More on evolutionary psychology and morality

I have been reading work by the evolutionary psychologists Peter Descioli and Robert Kurzban. Kurzban gave a great talk I saw last week at a conference proposing that the reason people have Kantian rule-based systems of morals is because morality serves as a way for bystanders to collectively coordinate which side to join in a conflict. As an illustration, imagine that you and I live in a communal house with ten people. Our housemates Adam and Bob get in a dispute. Adam is hungry, so he takes and eats Bob’s lunch. A fight breaks out. Because we tend to look to form alliances when in disputes, both Adam and Bob look to the other 8 members of the household for support. This dispute can potentially threaten us all. It could lead to a larger conflict or a war among all ten of us. Kurzban argues that morality evolves as a way for all 8 bystanders to pick the same side. The best way to do this is to use some clear rule that everyone can see. It can’t be a rule that is based on the participant’s identity or their relationship with bystanders. It must be something everyone can see objectively. Did Adam steal? Then Adam is wrong. Because stealing is wrong. This places the entire group on the side of Adam and the dispute is settled quickly and efficiently. People who fail to conform to this moral rule will be on the wrong side of the argument with less support, so it behooves everyone to be on the majority side.

This kind of “collective decision-making” is common in nature. For instance, it’s the way bees in a colony and brains make decisions. In social evolution, you can model the effects of these kinds of coordinated actions by considering how individual decisions feedback on individual inclusive fitness, or by partitioning the effects into individual and group fitness (multi-level selection). This sheds light on topics such as the evolution of society and multicellularity. The basic point here is that sometimes interests are aligned and it benefits everyone to do the same thing.

The more I think of it, the more I feel like a lot of what we know about how humans condemn others is consistent with this model of morality. It also explains some oddities in moral reasoning.

In another study, Kurzban posed the old classic Trolley moral dilemma to a sample of people. You probably know this already:



Version 1: There’s a trolley out of control. It’s going to kill 5 people. If you throw a switch it will change tracks and only kill one person. Do you throw the switch? Most people say yes.

Version 2: There’s a trolley out of control. It’s going to kill 5 people. But you can push a large fat man in front of it to stop it (your own body is too small). It will kill him but save 5. Do you push the person? Most people say no.

There’s a lot people have said about this finding. One basic point is that most people are Kantian in their moral reasoning. They follow moral rules like “Do not kill others” which is why the decision flips based on the action (flipping switch/pushing person) rather than the outcome. To a utilitarian, all moral actions should be based on outcome only.

Some people even find the utilitarian moral decision (killing 1 to save 5) offensive. It can seem cold and calculating rather than "human-hearted".

Some people even find utilitarian moral reasoning offensive. “Killing one to save the many” can seem cold and calculating rather than “human-hearted” approach of  following moral norms  like the Golden Rule or “Never kill anyone”

Kurzban gave both versions a novel twist. He posed the same problem but in one version he said the 5 saved and 1 person killed were all siblings. In another version he said they were friends and in another they were strangers. So what effect did this have?

People were significantly more willing to sacrifice 1 friend to save 5 other friends or to sacrifice 1 sibling to save 5 siblings. They were much less willing to sacrifice a stranger.

When people are dealing with kin and friends, they think more about welfare maximization (How many lives can I save?). But when dealing with strangers they worry more about following moral rules (Do not kill people.) This makes sense, if we think that the driving force for moral decisions dealing with strangers has more to do with how other people might judge us. By contrast, decisions to help or harm friends and relatives are treated differently in our brains. There is a different kind of moral calculation that goes on. Specifically, we have adaptations for true biological altruism with relatives (just like a mother would give up her life to save her children). And because of the importance of reciprocal cooperation to human social life, we also care directly about the welfare of friends, because they are valuable to us and their wellbeing feeds back on ours . With strangers, our moral calculation has more to with what decision is most consistent the moral rules, i.e. what is socially acceptable. It is not socially acceptable to kill a person by pushing them in front of a trolley.

In Kurzban’s view, the trolley problem pits altruism systems (maximize welfare) against moral systems (Kantian rule-based ethics). Surprisingly, he found that almost half of subjects
reported that they would not kill 1 stranger to save 5 siblings. This shows that moral systems might be able to over-ride evolved altruistic tendencies, which is a hallmark human pecularity. I would bet however that in an actual real situation most people would kill 1 stranger to save their close family. They just don’t think they would when answering a survey.

