Culture, Killing, and PTSD with Sarah Mathew
2025-12-16 13:00:00.000 +00:00

I'm David Pensoff. I'm David P. Trozicsky. And this is Evolutionary Psychology, the podcast, actual evolutionary psychology. By actual evolutionary psychologists. Today we have a really impressive and wonderful guest, Sarah Matthew. She is a professor at the School of Evolution and Social Change at Arizona State University. Yeah. Um we talked about that. That that uh that it's a really cool uh interdisciplinary institution. But even more interesting, this was a riveting episode, David. Uh yeah. This was uh honestly one of my favorites. So yeah, we start out talking about interdisciplinarity and and research and how it gets done, and then we get into Sarah's amazing work and her uh pioneering perspective on cultural evolution uh and the cultural evolution of warfare.

Uh, we get into so many fascinating topics like reciprocity, killing PTSD, um uh and just talking about with her work with the Turkana, where you know, she's really with with folks, really, you know, doing um uh doing violence um and h why that exists. But then also people not n not uh people who are you're not violent towards and why those rules persist. Um and the psychology of war and the consequences of killing. Um it just just incredible. Yeah, really wonderful stuff and we get into cooperation, self interest, uh and and just the the level of of detail that you get just being, you know, up close and personal with a group where half literally half the men are dying in warfare. And just familiarizing yourself with the cultural context there and just learning from her

was just uh so fascinating. Um uh really recommend listening through uh to the end for for this episode. So it's a it's a banger. Yeah, enjoy. Here we go. Um so today we're I'm really excited to have uh Sarah Matthew on uh the podcast. Um Sarah is at uh ASU in the anthropology department. Um And Sarah, how long have you been at the in the anthropology department, ESU now? So since uh 2013, but I will have to correct you on the anthropology department because we are actually in the School of Human Evolution and Social Change and the Institute of Human Origins. And both of those programs are actually an interdisciplinary research group. It includes anthropologists, but it also includes sociologists, um, you know,

psychology, even applied math people. So we are a we are an interdisciplinary group. That is a wonderful correction. And I remember looking at ASU. And was that something that Rob uh and Joan wrote Rob Boyd and Joan Silk started or helped found? Um, so the reorganization of ASU into these interdisciplinary schools started with President Michael Crowe. So when he started, when he took over as president of ASU, there was a huge reorganization into becoming a transdisciplinary school, like at its core, not like you know, you have Department of Anthropologies and then you make them talk together. No, it was just like break down all of old departments and disciplines and put like, you know, new new groups of people together.

So we have the School of Sustainability, we have the School of Global Futures, School of Human Evolution and Social Change, and School of Family Dynamics, School of Transborder Studies. And these are all, you know, these are the main kind of academic communities here at ASCII. It's a very special place. Yeah, that's fantastic. So is it that literally like the physical building, the people that you see in the hall, the people that you're like spreading into or having meetings with, they're all they're all in these different disciplines. Yeah. So our faculty meetings, for instance, are, you know, all of the School of Human Evolution and Social Change faculty. And there's about 60 or 70 of us. So it's it's pretty big.

But uh yeah, we're not um, we don't have a sub-community of anthropologists within that. We often have different programs, there's different kinds of you know collaborations within and across these schools, but yeah, we're sitting around with people who who are have um bought into the idea of of transdisciplinarity. That sounds fantastic. Do you find that um it works or are the barriers kind of hardier than you would like them to be? Because I often, you know, sometimes talking with people of different differ different disciplines, you have different vocabularies, uh different methodologies, it's it's hard to meet in the middle. It's hard to have collaborations. Uh they have different expectations about you know publishing in different journals.

I remember um I think it was Jerry Fodor who who said uh that the best interdisciplinary uh work is done within one's own skull. Uh you know, the idea there being like uh it's it's good to avail yourself of different perspectives in different disciplines, but as soon as you have to sort of, you know, work things out with someone in a in a different community, things get kind of difficult. So do you buy the the Fodorian uh perspective that it's it's better to happen within one skull, or are you more of an optimist that it really can happen and those bridges really can be made? Yeah. Um, I think I'm an optimist, but I also do agree that actually there's a lot of integration that does eventually need to happen within one single individual, but that's aided a lot by

who we're talking to, the kinds of vocabulary we're exposed to, the kinds of opinions we're exposed to. So I think that it has actually worked out pretty well. It is true that, you know, you will tend to um, you know, gravitate more towards the people that are talking the same things that you're talking, etc. But I also have um just noticed that there's just a lot more freedom because of this institutional structure to actually just do things that you want to do and not be constrained by what your disciplinary expectations are. So, you know, like you know, for for people coming up for promotion and tenure, it's okay that you know you'd got your PhD in anthropology, but you are not publishing in current

anthropology, you're publishing in you know sustainability journals or conservation journals or engineering journals or you know AI journals, like it just simply doesn't matter, like you know, uh there isn't a rigid expectation, and that really opens up and allows people to kind of explore things that they might have wanted to explore in a different setup, but but are not able to. And that also means that, you know, the way people evaluated within the university is very different and it's very individualized. And people kind of make it a lot more upon the individual to make their case of who they are, how they're kind of bringing things together and stuff like that, rather than an exogenously imposed um uh kind of set requirements type

of system. So yeah, I think the institutionally providing that freedom is um, you know, very useful um because otherwise, you know, in people might be interested but are constrained by by these factors. Yeah, I love this. I was just uh curious about if there was any particular project that you were able to get off the ground and get excited about uh b because of the absence of these constraints. Like um, is there anything that you felt uh liberated to pursue in this environment that you might have not otherwise pursued? Yeah. Uh yeah, I think so. Um so for I mean I'll start with kind of a little bit more of a standard kind of collaboration, which maybe many evolutionary anthropologists do engage in.

But you know, one of the directions that I took my work in was to try to incorporate an understanding also of the genetic population structures in Turkana, because I was doing some work on, you know, how does culture shape, groups and what's the population structure of cultural variation? But then that kind of begs the question: how is that different from the population structure of genetic variation? And that's a very genetics question, but it needs to kind of be integrated with the cultural evolutionary approach too. So for that, I've been working with geneticists, so with Ann Stone, who's an uh geneticist from the anthropology side, but Melissa Wilson, who's a, you know, a bioinformatics, genomics person who is very much in the school of life sciences and not

at all connected with anthropology. And that kind of was a bringing together of um, you know, uh two worlds in some ways and very different expectations about also how to work, how to do genetics research in small-scale societies, which, you know, when I have a collaborator here at ASU who's from the School of Life Sciences, I also know that, you know, they are free to like kind of step into the anthropological space and do things the way anthropologists do. So working genetics work in small-scale societies goes much slower. There's a lot, lot more need to like, you know, dialogue with the community, to like do different things, like not, you know, share the make the data publicly accessible for

anybody to like do work because the communities haven't consented to that. So it's like it's a really different kind of beast for a genomics person to like work with an anthropologist working in a small scale society. But because they are here, everybody's used to this idea that you don't have to be constrained by the way your discipline does things. You can work with anthropologists, you can slow down, you can um, you know, you can say no to some things that might be expected in the genetics community, such as you know, putting up um the um uh the your your data publicly um etc. so it's um so that's one example um another um is that you know i am working with um a legal scholar um now and um you know that project initially started with working on norms and that's kind of

close to like what i'm working um, I'm I'm used to, but you know, it has kind of also drawn us into, you know, working, thinking about how to build normativity into AI systems, because she's somebody who works as a legal scholar. She's worked on like how institutions, legal institutions need to change in order to accommodate new technology. And AI is like a big technology. So this is Jillian Hadfield, who's at Johns Hopkins University. And so now, you know, just about a couple months ago, we organized a workshop here at ASU in which we had cultural evolution folks, so very anthropology and psych people, but together with people from Google Deep Mind and people who are working on AI. And like I just feel that wherever your research kind of takes you, wherever your

collaborations take you, and whatever feels interesting, that's that's the next step. Um, another project that I'm doing is working with people who are in disease ecology. Um, so you know, to study zoonosis, because one of the things that we learned when we were working as anthropologists in the Turkana is that you know, the Tricana eat meat that is um even when they find the animal dead, they will eat the meat. And so that in a public health kind of outlook kind of is considered a very risky type of meat consumption. Yet in our observation, we're not seeing people get sick when they eat that. They eat meat of animals that are dying of certain diseases, like close to death from diseases and disease epidemics.

You know, even I've eaten that meat when I'm there. Like we had the Rift Valley fever epidemic going around, like lots and lots of animals were dying. And so basically, like, you know, just a couple hours before the animal is dead, somebody is you know killing them and sharing that meat out. Um and uh so yeah, that that question basically was uh well, maybe they have cultural knowledge of how to process this meat and how to make it safe to eat, and also to recognize when it can't be eaten, when it can be, and also what organs maybe to avoid, who should who are who should avoid these things, like you know, maybe pregnant women. So we don't know that, but we're gonna like delve into that cultural knowledge landscape.

