals, in comparison to other primates, may be these very dependent … We use the word, altricial offspring that we have.

Brett McKay: Why is it that, males in particular, in the human species have a tendency towards violence and aggression?

Dr. Carrier: That’s true among mammals in general. There tends to be relatively high competition among males in most species of mammals and it’s largely because they are competing for access to females. In mammals, females make this incredibly high investment in their offspring. There’s a long period where, instead of just laying an egg like a bird or a lizard, the female gestates the fetus for the period of time and then after the young are born, she nurses them. For most species of mammal, the dad’s not involved at all, other than the act of mating. Because of that, female mammals tend to be picky. They want to mate with the males that basically have the best genes. That puts the males in position of competing. Humans are similar to other species of mammal, in that regard.

Dr. Morgan: I also want to put out there that not just strictly violence in males … We don’t have the … What’s the word I’m looking for? We don’t have all the rights and I don’t know what I’m trying to say. We don’t own violence as the male of the species. I think, even though, predominately aggressive acts when you look at the male in behavior, come from males. There’s plenty of evidence out there, both in our closest relative, chimpanzees. Across the spectrum, of females engaging in violence and aggressive behavior … I think on your site before you’ve referenced a book, Demonic Males by Wrangham, I believe. He has a great accounting of one of the first witness events of chimp rating. One of the things I think was very interesting about that instance of that chimpanzee group rating and essentially tacking another group of chimpanzees, was that there were also females involved with the rating party. They didn’t play as big as of a role, in terms of … In leading, in terms of some of the actual physical aggression, that they were definitely a part of the process as well.

Brett McKay: One thing I’ve read is that of competition or the violence between … It’s conspecific, that means that it’s, same species? When males from other species fight or the same species fight other males of the same species, it’s almost like a ritualistic combat dance. There’s a lot of posturing, if that doesn’t work to scare the other guy off they’ll move to shoving. If that doesn’t work they’ll start … The goal of it isn’t to kill necessarily, it’s more to assert dominance and to show, who’s the guy and who’s in charge.

Dr. Morgan: I think it’s true, we commonly refer to these as threat displays. You see them manifest in different forms in different species. An animal with large canine teeth that might be gnashing and bearing of the teeth. In other animals it could be certain posturing, posing they’re bodies to increase the appearance of they’re size and they’re strength. One of the things that we were thinking about, that’s led us to some of our research, particularly our paper about the human fist, was did humans do? What sort of natural reaction when we get angry. If you look at a child on a playground in school and they get bullied, what’s one of the first things that you do? A lot of times you clench your hand into a fist. A lot of times that can be our threat display as human beings. There’s obviously vocalization and taunting and teasing and insults that come out, but as far as our physical manifestation, it’s that presentation of a weapon. Often times, there’s is that threat display that’s the first prelude to violence and aggression.

Brett McKay: Okay. This is interesting. The fist, then, the human fist, the ability for humans to make a fist … One of it’s benefits, besides being able to grasp tools, right? Making a fist is basically, you’re making a weapon as a possible threat display. Can other primates make a fist or is that unique to humans?

Dr. Carrier: As far as we know, it is unique to humans. The human fist requires a specific relationship of the proportions of the palm of the hand, the length of the elements of the fingers, the length of the thumb. If you look at the other extent, great apes: the chimps, bonobos, gorillas, they have longer fingers, longer hands, and a much shorter and weaker thumb than we do. They basically don’t have the hand proportions that allow them to make a fist. What we’ve argued is that, yes, these human hand proportions that we’ve always thought to be primarily about men with experience. That’s certainly true. There’s no doubt as humans do so much with our hands, it’s clear that that’s played an important role with the evolution of the shape of our hands.

The other thing that may be playing a role, is this ability to turn it into a weapon. Into a form of a club. The relatively delicate and vulnerable anatomy of the human hand, which is so important to our lively hood, can also be used as a weapon.

Brett McKay: So what advantage does making a fist to punch provide humans in fighting? Does it provide more power or force? What’s going on there?

Dr. Morgan: With the first paper that we published, looking at what we called the protective buttressing of the hand. Meaning, the nice compact shape you get when all of those proportions Dr. Carrier mentioned kind of aligned to form a fist. We studied the force that could be delivered with the formed fist versus what we could, at most, approximate would be the strike delivered by a gorilla or a chimpanzee or one of our closest ancestors who can’t make a fist. It’s kind of an open hand slap or a slap with the palm or the knee to the hand. We had volunteers come into the lab. We had a couple of great contraptions set up. One of them was a punching bag with an accelorometer. We had some force plates that we were looking at. We looked at the amount of force and whether the forces were higher with having this open hand, quasi-fist versus a fully formed fist.

