Social Science Bites

Carsten de Dreu on Why People Fight

July 5, 2023 1929

“We have been evolving into a species that is super-cooperative: we work together with strangers, we can empathize with people, we are really an empathic flock,” begins Carsten de Dreu, a professor at Leiden University. “And at the same time, there is increasing evidence from archaeological excavations all around the world that already 10, 20 and 30 thousand years ago, people were actually violently killing each other.”

Trained as a social psychologist, de Dreu uses behavioral science, history, economics, archaeology, primatology and biology, among other disciplines to study the basis of conflict and cooperation among humans. In this Social Science Bites podcast, he discusses how conflict and violence – which he takes pains to note are not the same – mark our shared humanity and offers some suggestions on how our species might tamp down the violence.

“Violence,” de Dreu explains to host David Edmonds, “is not the same as conflict – you can’t have violence without conflict, but you can have conflict without violence.” Conflict, he continues, is a situation, while violence is a behavior. Conflict, he says, likely always will be with us, but resorting to violence need not be.

The psychologist says behavior has a biological basis, and various hormones may ‘support’ violent actions. For example, greater concentrations of oxytocin – which helps maintain in-group bonds and has been dubbed “the love hormone” — is found in primate poo after groups fights. But, he cautions, that is not to say we are innately violent.

But when we do get violent, it’s worse when we’re in groups. Then, the potential for violence, as he put it, “to get out of hand,” increases, escalating faster and well beyond the violence seen between individuals (even if that one-on-one violence sometimes can be horrific).

“In an interpersonal fight, the only trigger is the antagonist. In intergroup violence, what we see is that people are sometimes blinded to the enemy – they might not even recognize who they were because they were so concerned with each other.”

What drives this violence is both obvious and not, de Dreu suggests. “Even among my colleagues, there is sometimes fierce debate – conflicts sometimes about what are conflicts! But if you zoom out, there are two core things that groups fight about:” resources and ideas.

Fighting over resources is not unique to humans – groups of primates are known to battle over land or mates. But fighting over ideas is uniquely human. And unlike resource conflicts, which have the potential to be negotiated, “for these truth conflicts … there is no middle ground, no trade-off.” Regardless, he argues, values have value.

Citing recent work with colleagues, de Dreu says he thinks “these values, these truths, these worldviews that we have, that we share within our groups and our communities, within our countries sometimes, they are the ‘oil’ of the system. To work together so that we all can survive and prosper, we need certain rules, a certain shared view of how the world operates, what is good and bad, what is right and wrong. These are very important shared values we need to have in order to function as a complex social system.”

But “when these values get questioned, or attacked, or debunked, that’s threatening.” Depending on how severe the threat is seen, violence is deployed. And sometimes, as even a casual observer may divine, it’s not the direct quest for resources or to protect values that sparks violence, but what de Dreu terms “collateral damage” from leaders cynically weaponizing these drivers – or even inventing threats to them — while actually pursuing their own goals.

But de Dreu ends the podcast on a (mostly) upbeat note. He says we can break the cycles of violence, even if there’s no neat linear trajectory to do so, and concludes by offering some rays of hope.

To download an MP3 of this podcast, right-click HERE and save. The transcript of the conversation appears below.

For a complete listing of past Social Science Bites podcasts, click HERE. You can follow Bites on Twitter @socialscibites and David Edmonds @DavidEdmonds100.


David Edmonds: Individuals fight, and groups fight, too: religious and ethnic groups, national armies, even opposing groups of sports fans. Why? What’s driving the violence? Carsten de Dreu is a psychologist at the University of Leiden. He’s devoted years to the study of conflict and group violence. Carsten de Dreu, welcome to Social Science Bites.  

Carsten de Dreu: Oh, thank you, Dave. It’s an exciting endeavor. 

Edmonds: So, we’re going to have a peaceful and civilized conversation today, I hope, on why groups of humans fight. Has fighting always been part of the human experience? 

De Dreu: I think it has been. We have been evolving into a species that is super cooperative: we work together with strangers, we can empathize with people, we are really an empathic flock. And at the same time, there is increasing evidence from archeological excavations all around the world that already 10-, 20-, 30,000 years ago, people were actually violently killing one another. 

Edmonds: Okay, so violence takes many forms—my kids fight, there are fights outside pubs—but you’re particularly interested in fighting between groups. Why groups in particular? Does group violence have interesting elements that are different from individual acts of violence?  