But we also want to look at the physiological adaptations that maybe the tricana have, like either immune or like you know, um genetic adaptations they have for like you know this high pathogen load meat. and so that requires working with again like people who are interested in public health, disease ecology, zoonosis, um and and maybe genetics, immunologists. So it's um, you know, I feel like my work has kind of just progressed in a way where I, you know, I have certain questions that I'm really interested in and that keep me you know, on one path. But then that path also opens up a lot of like questions that you just stumble upon and collaborations that you stumble upon. And wherever those lead, I feel free to just, you know, go and be

supported in every way by the institution and my department. I love that. And uh one of the throughputs that as I think about your work is um, and I don't know how much we've talked about this explicitly, is um as as I think the term you how you put it, um, which is sort of group structured cultural selection. And that's even a throughput of what we talked about already, which is like ASU has a different institutional selective regime. And so you're free to do things differently. But then even in the Turkana example, uh there might be cultural technology for people who may not know what that idea is. Um, can you sort of explain that? And then maybe I don't know if you the maybe the Turkana example, I mean it's sort of

simple, but just even, you know, what the idea is refracted through that example of uh of, you know, how do you why do they know how to deal with um meat that in a way that other plea places might not? So, yeah, I guess your question kind of touches on two things that I think are maybe useful to kind of separate a little bit. So, one is the question of um just culture and cultural learning, social learning that produces um cultural knowledge that gets transmitted in humans. And there's a large number of people who are trying to understand that in the evolutionary human um sciences. And you know I think that that is uh as as do many people think that that is a very important part of like how humans um became

very different from other organisms, our extreme reliance on culturally transmitted information, social learning. And that leads to um Variation between groups that might be genetically very similar, but have learned from different people, have had different role models in their past, and have been exposed to different environmental conditions in the past that have shaped the knowledge and the norms and the institutions, and then that gets transmitted, etc. So in the Tracana case, for example, yes, why do they know how to look at a day-old dead animal and figure out whether they can eat it or not? Whereas, you know, if we do, we will just say, no, that's not, right? We're both um uh kind of um on the face of it,

um, should they maybe be able to like reason about those things similarly, but the Turkana are able to reason about it in a very different way because of that of the accumulation of knowledge that has come from being pastoralists for perhaps the last 5,000 years. So one of the characteristics of pastoralists is that a lot of people think pastorals eat a lot of meat, but the truth is that pastoralists are really good about not killing animals for meat. They use, especially like East African pastoralists, they use a lot of their animals mostly for milk. And milk is a huge form of their sustenance. They also consume the blood from the animals, but milk is a big sustenance. And they're really, really reluctant to kill an animal, a healthy animal for

meat. They would do that for ceremonies, they do that, you know, like for marriage, um, where you have to kind of kill a bull, etc. They'll do that for like healing, like somebody is sick, and there's like a healing practice that says, you know, kill this kind of animal. But um just for food, it's kind of something that is done with a lot of intention and thought and very cautiously because you don't want to kill a healthy animal. Um, but when an animal is dying, when there's an epidemic going around, an animal is dying, then they kind of make use of uh the meat very um the same. They don't want to waste uh any part of that um animal if they don't have to. Um, they also sometimes find animals who've been killed.

So when I was there once, there was a camel that was found just maybe a couple kilometers outside of the settlement that I was staying in, where my campsite is based. And it looked like the camel was maybe killed by a snake bite, because there are like some very, very poisonous snakes in the area, something that can't kill a camel. Um, and so the camel was found dead. Um, but they didn't immediately kind of cut open um the camel and start eating the meat. They had to find out, you know, who the owner is because the owner could have been it the camels wander quite a lot, so the owner might be somebody in like some other settlement. And so, you know, it took like maybe half a day to a day to like, you know, find the um

the owner and then, you know, tell the owner camel's dead, we're killing. And then and then the meat, then, you know, in the evening we got a bunch of camel meat at our camp and heard the backstory of it. And I didn't even, I didn't, you know, even think twice about not eating it because, you know, everybody eats it. It's, you know, there is just no question that this is maybe something that's been, you know, sitting in the heat for too long. So they just they just know these things because they've had to deal with these challenges in the past. That's part of the cultural and subsistence package that they rely on. And it's a way of living that has allowed them to survive in habitats that you know

you and I would not be able to survive in without that knowledge, like a very arid environment where agriculture, the crop cultivation is very difficult, except along like the riverbeds and stuff. And so uh that is how they have um potentially a lot of um knowledge that um allows them to do that. And then I think your other question related to the culture group structured cultural selection, which I think is a different question, but I'm gonna let you interject before I go into that phase because uh I'll yeah, no, no, that's wonderful. I have I actually have nothing to interject other than just I I think it's so powerful that like the transmission of knowledge is so important. I think about like the is that the Rob um Rob uh and Joan example

of what was it that there was like you know, colonial travel or something, like traveling somewhere and they basically starve to death or almost starve to death. Do you do you know that is that yes that is um that is in their uh used to be in their um intro to anthro class at UCLA and uh uh here too and and also their textbook um but uh I believe um so yeah that is basically you know the thought experiment of if you think that um humans all have a um capacity, a psychological disposition, motivations, reasoning capabilities, cognitive skills, et cetera, that allow them to that that are sufficient for them to extract a living out of all the environments that humans currently live in, then your prediction is that uh, well, yeah, like you and I

could go um to where the Inuit are living, or could go into the Sonoran desert, um, into the Australian um desert, into the rainforest, and be able to figure it out and make a living. Um yet, you know, if you just think about it, I think I wouldn't be able to. What do you think, would you? I think I think there would be a really good movie about me on the knife's edge of death. Yeah. And I would there's a very likely chance that I wouldn't make it. Yes. There would be moments where, you know, it would be sort of like uh uh what is the the Tom Hanks movie with uh the Castaway? Castaway where there's some comedy in there, you know, like the macabre, yeah, the the f the you know per the theory of humor where you make a big mistake, but it's kind of funny

because it's really bad, high cost mistakes. No, totally. No, I mean, you know, um, for sure. Yeah. For sure. Yeah, no, for sure. We know how this ends for sure. Yes, exactly. Yeah. So, but then you know, sometimes I actually ask this to students when I'm teaching um the intro classes and um some of them actually think they can um like you know you know an 18 19 20 year old is filled with like confidence they've gone they've like spent a few nights out uh and they feel like the in Arizona we also have like um survivalist community where like you know there are people who are like very into being able to live off the land and who are like are making bows and arrows, hunting, et cetera. So uh you'll have a couple of people say that they think they can survive much longer than

I actually think they can. Um so um they haven't yet been humbled by the experiences of um life yet. Um, but you know, that's kind of why this thought experiment, this ex this historical experiment is a good um illustration of that because when we reflect on ourselves, we might be very confident of our capabilities, but we know that there were people, explorers, who were actually had a lot of information, just not the local information, but outside information, had a lot of technology, but not the local technology, but outside technology. And we, you know, some of the technology was really fancy, right? Like that the explorers had. They came from some of the most powerful and technologically developed countries

of the time. And yet there's just one thing they lacked. They lacked the knowledge that somebody who grew up there had. And they lacked the kind of much simpler tools and technology that people who lived there had. And, you know, many of them died. It did have that tragic finale part. So it is uh it it is really I think a very important aspect of humans. But that said, you know, I um as somebody who's you know really into um taking these cultural aspects seriously. I also think that there are kind of, you know, then universal psychological predispositions people have that make it possible for them to acquire this information. So the evolved psychology for social learning is really, really important.

And without that, you know, we wouldn't be able to get the relevant information, be able to prioritize what information we should be copying, know when to not copy, know when to innovate and ignore, know when to be a contrarian, those kinds of things. So the evolved psychology is very important. And that brings me to an ex uh an experiment that i always present to my undergrad students which date you feature in oh my goodness star actor there okay do you know what i'm talking i think i have an idea yes exactly yes uh this is the prepared um uh learning experiment that annie words and um you had um uh you were as I said, a star. I was I was an actor, I was a beautiful face. That was it. And he was the brains, yeah.

It was just the I was a prop. Yeah. I think that's a really uh excellent example of how you can have um yeah, there's a lot of structure in the psychology that and there's a lot of preparation for being able to hone in on the kinds of things that we do need to socially learn. I really think of the that experiment as one of the um the best illustrations of that complexity where it's not like you have um uh it's not like you come with just a ready psychology to learn XYZ but rather you come with a psychology that's prepared to learn that you should learn socially, right? Right. So that I think is maybe this area where evolutionary psychology has taken a slightly different take on this than maybe people in human behavior

ecology, cultural evolution, etc., where I think early on there was more of a resistance to how important culture was. But then, you know, that uh in some ways evolutionary psychologists were pushing back against an older model of witness in which there was no kind of preparation that the brain needed and it was um just this big container that could be filled with anything. But I think that I'm hoping that we're kind of in a space now where we can be doing more of the kind of sophisticated experiments that you start in and and really kind of parse out what is the evolved psychology and where is it much more open to taking in cultural information, and where is it more kind of you know canalized into learning

certain things a little bit more rigidly and you know how how does that structure come about that's another question that I think is open and um I uh feel like a lot of my early exposure to this uh to these ideas of modularity and prepared learning um Came from the from you know UCSB, from like um John and Lita's work and from Clark Barrett and Dan Fessler. Um, and so uh that's kind of how I I've been thinking about a lot of things, but I've also, as I've started working now with people in AI and cognitive science, I see a perspective where they are talking about how you can get these, yeah you know like for instance how neural networks are are um learning etc it seems like there is a lot about the brain that we don't understand and and it's possible

that you can get structure in the brain with very few priors early on but with more of uh you know what you're exposed to early can kind of like uh create those hierarchical structures, or you know, to what extent do you need a lot more richness in that hierarchy to like uh already function? Right. And it it actually seems interesting to me that maybe like uh artificial intelligence um research can give us a little bit of insight into what is possible here because it seemed like for long it was a discussion between cognitive science, evolutionary psychology, folks that uh still were limited in their methods because you can't probe the brain in some of the same ways that you can kind of design a

brain, like what the AI people are doing. Yeah, I yeah, I think that's great. And I think like computer science and AI, and Annie Wirtz and I just were working on a chapter about AI and EvSec. I think that's a really wonderful uh thing. And I think if you read some of the early AI work and even some of the later stuff by like Marvin Minsky, um, it's very much a person who's sort of a fellow traveler in the sense of there's problems in the world, uh, real world problems, right? Like focusing on on real world problems, even if they're if even if it's not maybe evolutionarily relevant problems, but still real world problems and analyzing them, doing a task analysis and saying what machinery do you need?