We thought for sure that maybe we’d have higher forces delivered with the fist, but that wasn’t the case. There was actually similar forces delivered between a slap and a punch, but what we did note was that when you bring the force down to a smaller pinpoint size, you get what’s called an increase in the force impulse. When it comes to doing damage, breaking bones, damaging soft tissue, causing fractures, the force impulse is really what matters. That element of the deliver of force that allows damage to happen. When you have a fully formed fist and you’re delivering a strike, the force impulse was actually significantly higher than it was with an open hand.

Secondly, having the ability to form a fist, protects the anatomy of the hand as Dr. Carrier said. The hand has a number of bones that are frequently injured and fractured. Forming a fist allows you to make a much more stable, stiffer, structure with which you can deliver that blow, decreasing your chances of injuring the hand. This is a common critique of our research is people say, “Well, people break they’re hands all the time,” I work in an emergency department and I see the results of interpersonal violence all the time. There’s a common fracture pattern that we see called a boxer’s fracture which is a fracture of usually the fifth and fourth metacarpal bones. It occurs by someone throwing a punch and landing with the force in a way that transmits force into those bones, and breaks those bones. When you actually look at some of the trauma data we have, you do see these fractures of the hand, but you see a lot more fractures of the face. Compared to how frequently the hand is injured when you actually look at the data. To me, that kind of supports that this ability to form this fist, not only provides us with a convenient, readily usable, weapon. Allows us to do more damage when we throw a strike, and allows us to protect our weapon, when striking.

Brett McKay: Besides the critique about the hand being damaged during a punch … It’s often damaged during a punch. Were there any other critiques of your paper? I do remember it caused quite a bit of a stir in the press, at least.

Dr. Morgan: It generated a lot of press about it. That’s always kind of an interesting phenomena because you find yourself scratching your head wondering if the people writing some of the news articles actually read the paper. It made quite a bit of pop science websites. It’s an interesting, kind of out there, study. There were certainly some other critiques, I think maybe Dave can talk to some about that.

Dr. Carrier: One of the most common criticisms that have repeatably been thrown at us is that we’re making up an evolutionary story, an adaptation story, and that a more reasonable explanation is that these hand proportions that allow the formation of a fist are just a coincidence. What a coincidence of the consequence of selection for manual dexterity. That’s certainly possible, but it’s also possible that selection on aggressive behavior was having an influence on hand proportion. What we’re presenting, is really an alternative explanation that’s not mutually exclusive with the original idea of it all being about manual dexterity. We’re throwing in another possible component that may explain the evolution of our hand proportions and the evolution of some of the proportions and configuration of our facial skeletons as well.

Brett McKay: Yeah, we’ll get to the facial skeleton as well, it’s interesting. I guess the theory, if I was listening to you, the theory about why our hand is the way it is. I have this thought, I just want to make sure I’m on the same page. Perhaps, it evolved the way it did because of aggression, like we turned our hand into a weapon, basically. Then, because of the proportions it made tools or weapons or rocks. Holding rocks, you could use it as a force multiplier and as a consequence, we’re more dexterous with our hands. Aggression led to tool making, is that the idea?

Dr. Carrier: Well, not necessarily. Primates in general, monkeys and great apes, all used their hands. They all have the capacity for manual dexterity. It’s important in all groups. We’ve taken it even farther and we have much greater capacity than the other primates. It’s clear that selection towards our use for our hands was always there. What we have suggested is that if you start with the hand of something that’s intermediate between a chimpanzee hand and our hand, something that we think looks close to the ancestral condition from basically our ancestral condition. If you start with that hand, we think there are a number of ways you could evolve, improve, you could change the proportions, in a number of ways that we can prove manual dexterity. We think there is only really one set of proportions of the different skeleton only, that allow the formation of the human fist.

We’re arguing that, yes, certainly manual dexterity is an important part of the shape of our hand, but if you want to actually explain the specific proportions, making a fist may do a better job than the use of our hand and using tools and forming or making tools.

Brett McKay: Okay. So, the other paper that you all put out, which is related to the fist making paper in a way, is that the human face may have been evolved to take a punch. How so? How does our face differ from other primates?

