The Evolutionary Psychology Of Anxiety & Depression - Ed Hagen

Our hypothesis was that the sex difference in depression is really a strength difference, not a sex difference. And so what we found is that when we controlled for upper body strength, the sex difference in depression diminished and actually went away in in some of our analyses, suggesting that once you control for the differences in strength between the sexes, there is no longer a sex difference in depression. And our our hypothesis for that is that stronger people are less likely to become depressed and physically weaker people are more likely to be depressed in our data. One of the phenomenons that I'm most interested in is depression. How should we understand depression through an evolutionarily adaptive lens? Yeah, well I think that if you look at depression, it's the most common mental health problem and it is it is a problem. I don't Nothing I say should be construed as as trying to diminish the fact that it is a a very serious problem. But when we look at the causes of depression, it's very clear. The evidence is overwhelming that it's adversity. Um folks uh that experience adversity are at much higher risk of experiencing depression. And folks with depression have been much more likely to have experienced adversity. There's quite a bit of evidence that that's a causal relationship that adversity causes depression. And rates are quite high uh in comparison to something like schizophrenia where the rates might be around 1%. Um rates of depression are at least 10 times higher than that if not more. So it's very common, it's caused by adversity, and the symptoms, unlike the symptoms of schizophrenia, which are kind of odd including delusions and hallucinations, uh the depressions of the symptoms of depression are things that we've all experienced. Sadness, loss of interest, inability to sleep, overeating or lack of eating. Um Anxious movements like this when we're we're stressed out. So their their their symptoms are are not um strange or um uncommon. They're things that we've all experienced in response to adversity. So I think these types of evidence suggest that um we should really think of depression probably as an extreme form of sadness or what Randy Thornhill and others have called psychic pain. And I think this is the best fundamental approach, an evolutionary approach, to depression is thinking about um physical pain. Uh it's unpleasant, we don't like it, it's costly, it prevents us from doing things. But we have special receptors for it and special neural circuits for it. And it is caused by physical injuries. Um And you might say why do we why do we have to suffer physical pain? Well, we suffer it uh for a number of reasons. One is if you injure yourself, stop doing whatever you were doing to injure yourself. So it's a signal that you're doing something that is going to harm your biological fitness, as we call it. And so that's one clear function of physical pain. And a second clear function is we we begin to think about what did I do to get myself into the situation and and learn how do I avoid this kind of situation in the future. So that physical pain, uh you know, when I broke my ankle, it hurt like hell, uh but it kept me off my feet, it made me think don't do that stupid thing that you did to break your ankle, uh and um I've more or less avoided breaking my ankle uh subsequently. And so Thornhill and others have proposed psychic pain is very analogous to that. Um something bad is happening to you, not physically, but socially perhaps. Um your wife has left you, your boyfriend has left you, you've lost your job. Um that's bad for your biological fitness. And you need to think about it. So you need to first of all stop doing whatever it is that drove away your romantic partner or got you fired um or causing your friends to um disown you. And you need to think about that and you really need to focus your attention on that and then maybe learn uh don't do whatever it was that you did um that may have uh caused your relationship to break up or you to get fired. And it may turn out that you didn't do anything wrong, but you need to think about it. You need to stop and say something really bad has happened and I need to address this. And so psychic pain, sadness, and even depression um are probably very analogous to psychic pain as a way to um stop furthering any problems that you have perhaps caused or other people have caused you. And and maybe somebody else has has caused the problem and you kind of need to deal with them somehow. So I think this this is the um Sorry about that. My cat. It's a cat. Get out of there. Um Uh we all need attention, right? Um So uh and this this work was uh there's many people that have kind of put forward this idea. Randy Thornhill, um Randy Nesse, uh Paul Andrews um is somebody that's been currently working on this. So I think this is is the kind of the the most likely uh evolutionary explanation for Why would being depressed cause us to act in the way that we do? The symptoms of depression like uh low energy, like not wanting to get out of bed and go and do things, like sometimes being antisocial. You know, if I was to design a coping mechanism for psychological pain, some of the time if I went through something in the past that had happened with my relationship or with my friends, I might want to reach out to them more. I want want to go out there and try and do things to fix it, but it seems like depression causes people to be less mobile in that regard. Yeah, and um you might even bring up the the most mysterious symptom, which is suicidality. Why, if something bad has happened, uh would you ever want to kill yourself? Uh that's a horrible way to increase your biological fitness. So not all adversity is going to cause depression. So in many cases, we do know how to deal with adversity. We do know what to do. Ed, just for a second, tell me give me give me the um uh the definition of adversity. What what like what what do you mean when you say adversity? So from a evolutionary perspective, it would be any situation or circumstance that's likely to decrease your biological fitness, i.e. decrease your ability to survive and reproduce. So losing a mate is obviously horrible for your reproduction. Um getting sick or can uh physical injury can often trigger um depression. So that is obviously something that is bad for your biological fitness. Getting fired, that's your source of resources, that's what you need to survive. So anything that would have a really dramatic negative impact on your ability to survive and reproduce um is what I'm referring to as adversity. And you know, natural disasters, um things that are going to basically reduce your access to resources and um mates and social partners, all the kinds of things that we needed to have access to on a daily basis over our evolutionary history. So that's what I mean by adversity. And we've all ex- or death of a loved one, that's one of the most common ones. And um if your parent dies or your spouse dies