My my take on, just just to say like my take on sort of how much structure you need, I think it's answering sort of two separate questions. Like I think the old school quote unquote sort of evps modularity stuff was sort of a discussion of what's the what's the sort of like full content architecture in the mind that's actually making doing the day-to-day stuff possible? And I think a slightly separate question is sort of how do you build that with the minimal genetic and developmental content? And I actually think a lot of the um machine learning uh and a lot of that stuff that's sort of asking how can we build the representations? It's a slightly different question, which is sort of what what's the minimal way, given

that there's structure in the environment? And this is how development works already. It's sort of natural selection itself faces this challenge of how do I store the minimal amount of information, or even better yet, sort of like chemistry in a developmental little packet such that it reliably interacts with the regularities in the environment to produce a whole body, right? Like, and and and it's sort of the what's the minimal packet of contingencies that's necessary. And I think that's true for even the mind too. So I do think there's probably a lot of reinforcement learning or machine learning, a lot of the principles that we're learning about in AI or computer science, they're but and they're answering the question of what's the minimal structure required to sort of within a

particular domain to extract a much ripper representation that isn't coded sort of by hand, or in this case, maybe in the genes, right? Or it, but it it's so it's sort of allows the environment to structure the thing and then the thing gets represented. So I think I kind of view it as it's it's actually complementary and it's actually kind of asking two different questions. It's sort of the old school stuff was sort of what is that final end state? Yeah. And then this stuff is sort of how do you get there in a minimal perspective? Yeah. Yeah. Yeah. So yeah, that that is um a a useful distinction for me to also get in my um mind because I think early on when I was um kind of absorbing the eb psych um view of modularity and stuff, I

think I kind of just lumped those two things together more. Like you know, yeah if you if you um uh assuming that if you have a rich structure that emerges early on that there has to be more content that is programmed into the genetic machinery for it. But I think you've separated it um it's an interesting point Dave. I mean is is the distinction between the uh the the phenotype or the developmental phenotype and the way that the developmental phenotype gets Yeah, exactly. And that the the feet yeah, and so there are different the phenotype could be highly modular, and yet the way that that modular phenotype gets produced and interacts with the environment could be very minimalistic in terms of genetic context.

Correct. Yeah. I actually think a lot of honestly, like I'm you know, I have a foot in developmental psychology too. Um it's not my only thing, obviously, but like and I actually honestly I read a lot of stuff between sort of what the quote unquote nativists and sort of empiricists in developmental psychology. And I actually think honestly it's the same thing. Where like I think they're both right and they're just sort of having they're kind of talking past each other because they're talking about the the process versus the outcome in a lot of cases. Mm-hmm. Yeah. Um yeah. So I guess that was a little bit of um uh um uh tangent to what I'd started off with, which is I guess uh uh the you know how the trikana are getting their

cultural information. But then you'd also asked me about group structured cultural selection processes. And I think this is actually a space where I have um it's actually what drew me into the field of cultural evolution was because you know when I was doing my undergrad um in ecology and evolutionary biology. That was as an undergrad was the first time I was actually like really getting introduced to evolutionary biology. But I just kind of really fell in love with the idea that you can explain so much about the world through through the through this framework. And the idea of like cooperation kind of stood out as something that is just, you know, uh counterintuitive but still can be explained and

so it was a it's very you know very interesting and intriguing in that way that it's just kind of a little bit not fully within the what you would expect but then there are like these narrow pathways by which you can get it and so I was you know super interested in like um sociality in ants and stuff like that. But being in a biology department, I realized like, you know, there's just a lot of uh potential here to think about humans, but nobody seems to want to do it. Like, you know, it's about bio evolutionary biology departments. We're still very focused on drawing the line. You know, we can explain a lot up to like chimps and then humans are just crazy and weird and we don't know what's going on.

But that's when, you know, towards the tail end, I I was really interested in the cooperation question and I read um um Robin Pete's 1985 book, Culture and Evolutionary Process. And um, you know, the this idea of um culture allowing for a pathway by which you can get selective processes that are otherwise unavailable to genetic populations and genetic systems was really very intriguing because I always felt like, you know when you think about human cooperation it's so it stands out in so many regards it's not just that um the scale of cooperation is large you know that's a lot of the times what we focus on that oh we cooperate in large groups in transient interactions with strangers so that is

spectacular we do do that and that's a big thing but there are other things such as that scale seems to not be constrained by the number of people, right? Like it has gone, it has changed from something that might be like 50, 60, 100 people to something that can scale up to like thousands and potentially millions of people. So the fact that that scale is something that can be moved so like quickly is very unusual in the animal kingdom, right? Like we usually have a lot more constant selection produces a constant kind of social scale at which the cooperation is happening to these other mechanisms. The other thing that I've really tried to emphasize more recently is that you know small scale cooperation in humans is also really different from small scale cooperation in other

animals. So we cooperate way more with kin, we cooperate way more in reciprocal interactions than other animals that have many of these pathways of you know kin based kin selection reciprocity available to them. So if you think about it, you know, uh animals that live in stable social groups have a lot of opportunity for repeated interactions. And you know, you there can be, I I I am of the view that the benefits of cooperation are potentially there in a lot of different ecologies, like there's turntaking, there's possibility for food sharing, for collective child care, for group defense, for collective uh predation, um, etc. So, but you are not getting the kind of intense um reciprocal cooperation that actually traverses reciprocity theory

predicts, which is you know, like WB greater than C is the condition for reciprocity to evolve. And like that means if you see somebody on if you're expected to see somebody more than two times, you should be cooperating like your full siblings. Um, so uh, but we're not there's so much of that cooperation, it's just absent. We're not seeing it. We're instead evaluating whether reciprocity theory is uh supported by saying, okay, conditioned on the fact that we are seeing cooperation, do we see it happening in a way that is balanced and suggests that there's some kind of contingency going on? That's how we are evaluating the theory empirically, but we're not addressing one big problem, which is that you know, by conditioning it on cooperation that's already

happening, we're not evaluating all those cases where cooperation is not happening when it should be, according to theory. But in humans, we engage in just an intense amount of reciprocal cooperation. And like we we do treat friends in ways that are comparable to how we treat kin. And even among um within families, there are people that we will share a lot more with because they're sharing back with us. And there are people family members will ignore. So uh and you know, just stepping into like the Turkana land again, Uh people have friends that, you know, like people are still walking many kilometers to go places. They don't have vehicles. But sometimes you'll meet somebody and they're traveling from like a place that's like 20,

30 kilometers away. And you ask them, like, where are you going? They stop by like our uh camp. Um and they're like, oh, I'm gonna say hi to my friend. He's like, you know, another 30, 40 kilometers down that way. So like somebody is just walking, um, you know, like three days or so. And his claim is he's gonna say hi to his friend. Now he's gonna say more than hi to his friend. He's gonna say hi to his friend. His friend is gonna kill a goat for him, he's gonna stay there a couple of days and then potentially come back. Right. But it's like this level of investment in maintaining close friends in places that are far and wide and that you can then trust your animals with to like, you know, kind of hedge your pets, spread your risk,

to call when you're going on a raid. So you know, when people are going on raids, sometimes they say, um, so I'm planning to go. Um and uh I sent this person all the way to that settlement to tell it so that he can go find my friend and tell my friend that I'm going. I'd like him to come and to meet me, you know, here. So the friendship uh and and even on the raids, they stay together with their friends. They're not staying with their family. They are um they're not supposed to stay with their fathers and older siblings because they're supposed to stay with their age mates, which means that they're you know together their friends. So that part is not that is extremely unusual in humans that we

are also cooperating much more intensively in small scale interactions, which technically theoretically should be supported for a lot of other species, too. Um And uh this is uh I think the other puzzle is or the other kind of um unusual aspect um is that um we are also co able to cooperate to a huge extent while still being fundamentally fairly selfish, I would say. Like, you know as somebody who studies pro-sociality and cooperative behavior I will say that we are a fairly self-interested species um so we've managed to solve the problem of cooperation without um having to commit to being purely pro-social um whereas um ants and you know they're so pro-social that they're just becoming obligately sterile.

And uh so it's just this very um kind of contradictory thing where like, you know, we can collaborate to like send people up to the moon to manage something like the International Space Station. Yet on a day to day basis, a lot of what we're doing is still, you know, going to be best predicted by what's in our interest. I mean, there is a little bit of like a real pro-social psychology there, but by and large, if you were to land, if an alien were to land here and try to predict um, you know, uh something about, for instance, economic models work really well, actually, like you know, prices go up, um, of wages go up, um We can make certain predictions about how people will respond to those incentives.