Dr. Morgan: The interest is, for that paper, was actually a critique that we had for our paper with regards to the proportions of the hand and the fist. Where someone essentially said, “If my hand evolved to make a fist, then why didn’t my face evolve to take a punch?” We said, “That’s a really good question,” We started looking back over a lot of the research … The known facial proportions, kind of the hominid lineage and found that there was an increase in robusticity in terms of certain proportions of the face that also happen to be the areas of the face that are most frequently fractured and injured in fights. We saw this increase in the strength and robusticity in these components of the face for a period of time. It’s not really what we expected to find but, we started looking into some of the current philosophies on why the faces were so robust. A lot of those center around our diet and having large jaws to attach large muscles of mastication to, or us to adapt to a new diet as a species, but we didn’t feel that that fully explained the increase of these proportions. I think Dave can, maybe, talk to a little bit more about the anatomic details of it. That kind of critique of, “Why didn’t my face evolve to take a punch?” Led to this second paper that you’re talking about.

Dr. Carrier: One of the things that’s interesting is that there’s a coincidence in terms of the timing of the evolution of these characters. Around 5 to 6 million years ago in the fossil record, we start to see evidence of early bipedal, we call the group hominid. This is the group that eventually gave rise to humans. They appear in the fossil record 4 to 5, 6 million years ago. They had body proportions very similar to chimpanzee but they were standing up on two legs. At the same time that our ancestors evolved to stand on two legs, habitually, and walk and run on two legs, the hand proportions that would allow the formation of the fist appear in the fossil record as well. At the same time that those two things show up, again this is 4 to 6 million years ago, we have this in robusticity of the facial skeletons. Specifically of the components of the facial skeletons that break when modern humans fight, today. All these things seem to be linked, temporary.

Brett McKay: I guess, maybe if I understand you. There was a period in our evolutionary history when our face got stronger, basically, but that has gone away. The human face today is pretty fragile.

Dr. Carrier: Yes.

Dr. Morgan: Yeah. Yeah. Specifically those, when we see trauma coming in from interpersonal violence, the most commonly fractured bones of the face are usually the mandible. In fact, I had a patient last night that had bilateral mandibular fractures as the result of getting beat up by two guys at the park. We see the mandible breaks, we see the nasal complex … Nasal fractures break, we see the zygoma break and then we see the orbit, the bony, protective cage around the eye, are most frequently broken. That’s also where we saw in increase in terms of robusticity in the fossil record of the hominid facial proportions.

Brett McKay: Why is it that it got weaker?

Dr. Carrier: It’s a good question and we don’t have a clear answer. There is a correlation in terms of upper body strength. These early bipedal apes, what we call the Australopithecus, had great upper body strength. That was true of the early species of homo, the first early humans about 2 million years ago. What you see with the evolution of homo through time is a reduction in upper body strength. That, again, coincides with … Reduction in upper body strength, which would be a reduction in the ability to strike with a fist, is coincident with reduction in the strength of the facial skeleton. The other thing is that somewhere around 3 million years ago, our ancestors started to use tools as weapons. The targets would have changed as well. The target, if there was homicidal intent, would have switched possibly from maybe the face to striking the cranium with the weapon. Both facts that we think the targets change, at least to some extent. Also there was a reduction through time of upper body strength that may help explain why the facial skeleton during the past 2 million years has become less robust.

Brett McKay: Earlier on we were talking about why, men in particular, might be more violent and aggressive than females. The idea that men have to compete. Sexual selection is what driving … That tricks men to compete. With that in mind, are there differences between the physiology of men and women that make men better adapted for fighting?

Dr. Carrier: Definitely. The face is a classic example of that as well. One of the most sexually … We use the phrase sexual dimorphism, to talk about anatomical, physiological differences between males and females. One of the parts of our bodies that is most different, most dimorphic, is the facial skeleton. Again, the biggest differences between males and females are the parts of the facial skeleton that tend to break the most when modern humans fight. The features of the face, the features of the skull, that distinguish a male skull from a female skull is the greater robusticity in the characters that tend to break when we fight. The greater robusticity that is in males as it seems.

Dr. Morgan: That’s not the only … The face is certainly not the only place where you see the dimorphism as well. You see it in the upper extremities. You see it in terms of, the skeletal structures and their ability to support a much greater muscle mass than on females. You see dimorphism represented throughout the entire body of men and women.

Dr. Carrier: Another good example that is consistent with the aggression hypothesis, is that dimorphism in body strength is most pronounced in the arms or the upper body than in the legs. Males and females, human males are at greater strength in the legs than females, but the extent to which there’s a greater strength is much more pronounced in the upper body.

Brett McKay: The idea is that men would be using their arms to throw punches, that’s why there’s that difference.

Dr. Carrier: Basically, fighting with the arms.

