Debra Lieberman is part of the 2nd generation of evolutionary psychologists. I’m proud to have introduced her to evolutionary thinking when she was an undergraduate student at Binghamton University, when I was still teaching a single course on Evolution and Human Behavior and before I helped to start EvoS, Binghamton University’s campus-wide evolutionary studies program. She obtained her PhD from the University of California at Santa Barbara with Leda Cosmides and John Tooby as her mentors. She is currently an associate professor in the Department of Psychology at the University of Miami in Florida.

Debra Lieberman

Debra’s research is an excellent example of how evolutionary thinking can inform a detailed research program in cognitive psychology. She recently visited Binghamton University to give a seminar in our EvoS seminar series, which was a homecoming of sorts. Her full-length EvoS seminar can be viewed here.DSW: Debra, you are doing the most wonderful work on the cognitive psychology of kin interactions and most recently the psychology of gratitude. You did your undergraduate work at Binghamton and then went on to get your PhD with Leda Cosmides and John Tooby--so you’re the perfect person to talk with about evolutionary psychology. I wonder if you might begin at the beginning, how you got turned on to this, your experience at Santa Barbara, and then fast forward to present. We want to center this on the whole topic of evolutionary psychology.DL: Let’s see… the beginning. I was always interested in human nature. At Binghamton I was a biochemistry major and when I saw your class, “Evolution and Human Behavior”, I sensed controversy and set sail. We read Homicide and The Adapted Mindtwo books that changed my life. It was bizarre to me that it was controversial to talk about humans in the same way that we talk about other critters.DSW: I remember you coming into my office and venting your anger and frustration at the other courses you were taking and how they didn’t get any of this.DL: As an undergraduate, you think all your elders are on the same page about what it means to be human and where we all came from. Talking to biologists it is fine to talk about sexual selection and parental investment but--wait a minute--when you’re talking about humans, it’s all “learning” and “culture” and I found this strange. Then you talk to psychologists about relationships and they’d say, “Wait, what is this sexual selection and parental investment? No, we’re humans.” It was a bizarre situation to see that the whole biological world was shaped by these principles, but it just wasn’t applied at all to humans. Strange. So there was controversy—I was in.At the time there were very few graduate programs that did this. You were pretty much the only one, and then because I read the books, I knew about [Martin] Daly and [Margo] Wilson at McMaster, David Buss at Michigan (back then), Randy Thornhill at New Mexico, and John and Leda at Santa Barbara. Those were the four applications I put in for grad school.When I met Leda, she told me I’d been accepted and that I should come work with her. I was like “Wow, that’s why I applied!” Santa Barbara was a great experience and I feel fortunate to have joined John and Leda’s lab.DSW: What was the intellectual climate there? Describe your experience.DL: As a first year grad student, I took a pathogenesis course in the biology department that I loved, because I was intrigued by the idea that disease organisms could manipulate host behavior. I started to work with one of the biology professors who studied fish that, when parasitized, would swim to the top of the water column where the parasite’s next host, the bird, would eat the fish. I wanted to understand what the parasite was doing to the neuro-circuitry of the fish that caused the fish to behave this way. So I started in on a project solo, and after a few weeks, John and Leda tapped me on the shoulder and said, “Look, this is interesting, we support you, we’re biologists, but if you’re going to do psychology you need to do more with humans or you should think about another program.”So immediately I dropped the project and John said that he and Leda really wanted to look at kinship and to understand the cues to kinship. That’s where we started. The “Westermarck effect” was well known -- the idea that early association during childhood leads to an aversion later in adulthood. But we wanted to ask, how do individuals figure out who their siblings are? What are the cues? So we developed a huge questionnaire. I started to analyze the data. I came up with a very weak effect of how co-residence predicts sexual aversions. I thought to myself, this is terrible. It was significant but in psychology an effect size of .2 is nothing to write home about. How could something so powerful as an inbreeding avoidance mechanism –if co-residence was really the mechanism – how could I get a .2 effect size? I always thought that if you truly carve nature at a joint, you should see very large effects! We started thinking about other possible cues and this less us to split the sample