And people do respond to those incentives to a large extent in those ways. So yeah, how do we get so much cooperation while still like not having a psychology that is is you know truly actually having that level of pro-sociality, right? So that that's that's one uh one question. Another question uh I think feature is that uh we um unlike a lot of cooperative breeders, so uh you know, if you look at um mere cats, if you look at cooperative breeding primates, etc., uh they have much more of a hierarchy in their cooperation. So there's somebody that's amassing the surplus of cooperation, which is the breeding female, but and the others are kind of you know getting the short end of the stick kind of

thing. And humans, we do have that too. We do have hierarchies that have emerged in the course of cultural evolution. We have status differences, um, wealth differences, and all that stuff. But it does seem that this idea of um fairness, of equity, and egalitarianism is one of the important pathways by which humans have achieved large-scale cooperation. That's very different from how it's been achieved in eusocial insects and multicellular organisms, only the, you know, um The sex cells, the gametes are getting getting to really reproduce, everything else is supporting it. So you don't really have a very good example of this kind of large-scale cooperation that is still built somewhat on the idea that everybody needs

to get something, that there's ideas about equity, fairness, and it doesn't always work, but when it doesn't work eventually like people get upset and they try to break down those systems and and um don't go along with with those things so you know we're intensively cooperative but we're also so different um from other organisms in many aspects of our cooperation at every scale and um so I think that when you have a situation like this, it feels like, well, something really is fundamentally very different about the conditions that are amenable to cooperation in humans compared to other animals. It can't be some, you know, sometimes I see people saying, well, mobility solves cooperative dilemmas, but then I'm like, well, zebras can move, right?

Um so like you we c we need an explanation that really can encompass the fact that humans have just a ton of stuff, ways of cooperating that other organisms don't have. And the explanation should then account for the lack of cooperation in other species. It shouldn't just account for cooperation in humans, but then if that mechanism is seen somewhere else, we should expect that kind of cooperation. That's, I think, a type of theoretical precision that we need to be bringing to the table. And so the idea of culture, I think, is one of the big like, you know, it stands out because it is something that humans really very much differ from other organisms in the kind of extreme reliance on imitation and culture, and the fact that that has led to

some things like abilities for norms, transmission of norms, variation between populations in those norms and institutions that was previously you know, not available in genetically structured populations like group group level variation, all that stuff. So I've been really drawn to this idea that there are various things about culture that are uh what is very central to why our kind of cooperation is very different from what it looks in other animals. And um the idea of cultural group selection has been one of the prominent ones. And because people don't like to use the word group selection loosely in in these contexts, I've kind of tried to resort more to group structured cultural selection.

Right. although the term hasn't caught on really so um i'm not really good with coming up with terms that that have to catch on but i'll continue trying to use yeah yeah not no yeah with like weird is one of these like oh my gosh like oh yeah that just I know that just spread like wildfire oh yeah yeah so um yeah anyway group structured cultural selection it's a bit of a mouthful but um uh I think uh that is one big way in which culture has changed something in in humans. So you know historically we always oh people were drawn to this idea of genetic group selection because yeah if you can get groups then you do and those groups are very vary, then you know you do get the potential for selection to act on these entities.

And if you can get selection at that level, you're going to get adaptations at that level. And those could be you know cooperative dispositions. But you know the reality proved those people wrong because you just don't get that kind of um population structure with genes. And we confirmed that in our study with the Tracana and neighboring pastoral groups that So when we did our genetics project, we sampled four different pastoral groups in the Northwest of Kenya, the Turkana, Samburu, Burana, and Rendili. And we sampled them at different social scales, so the scale of clans, subterritories, and ethnolinguistic groups, so that we could see whether there's genetic variation at any of those scales.

And no, the level of genetic variation is just really, really low. Like it's less than a percent, like even between uh ethnolinguistic groups. Um yeah, and just to clarify that we had just had Brett Beheim on, and he talked about there there's sort of the within group variation, between group variation. This is saying that the between group variation is very low compared to the within group. Exactly, exactly. So um uh it's not and this is actually um uh I mean I think that some geneticists would have say said you don't even need to like do this study, like we know this. Um don't waste money on this. And in fact, one geneticist that I spoke to before this project said, Why are you doing that? I mean, I know I know the answer to that.

uh, but and then I almost started not doing that project, but then I gave a talk somewhere where the question, the person asking the question almost assumed that that would be a thing, yeah. Because you know, like clans, for example, are like lineages of people who share a relative, and they're sometimes uh endogamy, and actually the tracana even though they don't have rules against uh ethnic exogamy most marriages are within ethnic groups um so most tracana are marrying other tricana because that's who they're seeing at dances and running into and things like that so but despite this high level of ethnic and endogamy it's still the border is kind of non-existent, the genetic border is non-existent, but there is a cultural border.

And we get at the when you look at the cultural variation, you get things on the order of like 10 to 15%. And maybe the highest value we had was like 18 or 19% at the scale of ethnolinguistic groups. So there is something different in how cultural variation and genetic variation gets organized in populations. And cultural variation does seem more amenable to these kind of group like structures. And so that I think is a very important premise of group structured cultural selection. And I was very excited by the work that I'd done with Carla Handley with these four populations that kind of showed showed that. And to me, it explains some things, not all things, but it explains some very important features about human cooperation,

which is why you get norms that make people want to cooperate at these really large scales, and why that scale can be so variable. So because of uh what cultural group structured cultural selection is saying is that you know the scale of intergroup competition um is going to be mostly along the scale of cultural variation. You know so um uh it in this case in Northwest Kenya it's going to be mostly intergroup competition between ethnolinguistic groups and selection is favoring norms and behaviors that then make people do things that benefit that cultural group. And that can explain, for instance, this really odd thing that you know, like the Tricana go on raids to get animals from other groups, but they

have a norm that says if you go and read another tricana, you're a criminal, that's banditry, that's criminal. And even if you bring animals back to our community and share those animals, we don't like you, we don't want you. We're gonna, you know, discipline you, we're gonna report you to those people that you stole the animals from, we're gonna make you return those animals. So there's the strong norm that is um telling people that there is this arbitrary group of people somewhere far down south but who call themselves trikana that you need to not harm in order to like bring something to your own community but then there's another group of people there that it's okay to um to and as long as it's benefiting us and in fact it's not just

okay to in in this particular cultural system it's you know praised and and really um encouraged and people get a lot of status and um glory from doing that. Um so you have to kind of explain that there's a particular scale at which that norm is operating and it's providing benefits at this ethnolinguistic scale. It's it's creating social order at an at at this scale of a million people and but it's breaking down at another scale, right? Like as soon as you step past that Turkana boundary, that's that norm is really would be useful, but it's not happening. It's um it would be useful in the sense that you know, along the border, half of adult male mortality is due to warfare. And so many people on both sides are dying.

And so if they could actually cooperate at this bigger scale, in which you know those other groups would be part of that in-group, everybody would be better off. But this is the classic cooperation problem. Even if we would both be better off if we both cooperated, if defection gives you even more, both sides are going to defect, and that's kind of what happens is that unilaterally raiding another group has huge benefits. So let's say the Turkana say we won't raid the taposa. Well, great time for the taposa to like go in and raid the tracana, right? Um, and vice versa. So you have the classic breakdown of cooperation between at that level that is uh causing so much um so much uh inefficiency, um, loss of lives, and no, and everybody even knows they don't want this.

Like it would be great if we didn't have to deal with this, but can't kind of overcome that problem. So uh I think cultural uh group selection is a very good candidate for being able to say why you can get the scale of cooperation to be something that's pretty big, but can all can also get bigger if like the cultural group just expands. Like the Tracana have expanded from like 250,000 people 20, 30 years ago to like a million people, but those norms have still persisted that say, you know, now this new million people still are ones that we can't harm. Right? Um back in the day it used to be 100,000 or 50,000 people, but now as they've spread and been successful, they've displaced a lot of other groups from that

area and they've occupied this big area, they're about a million people strong. And uh the norm now just extends to this much larger group of people. Uh, but there is a constraint on that norm, that is, that it's not able to go past a particular boundary. And uh if we were to think that humans are reasoning about this through their intelligence, through their recognition of the mutual benefits to cooperation, by sitting together and talking, by playing soccer games with each other and stuff like that, then you know this we wouldn't have this problem. They wouldn't be warring for like the last um 30, 40 years, probably longer. Um so I um I I I've talked for long, so I'll I'll I'll stop talking about interject.