The main point here is that Kurzban’s ideas are not a mere just-so story. They lead to a novel unique prediction: that people will be more likely to switch from utilitarian to Kantian moral reasoning when switching from kin/friends to strangers. It’s hard to explain this using past explanations of moral behavior.

A lot of people I know don’t like evolutionary psychology. Many folks associate evolutionary psychology with bad scientific justifications for conservative political worldviews or simplistic posthoc just-so story explanations for gender stereotypes: “girls like pink because ancestral females used to gather fruits and flowers, and boys like math because men were hunters had to count mastodons”. This is an unfair characterization to be sure. I’ve heard evolutionary biologists sometimes say that evolutionary psychologists get evolution wrong. And I’ve heard clinical psychologists say that evolutionary psychology researchers doesn’t have a real purpose: how does this work help anyone?

In my view, the basic theoretical approach taken by evolutionary psychology is exactly how we study animal behavior (that is adaptationism– testing the extent to which biological traits have a functional design). This has been one of the most successful paradigms in biology. People study function of a trait and this helps us to understand when it evolved, how it develops during the lifetime, and how it works.

It’s often harder to study the evolution of human social behavior because it’s so easy to bring our own intuitive baggage to bear on the problem, including our own introspections and political world views. It’s also easy to slip between talking about the design on behavior (e.g. “evolutionary altruism”) and the actual thoughts and behaviors that people have (e.g., “psychological altruism). This happens often when we talk about things like “strategies”. It’s clear what we mean when we say that root allocation in a plant is a strategy for competing less with kin. But this becomes a bit more ambiguous when we talk about a strategy in a human or vampire bat. People mistakenly think you mean conscious planning.

Basically, “anthropomorphism” is possible even for humans. We falsely believe that other humans think the way that we think we think (which is often wrong).

Ultimately, psychology has to be based firmly in biology (and that means evolution), just like biology has to be based in chemistry and physics. Of course physics doesn’t explain everything about how cells divide, what causes species to go extinct, or why mammals but not reptiles have milk. But everything in biology can be understood as going back to physical and mathematical laws. The greatest leaps forward in biology occurred when abstract concepts (such as disease, genes, mind)  were routed in real physical things made of atoms and molecules (viruses, DNA, and neural circuits).

So to with psychology as it develops into a mature science with links to neuroscience and evolutionary theory. Many of evolutionary psychology’s controversial ideas are completely accepted in animal behavior—  that minds are composed of modular functional adaptive specializations, that learning is not a general associative process but based upon instinctual rules about what to learn and when,  and that all the complex traits of human nature at some point increased inclusive fitness in the environments in which they evolved. These ideas will soon be completely uncontroversial among all disciplines within my lifetime (I hope).

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Live Vampire Bat webcam at Organization for Bat Conservation website

Image Click on image to view

Live at Organization for Bat Conservation

Live at Dropcam

Past clips

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Conference on Evolution of Morality: why do people condemn others?

Last month, I moved my vampire bats to the Organization for Bat Conservation in Bloomfield Hills, Michigan. I’m now working on a group of more than 30 bats.

I recently attended a small conference on The Evolution of Morality at Oakland University.

My favorite talk was by Robert Kurzban on the evolution of third-party punishment (in humans). Kurzban started his talk with the crucial point that morality and altruism are not the same thing. Altruism is about mostly helping other people. Morality is largely about judging people’s actions. There is an obvious adaptive reason to judge our own actions (mostly because other people will also judge our actions and reward and punish us accordingly). But here’s the real mystery: why do we morally condemn other people’s actions? Even people who have no effect on us? And why do we do evolutionarily-nonsensical things like condemn the actions of our friends and family, even when those actions do not hurt us? Imagine a scenario between a bully and a victim. The aspects of human nature that can drive bullying make evolutionary sense. The aspects of human nature underlying the actions of the victim typically make evolutionary sense too. But now consider a third-party observer that is unaffected by the dispute. Most third-party observers don’t involve themselves in a typical dispute (for better or worse), but interestingly, almost everyone passes judgment. That is, almost everyone mentally chooses a side. Why do people always perform moral condemnation (even though most people will never take a moral action)?

How do you feel about this picture? We condemn other people in a dispute, even when we do not plan to take any action ourselves, and even when the dispute will not affect our own lives in any way (and even when the characters are fictional).