De Dreu: I think it does. And of course, we have limited evidence from our deeper past, but violence between groups can get really violent. Violence between individuals—of course, we have domestic violence that includes all kinds of nasty things—but somehow, it seems that especially the violence, the conflicts, between groups of people can escalate really quickly. The organized ways of fighting each other really oftentimes get out of hand. So, I find those the most “interesting,“ if you want, because they also have the most destructive and long-ranging consequences.  

Edmonds: But that’s interesting. So, group violence is liable to escalate quicker than individual violence? 

De Dreu: I think there is good evidence for that. It seems to be related to the fact that we fight alongside each other, and we are more concerned with what my neighbor or my mate is doing and whether he will survive, or whether my strength is actually helping him rather than just the enemy. In an interpersonal fight, we see the enemy in front of us; the only trigger here is the antagonist. In an intergroup violence, what we see is that people are sometimes blinded to the enemy; they might not even recognize who they were because they were so concerned with each other.  

And that somehow creates a bit of a group mind that can lead to forms of violence and fighting that we would never think we are even able to do.  

Edmonds: Now, violence is not the same as conflict. Presumably we can have conflict without violence. For example, the UK and the US could have a trade dispute. That’s a kind of conflict. But fortunately, it’s unlikely to spill over into violence.  

De Dreu: Absolutely, yes. I think it’s super important to make that distinction. If you think about it, very simplistically, perhaps, we can say you cannot have violence without conflict. But you can have conflicts without violence. Of course, oftentimes, conflicts—we don’t see unless you start to really closely look. Your example of a UK, US trade dispute is a very good example, because we read about it in the news, and we’ll read on; we forget about it. But those are also conflicts. 

There are situations where we want something the other frustrates us of having, and then we can use violence to get our way. But—and I think this is super important—we don’t have to use violence. There are other ways.  

Edmonds: So, we’ll come on to the other ways later. But another point of clarification: are you mainly interested in physical violence? What about screaming at people that you might see at football matches with opposing fans just abusing each other? That seems very violent when you’re in the middle of it, as I’ve been now and again, but at least in law, abuse at a football match is usually permitted whilst punching opposing fans is not. 

De Dreu: Yeah, I’m a psychologist by training, and for me violence indeed takes various forms. A shouting game can be fun. It can be arousing, but it can also be super hurtful. There can be things said that are really painful words can hurt tremendously. And sometimes there are forms of violence that do not involve physical acts that still are more painful, more destructive, than getting a blow on the nose. 

Think about giving your child the silent treatment because they have been naughty. That stuff–if you are a coworker, and all your colleagues give you the silent treatment for a month, that actually creates burnout, depression, post-traumatic stress syndrome. So, there are forms of violence we don’t see immediately. They don’t come with bloody noses or property destroyed. And still they can destroy the human mind and hearts to quite some degree.  

Edmonds: And is that the subject of your own research? Or do you particularly focus on the physical aspect of violence?  

De Dreu: Well, I think most of us are immediately drawn to the physical part of it. I mean, that’s what we see, you know. You think about the war in the Ukraine, and there are these attention-grabbing stories, horrendous stories about physical violence and killing and injury that is going along with it. At the same time, I think we also can look at, for example, the war refugees that are also suffering from violence, but in their physical integrity, not so much. However, the damage that is done to them is also very, very important to understand. So, I would not only look at the violence in the physical sense, where groups throw rocks at each other and chase each other with sticks and everything. I also think we need to also look at either the collateral damage of that type of violence or the other forms of violence that emerge between groups, that is more than—Yeah, what I said, the silent treatment, or the shouting games, the nasty words that are exchanged. 

Edmonds: But in that sense, it seems like there’s a gray area between violence and conflict, because that kind of violence that you talk about—the silent treatment and so on—that could be considered an aspect of a conflict. 

De Dreu: As scientists, we tend to distinguish between these two things as follows: we say conflict is a situation, violence is behavior. So, if you think about that, we are in a situation and now you can perform certain behaviors, like running away from the situation, talking it through, or grabbing a stick and chasing the other. So, violence is one “behavior,” if you want, and I take a very broad definition of what falls under violence or not. And the idea with this definition is that all of these behaviors that we then call violence are somehow oriented to suppressing the other, to get the other down, and to triumph yourself.  

Edmonds: Okay, so we’ve got the definitional points out of the way. Before we turn to violence, as it were, this subset of conflict, can we make any generalizations about why conflict exists between groups?  