Yeah. I mean, yeah, so so many different threads that I would wanna go down. Is there one that you wanna go down most, Dave? Um, I I was gonna channel you because I think the last thing we said was sort of, I mean, the it sounds like that the Turkana example and the thing about why there's not sort of why why aren't they cooperating or why why can't we end the violence with the other group? I mean, I feel like that's I'm Dan Channel David is just it's a it's that the Turkana norm is sort of a coordination uh solution, it's a coordination technology of common knowledge that even if everybody on the border, for example, um says, like, as an individual, I don't want to do this, like you said, I can't be sure that the other people, even if like the one

person I know doesn't want to do it, the other people, I don't know if they're not gonna want to do it too, or they might just use it as the opportunity to like screw me over, right? Like that, that that the example you use, there was a Saturday Night Live, I think it was quotes by Jack Handy, where I can imagine a society with no guns or no violence and no warfare. And I can imagine us sneaking up on them and really clobbering them. You know, it was like uh it's exactly that um uh you know, that sentiment. Um, so I feel like the this Turkana thing of in in Turkana, in Scare Quotes sounds like it's just this thing of it's a packet of um expectations and knowledge and rules that evolved psychology is

sort of digested and used. And just to fill in the blank, too, the cultural group selection idea is as you said, we're sort of all selfish, or we all have this evolved psychology. And there's different sort of trial and error ways as groups of people to sort of stitch that together. And you can almost think about it as a metaphor of like building blocks. Like you try to build something out of a building block in one way or another way. And then at a certain point, you can kind of smash them together and see which one does better than the other. Right. And it could either be doing better because of conflict or doing better just by simple of like transmission or competition of just people are like, oh, that looks better than what

I'm doing, right? Or, or it's, you know, you kill the other group or whatever. Um, but then the idea is that some of the ways of stitching together the evolved psychology work better than others. And this work better means gets extended or transmitted or extends. Um, and uh, and if if that's the idea, then that it sounds like this Turkana packet way of dealing with an evolved psychology is doing relatively well. Um, and it's it's spreading. Um, and so the answer to the question of why the other, why we it doesn't work kind of to the other group, is just that what the Turkana is, is this sort of set of locked in coordination devices that just that it's really hard to sort of create um from in a

dynamic perspective. It's just how do you get that dynamic going? I I that's that's sort of my I I'm I'm sort of recapitulating what you've already said just in different language, but that's that's what I wanted to interject. Yeah. Yeah. I think that's very much the framework of um how norms work, right? So it is about solving a particular problem of common knowledge. So I know if I'm a Turkana, I know that you know you expect me to do this. And you know that I expect you to do this. And that um uh uh it it it is the fact that you are um embedded in this kind of shared knowledge that you and you can predict other people's response to your behaviors that provides the deterrence and the motivation to do things a certain way, which also gets to my earlier point about

why humans can be so cooperative while still being fundamentally selfish. It's because when we're following norms, we are being selfish. We are not being pro-social. We are simply doing what is in our interest. That, you know, if I don't do this, then people will do this or think this of me and might not interact with me, etc. So I think the norms kind of help you explain, the normative pathway helps you explain how you can manage to get high levels of cooperation while still being fairly self-interested psychologically. But yeah, I think like you know, norms do uh they are about solving this uh big coordination problem at uh either interpersonally or at a much wider scale. And I think the cultural group selection part helps you explain how you can get it at

this really big scale, in which there people can't just sit together and decide, oh, this is the scale at which we're going to cooperate. And that we've decided this is a useful scale. And so nobody has kind of gotten together to like deliberate on that. It's it's just kind of growing bottom up. And so then that growing bottom up is coming through this um these cultural evolutionary processes and the boundaries of that are being created by when these different normative systems are then clashing against each other. And one of them seems to do well, either because they align better with the evolved psychology. Maybe, you know, like the norm is one that allows everybody to see some gain to what they're um what to going along with the system.

And in another system, it's harder to see that you feel more like you're being gypped or something like that. So, in that sense, it's what you've said like which package is better at aligning with the psychology. But then there's also the other component, which is that which package is better at extracting resources from the environment, like psychological component, because um that is so uh in the Turkana case, their normative package does require men to take some pretty big risks. That can seem like, you know, not really something that you'd want to buy into. But what I think it has persisted because it has allowed them to get these ecological benefits. They're able to displace other groups from very scarce dry season pastures

and occupy those areas and as a result kind of start spreading um their um uh the area of land that they can call turcana and also just get access to an extremely valuable resource in the dry season which is going to literally be a huge determinant of population growth um right um if you don't get pastures in the dry season your animals are dying And so yeah, I think there's the alignment with the psychology part that's one in many places, that's why a normative package might work. But also there's the part about who's better at extracting resources, which package is allowing you to extract more resources from the ecology or be more competitive in intergroup contests or attract more people into your cultural group, et cetera.

And um the all of those factors I think can play a role in why a normative package becomes, you know, what it is. Or stays. Fascinating. I mean, uh so what you're suggesting to me, or what I'm hearing, is a really intriguing hypothesis about the origins of tribalism. So Dave and I are both interested in the human propensity to create groups and to um have conflict with the outgroup, uh, in some cases, uh aggress against the outgroup, dominate the outgroup. This is uh a huge part of the human condition. What you're suggesting is that this tendency toward tribalism, for lack of a better word, um may in fact be a cultural adaptation rather than a genetic adaptation. That is, normative packages that extract more resources from the environment and extract

more resources from other normative packages will by definition spread and proliferate. And that could very well be the normative package of uh protecting and defending everyone who shares that normative package and aggressing against and dominating and exploiting anyone who doesn't share that normative package. And so the possibility is that uh intergroup animosity, tribalism, there are lots of words for these things. We're all familiar with them. This could be a cultural adaptation, and that cultures that have these properties will, by definition, displace uh other cultures that lack these properties and will grow over time and will, in some cases, scale up as the group expands. As the normative package expands, the pool of cooperation and mutual protection and defense

will expand, and you get larger and larger uh normative packages, and with larger and larger normative packages comes competition with other larger and larger normative packages, which creates more and more scaling, and you get larger and larger groups of of collaborating humans. Um I number one, am I getting um this this view correct? And number two, uh are are you are you in fact making that argument that um the origins of of of intergroup animosity tribalism are better viewed as a cultural adaptation than a genetic adaptation? Yeah, so um I think your description of this process was nicely done, better than you know, I can visualize it. Um, so I appreciated that. Um, so whether it is um, you know, uh cultural or genetic,

I think that there's definitely a big cultural part to it, but whether it's happening completely in the absence of any psychological bias towards an ethnic psychology or an in-group psychology or a tribal psychology, I think that's more of an open question because it is possible. So, for instance, one way in which that could happen is simply that if cultural group selection like processes have been happening for a long period of evolutionary history, then you should uh be getting a prepared psychology that is expecting um something like that and um so you can get the kind of gene culture coevolution of a genetically um um uh specified tribal psychology but i think we don't i uh i am uh while I say that that is theoretically possible, I just think that it remains empirically

an open question. Um and I'm not yet willing to kind of um, you know, take sides on that. Um so um, for example, you know, I think uh this is now a paper that Matt Zafferman and I wrote on um warfare and how group structure cultural selection can explain human warfare. We argued about how potentially one could separate the component that is coming from the genetic psychology by thinking about, for instance, is it easier to get norms that make people want to defend their group, right? So, like we're talking that there's there are normative packages that work and that are spreading. But is that normative package that is calling people to kind of favor their in group and compete against the out group?

Is that normative package partly also doing very well because we also have a psychology that's telling us that we should expect norms like this to exist in the world that we are born to and we should be ready to learn those norms. Or is that norm just like any other norm that kind of can come about? Are we just as likely to learn a norm about group defense as we are to learn a norm about, you know, how to use a computer properly? Right? So that would be maybe a good experiment that can look at, yeah. Are we uh going back to where Dave starred in this great movie Unprepared Social Learning? It would be really nice if we could do an experiment that looked at the extent to which we are prepared to learn norms that have to do with uh

in-group um with a tribal psychology or a you know um uh intergroup competitive psychology or are all norms many norms kind of equally learnable if we get the same inputs um to them does that make sense dave Yeah. Yeah. And I mean, and also, oh, well, yeah. And I also just want to like say it's really interesting and really complicated. I want to clarify something too, which is that obviously when we say like as a cultural genetic, we're not saying that there isn't, as Sarah already said, a bunch of the evolved psychology in people that's constantly evaluating and enabling these norms to continue. It's just sort of what's tipping the scale, right? It's sort of the question of sort of what's necessary or why are we getting um, you know,

what's the lever, what's the, what's the thing that kind of flips the switch? And is it better explained by culture, uh, the call the the content of of what's of the norm versus in the rule, right? Like so sort of like let's say I'm an American uh right after 2001 and I go bomb Afghanistan, right? Like, is that because of my evolved psychology, or is it because I'm in an institutional structure where somebody told me, you got to go do this. And if I don't do it, I I don't get paid, you know, like that, right? Like, um, you know, and and and so obviously there's an evolved psychology of a lot, lots of things, but then there's a question of sort of um what is that institution? Um, what's the cultural institution to?

Um, I don't know if that's helpful or clarifying. I just want to say one other quick thing, which is that even if there is an evolved psychology for expecting to be in these situations, to the extent it is naturally selected, it might, it's also going to be sort of like, okay, I'm somebody, I'm a male who's being told to go possibly die for some for some person in power. There's gonna be really strong selection pressures on being like, is that a good idea, right? Or like, what are the cues that that's a good idea? And then you would expect cultural institutions to sort of um hijack the ones that work, right? Hijack the cues that make it seem like it's a good idea. Like, oh, our probability of success is very high.

So let's have lots of parades where I'm just surrounded by incredible amounts of power. So I feel like, well, of course it's a good idea for me to go do this because of course we're gonna win, right? Like, so that's just one other example, too, where um even if there is evolved design, it might not be as simple as there's a bias to go do it. It might just be that there's evolved design to sort of evaluate it in a really smart way. Yeah. Yeah. I guess that's also that layer that I was talking about of um yeah, are we do we come more ready to acquire social norms that are in particular domains that have directions. So like for instance, if the norm says you know don't fight with these people, is that norm

easier or harder to learn than a norm that says you can't fight with these people? Like or a norm about uh you know getting um something arbitrary that's unrelated to group level competitive processes. So that's maybe the middle layer, which I thought like, you know, is a good space to explore because I really haven't seen any studies about that aspect. You know, it's it's either like, okay, are we kind of biased towards tribal psychology or is it just the norm, but not is there, are we biased towards a learning a norm that will tell us to do X over a that tells us to do Y? Yeah. That's a really great I love that. Yeah, like it's what's sticky. That's a great question. Yeah, that's that's great.