or a child dies, that can be really bad for your biological fitness because we really require our social partners to and we always did to survive and reproduce. We needed hunting partners and mates um and folks to share food with us um and take care of us when we're sick. So if one of those folks dies, that's really horrible potentially for your own biological fitness. So that's what I mean by adversity. And um what Paul Andrews argues, I think um quite correctly, is when something like that happens, you really need to shift your cognitive resources to begin to think about these problems cuz they're not easy to solve. Um if a mate leaves you, uh what do you do? Or if someone dies, you can't bring them back to life. So these kinds of problems, this is where we think depression is going to really kick in is when you suffer adversity where the solution isn't obvious. Um you know, what what you need to do to address that kind of adversity um isn't clear and you're going to it really takes a lot of thinking. So you're going to shift your attention to the problem and it's going to take a lot of thinking to figure out what you need to do. And when you're doing that, you can't be doing something else. So there's a trade-off. And that may just require you taking a lot of time to yourself to really think through these things. And the the strongest piece of evidence for that is that rumination, intense rumination, is a really major component of depression for for many people, not all, but it's a very common component of depression that when people get depressed, they really start thinking over and over and over about what happened. Why did, you know, so-and-so leave me or did that. And I'll just give you a personal example. When my dad died, uh he died of cancer and my mom became depressed. And she was really withdrawn. And what she was thinking about is could she have noticed something sooner and gotten him to the doctor sooner. Could she have noticed uh you know that something was wrong? And um you might say, "Well, he's dead. What what what could that help?" And it's not going to help obviously bring back her husband, but it could help her when she's now interacting with other family members to really pay closer attention to things that might be indicating some health problem. And so all of that rumination about my dad's cancer and the months leading up to it before it was diagnosed, um obviously wouldn't bring him back, but could have helped her um potentially notice problems other health problems in folks before they become untreatable. And in fact, um because my dad died of colon cancer that's highly heritable, she just started pestering me uh to go get checked out and get a colonoscopy, which is of course the last thing anybody wants to do. And so after months and months and months of pestering, I finally did it. And guess what? They found a huge polyp. So, uh maybe she saved my life by thinking by becoming depressed and really thinking carefully about um what happened to my dad. Wow. So, that would be an example of how this might work. Yeah. Oh my I so okay, I I really like uh peeling apart a phenomenon that everybody that's listening to this will be familiar with, you know, low mood then getting across into depression. Some people maybe even that have dealt with suicidal ideations and stuff like that. And actually looking at them from uh through a lens of okay, why did this come about? Because especially if you are dealing with severe low mood, even more if it's chronic, if it's over an extended period of time, it feels like a personal curse. It feels like some evil god from on high has decided to hit you with an arrow, but it wasn't Cupid's arrow, it was this depression arrow. And it's just the the perfect storm of your thought loops poking you in exactly the place that it's going to hurt you. And it feels so curated. It feels so individualized for you. Uh and I think that looking at it through this lens hopefully kind of helps to just, you know, relieve a little bit of that sense of it's about me. Mhm. Well, it seems like it's not about you, it's about the evolutionary pressures that would have made these kinds of emotions useful ancestrally. And that story of you with your dad and and and your mom is, you know, like it couldn't be more perfect of an example. Yeah. Um and it again, depression is really um adversive. Um it's just like physical pain. Nobody uh you know, if you break your ankle, you'll know that um you won't be able to sleep. Um you won't be able to do all kinds of things that you could normally do. So, you know, and psychic pain is is very analogous um to that. Now, I want to bring up a a second possible function of these kinds of symptoms. I think the ones that I mentioned are probably the the primary ones that hold across most if not all cases of depression. But just like when we suffer a physical injury, um it hurts. That's our own personal experience of it. But in many cases we're going to signal. If we're a young kid, um we're going to cry. Uh we may yell out. We're going to be um we're going to have expressions of a physical pain on our face. And those are likely signals and signals of need because when you uh suffer a physical injury, um or health problem, you often can't uh deal with it yourself. Uh you need people to help you. If you break your ankle, uh you're not going to be able to feed yourself. You may not be able to do all kinds of things that you could normally do. And you may need to signal uh for help. And we have all kinds of evolved signals like tears and crying and and screaming um to signal that. And I think depression also uh involves a component of signaling. So, psychic pain, just like physical pain, often we can't address adversity completely by ourselves. Um and so there's going to be facial expressions. And I think some of that those physical manifestations of depression where you're not doing anything, our social partners are going to pick up on that. And um they're going to make inferences about our state of mind um that something's wrong. And um I think that's ex- that's another evolutionary reason why depression does involve some of these um im- have some of these kinds of impacts on our behavior that they are also to signal our social partners that we are suffering adversity and uh we do need help in in addressing some of these things. So, that's probably a second reason for for some of these symptoms is that signaling component. Why is there a sex difference in depression? Why do men and women get it at different rates and in differing intensities? Yeah, we don't know. Uh so, this has been a huge area of research. It's a it's one of the biggest sex differences out there. Women are about twice as likely to be depressed as men. And um there's been all kinds of is it different rates of adversity? Are women um experiencing adversity at higher rates than men? Are they somehow more vulnerable uh to a given level of adversity having these emotions trigger? Um and there's some support for all these ideas. One idea One factor