De Dreu: I think there’s a lot of thinking about it. And even among my colleagues, there is a fierce debate conflicts sometimes about what are conflicts about that. If you look at us, zoom out, really, I think there are two core things that groups fight about. Throughout history, we have always been fighting about stuff: we want some resources for ourselves, others want those resources too, there is not enough for everybody, and then sometimes we get into fights over who owns what and who gets how much. These are what we call resource conflicts. And these are important because these resources oftentimes are what we need to survive—myself, but also my family, my group, and so on, so forth. And then there is a second type of conflict that is, I think, almost reserved for the human species. And that is: we fight over ideas. We fight over the truth. “My truth is the truth, your truth is stupid.” And somehow this seems to be divorced from resources. It can take a life of its own, where we find it super important that our truth is respected, perhaps even seen as superior to any other truths or “values,” if you want. 

Edmonds: Let’s talk a bit about the latter, because the former–resources—that’s much more intuitively comprehensible. So, groups tend to share some values. There aren’t any societies, as far as I know, who think it’s okay to murder innocent children. But there are clearly major differences between groups. We believe in different gods or we believe in no God, for example. We have different forms of government, we have left government, right government, totalitarian government, democratic governments. Obviously, these are often the sources of conflict and violence. Do you have an evolutionary explanation for why values should matter to us so much? 

De Dreu: What I think—but this is also very recent work that has been done by colleagues and myself—is that these values, these truths, these worldviews that we have and that we share within our groups or communities—within our country, sometimes—they are the oil of the system to work together, to make sure that we all survive and prosper. We need certain rules. We need a shared view of how the world operates (what is good and bad, what is valuable, what is right and wrong). These are very important shared values we need to have in order to function as a complex social system. When these values get questioned or attacked or debunked, that’s threatening. It’s threatening because the oil of our society has been taken away, or it becomes muddy. And we may not allow that to happen. This may be one very important reason why threats to our values and worldviews are almost as vital as threats to the resources we have. 

Edmonds: Seems totally plausible. What kind of evidence can one offer in support of that theory? 

De Dreu: None. Except, you have to make the case. When you look at conflicts, especially conflicts between groups, it’s a very, very muddy type of analysis, especially when you’re looking at real-world conflicts. And I’ll give you one other example: many of the conflicts that seem to be about resources or truths and values may actually be not about that at all. They sometimes are. And I think oftentimes, actually, they are collateral damage, I would call it—collateral damage of some internal dynamic within a group or community or city or nation-state, an internal power struggle, an internal status context among some people for whom it becomes interesting to create a conflict with an outside enemy, because that benefits themselves and it hurts many in their own group, and they may sometimes know that, not know that. There is this “common enemy tactic” that we often hear about the—where the idea is that leaders in a country or a group leader creates some nasty image of a neighboring tribe or a neighboring country: “They are the enemy. If we don’t strike now, they will come and grab our stuff and rape our women.” This kind of rhetoric is oftentimes not because the leader actually thinks the other side is that bad. But if everybody within one’s group believes that, they may forget about other things. They may reelect the leader, they may give them all the perks. This is what I call, in conflicts, are collateral damage. And at the surface, if you look at history documents, for example, we think it’s about resources. We think it is about truth. But in the end, it is about an internal power game that spilled over.  

Edmonds: But you said a few minutes ago that you have a kind of twofold explanation. One is resources, the other is values. And yet here’s a whole category of violence, which doesn’t seem to fall within that framework.  

De Dreu: Now, I agree with you. And this is also puzzling to me. The point is, and you asked, is this fighting over truth and ideas just as have an evolutionary explanation, and I think there can be. At the same time, I think that oftentimes these conflicts over truths and ideas and values may actually not be really about that. But they may be what I just called the “collateral damage” of an internal power struggle where we sort of attack ideas on the other side of values on the other side, but it’s a tool to actually get the internal solidarity, loyalty, reelections, and so on, and so forth going. So, when we think it is about truth and ideas and values, it may actually be about something else.  

Edmonds: And I mentioned earlier football hooliganism—that can be very violent. Again, it would be a bit of a stretch to say that’s about resources or about moral values. 

De Dreu: Exactly. And I think these are then what I just called the “collateral damage” conflicts. It is an internal dynamic within a group of hooligans, where some want to show off, want to build a reputation, perhaps they are too high on adrenaline or booze. And they pick a fight with the other group in which we have a similar dynamic, also a few who will really benefit somehow from having a fight with the other side. And the rest follows. 

Edmonds: There are, as you say, some apparently distinctive human aspects to violence. Is there any benefit to be got from studying our newest evolutionary cousins? From studying primates and the violence they have towards each other?  