Yeah. Yeah. I mean, it's interesting that in so many intergroup conflicts, um, the outgroup is demonized as being anti-social or exploitative or dangerous, right? Or, you know, dirty, well, whatever. Any we have this rich psychology of partner choice where we're evaluating with whom we should cooperate. And when we look at the narratives that are uh engineered about the outgroup, you just go down the list of everything that is bad in a social partner, the outgroup has, right? Uh and that can't be a coincidence. W and so if it were um purely um it almost speaks to in favor of the of the of the cultural view. Where if we had a genetic uh disposition to aggress against outgroups, we wouldn't need

those narratives, right? They're they're in the outgroup, let's just kill them and dominate them and exploit them. It doesn't matter how good they're maybe maybe even if they're better than us, we that's that's a better reason for us to attack them, right? So it shouldn't it shouldn't matter. We shouldn't need those narratives if it's if it's a purely genetic disposition to uh attack outgroups, right? But if it's a cultural evolutionary package that that harnesses aspects of our evolved psychology in service of intergroup competition, then you would expect that cultural package to harness pre-existing features of the psychology that allow uh hatred, aggression, uh anger-based bargaining, et cetera.

And so what it's doing is it's harnessing aspects of our partner choice psychology in service of intergroup competition, because the only groups that would have been successful in coordinating out-group aggression were the groups that had normative package packages and narratives that demonized the outgroup in whatever way was possible. I don't know. I'm curious what you think. So that kind of just made me remember about a very recent paper that um Matt Zaperman and I are working on a chapter that will come up in this edited volume on essentialism that Christina Moya um uh had invited us to um contribute to. Uh we looked at um you know the attitudes that the tracana have towards the Toposa, the group that they um you know are engaged in very lethal conflict

with. And you know, most Tracana have know somebody who's been killed by a taposa. Most tocana, especially in the border area, have know somebody or have personally had their animals taken in a raid and stuff like that. So you'll fe think that this is a place where maybe this kind of dehumanizing kind of uh framework should get mobilized. And so, and then when they talk about you know going to raid the taposa, they gather together and they talk about you know revenge and like we need to retaliate because they came and they took our stuff. So it's like building up that anger, um, uh, etc. But uh really, really interesting. We did the switched at birth task um for uh the tracana and toposas. So if a baby is a toposa baby is raised by the trikana, spent all their life in the

Tracano, would that baby be Toposa or Tracana? And vice versa, if a Tracano baby was adopted by the Toposa and grew up there, would it be Tracano, Toposa? And um can I ask you to guess what you think people would have said? People are not essentialistic. I guess I gave it away. No, but I mean then this is actually because this was my literature though, which is sort of that um well no I'll let you I don't yeah yeah. I mean, I was personally surprised just at how low it was. I knew it wouldn't be potentially that high, but we had only about two percent of our subjects um give the essentialist response. That was like four subjects. Um give the response that a tricana is still a tricana if they're raised by the opposite

group and and vice versa. So they're thinking that if you're raised in that group, you're a member of that group. That's who you are. And if a toposa baby is raised by us, uh baby's a tricana and not a taposa. And so we kind of delved a little bit into the literature on ethnic essentializing beliefs. And it does uh some people have argued that it's those beliefs that can allow you to more easily dehumanize the the outgroup because they are they're different from you. They're not, they don't have the same things you have, the essence that you have, and the prejudice, hostilities and and dehumanization kind of is more easy in that context. But um yeah, we see uh literally like no um uh yeah I I would say you know close to zero um essentializing beliefs.

Um fascinating fascinating result. Yeah. Yeah. And um we, you know, this was part of the study we did on post-traumatic stress disorder in Tracana Warriors with Matt Zefferman. Yeah, I wanted to talk about that and make sure we get to that. That's fantastic. Yeah, but please, yeah, yeah. Um, because actually I I think that study also relates a little bit to your question about, you know, how the genetic psychology versus norms are playing into warfare, etc. So um uh just so just stepping back um a little bit on that question, because the trikran are exposed to these really high rates of lethal violence and raids, you might yeah, it's a very um important context in which you can ask that question.

Are warriors having combat-related PTSD? And um going into this project, I had very I had literally like zero idea of what we will find. I would not have been surprised either which way. But because uh purely because in like the many, many interviews that I had done with people and when people recounted raids that were fairly traumatic, et cetera, nobody ever mentioned anything about you know having intrusive thoughts afterwards or anything. I mean, I didn't specifically query about it, but it never like spontaneously came up in any kind of um thing. Um and uh so that that that empirical impression was that maybe this is not a thing here. Um but then theoretically we were Matt Zaperman and I uh were kind

of putting on our our hats as well-informed evolutionary behavioral um sciences researchers and thinking, you know, what what what what does uh everything we know about um human evolution tell us that we should find here? And we made a we made predictions that basically integrate kind of like these evolved psychological dispositions with the norm psychology. So what we said was that, well, you know, if PTSD is about learning to respond to physical danger and protect yourself from that then that is a universal threat um and that you know all human populations should have evolved uh should have the psychology um the evolved psychology to um to protect yourself from that um kind of situation. And if you look at the PTSD symptoms, um there are 20 of them, but only a few of them

actually align with that kind of response. So those are called the learning and reacting, we call them the learning and reacting symptoms, and these are the symptoms of hypervigilance, startle, um so that essentially uh uh acute distress so like you know everything's uh your body is getting pumped up um to deal with um this risk and an intrusive thought so you're like learning about it and thinking about it even after the event so that you can kind of seal it in your head that when this happens what I do. So we uh we basically predicted that learning and reacting symptoms make a lot of sense cross-culturally, universally. You know, humans should evolve a psychology that makes them react in this way to physical

danger. So in that sense, the Turkana should have that. But there are other symptoms of PTSD that are a little bit more unusual. And one group of symptoms are more overlapping with like depressive symptoms. So they make people feel, you know, you feel estranged and you don't feel like interacting with others. It's like a negative mood. And these seem more about affecting people's motivation, right, to engage in that. Um now I know there are many theories of depression, including um from you know evolutionary psychologists like I think Ed Hagen, yeah, um bargaining, uh yeah, exactly. Um, but you know, essentially one way to think about this, and that does overlap with with the what's uh been said in the literature is that uh depressive symptoms change your

motivation to engage in that thing. And so that's kind of the framework we adopted is saying that so there is another class of symptoms that's affecting your um your motivation. Um and uh we kind of conjectured that those symptoms are going to be something that um that plays more uh that that is influenced also not just by the physical risks of going to war but the normative landscape that is the social rewards and social costs of these actions um and uh uh and and uh the reason why we felt that is because you know if you think about um humans, one of the things, one of the really tricky things about war is that it's making people do something in some ways that's very unusual, right? Like by and large, people are told, you know, you can't harm this person, you can't kill

this person. People, you kill somebody even in rage, accident, you can be ostracized from your society, the rest of your life's over. It's like this really heavy and loaded thing in in a huge normative context. But then there's this kind of normative context where it says if this these conditions are met, then is okay to do. And the thing is that in many war contexts, those norms are really very, it's a fine line. Like if you look at clan warfare, for instance, there are rules about how much damage you can inflict on this other clan and like what kind of weapons you can use, and like how you need to compensate. So it's still structured in a normative landscape in many, many societies, like the

violence that is allowed, the extent to which it's allowed, and exactly who it can be targeted to, whether it can be targeted towards women and children. What should you do when you know somebody's unarmed? Can you take them? Can you ambush people when they're not ready for a battle? And all those kinds of things. Um to what extent can you destroy their property in the course of the war. And in different societies at different scales, you can have different norms. Like, okay, if it's another clan in your same ethnic group, maybe there is like more of a ceremonial kind of warfare where we're not inflicting too much damage. But if we go a little further away towards these other people, we can go all out, etc.

So that moral landscape is a kind of like walking through a moral landmine in some ways. Like there is a way to walk and do it right, but there's also many ways in which you can do it wrong. And so we predicted that, you know, humans, if if you know, combat-related PTSD has evolved to deal with human warfare, then it's going to have to deal with these kind of normative dangers, the moral risks, uh, because the the conditions for war in humans are very much specified by the specific norms. And so we kind of predicted that it's these moral violations, either as victims of violation or as perpetrators of violations, that should be more strongly associated with the depressive symptoms. And we found that in the Turkana, that is the case.