that we highlight that I think is really is very well established empirically, um but it's it's not really part of the the national conversation about depression. And that is that depression is really intertwined with social conflict. Um that there's a lot of anger involved typically. And you think about it, if your, you know, partner leaves you, uh you're going to be sad, but you may also be angry. And of course, that person is leaving you probably because there's some conflict between you in your relationship. Um And or if you get fired from your job, again, that suggests social conflict. Or you're having some kind of family situation. Social conflict. And so the evidence for this is really overwhelming that social conflict and anger are deeply intertwined with depression in many many cases. And so that's kind of our uh the angle of my research group is taking on depression. It's really looking at this aspect of conflict because that's an area where evolutionary thinking, where evolutionary theorists have pretty much spent um ever since Darwin, conflict and the struggle for existence has been part of evolutionary theory from the beginning. And it's really striking how important a theme that is in depression. So, how might that explain the sex difference? Well, one way that we all deal with conflict, often not just us humans, but across the animal kingdom, is physical aggression. Um and so when there's uh conflict between males, there's physical aggression. Or male female intersexual conflict often involves male coercion. So, the way that many many animals, including humans, um deal with conflict is physical contests. And in physical contests, in animals and in humans, individuals who are physically stronger will often prevail in those conflicts. So, our hypothesis was that males are physically stronger than females. Um and that's actually an extremely dramatic sex difference. Um there's almost no overlap in upper body strength between males and females. Almost all males are um have greater upper body strength than almost all females. And that means in many many conflicts, especially between men and women, men are going to prevail due to that physical advantage. And that means that um if you're in a situation where you might be experiencing depression, um if you can prevail due to your physical advantages, then you're not going to get depressed. And so what we did to test this idea is we have a huge uh nationally representative database of upper body strength as well as uh depression levels. And our hypothesis was that the sex difference in depression is really a strength difference, not a sex difference. And so what we found is that when we controlled for upper body strength, the sex difference in depression diminished and actually went away in in some of our analyses, suggesting that uh once you control for the differences in strength between the sexes, there is no longer um a sex difference in depression. And our our hypothesis for that is that stronger people And that's exactly what we see that stronger people are less likely to become depressed and physically weaker people are more likely to to be depressed in our data. And that presumably tracks within the sexes as well. That weaker Yes, it does. compared to stronger men have greater propensity to depression. Okay, which direction is the arrow of causation going? Can I make myself less depressed by becoming stronger? Yeah, we don't So, there is a a quite a bit of evidence that physical exercise uh does help with depression. But whether that is because it's increasing um some sense of an ability to deal with adversity, uh we don't know. But you're you're absolutely right. Those are the right questions to ask always with these correlational studies, which ours is as well. Um what is the direction of causality here or is there some third confounding variable? Now, in our study, we controlled for everything we could think of to control for and we still see this uh dramatic effect of strength on um depression, this negative association, despite controlling for all kinds of things, socioeconomic status, age, hormones, uh health status, all kinds of things. Um it looks like there's still this very clear negative association between upper body strength and depression. But yeah, could you uh go to the hit the gym and and uh get rid of that depression? I don't know, maybe. Something that we should uh talk about. I wonder what it is about strength. What was the measure of strength that you used? Was it hand grip? Hand grip, yeah. That's right. Yeah, okay. I wonder what it is about strength because that's not the only measure of physical fitness, you know, we're persistence hunters ancestrally. Why is it not your VO2 max? Why is it not your uh level of zone two uh fitness or your lactate threshold or some other uh measure of fitness cuz there are multiple ways that you could measure this, right? You know, cardio Why is it not your uh flexibility, your um ability to get into the box splits or um whether you can do a a good lunge without getting into pain or something like that. Um presumably hand grip strength it's it's not about the fact that the person that can grip the stone or the piece of wood the hardest has something it's that that is an indicator downstream from a bunch of other things. So, hand grip strength is a very good index of upper body strength and upper body strength is a very good index of prevailing in physical fights. So, we think given the clear evidence that social conflicts are deeply intertwined with depression um and given the evidence that upper body strength is the one of the best predictors of prevailing in physical aggression and physical conflicts that this is the key index. So, it's not these other aspects of health, it's not a health thing, it's a it's a physical fighting thing to resolve conflicts in your interest. So, um That is so interesting. MMA fighters should be the least depressed people on the planet by this. Yeah, unless they got unless they got beaten by somebody else, but yes. Yeah, these guys uh we would expect I mean, that's what our data show at least. We don't we don't obviously have uh in our data anyway um you know, fight outcomes. But we do it's it's very clear that that the folks with the greatest upper body strength are the least likely um to be depressed um and it's not necessarily cuz they had to get in a physical fight, but they just when there was a social conflict um that conflict, at least our hypothesis is and this is going to require a lot of additional testing is that they're the ones that are going to more often than not prevail um and by prevailing um that means that their conflict resolved in their interests and there's no need to get depressed, things worked out their way. Does this get flipped on its head a little bit when we talk about people who commit suicide? Because I think I'm right in saying that women commit suicide or attempt suicide, sorry, uh at a significantly higher rate than men do uh but presumably one of the reasons why men are able to be