into older and younger siblings. It totally changed the results. In our data, for people with younger siblings, co-residence no longer predicted sexual aversions, but for people with older siblings, the effect of co-residence was huge. It was a moment of holy crap! A true eureka moment. We talked about it and developed another survey to further test it. That’s what led to our understanding of how siblings recognize each other.DSW: Which is that it differs because of the information available. Maybe you can summarize those results.DL: We were interested to know if there was a particular mechanism in the brain that lets siblings know they are related. A very reliable cue to knowing that another individual is your sibling is seeing your mother give birth to and care for it--but that’s only available if you’re the older child. What does the younger child do? The next reliable cue is seeing who your mom invests in over the long haul and that’s what we’ve come to know as “co-residence duration”. This is what happens when you live with someone for a long time and see evidence of shared parental investment. It turns out that if you’re the younger sibling you track parental investment: the longer the co-residence duration, the more certain you can be that the older child is, in fact, your sibling. The older siblings use the cue of watching their mother invest in a newborn. They don’t also use co-residence duration, presumably because of the reliability of seeing mom care for an infant. But in terms of computations, the two cues could have combined – but they don’t appear to.DSW: It looks like one trumps the other.DL: That’s right. With this information in hand, we were off to the races. We thought--is this a strange thing that’s happening in Santa Barbara? So I tested it in Hawaii, in Dominica, and working with colleagues we replicated it in Belgium, and in Argentina, so it’s been replicated in a number of places.DSW: One of the distinguishing features of the Cosmides/Tooby school of evolutionary psychology is massive modularity: that there are many special purpose adaptations to solve the many adaptive problems of life in the ancestral environment. This is a case of an adaptive problem. You want to help your kin but you don’t want to mate with them. Presumably all this cognition came to exist somehow and the supposition is you can’t learn this stuff, it doesn’t even happen repeatedly.DL: I would say you do learn this stuff. What counts as learning? You’re taking in very specific information from your social environment regarding parental investment in another child.DSW: Yes, but it’s a very highly structured form of learning, and one that is so context sensitive that it can be different for an older sibling compared to a younger sibling. All of that has to be scripted and the scripting takes place through a process of genetic evolution. So this becomes a poster example for the concept of modularity. One of the best examples I know, at least. Am I rendering it the right way?DL: Yes, I would say so. In my work, I like to put together information-processing models: I think, if I were natural selection, how might I have designed the system to achieve inbreeding avoidance or kin directed altruism? [In the case of sibling detection], you have cues from the environment that are input and our data tell us that they’re not just added together, they’re integrated and that’s suggestive of a [neuro] mechanism that’s doing the integrating and then calculating the degree of kinship.Is that integrator, that kinship cue integrator, is it specific for siblings? Is it a general mechanism that takes all kinship cues and then estimates relatedness? If so, what are the inputs into this kin detection estimator? Are they specifically sibling cues or is there a separate father detection system, mother detection system, and so forth? These are things we don’t know. Right now, I’ve actually stopped short and not said it’s sibling detection but rather it’s a kin detection mechanism until there’s further evidence that it needs to be split up. The Santa Barbara school of thought is computationally, functionally specific, and until there’s evidence that something can be split off, then it should be retained in a more general system (and by general, I mean functionally less narrow). That’s what we currently see in the kinship system and my work on disgust is the same: Is there a singular disgust? What might that look like computationally?DSW: That’s a good example because we both know from Paul Rozin’s work that disgust is something that has phylogenetic roots but has been culturally elaborated in humans so that we now feel disgust for all sorts of things. That’s a great example of the middle ground I’m searching for which has both these biological and cultural inputs. Your work gravitates toward this middle ground.DL: Robert Kurzban and Peter Descioli have two papers on the evolution of morality, on the mysteries of morality. They thought through how disgust has a flexible relationship with morality and how disgust can lead to such a rich array of norms.. My ideas about the