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Burt Simon, Gil Henriques, and Yaroslav Ispolatov are part of a team that developed a mathematical model to help explain the causes of intergroup conflict. Their results suggest that acculturation — the adoption and imitation of a victor’s culture following defeat — could promote the evolution of intergroup conflicts. In other words, groups may evolve to fight for fighting’s sake, despite the costs. They discussed their research with us.
SCIENTIFIC INQUIRER: What was it about more conventional explanations regarding intergroup conflict, namely struggling over various forms of resource scarcity, that prompted your group to investigate alternative approaches to the question?
BURT SIMON: We originally built the model to simply study the trade-offs between a group being strong against other groups and being strong internally, in the context of “shepherds and warriors” and cultural evolution. The model was complicated enough that we did not know what to expect, and we tweaked the model a few times as it became clear what was going on. We did not know at first that the model would reveal a new explanation of intergroup conflict,
GIL HENRIQUES: In traditional explanations, groups fight over scarce resources: things like food and territory, but also reproductive opportunities. For example, among the Yanomamö (an indigenous population living in the Amazon basin), men who kill an enemy during a raid tend to have higher reproductive success. The problem with this is that having food, territory, or mates is only good if you are alive, and yet we know that conflicts were extremely deadly, causing an estimated 14% of total hunter-gatherer societies. So the implication would be that individuals acquire so many benefits out of conflicts that they outweigh these huge risks. Conceptually, that could be true, but we wanted to know if there can be other factors driving intergroup conflict, that don’t rely on this idea that conflicts are net-beneficial. This is especially relevant because the literature tells us that there is no robust link between resource scarcity and intergroup conflict.
SCINQ: How do you define acculturation as used in your model?
GH: In our model, acculturation is when after a conflict, the defeated group adopts (either by coercion or imitation) some cultural traits of the victor. For example, after being defeated by the expanding Roman Empire, European tribes adopted Roman cultural traits such as language, eating habits, religion, and laws.
BS: In the model, “acculturation tendency” is a group-level trait, i.e., a property of the group itself, and not a function of the traits of the individuals in the group.
SCINQ: Can you explain the model that was created in order to study intergroup conflict?
GENERAL: We set up a mathematical model where we keep track of individuals within groups. Depending on the cultural traits of individuals in the group, their offspring are more or less likely to become “warriors” or “shepherds”. These are individual-level cultural traits. Furthermore, depending on their group-level cultures, groups also have different tendencies to engage in conflicts and different ways of resolving conflicts (do they pass their culture on to the defeated group, or do they kill everyone in the group instead?). We then see how these individual- and group-level cultural traits evolve over time, by a process similar to natural selection.
GH: Becoming a shepherd or warrior, of course, is a simplistic description of a real-life career choice, but it’s still insightful for our purposes.
BS: Our model is one of pure cultural evolution. There is no genetics in the model, only cultural traits. Even at the individual level the traits passed down from parent to offspring are cultural traits.
SCINQ: What results did the model yield?
GH: At first, it seemed like we were not going to be able to explain the prevalence of intergroup conflict. After all, even if groups with many warriors are more likely to win conflicts, it is still safer to avoid conflicts altogether. But when you allow acculturation to occur, the most belligerent groups start passing on their own belligerent culture to other groups. This way, conflicts can become common, even when they provide no benefits or resources.
BS: The model also points to another example where group selection might have been important in human evolution. Group selection is usually associated with the evolution of cooperation, but here it contributes to the evolution of conflict.
SCINQ: You posit that cultural evolution may play a significant role in spreading conflict among groups. How?
GH: When you have a cold, it only spreads if you interact with other people. Cultural traits can work the same way: when groups have a conflict, that conflict is an interaction that can lead to cultural exchange (like in the case of the Romans we mentioned before). What’s special about conflicts is that the culture that is being copied is typically the culture of the victors, who are likely to be the most belligerent party. This process leads to the spread of belligerence and conflict.
SCINQ: If acculturation coevolved with belligerence and warrior production and the warrior-heavy groups consistently emerged as victors would that eventually result in a homogenous warrior-civilization down the road, presumably with nobody else to fight other than each other?
GENERAL: Like we said earlier, conflicts are very costly. Individuals run the serious risk of dying during conflicts. More importantly, groups need shepherds to sustain big populations. Warriors cannot subsist without the shepherds to sustain the group, and shepherds need warriors to protect them from other groups. So you can never end up with a homogeneous population in the model.
YAROSLAV ISPOLATOV: There is another effect that is more particular to our model. When the pro-conflict traits evolve to the extent that most of losing groups do not undergo any changes as their level of warrior production, acculturation, and belligerence are already close to that of the winner, the conflicts become meaningless as no losses or cultural changes occur. Thus, the belligerence becomes free of selection pressure and often decreases. With fewer conflicts, the warrior production, detrimental to groups’ well-being, drops. Then conflicts become meaningful again, and the belligerence evolves back to its maximum. This loop sets an oscillation between relatively peaceful and war-filled epochs.
SCINQ: Obviously, even in hypothetical groups divided into warriors and shepherds, there would be subtle differences in how warrior-like shepherds are and shepherd-like warriors are. How can future models similar to yours begin to address increased societal complexity?
GENERAL: There can be more than two types of individuals in a model without major complications, but we were simply interested in seeing where the “simplest” model would lead; whether there were any plausible explanations for intergroup conflict other than the traditional resource-acquisition theory. So our model was no more complex than necessary in order to answer our question. So of course, you are right that the model doesn’t even come close to being a realistic depiction of typical hunter gatherer populations.
YI: We believe, however, that the results of our simple model are quite universal: A more realistic alternative to our shepherd-warrior polarized society would be, for example, to ascribe to each individual an amount of time dedicated to the military service and to assume that the outcome of a conflict is controlled by the number of individuals currently in service. For large groups, such a model would yield observations very similar to ours.
GH: If we wanted to incorporate more realism, we should include things like sexual reproduction, migration, and resource dynamics. Our model is also unrealistic in considering primarily large-scale battles; much of intergroup conflict in hunter-gatherer societies took the form of small, localized skirmishes. Finally, we should also consider other types of group interactions that can lead to cultural exchange, such as trade.
SCINQ: What do you mean by mathematical anthropology?
BS: I used that phrase before somewhat jokingly, but researchers like Peter Richerson, Samuel Bowles, Joseph Henrich, Peter Turchin, and others would probably not complain about being called mathematical anthropologists. There are puzzles in human genetic and cultural evolution, like the evolution of individual-level cooperation and group-level conflict that can be studied with mathematical models. Ideally these models are informed by real anthropological data, but using a mathematical model this way is certainly not traditional anthropology. With mathematical models you can study hypothetical societies like the shepherds and warriors.
SCINQ: Finally, what is next for you in terms of research?
GH: I am focusing on finishing my doctoral studies. My thesis focuses on mathematical models of the evolution of social interactions, such as conflict and cooperation.
BS: As mentioned, our present model is somewhat simplistic relative to real hunter gatherer populations, but actually it is a rather complicated model. Individuals have births and deaths; groups fission (split into pieces), die, and get into fights. The model can only be analyzed by simulation. I am interested in looking for much simpler (and more abstract) models of cultural evolution and gene/culture coevolution that can be analyzed more exactly. The goal is to understand, at a theoretical level, how genetic and cultural evolution are similar, and how they are different.
For more information or questions regarding this research, Burt Simon can be contacted at burt.simon@ucdenver.edu
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