successful, if that's the right way to put it with their suicide attempts is that they do have this extra degree of lethality. They do have this extra amount of physical strength, which perhaps can mean they can carry through with this. What How do you conceptualize the fact that women attempt suicide more, but men uh uh commit suicide more? Yeah, that's definitely true in the United States. It's true in a lot of populations. It's not true in every population, but it is a pretty good it not true? Um I have to check to make sure I had my stats right in this, but um I think in China, we see really high rates of female successful suicides. Um but I'd want to double-check that to to be sure, but I think that's one of the the major exceptions with the little asterisks that I have to go back and look at my notes. Um And what most people will think and what I think seems really plausible is that men are more likely to use lethal methods like guns um and that's one of the major reasons why uh the suicide rate for men is much higher than for women. But you're right, the attempt rate for women is much higher. I think the key thing here is that the attempt rate for both sexes is dramatically higher than the success rate. So, for men, there's about 10 suicide attempts per completion in let's say young to middle-aged adults. Uh in women, it may be especially in young women, it may be as high as 100 or more attempts per completion. So, what we argue That's is that really the phenomenon of interest here is the attempt, not the success. And what we are arguing is that um for the vast majority of suicidal behavior, the the phenomenon of interest is is the suicide attempt and that the su- the successful, quote unquote, or the suicide deaths are the unintended um accidental consequences of making an attempt that is serious, but hopefully won't actually succeed. And our argument here is similar to what I was mentioning before that there's a signaling component to depression. You need to signal uh that you're in need, that you've suffered adversity. But if there's conflict, as I've emphasized, people may not believe you. Um and so we all know situations where, for example, women are experiencing sexual harassment or sexual abuse and they're not believed. And the reason they're not believed is there's conflict. Um do they have some incentive to lie or um and that's of course what everybody immediately will say on social media, oh she's just trying to manipulate the situation. So, how do you convey And it's a it's a kind of behavior that's often private, it's it's, you know, he said, she said. How can you convince other people that you're telling the truth? And again, this is where evolutionary theory comes in. There's a whole area of research called credible signaling um because uh in animals, within species and between species, there's often conflicts of interest between predators and prey, between males and females um between two males of the same species. And yet there's a big cost of actually fighting or chasing down the prey. So, there's all kinds of signaling going on in non-human animals and biologists uh for a long time have wondered why are those signals honest? Why should if there's a huge conflict of interest uh between the signal sender and the signal receiver, why um should the receivers believe the sender? Why aren't they just exaggerating um their qualities if it's a mating situation or their formidability if it's a uh aggressive situation. And so there's a a body of research on ways that credible signals can evolve and one of them is that the signals have to have um some cost or more accurately that the the benefit of signaling has to outweigh the cost for the sender um but the cost of the signal have to outweigh the benefits for potential cheaters. So, cheaters can't actually send the signal cuz they can't afford to do it. And so what we're arguing is that suicidality might be exactly one of these honest signals of need. And how it would work is uh if your life is going really well you can't afford to actually do something that puts your life at risk. Um you can't take that 1% or 10% chance of killing yourself um to get whatever benefit you might get from social partners because your life is already going really really well. But if your life is not going well, if your mate has just left you, your potential fitness is really taking a huge hit. And in that case, the benefits that you might get from social partners by convincing them that you genuinely are in need might outweigh the cost of taking a 1% chance of actually killing yourself or a 10% chance of killing yourself. So, we're arguing that suicidality is a credible signal of need in situations of adversity that can convince skeptical social partners that you're telling the truth, that you really do need their help. And what you hope is you'll you'll engage in this kind of behavior where you put yourself at real risk of actually killing yourself but most of the time you won't, you'll survive and then social partners will believe, yes, that person really does need my help and you'll get the help you need, but unfortunately, because the signal has to have those uh has to take a genuine risk of death um at the margins. So, that in our view explains these these tremendously high rates of suicide attempts to completions uh in both men and women. Um And then the sex difference in those um may be because uh in our society um we have guns. It's an extremely efficient way um to kill yourself, unfortunately, and men are much more likely to use those than than women, maybe for cultural reasons. How did natural selection create an animal with the capacity to willfully kill itself? How How it that suicide hasn't been selected out of the population? I don't understand how something can be adaptive and and on top of all of that, suicide is moderately heritable as well. Like what what the [ __ ] does that mean? Yeah. So, let's think about the case of a young woman who's experiencing um sexual harassment or sexual abuse. That's enormously costly to her biological fitness. It's going to prevent her from you know, may physically injure her, may infect her with a serious disease that could sterilize her, it may get her pregnant by some person who's not going to invest in her. So, it's an enormous enormous cost to her fitness and needs to stop. But because of that physical formidability difference that I talked about, she may not have the ability to stop her abuser by herself. She needs help. And yet, due to the privacy of those kinds of behaviors, um he said, she said situation, she may not get that help. Um people may be skeptical. Uh the man's um friends and family may back him up. And so, what can she do? Uh she can't easily physically resist him. She's not getting the social She may have married into his family and be physically removed from her own family uh in evolutionary contexts or in many traditional contexts today. So, she just doesn't have the social partners and back up and yet, she's suffering a huge It may be worth the 1% or