relationship between disgust and morality really came from the two of them.DSW: Great. Let’s now talk about evolutionary psychology. As you know TVOL is doing a multi article theme on it. Talk to me now about evolutionary psychology’s reputation – is it deserved, undeserved?DL: I strive to understand the scientific gripes people have [with evolutionary psychology], not the personal ones, which have no place in science. I often find that people say John and Leda are wrong because they completely misinterpret or ignore what John and Leda say. Don Symons is fond of saying that you have to understand whom someone is arguing with to understand why they’re writing what they’re writing. John was arguing with cultural anthropologists and Leda was arguing with social psychologists. So their beef was largely with existing strands of academics that didn’t take evolution seriously or didn’t believe there could be structure to the mind. The Adapted Mind will be a book for the ages—love it or hate it! Some have argued that they went too far. I would say that to make a point you have to go to the wall. I personally don’t think they’ve gone too far in their discussion about the Standard Social Science Model (SSSM) of the mind.DSW: Describe that for our listeners.DL: It’s a view that the human mind is blank slate and has content independent mechanisms, which means that you can feed these mechanisms with any content and they will operate under any circumstance with equal functionality and produce equally effective behavior. That’s just not the case at all. Non-human animal studies show the insanity of the SSSM. People might be uncomfortable and squeamish with an evolutionary perspective, [thinking] that it might hold them to a certain moral disposition. But you can follow the principles of evolution, apply them to human behavior and still be a good person—still believe the best in humans. In the Adapted Mind, Leda and John say that if you’re concerned about genetic determinism, you should be no less concerned about environmental determinism. Another thing that bugs me is the claim that John and Leda ignore culture. Did these folks not read the subtitle of The Adapted Mind? It is “the generation of culture”. People forget that they were very interested in how we get human culture.DSW: Can you take a few more steps and describe how culture is generated.DL: Sure, but what do you mean by culture?DSW: I would rely on John and Leda’s distinction between evoked culture and transmitted culture. They associate transmitted culture with the SSSM as though people were open vessels and culture is poured into them from the previous generation. Whenever human populations do something different, this could be attributed to transmitted culture. Against that background they made an important point. Since we’re all phenotypically plastic, if you place us in different circumstances then we behave differently because our minds react to our environments. That’s evoked culture. Evolutionary psychology should embrace both of those. If you were to say, evolutionary psychology is about evoked culture and that transmitted culture is something else, I would not agree with that.DL: My own research speaks a lot to culture. If we in fact have representations of who counts as siblings, then it’s not surprising that we have linguistic terms that map onto these very specific representations. I’m told that the Chinese language even has different terms for older sibling versus younger sibling, which is fascinating. We delineate different relationships linguistically and so this enters into our culture, but just looking at the kinship terms without the psychology is just strange, since that wouldn’t give you a full-fledged understanding of kinship. If you started with the psychological adaptations and had an informed model that you can test and understand, you see that there’s a system in all humans that generates representations of different types of kin. And this structures our social interaction and cultures in various ways.One of the tools I gained at Santa Barbara is to get very specific when discussing kinship, and to ask, what domain are we in? What’s the system? Is this a novel human thing? Maybe there’s not a dedicated system for a particular behavior, or maybe it’s piggybacking on something, or maybe it’s a byproduct of something else. I try and ask all of these questions.I think evolutionary psychology provides the tools to develop and test the models and to understand the structure of the human mind. It provides predictions about the sort of models out there in the world of culture that you might see. Human culture is not random. There’s a lot of flexibility and variety to be sure, but we tend to observe only a limited set of what’s possible.DSW: That’s a great topic because kinship systems are famously diverse. To quickly cut to an example: the Nuer African tribe were in the process of replacing their neighboring tribe, the Dinka, when contacted by Europeans in the 19th century. Part of the reason is because the kinship system of the Nuer enabled cooperation between the