Evolutionary Psychology

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Robert Kurzban

The Evolutionary Psychology Blog

By Robert Kurzban

Robert Kurzban is an Associate Professor at the University of Pennsylvania and author of Why Everyone (Else) Is A Hypocrite. Follow him on Twitter: @rkurzban

Cultural and biological evolutionary perspectives on disgust – oil and water or peas and carrots?

Published 27 June, 2013
Guest blogger, Josh Tybur

Guest blogger, Josh Tybur

Today’s post is by my friend and collaboroator, Josh Tybur. His biography appears at the end of the post. – Rob Kurzban

Disgust is, at present, a hot topic in psychology. It is also a topic that has become thoroughly “evolutionized.” That is, with a few exceptions, most researchers, whether they label themselves evolutionary psychologists or not, agree that disgust toward things like maggot infested carcasses and juicy piles of vomit has a specific function that has been shaped via natural selection: to motivate the avoidance of the pathogens potentially contained within the disgust-eliciting object.

People are not only disgusted by corpses and vomit, though. They self-report disgust and make disgust faces when they think about having sex with a close relative, when they watch sexually explicit videos, when they hear about others having sex with a close relative, when they hear about people stealing from old ladies, and when they hear about others swindling people out of money. A job for disgust researchers, then, has been to develop and test theories that can explain why and how so many things seem to elicit disgust.

In a recent paper, some colleagues and I argued that, although researchers generally agree that a comprehensive understanding of disgust must use an evolutionary perspective, two of the core contributions of mainstream evolutionary psychology have not been all that well integrated into disgust research and theory.

First, we suggested that some well-cited hypotheses of non-pathogen-avoidance evolved functions of disgust (e.g., to neutralize reminders that humans are animals, and the purported existential terror that accompanies such reminders) seem unlikely given the posited adaptive problems that would have shaped the evolution of disgust. We also discussed alternative selection pressures that may have shaped the evolution of disgust.

Second, we suggested that researchers have typically not adopted one of the key insights offered by evolutionary psychology: that of how modular, functionally specific information processing mechanisms should be structured for psychological adaptations to be executed. We argued that increased attention to both of these issues can be useful for generating testable hypotheses regarding both the form and the function of disgust (see Cosmides and Tooby’s primer on evolutionary psychology for a review of these principles, and a nice example about dung beetles and disgust).

Paul Rozin and Jon Haidt (hereafter RH), who have had tremendous impact on disgust research, recently wrote a commentary on our proposal  in Trends in Cognitive Sciences. In their piece, RH suggested that our approach can be useful, but that it is limited “because [it] ignores the powerful role of cultural evolution.”  RH concluded their commentary by stating, “Cultural and biological evolution…should not be seen as providing mutually exclusive views. We urge an integration.”

Now, I find cultural evolution pretty cool, and my co-authors and I took some efforts into crediting its importance in our proposal. Indeed, a quick search of our paper revealed 19 instances of words containing “cultur*” (excluding references and headings), including some explicit references to the importance of cultural evolution:

Other aspects of cross-cultural variability in disgust could arise via cultural evolutionary processes

individuals must acquire culturally evolved information…they need to acquire information from their social group to deploy disgust in a fitness promoting fashion

if rules evolve culturally (Richerson & Boyd, 2005), expressions of moral disgust could be targeted toward violations of culturally specific rules

We never wrote – and I hope that we didn’t imply – that cultural and biological evolution are mutually exclusive perspectives, or that cultural evolution should be ignored when investigating disgust. Still, RH pose an interesting question: how can a consideration of cultural evolution help us understand disgust? I’ll briefly mention two ideas, both of which concern pathogen disgust and food.

First, how might cultural evolution influence which cues are taken as input into the pathogen disgust system? Readers who have traveled internationally (especially to non-WEIRD countries, if you happen to be WEIRD yourself) – or anyone who has seen Bizarre Foods with Andrew Zimmern – know that many of the foods happily eaten in other cultures can seem pretty disgusting to people from other cultures. Why might cultural variability in the types of food that elicit disgust exist?

We suggested that putting things in the mouth increases the probability of pathogen acquisition compared to not putting things in the mouth, and swallowing things increases this risk further. The best pathogen avoidance strategy, then, is to never put anything in the mouth. This type of strategy, while good for mitigating the fitness costs imposed by infectious disease, is poor for getting calories and nutrients. But how do you know which things you should put in your mouth and ingest? Generally, this question underlies the omnivore’s dilemma, a term coined by Paul Rozin (and adopted as the title of a great book by Michael Pollan).

It’s probably a good idea to watch what other people are eating when you’re young, and to further engage in a little trial by error to see if some things that seem similar to “acceptable” foods (e.g., novel berries) have a nice taste, which presumably informs the probability that they contain calories (good) or toxins (bad). Hence, the information processing structures that underlie learning what foods one should eat, and what foods should elicit disgust, should have evolved to take both individual experience and socially (i.e., culturally) transmitted information as input.

The types of foods that someone sees other people eating – and the rituals that go into acquiring and preparing those foods – are presumably shaped by cultural evolution. If certain rituals are more successfully transmitted in a particular ecology than other rituals, then the types of potentially edible plants and animals that are viewed as “disgusting” versus “delicious” can vary quite a bit across culture.