even 10% chance of killing herself if in the 90 to 90% number of times that this kind of behavior would happen, she convinces people that she's telling the truth and that actually stops the abuse. So, it's the potential benefits of convincing social partners that you really do need to help that would outweigh the uh cost that you might actually end up killing yourself. It's that benefit that explains in our view, at least in our theory, uh why people are willing to take that extreme kind of action. It's a It's a way to convince people that you really do need help. Yes, I understand. Have you got any idea about whether ancestrally men were more successful at suicide attempts than women? I'm wondering whether this is this signaling is is the same ancestrally and we have a an evolutionary mismatch between the tools that men now have access to that means that they can be more successful at attempts. I think that's a reasonable hypothesis. We have with my former student and collaborator Kristen Seim, we've combed through in depth our field. We've combed through the ethnographic record on suicidal behaviors. Now, these are modern groups, but modern groups, many of whom are living in ways that are similar to the way we think were our ancestors lived, traditional societies, hunter-gatherer societies. Um and we've scoured the ethnographic record for every example of suicidal behavior. And these records are not systematic, so they don't allow us to estimate rates of lethal versus non-lethal uh behavior or anything like that. Um what they do do is what we we do see in in some of these societies that almost all of the cases are female. In other cases, almost all of the the cases are male. Um in others, it's kind of a mix. So, we can't uh if men ancestrally actually uh took riskier kinds of suit, you know, engaged in riskier kinds of suicidal behavior, that would have led to their deaths. Um that's uh just something that I think we can't see in the the ethnographic record. Um but we do see all of the other things that our theory would predict. We see social conflict, we see adversity. We see that if you survive, uh you do get help um in most cases. You do get social benefits. Often, somebody's being abused by their parent and they um attempt suicide and then the whole village realizes and they they start pressuring the family to to treat this person better. Um or they engage in a a suicide attempt and they get their mate uh to return. Somebody who had left them comes back. Um or they get their husband to leave his leave his, you know, concubine or mistress and come back to the family. So, it's all the kinds of things um that we see today that trigger suicide attempts. Uh we see in the ethnographic record. And we also see that these often uh if the person does survive, they do generate benefits. But yeah, this the sex difference is not something we can address with the data that we have access to. Maybe somebody who is more clever than I am will figure out a way to do it, but I haven't figured out any way to do it. Maybe by studying some of the few hunter-gatherer societies and small-scale societies that exist today, if we study them more systematically for suicidal behaviors, we might be able to begin to address that question. The problem is it's a it's an incredibly stigmatized behavior and so it's incredibly difficult to to study this and we have tried. Kristen uh has made several efforts to try and collect these data and just the the resistance of the community to to actually talk about this stuff is um we haven't been able to overcome that that challenge yet. One of the other things that I've been considering, sex difference is one of them, but age as well is another one. What can we learn from the onset of suicide in relation to age? So, what we see is that both depression and suicide begin to really onset in kind of middle adolescence to early adulthood. And that's when they really peak the suicidal behaviors. Um and then they gradually decline with age. Um we see the successful suicide rate um actually increasing with age, but it's always much much lower than the suicide suicidal behaviors um until you get up to about age 70 or so. Um and what's striking to us is that these behaviors are on setting as people are transitioning from the juvenile phase to the adult reproductive phase of life. And of course, in the juvenile phase, typically most of us um have protection from our family and our parents. Um we're not engaged in inter- or intra- sex you know, intersexual mating competition. We're not competing for mates, we're not competing for resources. And when we see these behaviors onset is right when we're transitioning from the juvenile phase, when we aren't engaged in all these kinds of competition, to the adult reproductive phase, when intense uh competition can become very very intense. So, mating competition, resource competition. So, our hypothesis for the onset of depression and suicidality in adolescence is that this is when individuals are transitioning to um mating competition and resource competition. And they kind of peak in early adulthood, when that competition is probably most intense. And then it seems to gradually decrease over the lifespan um as mating competition uh is probably decreasing as well. Isn't the current highest risk group in the US for suicide men aged 40 to 45 or something like that? I think white white men are suicidal uh the risk Yeah. The risk of completion goes up with age. But the the risk the frequency of suicidal behaviors is going down. Um so, you've got this kind of uh suicidal behaviors really just spiking incredibly in adolescence or in early adulthood um in their sort of mid-20s or so. Um and actual suicide deaths very very low. And then the suicidal behavior begins to decrease as you go into middle age and older age, but the actual uh rates of actual completions are going are climbing. Um but they're still well below And climbing but climbing presumably at a rate if if the number of attempts is lower, but the percentage of successes is higher. Given the fact that we have I think it's five times more men in middle age commit suicide successfully than girls who are adolescents. Given the fact that we have a mental health crisis around young girls at the moment in the US, but I think it's 60% of uh teenage girls in America say that they have persistent feelings of hopelessness and doom or something like that. Um they their ability to be successful in this regard has to more than compensate for the fact that you have significantly lower uh numbers of attempts. That's right. And so, we don't have a great explanation for that yet, but what we look and we look at just mortality rates uh from any kind of cause, they kind of follow the same kind of pattern. And so, something about um So, if you actually fit the curves, they're very very similar. So, it could it be and we we really don't know. Um So, is it the case that maybe older individuals have to engage in costlier signals to convince folks um that they need help for some reason. So, they're