Now, the tri well, the one first thing we found is that first, you know a third of the warriors in our sample did have um sufficient symptom severity that would qualify them for a provisional PTSD diagnosis here in the West. Some of them were describing symptoms that you know you wouldn't be able to tell apart if it was a tricana or an American um soldier talking about like the hypervigilance like and and startle and things like that. There was one person who talked about how he just heard a sound um put put at night and just woke up, took his gun and fired, and it was he shot a donkey that was just walking. Right. So um so there's a lot of cultural parallels, which does speak to this kind of like a universal evolved psychology for this kind of physical danger

response. Because the really interesting thing about Turkana is that they have they don't have a concept of this set of symptoms. They don't have a name for this condition of what um uh that that embodies these set of symptoms. So it's not that because they know it, they are they match their this thing with that cultural framework. When we asked people, we're like uh a lot of people were talking about these symptoms, but they were like, Yeah, I told my friend, and my friend was like, just forget about it, just don't think about it. Like it, yeah, there wasn't like a thing that people identified, oh, you're suffering from this, and this is how we deal with the startle, hyper startle, um, hypervigilance

of startle. So I think that's a very powerful indication that you know there is there's something underlying in the psychology in which you can get such strong convergence between two populations that are experiencing very different kinds of warfare, one which is like, you know, so familiar with the concept, one which is not, but get them to literally be saying the same thing. So I thought that was uh that was a very interesting aspect of this work that struck me. But um when it came to the depressive symptoms, we found that the tricana do have that too. Um uh, But when we compared it to the Western sample, we found that the US for any particular symptom severity, the US soldiers had more of those

depressive symptoms compared to like the Tracana warriors. So there's more of a cultural difference between these populations on that front than there is on the physical danger response front. And our hypothesis was that this has to do with exposure to moral violations. And we found that within the Turkana, people who had more reported more exposure to like moral violations and social sanctions as a result of their participation had more depressive symptoms than those who didn't. So at least within the group, we kind of found some support for that. But we haven't yet done that with the US sample. But one of my graduate students, Michael Baumgarten, who's an a retired Army ranger, is for his dissertation work doing a project with the US veterans to kind of test this moral

injury, whether you know, exposure to moral violations specifically has an effect on depressive symptoms and not on the other kinds of symptoms. Um so I think that that uh work provides um some support for this idea that our war psychology is one that is prepared to um anticipate moral risks and and and and be vigilant about you know the normative landscape, right? And so at least that it has evolved in a in a space in which norms played a big role in shaping how we deal with uh these dangerous war-related situations, um, physically dangerous and morally dangerous, morally dangerous because of the the normative landscape in which it's happening. So I wonder uh you know I it's not directly speaking to the question that

David you asked, but it is talking, it is, I think, indirectly getting at the fact that yes, we do have genetically evolved psychology that is making us vigilant to a norm, to the normative complexity in in war. Um and uh that means that norms have been an important part of the EEA of in which warfare evolved um right and um or an important part of um the psychology that has shaped our motivations Interesting. Absolutely fascinating stuff. To me, I think that um is supportive of this cultural view of warfare. Uh, because uh if we had a genetic uh psychological disposition toward outgroup aggression, we wouldn't need this convoluted package of robots. We'd be like, push the war button. Good. Yeah, push the war button, let's let's kill the outgroup members.

Who cares, you know, and about but precisely because we need this rich set of norms about when to attack, how we attack, who is worth attacking, who is not, uh, why they're attacking, you know, what what the harm they've done to us. We need these uh elaborate rituals where we get together and dance and and you know feel formidable, like this huge convoluted package of cultural stuff. You would not need it if it was a a purely uh a genetically uh uh It was purely genetic adaptation for warfare, right? The elaborateness of of of the cultural stuff here that is driving warfare speaks to adaptation more at the cultural level than at the biological level. At least to me. I think it speaks to that kind of more middle intricate part where it's saying that

so yes, war in humans is being made possible by norms. But because of a long history of that having played out, we are also having a genetically evolved psychology to be prepared to be vigilant of when we are committing norm violations. And be prepared to like lose our motivation to engage in this action if we perceive that we're not getting the social rewards that we anticipated because I mean it's a big deal to go and like put your life on the line and then not get the social rewards, right? So it it I feel like it kind of um is getting at that sandwiched layer that I keep kind of coming back to where like yes the norms are are l I think, you know, the driving force, but because of a long history of that, we have

genetically evolved psychological mechanisms that anticipates there to be norms related to how you handle killing of outgroup members and be extra vigilant when you are in that context and respond appropriately by withdrawing. hypervigilance to moral violations in other contexts that are more evolutionarily novel. Right. So I yeah. So I've I have a question about you mentioned that um among the Turkana who did show symptoms of depression associated with their PTSD, that those were the Turkana that um experience social sanctions or disapproval from uh their their groupmates uh about the violence. And so I'm curious about what those social sanctions consisted in. Was it was it sanctions about the participation in the violence itself for being, say,

cruel or or or something like that, or was it more about cowardice and and uh not being cruel enough? Yeah, so it it was actually a huge package. Uh so we kind of lumped together a all the kind of moral events uh, violations as either victims or perpetrators. So that um uh you know part of the reason for doing uh that is because that's how it's done in the moral injury literature in in the West. Uh, but also it's because sometimes if you ask people directly about perpetration, um they uh might feel more resistant to like disclosing it so the questions are a little bit phrased like were you um involved in or witnessed you know something like this and so we cannot necessarily tease apart whether they were

involved in as you know um uh so there's a little ambiguity about how they were involved in that moral violation um But the the kinds of moral violations span a a range. One some is that you know you took your friend, you made your friend come with you on the raid, and um you came back and friend is friend died in the raid, you go tell your parents that um uh this is what happened, and you know, you will literally face like they will blame you for having taken their son and come back without him. There are people who've had to, when when somebody gets injured on the battlefield, um they are sometimes 50 kilometers, uh, they have to walk back, run back 50 kilometers, right? So if somebody is injured, they can't necessarily always transport that person back.

They would have to carry that person and um and hide or you know, still kind of slowly trudge back. So many times they make like painful decisions about having to like abandon somebody, a friend, um, a group of people will say, No, we can't do this, and they'll like hide this person in a bush or so, hope that he doesn't get seen by the enemies, but eventually can like slowly make his way back home. But many of the times these people die. There are times where people run out of water, um, uh, and they, you know, couldn't share water with uh, you know, they uh maybe they couldn't share their bullets or share their water with somebody who needed it because they didn't have. So there's many um uh instances like that.

There's also instances of people feeling let down by like the diviner, for instance, who is so some raids are organized by diviners who say like they had a vision that if you go to this place and if you do X, Y, and Z rituals along the way, that you know, we are going to have a good outcome. And um they do all of that, and then you know, things go disastrous, catastrophically wrong. People get killed, they're ambushed, um, the enemy knew that they were coming, whatever. And then they feel like they were lied to by the the leader in that way, the diviner. The diviner doesn't, it's not like he's a general, he doesn't go on a raid, he just is a prophet who sees So he has no skin in the game from a game theory perspective.

Um and um there are instances where people have come across like young kids who are um uh you know unarmed, but sometimes they get killed. Um, like some people think it's okay to kill a kid that's unarmed, some people might think it's not. Um uh and so they might be exposed to somebody kind of like kidnapping a kid or or shooting a kid, even though they personally think that that shouldn't have been done, etc. So there's a whole range of moral violations that kind of end up in the picture that we haven't been able to tease apart, like which kind kind of yields this. That we don't have that level of fine-grainedness, but we know that as a package, the people who have had more moral violation-related

issues have more of the have more depressive symptoms. And it could also be cowardice, people being accused of having done something, but they might feel like, well, I actually was in the wrong place, like I was getting fired at, you didn't see, or I was out of bullets, um, etc., and being blamed for um for that, etc. So uh it is um yeah uh we have we haven't been we don't have the kind of data that could tease apart exactly which types of moral violations lead to you know more or less symptoms can i ask a clarification question it was david's question and i was thinking along the same lines is that um there were cues that the people back at home were displeased. Uh, and obviously, like some of the stories are like you, you, you killed my son because

you invited him. So obviously that happens. But I'm wondering, like, in some of these other cases, like where if I'm on the raid and I don't, you know, and like the people I'm with like just kill this kid. Um uh like that's a situation where like, you know, I'm evaluating that as like this is a really horrible thing. I feel really bad about this. I feel like, I mean, this is not maybe conscious or maybe, you know, people are gonna think really badly of me. But that may not happen in the sense of I'm designed to not even talk about that because exactly I'm worried about like the social consequences of people knowing that. Um so d were you able to look at sort of or or I'm just sort of wondering like the the and I don't want to hem and ha too much, but I'm wondering sort

of like the design in each of the people who was feeling depressed is probably to sort of like keep this information away from people. Right. You know, do you do you see what I'm getting? So I'm kind of wondering like how much of it is sort of anticipating that I'm gonna be socially sanctioned, and actually as a consequence of that, not actually presenting the information. So you don't necessarily get cues, but you're sort of imagining that you'll be socially sanctioned. But then in other situations, you are socially sanctioned. Is that are both things happening? Um probably. Um, if I understand you correctly, the first part will result in an underreporting of moral events. Well, maybe not necessarily, but just a thing of I'm actually thinking, like, number one,

what's the Q structure of I've committed a moral offense? Right? Which is sort of you can imagine a situation where it's sort of like you're the I don't think this is true, but you can imagine a design of the human psychology where it's like the warfare button has been pressed. This is all awesome. We're doing all these horrible things, but we're in war mode, so it's all fine. But then we get back to the village, and then whatever people hear, we just sort of, whenever somebody says, Oh, that's actually bad, we're like, oh no, now we're now we did something wrong. And we're just going to use like the social reaction of the community as our moral comp or sort of moral compass. But there's another version where there's already sort of an internalization

or even an anticipation of sort of like what I think people will react to. Um, and consequently, you don't even need to get the reaction from people. Yeah. So I think that actually, yeah, I think there's both going on because there are so it that actually brings me to something that I really should have said. Uh one of the uh things that we looked at is whether people have been had uh killed an enemy in combat, right? Um and very interestingly, um I would this is definitely went against my prediction. I would have predicted that that would not be um a um source of a moral violation in the chakana context because they have a lot of cultural institutions to actually like reward warriors who have killed in combat.

