Speaking of Psychology - How the threat of disease has shaped human behavior, with Mark Schaller, PhD

Episode Date: March 24, 2021

The COVID-19 pandemic is a grim reminder that infectious diseases have been a danger throughout human history–so much so that the threat of infection has actually helped shape human evolution. Disgust, wariness of strangers, cultural norms around food and cleanliness–all of these behaviors may have evolved at least in part to keep us safe from infectious disease. Researchers call this suite of protective mechanisms the behavioral immune system. University of British Columbia psychologist Mark Schaller, PhD, who coined that phrase, discusses the origins of the behavioral immune system and how behaviors that evolved to protect us from diseases may not be suitable for the threats we face today. We’d love to know what you think of Speaking of Psychology, what you would change about it, and what you’d like to hear more of. Please take our listener survey, visit www.apa.org/podcastsurvey. Links Mark Schaller, PhD Music Minimalist Piano w/ Cello by tyops via Freesound.org Freesound.org Learn more about your ad choices. Visit megaphone.fm/adchoices

Although we are currently in the midst of a global pandemic, we should not forget that we are fortunate to live in a time where we have vaccines and other public health measures we can take to avoid illnesses such as polio, smallpox, cholera, even bubonic plague. And we hope that soon COVID-19 will be vanquished by vaccines. But for our ancestors, infectious diseases were a constant danger, so much so that the threat of infection has actually helped shape human evolution. Disgust, wariness of strangers, cultural norms around food and cleanliness, all of these behaviors may have evolved, at least in part, to keep us safe from infectious disease. Researchers call this suite of protective mechanisms the behavioral immune system, but are the defenses that humans evolved thousands of years ago to ward off infection suitable to protect us from the diseases we face today?

Do they do more harm than good in some cases? and what is the role of disgust in keeping us safe and healthy? Welcome to Speaking of Psychology, the flagship podcast of the American Psychological Association that examines the links between psychological science and everyday life. I'm Kim Mills. Our guest today is Dr. Mark Schaller, a professor of psychology at the University of British Columbia.

Dr. Schaller coined the term behavioral immune system, and he studies how the perceived threat of disease has shaped human psychology. He's also interested more broadly in human social cognition, stereotyping, evolutionary psychology, and cultural psychology. Thank you for joining us today, Dr. Schaller. Hey, thank you for having me. I'm delighted to be here. Let's start with a broad question. What exactly is the behavioral immune system and how and why did it evolve?

The behavioral immune system, I think, can be kind of thought of as a suite of psychological responses that evolved to help defend against the threat of infection. diseases and it's comprised of psychological mechanisms that help us detect potentially infectious things in the immediate environment to respond to those things in a way that might help us avoid them and therefore to help keep us from getting sick. The second part of your question, why do we even have this set of mechanisms? When I think of this, I think of it, it's useful to think about the benefits as well as the costs of what we might think of as the real immune system. You know, our immunological defenses against infections kick in when those things, bacteria, viruses, whatever, when they get inside us. And it's awesome that we have these immunological

defenses that can mount a defense against those things. But it's hugely costly. And to actually mount an immunological defense against bacteria and so forth. It consumes an enormous amount of caloric resources. It can be debilitating. It prevents us from doing all kinds of other things. So in a sense, I think you can think of what we call our immune system is kind of like medical insurance. It's great to have, but it really stinks when we have to use it.

It'd be better not to have to use it at all. And that's where the behavioral immune system comes into play. It's a kind of a form of preventative medicine. These mechanisms help prevent us from having to actually mount that costly immunological defense and so serves as kind of a complementary kind of defense against the threat of infectious diseases. You found that one of the biggest implications of this system is how it affects our interactions with other people, particularly people who are different from us in some way. What is the relationship between the behavioral immune system and prejudice or xenophobia?

Generally speaking, when people are more concerned about the threat of disease, if they feel more vulnerable to infection, they tend to respond more harshly to people who look different, to people who act different, to strangers, to people who they perceive as being from strange or different places. And there's a couple of different reasons why that might be. One is this idea that historically people from who are strange or from strange different places might have been more likely to bring with them more exotic parasites, things that are more likely to make us sick. And that might be possible.

But I actually think a less obvious answer is probably a more compelling answer to the question, which has to do with the first. fact that a lot of the things that people historically have done in order to avoid infection had to do with doing things a certain way. Prepare food a certain way. We have these norms of hygiene, and we have norms that govern what are appropriate ways of engaging in intimate, interpersonal contact with other folks. So we have these rituals and norms. And prior to contemporary technological advances in medicine and pharmacology and public health, these kind of rituals and norms were kind of most of what people had to help them figure out how to avoid coming into contact with infectious diseases.