There are many ideas about this, but most of them don’t predict the weird ways people make moral decisions to condemn or not condemn others. And they don’t answer why we should even take the time to pass judgment at all. Kurzban makes a very compelling argument that the adaptive function of moral condemnation is for each third party bystander to choose the larger side in a dispute. All bystanders want a consensus to be reached on who is right in a dispute so that there won’t be a long drawn out conflict. And they also want to be allied with the larger, winning side. But how do we know which will be the largest side? Well, let’s examine some choices of strategy.

One strategy would be to always side with your friends and family. Here the problem is that many other people will be against you. If your friend murders someone and you take his side, now you have to defend yourself against the victim’s family and friends. The result is a lot of fighting. Not good. Another option: you could always side with the most powerful people. The disadvantage here is that it will quickly lead to a situation where certain people will dominate and repress everyone, including you. Not the best outcome long-term. Kurzban argues that people have evolved to conform to an implicit set of rules within each group for coordinating whose side to take. Conforming to these rules itself requires cooperation, but it’s easy to see how it would benefit everyone to have this set of rules. Crucially, the rule has to depend on people’s actions, not their identities. For instance, the rule might be something like: “If person A tries to kill person B for personal gain, then person A is wrong and take the side of person B” or “If person A steals from person B, then take the side of person B”, and so on.

Obviously, the actual moral rules we follow are more complicated and also not always so explicit or conscious. We often don’t know what they are, except through gut feeling. We can’t articulate why certain things just “feel wrong.” Compare moral rules with language. In language acquisition, we each adopt words and rules from a local language, but we all have an instinct to learn a language. A spot in our mind that says “language goes here”. Likewise, humans have an instinct to adopt a local set of moral norms and to want other people to agree with them. Those moral rules might differ a bit place to place, but they will serve the same functions and so have many similarities. That is how you get the evolution of morality. And this view explains why people make moral judgements in some very strange ways, based on rules rather than always on actual welfare. Now to be honest, I don’t know how much of what I just wrote is Kurzban’s ideas versus my ideas, extrapolating from what Kurzban and others have said. But I think it’s a very interesting view and I will be interested to read more of his papers.

I also enjoyed talks by Sarah Brosnan (moral emotions in primates) and David Buss (human sexuality), and I thought Randy Thornhill’s talk on his theory that pathogens have largely shaped human social behavior was really interesting. I enjoyed talking to Peggy Mason about her prosocial rats, Brock Brothers, Chinmay Aradhye, Mark McCoy about what personality traits predict religiousity, and why the incentive structure in academia are often bad for science. I also had interesting discussions with Michael Pham and Sylis Nicolas (who also study human sexuality) about all kinds of things I won’t discuss here, Alexis Garland (about counting in animals), and about all kinds of stuff with Bailey House who has studied the development of reciprocity in children. I had some other discussions with many other people that I can’t recall right now. It was a fun conference.

The most memorable talk was by a philosopher named David Benatar who made the most cringing (but intellectually brave) philosophical argument I’ve ever heard in my life. I don’t have time to go into it here, but you can read about it in this review which summarizes the argument (and by coincidence, my response to it was fairly close to what the reviewer said).

I was particularly impressed by the way that Todd Shackleford and Jennifer Vonk were very supportive of their graduate students. Young faculty tend to promote their graduate students a lot, and this is always heart-warming to see.

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Some recent studies on cooperation

Brood Parasitism and the Evolution of Cooperative Breeding in Birds (Science)
Brood parasites (like cuckoos) do best when they lay eggs in the nests of cooperative breeders. But cooperative breeders are better at rejecting brood parasites, because having more eyes and ears at the nest also helps keep out brood parasites.

The result of brood parasitism. A reed warbler feeding her "baby" that's actually a cuckoo.

The result of brood parasitism: a reed warbler feeding her “baby” – which is actually a big fat cuckoo.  Talk about a strong maternal instinct. This is also what it looks like when I visit my mom for the holidays. Image from wikimedia.

Evolutionary routes to non-kin cooperative breeding in birds (Proceedings B)
Direct fitness benefits are important in cooperatively breeding birds. Out of 213 cooperatively breeding species, 30% of species form nest with non-kin and another 15% nest primarily with non-kin. Cooperative breeders that require helpers are more likely to have non-kin helpers, than species where cooperative breeding is optional.