they're engaging in riskier behaviors. But also, as we get older, we're more vulnerable to dying from any kind of cause. And so, it might be the case um that it's kind of a combination of of engaging in in maybe costlier signals, if you will, riskier kinds of behaviors uh to actually get that signal across to other people, but also being more physically vulnerable to having something going wrong and the doctors not being able to save you. Yeah. So so interesting. Is there a link between suicide and intelligence? So intelligence is not So I I look at intelligence from you know, humans compared to all other species and we've obviously got these huge brains, but I don't really I've never really looked at variation in intelligence within species. So I can't say too much. It's not a variable that we have a very good Um sort of the proxy for intelligence in in most studies of evolution is is kind of species level brain size. Uh so if you look at you know, us versus chimps and other apes and other primates and other mammals, um there's lots of good work in that area, but we When we try to think about what does it mean for differences in intelligence within species, um it's not an area that I'm an expert in, but I haven't really seen any great uh operationalization or evolutionary rationale for within species variation. So I can't really answer your question on that one unfortunately. One other kind of weird to me at least phenomenon is postpartum depression. So women who have given birth and then after that they have this onset of depression. Have you looked at that through an evolutionary lens? Could you give some potential adaptive explanations for that? Yeah, so that's actually was my dissertation research and that's was kind of entry point into this whole area. And from an evolutionary perspective on the one hand, postpartum depression is really odd. You've just had reproductive success. That That is you know, as we learn from day one is the whole how our whole physiology and psychology is organized to reproduce. And so you've now successfully reproduced. You in most cases have a nice healthy baby. Um you are a mom in one of the richest countries that has ever existed. You have more resources than anybody in the past could ever imagine. Your baby is very likely, you know, that the probability that it's going to die from an infectious disease is vanishingly small these days, at least if you are lucky enough to live in a high-income region. Uh so what the heck is going on? Uh you are feeling miserable. You don't love your baby. Um you may not be able to eat. You may not be able to care for your other children. It seems like just the most incredibly paradoxical kind of experience you could imagine. Um And so what I started to do is look into what are the circumstances that seem to be associated with postpartum depression. And the big one is lack of social support. Lack of social support from your husband, lack of social support from your family. And we know that we humans are cooperative breeders. We really, you know, it takes a village. We never by ourselves. We were always reproducing in family units where husbands and siblings and older children and grandparents were helping us and we were hanging out with the other moms and the other parents and we were helping them take care of their kids and they were helping us take care of our kids. And if you didn't have that, uh there was no way that you were going to be successful in raising that kid ancestrally. And what I found and the evidence for this is overwhelming is that many, not all cases, but many many many cases of postpartum depression are occurring in contexts where mothers feel they don't have social support, often from the husband or maybe from their other family members. And that would have been a cue ancestrally um that this child isn't going to make it. And um so what I've argued is it's exactly this kind of adversity where we should be experiencing psychic pain. We should really start thinking, what is wrong? Why am I not getting this social support I need to help raise this kid? Um and what can I do about it? Can I get that social support somehow? Can I juggle responsibilities? Um and um if I can't, then I really should just stop caring for this kid. I and we know in in kinds of populations that approximate our ancestral past, uh if you didn't have the resources, um you might just not take care of that kid to begin with. And we often see very high infanticide rates in situations where there is extreme uh extremely limited access to resources. But you shouldn't commit infanticide immediately. You should start signaling that you are genuinely in need and you really can't raise this kid in the in the circumstances the way they are. Something's got to change. And so I'm arguing that a lot of the uh postpartum depression symptoms are a form of psychic pain. You're not getting what you need. And and we also see it when the kid is unhealthy, if it's if it's if there's pregnancy problems, if there's health problems in the child, if the mother has health problems. Um these kinds of things are also strongly associated and probably causes of postpartum depression. Um and then you should signal and you should use one of these costly signals that is going to convince people that you're not just trying to manipulate them and get more help than you deserve, that you really are in need and you really do need extra help or you're going to stop taking care of this kid. And that kid is not just your kid, it's your husband's kid, it's your grandparents' grandkid, it's your sibling's niece or nephew. And biologically, if you don't take care of that kid, it's going to have a negative impact on their fitness. So they have an incentive, if you really are in need, to step in and help you get what you need to to successfully raise the child. Seeing suicidality and depression through a lens of signaling, there is something going on, please give help. Having especially suicide attempts be something which is a very costly signal to try and do it if you're just [ __ ] about and you just want some attention, but you don't actually feel that bad, is you're flying pretty close to the wire. Um I love the idea of in older age, it being a combination of perhaps the signal needs to be more reliable, I mean more costly, which means that you fly closer to the wire of mortality with your signal and the fact that maybe your physiology is just a little bit more fragile in some way, you're a little bit more vulnerable to this. I don't know if I would think that a 45-year-old man would be more vulnerable than a 16-year-old girl. Um they both seem I don't know. I There's some pretty robust 45-year-old guys out there. I I don't know. That that that's interesting to me. Um but I I I just this conception is very very uh fascinating and I think hopefully should help people to feel yeah, a little bit less sort of personally cursed. One of the other topics that I saw you get into on Twitter recently was a discussion about whether or not race science