They get to scar themselves in a particular way that permanently marks them as like, you know, a warrior and be proud of it. And uh and but in the US we know that uh there is an association between um having killed in combat and having more um higher severity of uh mental health uh issues. But interestingly, we found that even though it's highly rewarded, um people who had killed in combat were more likely to have depressive symptoms, had higher depressive symptom severity than those who had it. So killing was one of our moral this thing. We kept it separate because it's such a salient category. Um, but it essentially so then we probed that a little further. Um and uh there is a researcher who works in the Samburu,

Velinda Strait, who has done a lot of work also on the kinds of emotions that of haunting that people feel, that Samburu warriors feel when they've killed in combat. And we found a lot of analogues of that in the tracana, analogues of what she had described in the Samburu, which is that people, even though this is so culturally rewarded, there is a uh people report often feeling haunted by the ghost of the enemy. And that is an intrusive thing, it keeps coming back, they can't get it out of them. Um, and uh, they have to do cleansing ceremonies in order to like kind of help them uh alleviate that uh psychological distress in some ways. Um, And I think that maybe gets at this fact that killing is just such

a salient kind of moral violation. And it might have a uh it might be really hard to override it even with these cultural signals of this, because it's I, you know, the main reason is that you know killing can't be compensated in some ways, right? Like, I mean, cultures have come up with ways of compensating and making up for having done that wrong, like you know, you compensate the family. But there's no like you really can't compensate the individual that that has been killed. It's a very uh stark kind of moral violation in that way. Whereas other moral violations, I think, are you know, okay, you screwed up, but you have a chance to kind of rectify that and do differently, do better, signal that you are

remorseful by, you know, maybe having these depressive symptoms, etc. But killing seems uh killing does seem to be special in that sense and um I I think that's interesting because it both gets at something that can't be overridden by the cultural uh by the cultural institutions but also that I think that's an indication of maybe how um morally treacherous killing is even in the context of warfare, right? Like it's um uh we come very prepared to be very hyper vigilant about engaging in that um um in the context of war even because yeah like what the truth is that today people might have said it's okay to have killed this person but tomorrow they'll say, Oh, you did that. Like, no, we should not be doing that.

We should not be killing uh these people, there's they're one of us, um, or those were not acceptable conditions for having killed, etc. And there's nothing you can do, the person's gone, there's no reparation that can be made. Wow. I mean, that's uh uh uh truly fascinating and um sobering stuff. Um I I mean, you I I don't know if there's that much left to say. Do you have any other questions about this, Dave? I was gonna say hopefully this is well, I mean it's a good and bad thing, but like just swinging back to AI and robots. This is like all the uh they're building now ro this is why there's gonna be robots that are doing the killing, right? Uh but maybe the robots will just start killing the other robots and it'll just be robot

attrition and nobody needs to die in war. So yeah. I mean, again, this this also sp speaks to me that a lot of the psychology of warfare and intergroup violence and intergroup hostility is a kind of cultural technology to overcome uh aspects of our psychology that would otherwise be compelled against it. Um, that we have these powerful drives to not kill, to not be cruel. Um and uh it takes a lot of cultural machinery to overcome that. Um and it may be that, you know, in the United States, our cultural machinery is not as good or as well adapted, and that might explain why we have higher prevalence of of depressive symptoms among our soldiers. Whereas in the tricana, their cultural machinery might be a little more well adapted, which

allows them to overcome some of that depression, but clearly not all of it, because it still exists to a significant degree. And it just speaks to how difficult a challenge it is to knit together these groups of uh, you know, reputation conscious, status conscious, self-interest to humans, and knit them together into cooperative groups that can compete with other groups. Uh, and there are a lot of barriers to overcome in that in that knitting problem. Um and and cultures can evolve over time to solve it. But you know, there's only so much that can be solved. Yeah. And I think I want to just swing it back too to like the almost the ASU interdisciplinarity part too is is um like Europe, for example, you know, was just

it was full of violence forever. I mean if you watch like these YouTube animations of like or any any area like you know China or anything, you know, it's just like oh my God, so many people dying. This the colors on the map keep changing, you know, and then yeah, it's and then there's a change at some point in and so like the the idea that sort of you know the groups that succeed are the ones that are extracting resources for the people in the groups, right? Uh but but you can sort of change the the rules, people can change the rules sometimes. So something like the EU, right? Where all of a sudden it's no longer there's big costs now to uh to fighting, to the point where if I'm like a French farmer, it's

actually better that I'm not shooting at the Germans across the Rhine because actually I'm getting, you know, the food from them, you know, and like it doesn't help me at all. Because and so somebody sort of, or or a group of people, big enough group of people, sort of decided maybe we can change sort of the what's what's the selection dynamic of the institution in a different way. And I think that I hope my hope would be that something like I think there, there's always this golden uh million dollar, which is now ridiculous because you know, we're in we're in, you know, America where a million dollars like buys you, I don't know, a mobile home or something in Santa Barbara. I don't know. Um, but uh, but like the billion dollar question, the trillions of dollar question is sort

of how do you reduce war? Um and with the like po PTSD, the cultural selection is all sort of on the front end in the in America, right? It's not like we're we're not selecting institutions that sort of like help people not go to war. You know, it's sort of so I think in in this ASU way, if I'm sort of not being super clear, but I think the idea would be if we can be mindful or better understand the cultural selection of why belligerence happens, for example, like in the Turkana, then there may be ways of of thinking about, well, might there be ways to sort of what are the on-the-ground ways to make it in more people's interests to not shoot across the river anymore? It's a hard question, but I think like this this is starting to get at the tools to do

that. And something like the ASU thing. I mean, you can't, you know, that's a lot of social engineering and there can be unintended consequences, and you have to be really careful about that stuff. But um, but I don't know. I just I I think the the more we understand why people might be doing this thing in the c the benefits they're getting, then maybe we can think about ways to maybe make the benefit structure and the environment a bit different. That is the optimistic view. And uh yeah, I I would hope there's some room for that. And we know historically institutions have emerged between like you know, huge units like nations. Um and yeah, like you have things like the EU that have norms of war and things like

that. Um but yeah, it also seems um It seems like one of the harder problems to solve. It does get, it does happen. So humans have occasionally found these pathways, but they have also often not found these pathways. And so whether the glass is half full, half empty, that's um whether that's based on whether you live in Santa Barbara and you look over the ocean or into the dry desert. Yes. Exactly. Yeah. All right. Well, this time absolutely flew by. Uh this was such a fascinating conversation. Um my mind is still spinning. Um but it's time for us to ask the uh two hours would be like so long. Yeah, no, it just goes like that. Yeah. Yeah, it really flies by. Sarah, yeah, no, thank you so much.

Uh we will have to have you back on because I mean we really just skimmed the surface, but um really fascinating, really important work. Um, Thank you so much for doing it. The stuff with the the all of the work that you've done in uh with the Turkana and both theoretical work and empirical work. It's just, it's so it's such a um, I don't even know, it's sort of silly to even give it an adjective, but it's just such wonderful, strong. I feel like your work is one of the great pillars of like our generation of evolutionary sciences. So so thank you for doing it. It's just, it's just fascinating and um it's so interesting. And it's such an important thing about you know war and violence and killing.

Um what could be more important than that? And so uh it's not a and as always, I mean Dave and I always joke like whenever we have an anthropologist on, like we should be saying thank you for your service, right? Like it's a very difficult um and dangerous you know thing to do. So thank you for for doing it. It's been one of the most fulfilling aspects of um my academic life has been to like get to see a different culture and get you know kind of see the world through like a different cultural lens. I think it's actually really worth it. Hard as it is, it's it's totally worth it. Yeah. So I love the my leaning my ending thing is here norms are selfish and I love that. That's like that will stick with me for following norms is selfish, but that's maybe good.

Um so yeah. So uh I it's a really complicated and sophisticated, mature way to think, I think about the world. Yeah, it it was a wonderful yeah, that that's another thing that stuck with me is a wonderful perspective shift on the psychology of fairness and egalitarianism. That we commonly have a very sunny and idealistic view of these things, but in reality, they're just mechanisms for ensuring that everyone's self-interest is is being enhanced. Coordinated. Yes. Yeah, exactly. So that so that everybody's happy so that people don't blow up the whole deal. We got to make sure that everyone's happy, and that's that's just what fairness is, right? Yeah. So it's a wonderful perspective shift. Um and uh this is a really great conversation.

So thank you so much, Sarah. Yeah. I'm not sure the philosophers would like that take, but well the philosophers are there's gonna be a long there there's gonna be a lot of philosophers unhappy about a lot of science for the next thousand years. So All right. Thank you, Sarah. Well, you're still here listening, um, which means we must be doing something right if you're listening. Yeah, or or we're uh some of us are doing something right enough. Yeah, or maybe you just forgot to turn us off and we're just uh talking about it. Just keep sleeping tools. Just keep sleeping. Sleep is so important. It's so hard to get in this day. And if you're driving and sleeping, wake up. Yes, because we wouldn't want you to get into an accident.

That would be bad. I might have just saved I might have just saved somebody's life for all we know. Yeah, that's true. And if you want us to save more lives by putting us in more people's ears, you can uh spread the good word, uh support us on Patreon, write you know, write us a kind review, say nice things about us on social media, uh, And you know, reach out to us. Send us an email if you have ideas for episodes, possible guests. We are open to suggestions. I love the idea of a review that whose title isn't might save your life. Mm-hmm. That's right. That's what we're doing here. We're saving lives. One podcast episode at a time. Okay. On that note, see you next week. See you next week, everybody.

Okay.