Which means that anybody who is likely to violate those norms to do things differently, to prepare food differently, to violate, you know, violate norms of. sanitation and hygiene, they posed a threat not just to themselves, but to anybody in the community. So people who seem likely to act different, people who are from foreign lands, it may kind of activate the sense of these people don't do the things that we're likely to do. And so getting back to your question, the idea is that this kind of xenophobic response to people who are different maybe have historically served the function of trying to avoid and keep away people who would violate local rituals and social norms. So some of these things sound like they could be traditions, things that would be passed down from generation to generation, but was there something going way, way back that maybe the humans who prepared food in a certain way just tended to survive,

and therefore it got passed along in that way, almost like an instinctive thing? I wouldn't say an instinctive thing, but more of a kind of a superstitious thing. So food preparation is one of my favorite examples of this, because biologists who have studied spices have found that the use of culinary spices is a natural form of antibiotic. It's not just hot peppers, but just about every kind of herb and spice that people use to flavor food actually has some anti-bacterial properties. And so what's likely to have happened is that people just kind of through trial and error

kind of figured out that, hey, if we prepare food in this kind of way, you know, we put hot spices on our meat, then people are less likely to get sick. Nobody really knew why, right? Yeah. Yeah. Way back when before people even had a concept of germ theory. But I mean, you know, you can figure out, all right, people get sick if we prepare food this way and they don't, if we prepare food this other way.

And so this kind of, it's like, well, let's do that. Let's do the thing that keeps us from getting sick. They might have had a whole mythology around that. But the idea is that they would for sure tend to teach their children. They would pass that on. And so it becomes kind of a cultural norm without any necessary reason as to why it works, there would just be this sense, this superstitious sense of this is what works. And so folks who don't do that or seem likely not to do those things,

people who seem likely to violate these norms were viewed as threats. You've conducted some very interesting studies that suggest that feeling threatened by infectious disease can make people more conformist, more likely to follow rules. And you found this play it's out both at the individual level but at the societal level. Can you talk about that research? Yeah. And that follows directly upon what we were just talking about. So generally speaking, this tendency to be to respond adversely to things that seem like they might pose some sort of threat of infection,

whether it's, you know, some thing that actually seems immediately infection. or some person who seems like they might pose a threat of violating norms, we tend to be hypersensitive to these perceived threats under circumstances in which we either are more vulnerable to infection or for whatever reason just kind of feel more vulnerable to infection. And so in psychology experiments, experiments that I've done, experiments that other people have done, we've used manipulations that temporarily just make people

feel a little more freaked out by disease. And we find that when people do feel more freaked out by disease, they tend to be, to endorse more conformist attitudes. They want other people to conform more. And they also are more likely to conform themselves. They are themselves less likely to violate norms, they're more likely to go along with majority opinion and so forth. So that's kind of what's happening at an individual at a psychological level of analysis, but you do see this analogy at a much broader worldwide cultural level of analysis too. So in some countries, simply because of meteorological variables and other sorts of things, some countries tend to just have more infectious diseases going around.

And it turns out that in countries that have historically had more infectious diseases, people in general are more conformist. They're more likely to encourage obedience in children. They're more likely to conform to majority opinion themselves. They're more likely to do whatever they can to encourage. not just themselves, but folks around them to uphold existing cultural traditions. You talked about meteorology playing a role here. So are you saying, for example, in the tropics, we always talk about all of these tropical diseases.

So that's one of the places where weather would be playing this role, whereas if you live in the Arctic, where it's cold and the germs can't reproduce the way that they can, right, as they can in warmer weather. I'm not a parasitologist, so I hesitate to be on my area of expertise, but that is my understanding that. But that's kind of what we're talking about. There's just more of these harmful bugs, parasites of one sort or another, just more of them can thrive in hotter, wetter places. So do you think that some of this behavioral immune system behavior, particularly around xenophobia and prejudice, is playing out now? during the COVID pandemic, are people becoming more conformist or less so? I mean, the news would tell us that people don't want to get vaccinated, and yet, as you

see the numbers creep up and more vaccine becomes available, people are getting vaccinated. So what's at play here? Well, that's a great question, and it's a complicated question because people have particular groups that they seem especially more willing to conform to. So let me go back to the broader question that you asked about whether these kind of phenomena in general seem to be playing out in the pandemic. And it is an empirical question. I'm a scientist, of course. So it's like, I want to see the data.