is deeply embedded in evolutionary psychology. Where did this come from? Is it true that race science is a foundational part of evolutionary psychology? Is evolutionary psychology racist? Yeah, I would argue it's it's probably the least racist discipline in the social sciences uh because the social sciences for decades have really foregrounded race as this fundamental aspect of our psychology um that we code everyone by race immediately. And there's quite a bit of evidence that people do encode, you know, as soon as you see somebody, that one of the first things you're going to think of is that a black guy or a white guy or you know, Mexican or Asian. You're going to code race really quick. It's going to influence all kinds of decisions and behaviors. Um and that's been part of, you know, non-evolutionary social science forever. So uh what evolutionary psychology um has proposed is that we humans evolved in Africa. And if we go back two two and a half million years ago, our brains were about the size of chimp brains, about 1/3 of um the human size that we have today. So 400 cubic centimeters versus about 1,200 cubic centimeters. So it's a tripling over that 2 million years and that all occurred in Africa. And then very very very recently, modern humans with modern human-sized brains and modern behaviors and modern capabilities um expanded out of Africa and colonized the rest of the world. So all of us, uh just a few minutes ago in evolutionary time, were big-brained modern humans in Africa. And what we argue is that that massive brain expansion, we evolved a our unique human cognitive abilities that are shared by everybody today because we all came from that same population of of Africans just a few tens of thousands of years ago. So as you may notice here there's no race anywhere in that conception. And the races quote unquote um come about because um in that very very recent expansion of modern humans out of Africa of course you're colonizing Asia and Europe and the Americas. And um in that relatively short time frame some very very minor physical differences have evolved skin color um you're actually really hard you can put almost all of the differences on you know a little infographic there's so few of them. Um there are a few things where there's really strong selection pressures like solar radiation um or pathogens or diet or if you're at high altitude um oxygen levels or things like malaria resistance. But they're very very very very minor in the scheme of things. And what we argue is in that very narrow sliver of time there just wasn't time for much of any um evolution of of complex psychological differences. Any differences that might exist between populations would be about as significant as having a little bit more versus a little bit less um melanin in your melanocytes. So your skin cells. Um And so that's been the perspective of of evolutionary psychology for uh since its inception. However, there is a real problem. I don't want to diminish this. We do have folks who have kind of latched on to the evolutionary psychology label. Um who uh are very interested in the possibility that just as there are physiological population differences, there might be psychological population differences. Um And that's never been part of mainstream evolutionary psychology, but some folks are really interested in that. Um it's obviously a hugely controversial topic. Um some of the evolutionary psychology journals have accepted papers that have been uh purporting to provide evidence for that. Those papers have relied on a uh national IQ database that is extremely problematic um and has really no claim to have accurate numbers on nation level IQ for many many nations. Getting basically nation boiling a whole nation down to a single number uh we can do it, but it's it takes you you know literally might take a million dollars to do it right. Um and that kind of money was not put into this research I can tell you that. Uh and that'd be for one nation. To get that one accurate number for that one nation on any one number that you wanted uh is a very very expensive thing to do. Um and this data set doesn't do that at all. So yes, there is a problem now uh that some evolutionary psychology journals are publishing some very uh suspect papers uh promoting the idea that there are population differences in intelligence. Um and that's going to take some work to deal with that to begin to um uh counter some of those narratives uh with much better research um and much better reviewing um I think there's quite a bit of evidence that the quality of reviews that are going on subpar. So we're working on that. Um is it part of the what has inspired literally hundreds of uh social scientists to adopt evolutionary ideas? No. Um it's really not been the inspiration. The inspiration has been this kind of vision of a the psychic unity of mankind that that we all have a common repertoire of psychological mechanisms um that unite us. What do you say to the people that accuse evolutionary psychology of being just so stories? Well um you could say I could say I'm a fan of just so stories. The more the better. Uh we you know all science starts off with a just so story um that we have some we see some phenomenon nature that we find interesting and we come up with a story about it what explains that phenomenon. Um and so we evolutionary psychologists are as liable to do that as everybody else and all the other scientists and all the other sciences and all the other disciplines. Uh but then you got to test it. And just um as every scientist in every other discipline does we begin to design experiments to test these ideas and some of them pan out and some don't. Um so yeah, we we love our just so stories, but we also love uh science um and the scientific method and empirical research. And if you look at any evolutionary psychologist they have a very robust empirical research program to test their ideas and some of them panned out and some haven't. I'll give you one that that didn't pan out or doesn't seem to uh this debate is still there, but um there's a lot of there were a lot of very interesting I thought just so stories that uh mating preferences might for women might vary across the menstrual cycle. And there was some preliminary empirical evidence in favor of that, but much bigger uh and more controlled studies um have really failed to find that mating preferences change across the menstrual cycle. So that's an example of a great theory uh it was one that suggested empirical tests. Um it was amenable to empirical testing those empirical tests have been done and have not found support for the theory and that's how science works. Um it's hard to figure out how the world works. Uh so we're going to have many many just so just so stories that just uh don't pan out and we that have we have to be okay with that. Um that's the only way we're going to make progress. If we rule out uh telling stories then science dies. It's such a shift that the it's such a shame that the ovulatory shift hypothesis didn't end