villages. They added an extra tier to their kinship terminology so that you might have someone classified as a kin in some distant village. By virtue of having this kin [which was fictive as far as genetic relatedness is concerned], they combined forces in warfare. Because the Dinka had another kinship system that didn't extend so far, they couldn't form as large a fighting force. None of these kin were strictly speaking kin and if they were, their coefficient of genetic relatedness would be low. The Nuer even had a convention of ghost marriage where if the Nuer husband died they'd replace the household with a Dinka male who was captured in warfare. This makes no sense genetically but it kept the social organization intact. These are wonderful examples of kinship systems that go way beyond one based on genetic relatedness. This kind of cultural construction can interface with genetic adaptation and will result in some forms surviving and replicating better than other forms. There is an ongoing process of cultural evolution.Now I want to go in a slightly different direction, involving another toolkit for understanding these mechanisms. It would be nice to go bottom up through neuroscience. Who is doing that well? Is there anyone you can point to, or is that an area that needs more attention? And how about Leda and John? Are they doing it or encouraging it to be done?DL: It would be very nice to have the whole story for each psychological adaptation. To have a catalogue of human psychological adaptations and describe the genes that are required all the way through the regions of neural tissue that tend to embody certain functions. I’m interested in describing adaptations at an information-processing level. I’m not as interested in the specific genes or the location. I assume there are genes that associate with kinship systems and they organize neural tissue to do this somewhere. If had multiple lifetimes to completely do it I would explore this.DSW: I know Evolutionary Psychology was inspired by the work on the cognition of vision, which is massively modular, so on that level it has been the main event for neurobiologists for a long time. I want to end by taking about what EP has to say about sex differences. I know some feminists are critical of EP and that you have an interesting take on it.DL: What do I think of sex differences? That they exist! I'm impressed more and more about how they exist. Specialized types of sex differences constitute mating psychology. Having been out on the mating market recently, I found myself talking about relationships A LOT. When I would talk to some of my male friends about how to get a mate, I could swear they were speaking English, but it just didn’t compute. It has become even more clear that men and women see very different dimensions when it comes to finding a mate.On a related topic, in Binghamton I read Camille Paglia and she said something that rang true with me. She pointed out the importance of being responsible for your own actions, and part of that, in my mind is equipping yourself with knowledge and when it comes to sexual abuse and rape, this means knowledge about the other sex. In a perfect world, women could wear what they want, walk the streets naked if they so desired. But we don't live in that world. Men and women have different psychologies. Understanding psychology would help women understand and navigate the sexual world and also be more safe.DSW: That puts you in agreement Randy Thornhill and Craig Palmer who criticized feminism about practical things.DL: I wouldn’t want people to interpret what I say as justifying rape. I am not blaming the victim. The fault is with the person who does harm and forces himself on another person. The question is, could it have been prevented? I think it’s preventable if women have greater knowledge about male psychology. A new chapter for sex ed.Books referenced above:DeScioli, P. & Kurzban, R. (2009). Mysteries of morality. Cognition 112, 281-299.DeScioli, P., & Kurzban, R. (2013). A solution to the mysteries of morality. Psychological Bulletin, 139(2), 477-496.Lieberman, D., & Patrick, C. (2014). Are the behavioral immune system and pathogen disgust identical? Evolutionary Behavioral Sciences, 8, 244-250.Tybur, J., Lieberman, D., Kurzban, R., & DeScioli, P. (2013). Disgust: Evolved function and structure. Psychological Review, 120, 65-84.Lieberman, D. & Lobel, T. (2012). Kinship on the Kibbutz: Coresidence duration predicts altruism, personal sexual aversions, and moral attitudes among communally reared peers. Evolution and Human Behavior, 33, 26-34.Tybur, J., Lieberman, D., & Griskevicius, V. (2009). Microbes, mating, and morality: Individual differences in three functional domains of disgust. Journal of Personality and Social Psychology, 97, 103-122.Lieberman, D. (2009). Rethinking the Taiwanese minor marriage data: Evidence the mind uses multiple kinship cues to regulate inbreeding avoidance. Evolution and Human Behavior, 30, 153-160.Lieberman, D., Tooby, J., & Cosmides, L. (2007). The architecture of human kin detection. Nature, 445 (7129), 727-731.