And there have been a lot of people who have been collecting data of one sort or another bearing on these kind of questions over the last year. And some of those results are now appearing in academic journals. And there is evidence that some of these things that we've seen in artificial psychology experiments are playing out in the real world. So, for instance, early on in the pandemic, political scientists collected data that was looking at whether the pandemic, the onset of the pandemic was affecting Americans' attitudes toward folks from China specifically, toward Asian Americans, toward immigrant. more broadly, and they found evidence that it was that these more xenophobic responses were being heightened by the onset of the pandemic. There was some work that I saw recently that some psychologists, an international team of psychologists collected data in Poland that showed that the pandemic was associated

with an increased endorsement of very traditional attitudes, including. including more negative attitudes to people who violated traditional sexual norms and things like that. So in various different places, we are seeing evidence that some of these phenomena that we just talked about are being exaggerated because of the fact that at a broad population-wide, worldwide level, the pandemic is making

the threat of disease just kind of extra salient for people in general and people are just in general feeling more vulnerable to the threat of infection. And it's having these these social consequences. There's also research that suggests that the behavioral immune system may influence our choice of mates and our romantic and sexual behavior. Can you talk about that research too? I mean that just sounds fascinating. How does that happen? Well, it's a great question and in fact some of the first work that people people did in this general line of work looked at its effects on people's mate preferences and attraction and so forth.

One line of work looks at physical attractiveness in the extent to which people prioritize physical attractiveness in a potential mate. And work shows that in places, for instance, that we're where diseases have historically been more prevalent, people place a higher priority on physical attractiveness. So why might that be? And the answer, there's a couple of answers possible. One is that generally speaking, physical attractiveness serves as kind of a quick and dirty proxy for health.

That is, when people are sick, it affects their appearance in a variety of ways. And in general, people find less attractive. So even among folks who are healthy, there's a tendency to just kind of view physical attractiveness as kind of a proxy for health. And in addition to that, people have argued it can also perhaps serve as a proxy for the idea that this person is going to be producing healthy children. So for a variety of reasons, the argument is that with people, when diseases are more prevalent, or when people are more freaked out by the threat of disease, they place a higher priority on physical attractiveness. There's other ways in which the behavioral immune system can affect people's inclinations,

their romantic inclinations. There's intimate sexual behavior and just intimate social contact in general poses an interesting dilemma for folks, because on the one hand, we get a lot of benefits from it. Right. But on the other hand, it makes us more vulnerable to the kinds of diseases that people might spread amongst themselves. So there's this kind of constant trade-off,

and the idea is that people will resolve that trade-off somewhat differently, depending upon whether they are or not, feeling worried about the threat of infectious disease. When people do feel more vulnerable to infectious disease, the idea is that they'll just pull back a little bit from these romantic inclinations. And there's research that shows that people are just less likely to pursue romantic opportunities when they're feeling more worried about disease.

And it's not just in the realm of romance either, for that matter. There's work that shows that people, just in general, are less socially gregarious when they're worried about infectious diseases. Because after all, it's not just intimate sexual contact that poses a risk, but close interpersonal contact in general does. And so for the same reasons, close interpersonal contact can, you know, has this tradeoff. There's lots of benefits from hanging out with friends, from meeting new people and so. forth, but it also carries this risk of disease transmission.

Consequently, when people are more worried about the threat of disease, they tend to just kind of pull back from social contact. Let's talk for a minute about the role of disgust and how that fits into our behavioral immune system. It obviously plays an important role for us as living beings, but what role is that? What is the purpose of disgust? A lot of people have studied disgust for a lot of years and have suggested a variety of roles that disgust plays. And the idea that this emotional experience that we call disgust has evolved.

So, for instance, one expert on disgust has suggested that really a long time ago, evolutionarily speaking, disgust or some early version of disgust, distaste, served a function. of just keeping, you know, potentially contaminated food stuff out of our mouth. And since it's through our mouth that a lot of potential infections can happen. And over time, particularly as our ancestors evolved into more and more of kind of a social species discussed kind of evolved and took on it kind of a broader role that we would not just, It didn't just serve as a way of alerting us to the threat of, you know, contaminated food stuffs, but it's kind of a first alert system for the threat of anything that might be

contaminating or infectious. And so what disgust does in folks nowadays, it really, like many emotions, it serves as kind of an alarm system. It's sometimes in a really powerful, immediate way is alerting me to, here's a potential threat of infection, and it's leading me to respond in an avoidant way. You've talked about evolution a little bit as we've been chatting here, and I'm wondering over the long term, do you think this pandemic is going to change people's behavior in any lasting way? I think it would be probably silly of me to speculate upon in terms of whether this will actually have evolutionary consequences.