Female rhesus macaques discriminate unfamiliar paternal sisters in playback experiments: support for acoustic phenotype matching (Proceedings B)
Most kin discrimination in primates is thought to occur by individuals simply learning who are their maternal kin. Female macaques responded more to calls from their paternal half-sisters than non-kin, regardless of familiarity. This suggests that primates might be able to identify relatives they have never met by the sound of their voice.

Reciprocity and conditional cooperation between great tit parents (Behavioral Ecology)
Parental care requires cooperation between parents; each parent would rather have the other do more work. One way to resolve this conflict is through reciprocity. This experiment showed that songbird parents increased and decreased their feeding rate based on their mate’s feeding rate, independent of offspring begging.

So those these birds seem to “negotiate” over cooperative investments. What about wasps?

Do paper wasps negotiate over helping effort? (Behavioral Ecology)
No, it doesn’t seem that they do.

Just finished preliminary trials on the effects of oxytocin on grooming and food sharing in vampire bats. But I’m hoping to replicate my results in a second study group before I publish anything.


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Video on white-nose syndrome

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More on vampire bat control and rabies

Previously, Daniel Streicker and colleagues argued that vampire bat control methods (targeted poisoning) might actually increase rabies rates in vampire bats. I wrote about that here. The team has since published a new model to examine hypotheses regarding why culling vampire bats does not reduce, and worse may even increase, rabies rates in vampire bats. Here’s the article and a press release.


This image is unrelated to the post, but I thought it needed a picture of a vampire bat.

Surprisingly, most of the vampire bats that are exposed to rabies develop resistance. This doesn’t mean that they are lifelong carriers, but rather that they have fought the infection and have been, in effect, immunized. Previous lab studies have found that most of the bats (50 to 90%) exposed to the rabies virus in a lab setting will die, but the authors estimate that only 10% of wild bats bitten by rabid conspecific actually develop a lethal infection. From an evolutionary standpoint, this outcome probably helps the virus from going extinct by wiping out a whole bat colony before the virus can be transmitted. From the virus point of view, it has to get into from one bat to another bats it kills the host, and it has to get from one colony to another. Therefore, the maintenance of the rabies virus over time at high levels relies heavily on dispersal of bats between roosting sites. This is key to why killing as many vampire bats as possible at a site doesn’t effectively get rid of rabies.

But why might culling vampire bats actually lead to higher rates of rabies? One explanation was that the poisoning (which is spread by social grooming) disproportionately targeted adults more often than young, and the adults had developed more resistance than younger bats. I became dubious about whether this made any sense. The authors explicitly based this explanation on the assumption that juveniles are less likely to groom adults, and thus less likely to expose themselves to poison-treated adults. However, in contrast to this claim, juveniles and subadults lick the fur of adults more than adults lick each other. In a roost, young vampire bats should therefore be exposed to vampiricide more, not less, which removes a key assumption for this “selective adult culling hypothesis”. I suggested that either a different mechanism explains the negative relationship between culling and rabies, or that this correlation was spurious.

But there’s another explanation that makes more sense to me. Male bats guard roosts like territories to get access to females. If culling removes these male bats, than males from other areas are more likely to move in. Likewise, killing a group of females could open up a roost for new residents. In other words, culling could increase dispersal, which could increase rabies transmissions.

Culling could also increase dispersal if bats are more likely to leave an area after many of their conspecifics have died. Either scenario seems plausible to me.

Overall, the study highlights the complexity of host-pathogen dynamics and makes the important suggestion that killing vampire bats– even using targeted methods such as poison spread by social grooming– is probably not a good way of fighting rabies in Latin America. This reveals why the task of rabies control is so daunting. It’s also good news for me, because having seen these vampire bat control methods, I am not a fan. I would very happy to see them retired.

But I don’t see vampire bat control disappearing completely anytime soon. Even without rabies, vampires would still be considered an agricultural pest. Farmers and ranchers in Latin America still see 20-30 bites on a single cow. They are like wolves and coyotes to a sheep rancher or deer and groundhogs to a vegetable farmer. Except they can fly right over your fences.

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Talks on analysis of animal vocal sequences

Videos of talks from the NIMBioS Analyzing Animal Vocal Sequences Workshop that I attended are being posted here.

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