De Dreu: I think there is and then we return to these conflicts over resources. This is where we see strong parallels with the conflicts that other primate species, to chimpanzees, baboons, for example, get into. What you see there is they, as a group, can attack other groups, and this can be very violent lead to lethal injuries, killing. And always this is about territory, access to mates, protection of territory, about resources that each group needs to survive, to prosper, to grow, to support itself. And when these resources get scars, then groups enter new territory, may run into the local owners of the territory and conflicts emerge. 

There are very strong parallels with the conflicts that we suspect have been going on in our deeper past. So, the archaeological excavations that we see all over the world, when you think about how people in those times lived, it’s not so different, or at least closer to how chimpanzees and baboons operate than we are doing today. So, this suggests that indeed, it’s very basic. There are some cross species parallels, if you want, and by looking at other species, we can actually learn something about why humans fight as well. 

Edmonds: What about a biological, physiological perspective on violence? Are there things to understand about the nature of group violence through an investigation of what goes on in the body during conflict? 

De Dreu: I think behavior always has a biological element; it rests on what happens in our brain, rests on hormones that float around our body. So, behavior has a biological basis. That means that also the behaviors we perform in conflict has a biological basis. That’s not to say that we are innately violent or innately set for conflict—hardwired. But when we act in conflict situations, a variety of hormones also support those behaviors. 

We just talked about chimpanzees and humans, and one interesting thing, for example, is that both chimpanzees and humans seem to fight not only because they hate the enemy, but also because they care for their own. And there is one important hormone that is called oxytocin, and some people may have heard about, it’s also called the “cuddle hormone” or the “love potion,” and this hormone is super important for building bonding between people, between parents and their offspring, between friends. And what we now saw is that when groups of chimpanzee get into conflict with another group in another territory, you see an increased level of this hormone, this oxytocin, in their poo. The more these individuals—they affiliate with one another, they groom, that builds up oxytocin, but also solidarity—that then helps them to fight as a group. And the exact same thing we see in humans. So, we have done experiments where we showed the exact same thing. 

Edmonds: So, an investigation of primate poo shows that what conflict is the flip side of love or caring?  

De Dreu: Yeah, to some degree it is. And I earlier said conflict oftentimes is collateral damage, because of a leader who tries to pick a fight and gets the internal solidarity going. But oftentimes, we also care for each other, and we want the stuff and the truth and the values for us to be secured. And then when there is too little of it, but the neighbors have a lot, out of the care for us, we may pick a fight with them. 

Edmonds: And when a leader, for their own purposes, denigrates another group, why do people go along with that? Why are we so naive? Why aren’t we cynical enough to acknowledge the cynical motives? 

De Dreu: I think it’s a super important question. And I think if we have good answers to that. We are getting pretty far to also preventing a lot of violence, because a lot of violence is emerging, not because people want it, because they somehow get drawn into it, and then it takes a life of its own. And oftentimes, this is instigated by leaders. 

Now, we have a tendency to follow our leaders, following our leaders believing what they say, going along with their directives is super important to make societies function. And this has been the case for thousand and thousand of years. So, one possibility is that we automatically go along with the leader, and then only on second thought think, “Hey, but wait a minute.” At the same time, if everybody goes along with the leader, who am I to question that?  

So there is this very ironic and also bit cynical process where we learned how useful it is to follow and then when others follow, we automatically follow ourselves, and you get a sort of reinforcing cycle of following behavior, where you almost—whenever the leader is a little bit smart, we go along and the rest is history. Or at least conflict is starting. So we have not only this very strong capacity to care for each other, and that may lead us to fight the outside. But we also have this very strong capacity to align with others, to synchronize with others, to follow directions—to be obedient, if you want, and this is super important throughout our evolutionary history, and again, some collateral damage emerges here. 

Edmonds: Now, some violence looks like it’s almost inevitable, in the sense that Hitler wasn’t going to be stopped without violence. The same is possibly true of Putin. But often one might imagine that violence could be avoided. Are there any general rules for how one can ease tensions and diminish the prospect of violence? 

De Dreu: There are two ways to approach this issue. One is can we prevent violence from happening—we have conflicts, we always will have them—but we deal with them in various ways, and sometimes in violent ways. And the question is, can we get on the other track, not on the violent track, but other ways? And I think oftentimes, we actually do; these are the conflicts that we barely pay attention to. So, the violent conflicts that are so attention grabbing and so destructive are perhaps only a minority of all the conflicts that humanity faces. 