Brett McKay: Right. I think I heard one guy describe the shoulders of the human male as our version of antlers. Male stags, they grow big antlers because they use that to … In these ritualistic battles between other males, to find out who’s the top guy. The guy with a larger upper body torso and bigger arms is displaying, “Hey, I can punch really well, so don’t mess with me,”

Dr. Carrier: I think that’s right, I think we do tend to pay attention to the shoulders and the strength in the upper arms and possibly the strength of the neck. In terms of evaluating and individuals ability to … Basically, evaluating their formidably. Both males and females look and can distinguish … From looking at that part of the body, can distinguish a males ability to fight. On top of that, there is a number of studies out there that show that we can look simply at a males face and have a pretty accurate assessment of they’re fighting ability, just from looking at the face. I tend to agree with your observation.

Brett McKay: I’m curious. I’m sure people are listening to this like, “Why is it important that we know or study why violence and aggression may have influenced our physiological evolution?” What can we do with this information that you all are uncovering or putting out there?

Dr. Morgan: That’s really the meat of our interest in this particular field. Coming to a deeper understanding of, let’s call it human nature, for lack of a better term. For a long, long time in the science community people really wanted to hang on to this idea of the noble savage and these humans were superior in a certain way because we were masters of our domain. We had the ability to be selective of whether or not were violent or aggressive. I think when you look at the evidence, we’re arguably one of the most violent species. If you look further at some of the data, you can track historically that I think we’re becoming less violent as a species, but those tendencies are still there.

My argument, I don’t know if Dave would agree with me, but my argument is, a lot of that is displaced behavior. There was one point in time in our development as a species where violence was absolutely critical to our survival. It meant that you were going to eat. It meant that you were going to survive. It meant that you were going to be able to mate and be able to carry on your genetic information to the next generation. You’re ability to defend yourself, to defend your food resource, to defend your mating rights determine that. Determine your survival. I think that that’s been such a huge part of our evolution. Getting back to that discussion of, these are the environmental pressures that effect our socialization, that effect our behaviors, in groups. I think now a days we have a very different society, very different social structures, than in the long, long history of human existence, it accounts for just a small, small fraction of time.

We have behaviors and these tendencies that are kind of displaced. We no longer have the evolutionary pressures. You don’t have to fight for your food anymore. You don’t have to fight for your mate anymore. You don’t have to defend your territory anymore. We still have something about us and something inside of us that makes aggression part of our make up, part of who we are. I feel that, the better we can understand that, the better steps we can take towards managing that and using it responsibly. Using that energy towards better endeavors rather than in harm of one another.

Dr. Carrier: Yes. To add to that, if in fact our muscular, skeletal system is specialized for aggressive behavior. If that turns out to be true, then this debate about human nature, we think, basically, just goes away. What you end up with is the acknowledgement that a tendency towards aggressive behavior is in fact, part of who we are. It’s not all of who we are. We have just a great capacity for cooperation, empathy, wanting to have a secure peaceful environment in which to live in. Those are both aspects of who we are, but I think there’s value in at least asking the questions we’re asking. It has potential to resolve this argument that’s been going on for hundreds of years about human nature. If we could get past that argument we can focus our attention on specifically, what we need to do to secure a more peaceful future.

Brett McKay: Dave and Mike, where can people learn more about your work and perhaps read these papers you put out?

Dr. Morgan: I believe our fifth paper is on PLOS1, it’s open access so anybody can find it online and read it. The paper that we did looking at the proportions of the human face was published in a journal of biological revues and that one you can usually access through various academic libraries. There’s plenty of writing and criticisms and critiques out there to get through online regards to this stuff. Dr. Carrier had another paper that, I think, is in publication right now, that you worked on? Looking at the screen that’s on the hand …

Dr. Carrier: Yeah, that’s been published as well. That was published in a journal called The Journal of Experimental Biology.

Brett McKay: Great. Well, Dr. Dave Carrier, Dr. Mike Morgan, thanks so much for your time, it’s been a pleasure.

Dr. Morgan: Our pleasure, thanks so much for having us Brett.

Dr. Carrier: Yes. Thank you.

Brett McKay: My guests today were Dr. David Carrier and Dr. Michael Morgan. You can find more information about their work, just Google, “punching fist evolution,” you’re going to find a lot of papers that they’ve put and just news articles about their research. Also, check out the show notes at AOM.is/aggression for links to resources that we mentioned throughout the show so you can delve deeper into this topic.

Well, that wraps up another edition of The Art of Manliness Podcast. For manly tips and advice make sure to check out The Art of Manliness website at artofmanliness.com and if you’ve enjoyed this show and got something out of it, I’d appreciate it if you gives us a review on iTunes or Stitcher. That helps spread the word about the show. As always, I appreciate your continued support. Until next time, this is Brett McKay telling you to stay manly.