up being true because it's just so interesting. There was so much it will. You know, it is very cool and but maybe there'll be some new twist on it. Um I don't know that we've heard the last word. Uh but yeah, right now I I don't in my intro classes. Yeah, it may not be dead yet. Uh who knows? Um Who knows? Uh there may be some new twist on it. Um we'll see. Uh but yeah, for right now uh it's not looking good. One of the other things that you've studied is music and ancestrally evolutionarily the role that music and dance and other uh actions had. How does that fit into anything resembling an evolutionary or adaptive story to for humans? Yeah, so my career I thought when I first was introduced to evolutionary psychology I thought well if this is right it should be able to answer questions that nobody's been able to answer. Be really make some progress on some of the big mysteries things like depression and suicide. And music is one of those big mysteries that Darwin himself puzzled over. Um it seems if we look at you know food and mating these are all behaviors that have clear evolutionary utility um and you look at something like music and it's just what is the what could be the utility with that kind of behavior? There's just it's not at all obvious. Um so if if evolutionary approaches are going to prove their worth they should be able to begin to give us insights and it and it won't be any surprise based on everything that I've said that I kind of take a signaling approach here and a credible signaling approach because a lot of the strange things that we see in animals end up being signals of some sort. Um uh and often costly or uh the kinds of signals that you can't fake. And so um when I began thinking about um music and what the heck uh is going on there I thought well what's what's really distinctive about it? And there are there of course many distinctive features when we compare it to language or other kinds of auditory signals things that we know are signals. Uh but the thing I decided to tackle was um the joint performances that and they're incredibly well synchronized. In fact, the way I was driving to work one day um as a grad student and an old song came on the radio that I hadn't heard in you know since my high school days and I was able to immediately sing along with the song in perfect synchrony the lyrics just came back effortlessly. And if this had been a you know a verbal account you know linguistic just a normal I would never I wouldn't be able to remember anything. Uh and yet I could remember this thing and not only remember but just engage with precise synchrony. And so that's what really fascinated me that precise synchronization is this key element of music. It's not the only thing obviously, but it's really critical to the whole experience. And I thought what could be the the function of precise synchronization and this musical memory. I thought you know the only way I could remember this is if I had a specialized psychological adaptation to to remember music. And I thought that precise synchrony uh could be a signal of coalition quality. Uh that the only way that you can achieve that precise synchrony is with a lot of practice. Uh it's really hard to learn a song and get everything synchronized. And so when we learn music uh we've got to practice to master instruments and then we practice songs together. And so uh receivers if they um it might take and in fact when I began to look in the ethnographic record sure enough folks would be spending weeks and months practicing songs and dances for an upcoming feast. But they're going to give that song they're going to present it in just a few minutes or maybe an hour. In a very short amount of time so it would allow observers. To observe something that would be very very difficult to assess otherwise how much of these people how willing are they to cooperate with each other how long have they known each other are they a really highly coordinated coalition and if you observe a group of musicians and dancers you can tell very very quickly whether or not they have been practicing together for a long time or not and that would have been critical in our evolution. Because humans are quite unique in that we. Cooperate not just at the individual level but at the group level groups cooperate with other groups so groups really need to assess the coalition quality of the folks that they made ally with because they may depend on them for their lives in military conflicts and battles or if they're sharing food those guys better be good hunters so the hypothesis is that. These joint musical performances may signal to potential allies that yeah we are a really high quality coalition and you guys should ally with us. That would explain why I can't remember songs from. 14 15 16 years ago and yeah I I you're totally right I can't remember I can barely remember anything from my entire university degree but if you play me any emo slash pop punk song from 2003 to 2009 I can recite it pitch perfect I can tell you what the lyrics were because I looked up the lyrics online and then went back and updated my programming around that word that sounded like another word and I used to go ah ah instead of actually saying what the word was. Yeah I I it's very interesting that. That we almost have this purpose-built circuitry. For it. What's the reason that music have you considered a reason for why music makes us feel good or why it can create a psychological state change within us. Yeah I don't have a any I think it's just be the kind of obvious thing that anything that we do that increases our biological fitness we're going to probably feel good to encourage us to do that thing. And anything that decreases our biological fitness is going to probably make us feel bad so. Ah. Practicing music and then you know when I was in the jazz band in high school nothing was more fun than just you know playing gigs and having people kind of rock out or dance to the thing it just was this thing you just infusion of good feelings. And the argument would be because you're doing things that actually are going to increase your fitness you are. Learning how to send a signal that you've got a really strong coalition and other folks would benefit by cooperating with you instead of those guys in the other Valley. So yeah it's it's in our fitness to to master these things and do well at them and we feel good when we when we do that. Ed Hagen ladies and gentlemen if people want to keep up to date with the stuff that you do online where should they go. Just Google me Google Ed Hagen and you'll find me real quick on Google you'll find my faculty page and also Ed Hagen on Twitter if you want to see me rant about evolutionary just so stories that I love. I do I do indeed Ed I really appreciate you thank you for today. Thanks for having me on. What's happening people thank you very much for tuning in if you enjoyed that episode then press here for a selection of the best clips from the podcast over the last few weeks and don't forget to subscribe. Peace.