Then the other approach is, once we have been in a violent conflict, or we are, can we stop it? Can we wait a minute, ceasefire, let’s start to talk. And that also happens, oftentimes. Sometimes there are these intractable conflicts that go on for decades. The Troubles in Northern Ireland is a good example. And at some point, it stops and the leaders on both sides start to talk. This can be very difficult and very tough, talking, and it might actually break down and then they resort to violence. So, it’s not a linear trajectory. But we oftentimes see throughout the world throughout history examples where violent conflicts at some point stopped and leaders started to talk. These are what scientists call “moments of ripeness,“ where somehow on both sides, there is there’s realization that this is not leading anywhere, that nobody can win it. 

Edmonds: But can you get a conflict to ripen earlier? 

De Dreu: [Laughs] Fight harder? Well, one of the things that we do, of course, and you see this also now in the war in the Ukraine, is that the rest of the world puts pressure on the aggressor here, with economic sanctions, for example, to reduce the resources they have. And if they have less resources, the moment of ripeness will come earlier. 

Edmonds: One can see easily how, if it’s about resources—let’s say there’s a conflict over water—you come to some kind of resource compromise. But when it comes to values, if you’re ISIS, and you think your opponents are the infidels, or, I don’t know, your evangelical Christian, and you’re trying to save souls, it’s difficult to see what the middle ground there is. 

De Dreu: That makes these conflicts particularly problematic. So indeed, resource conflicts can oftentimes be negotiated: “we get a little bit more of this river and you get a little bit more of the mountain.” That’s a workable solution for both sides. We may not see it immediately, we may fight and violently so for quite some time, and then we start talking and find out more or less creative solutions for our resource conflicts. 

But for these truth conflicts, “what’s the truth,” there is no middle ground. There is no trade off to be made. We cannot have “a little bit of your truth and a little bit of mine.” Of course, sometimes there is, right, sometimes we can say actually, “there is a third way, a third perspective, that’s actually even better, that’s more true than what both sides thought before.” But most of these conflicts somehow require that one side fully gets into the other and internalizes the other sides’ truths and values. Or that we decide to leave each other alone, that we say your truth, your values—good luck with it. We think they’re wrong, but it’s your problem. This takes some grandiosity on the humanity part to say, “I need my truth, I need my values, because they are important for my society to function, that you guys do it differently. That’s your call.” 

Now, I think this is almost the only way out of these value conflicts. But mind you, earlier I said that oftentimes, these value conflicts are invented by people in order to serve their local personal interests. And those conflicts can of course then very easily be solved by identifying and exposing these personal interests, and showing that the value conflicts are actually about something very differently. 

Edmonds: You describe yourself as a psychologist, but it seems to me your work is extraordinarily multidisciplinary, in the sense that you’re drawing on history and archaeology and biology. Is your primary identity, a psychologist or social scientist? 

De Dreu: Well, maybe even just scientist. I’m trained as a psychologist, a social psychologist, so we are studying the human in its social context and its group—that’s my starting position. But throughout my career, I realized that I cannot understand humans in their social context divorced from history, from biology, from economic systems, all those things we need to bring into the game, so to speak, to truly understand human behavior, human hearts and minds. So when I call myself a psychologist, it is true by training. My PhD is in psychology. But when I call myself a scientist, it’s also true, because I’m just interested in science, and especially how it helps us understand human behavior. 

Edmonds: Let me finish with a personal question about you: do you have violent instincts, and now that you understand the roots of violence, has that helped you keep those instincts under control? 

De Dreu: I’m a very peaceful person. I read about violence, I look at it in movies, and think about it a lot. And of course, yes, I also have violent instincts. And I remember one case where I was walking with my toddler then, but one of my children was very small, and there was a bit of a adolescent high on the testosterone, and he didn’t want to go out of the way, and I felt somehow he was threatening, he was not giving me the space that I and my young child needed. And I actually violently grabbed him and pushed him against the side of the road. And he was completely struck with what happens here. I saw him as a threat that needed to be preemptively neutralized. There was nothing going on, but I was so vigilant about my child’s safety, that indeed, I acted quite violently and totally unjustified. So I think this is a little example of, yeah, I’m a very peace-loving person, but I do have a violent streak as well. 

Edmonds: Carsten de Dreu, thank you very much indeed. 

De Dreu: You’re welcome. Thank you. 

Welcome to the blog for the Social Science Bites podcast: a series of interviews with leading social scientists. Each episode explores an aspect of our social world. You can access all audio and the transcripts from each interview here. Don’t forget to follow us on Twitter @socialscibites.

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