But rather, I think where one is likely to see it is in terms of kind of not genetic evolution, but cultural evolution, that the pandemic is likely to have some lasting effects on what kinds of norms govern how people. interact with each other. And I'm sure I'll be wrong about some of this because I've learned from sad experience that it's really hard to predict the future. But I wouldn't be surprised if the tendency for people to be concerned about being in densely populated close physical spaces,

people will be a little bit more resistant for some chunk of time in the future, to going into these kind of crowded places. So the era of mosh pits may be over. Yeah, well, you know, this is why I think it's hard to speculate. People have short memories, right? We'll still do stupid things. And, you know, so I may be less likely personally to dive into a mosh pit two years from now,

but my kids might still be moshers in the future. I think it's really an interesting question because it gets back to this idea that a lot of the things that help serve as buffers against the spread of disease are also taken away things that people value like close interaction. And so I think that because there is such a power, people do have such a powerful need for social contact and so forth that that probably will recover. What I do expect, or at least I'm very interested in seeing this, is the extent to which there will be kind of more of a persistent norm of wearing masks. You know, in many parts of the world, people well before the COVID pandemic tended to wear cloth masks over their faces as a way of helping to, you know, prevent the spread of, you know, just seasonal flu and colds and things like that. Yeah, and so now that's, you know, that's. That may persist. We can't say it's a norm with everyone everywhere,

but it has become much more of a norm worldwide. And I'm sure that when the pandemic is over, there will be a lot of folks who will be happy to throw their masks away and want to never touch them again. But I also bet that there will be a lot of folks who will hang on to their masks and will break them out pretty regularly during cold and flu season. and it's likely to have a lot of benefits for public health worldwide. Yeah, I mean, it has, right?

The seasonal flu numbers have been way down this year, so it's absolutely working. That's right. Well, last question, what do you think are the most important questions about the behavioral immune system that remain to be answered? What else are you working on? I can't say I'm working on this. I'll speak more broadly on the kinds of things that folks in the broader research community are working on. and what folks are likely to be working on. I think one really interesting question.

HAT goes back to how we opened and talking about that not only is there a behavioral immune system helps us from beginning getting sick in the first place, but there's also the real immune system, these immunological defenses that fight off infections when they do get inside us. And a really interesting question is the extent to which these two different kinds of immune systems, actually talk to each other, how they interact. And there is various hints of work that do suggest that they are related and they're not just fully independent.

So I'll just give you, I'll give you two examples. One example comes from some work that folks have done that shows that when people actually are actually immunologically suppressed, you know, that they're immune. system just isn't working as well. Those folks compared to other folks tend to show more xenophobic responses to foreigners and things like that. The idea being that when people actually are immunocompromised, they compensate by ramping up the behavioral immune system. And here's another example that some colleagues and I did a study on this and some other folks have done similarly. studies that shows that when people perceive things that are that pose a threat of infection

in their environment or when let's say we look at disgusting pictures that it actually tends to ramp up our actual immunological defenses people who do psycho neuroimmunology have known for years that Any kind of stressful event can ramp up our immunological defenses. But even more so than encountering other stressful things, for instance, even more so than looking at pictures that scare the hell out of me, if I look at pictures of people who themselves look sick, that tends to lead my white blood cells to mount a stronger immunological defense against infections.

So it's a different part of the body that's reacting. It's not like a cortisol level. It's white blood cell. So it really is immune suppressing. It's not just a stress response. It actually is an immunological response. So I mean, these are some really interesting hints of how these different kinds of mechanisms, these immunological mechanisms, these psychological mechanisms, are in some way deeply connected.

And some folks have suggested, hey, you know, it probably makes sense to talk about this as all part of the body's integrated means of of defending against infectious diseases and within an evolutionary framework it makes sense that these things would all be kind of deeply connected in some way so a really interesting line of work and I think it'll take years of work ahead is to kind of sort out how the behavioral immune system interacts with the real immune system. So that's just one example of something I think is going to be really important and interesting. Well, thank you for joining us today, Dr. Scha.

This has been really interesting. I think you've given us a lot to think about as we make our way through the pandemic and flu season and the whole winter. I appreciate you spending time with us today. It's been a pleasure. You can find previous episodes of Speaking of Psychology on our website at speakingofpsychology. or wherever you get your podcasts. If you have comments or ideas for future podcasts,

you can email us at speaking of psychology at APA.org at speaking of psychology, all one word, at APA.org. Speaking of psychology is produced by Lee Weinerman. Our sound editor is Chris Kondyne. Thank you for listening. For the American Psychological Association, I'm Kim Mills.