Second, how might cultural evolution have contributed to the evolution of the information processing structures underlying pathogen disgust – that is, the universal psychological architecture of interest to evolutionary psychologists?

Dan Fessler and Carlos Navarrete have summarized the literature suggesting that aversions to meats are easier to condition than aversions to non-meats, that food taboos involving meat outnumber food taboos involving non-meats cross-culturally, and that people only eat a small proportion of the total meats available in the local ecology. Presumably, the cultural evolution of tool use and hunting techniques resulted in humans consuming more meat. Greater consumption of meat in turn led to new vulnerabilities to pathogens. This in turn constituted a selection pressure that might have then shaped the information processing structures underlying pathogen disgust to process “meat” stimuli in a functionally specialized manner.

I’ll close by posing a few “food for thought” questions:

In what other ways might cultural evolution have shaped the information processing structures underlying disgust?

Why might some things elicit disgust more consistently across cultures than others?

And – as a bonus for those who are familiar with the animal reminder theory of disgust advocated by RH, but not favored by others of us – what information processing structures might underlie animal reminder disgust?

References

Fessler, D. M. T., & Navarrete, C. D. (2003). Meat is good to taboo: Dietary proscriptions as a product of the interaction of psychological mechanisms and social processes. Journal of Cognition and Culture, 3, 1–40.

Rozin, P., & Haidt, J. (in press). The domains of disgust and their origins: contrasting biological and cultural evolutionary accounts. Trends in Cognitive Sciences.

Tybur, J.M., Lieberman, D., Kurzban, R. & DeScioli, P. (2013). Disgust: Evolved function and structure. Psychological Review, 120, 65-84.

Josh Tybur is an Assistant Professor in the Department of Social and Organizational Psychology at VU University in Amsterdam. He received his PhD in evolutionary psychology from the University of New Mexico in 2009. His research is currently focused on understanding some of the puzzles posed by disgust, and how the solutions to these puzzles can inform our understanding of food preferences and aversions, mating psychology, and moral judgment.

  • http://jaymans.wordpress.com/ JayMan

    I’d posit that plain old evolution (in the form of gene-culture co-evolution) is partly involved in group-wide differences in disgust response. For example, it is known that the same foods taste different to different peoples. This exemplifies some of the things involved in the regional variation in disgust, especially with regard to meat.

  • Vesna

    non weird countries??.. beside, we know each other personal I will ask very open:Do you really consider that fact that you used word weird in semi scientific text is ok? Due fact that in the reading of geography, anthropology, psychology I did not find such term, a and due fact that I am also psychologist I can say just single word… ” modernity” catch all..best regards

    • Josh

      WEIRD (coined by Joe Henrich and colleagues) stands for Western, Educated, Industrialized, Rich, and Democratic, though I did not note this above (perhaps I should have). See this paper:

      Henrich, J., Heine, S. J., & Norenzayan, A. (2010). The weirdest people in the world. Behavioral and Brain Sciences, 33(2-3), 61-83.

  • Lee_Kirkpatrick

    Nice post, Josh. I’ve got lots of thoughts, some of which I might I post on another occasion, but for now I’ll focus on just one particular issue that I’d like to hear your thoughts on. I haven’t been keeping up with this literature recently, so maybe there’s stuff out there that I haven’t seen yet — if so, please point me to it — but it has long seemed to me that one very important perspective that has been missing from the evolution-and-disgust literature is a developmental one. What do we know about the developmental trajectory of the disgust system? For example, it seems potentially relevant that babies will react with disgust to certain kinds of tastes/smells/textures as soon as parents start offering them solid foods, suggesting that some aspects of the disgust system are “hard-wired” or “built-in” rather than “learned” or “acquired.” (Note that I’m using this loose terminology only to differentiate two different ways in which the system might be designed to identify disgust-eliciting stimuli, not to perpetuate a false dichotomy between biological and cultural evolution, etc.) Second, however, it seems that as soon as a baby is physically capable of putting things in its own mouth, it will (much to the chagrin of parents) indiscriminately put pretty much anything within reach in there. I presume there must be a fairly extensive developmental literature on such things, but I’ve not seen much attention paid to it in the evolutionary literature on disgust. It seems to me that a developmental perspective would be invaluable in addressing questions about the design of the disgust system, and questions about whether differences and similarities across cultures are the result of “evoked” versus “transmitted” culture.

    • Josh

      Thanks, Lee. Regarding development – there seem to be a few different reasons why selection might have led to what seem like “delays” to us now in the development of pathogen disgust. There’s the weaning hypothesis – that is, that typically, babies are being held by mothers and mostly drinking breast milk for the first few years of life. There’s a related protection hypothesis – that mothers are going to be watching infants for the most part and can stop them from contacting anything really bad. Contacting other things might aid in some immune training. But, yes, I agree that some interesting work could examine development, especially work investigating differences in developmental trajectories across disgust “domains” (that is, differences in development of pathogen and sexual disgust, for example).

      • Michael Palmquist

        I have an anecdote that may be relevant to this topic, and the correlation may be false, but there is some evidence that prenatal something-something levels determine both how interested in breastfeeding both the mother and child are. Both my son and I basically refused breast-feeding and became very picky eaters. I observed this actually very closely in my son and we never had to keep him from putting anything in his mouth. Interestingly, I have low disgust in almost every other major topic that people find “disgusting” on average. Food is my hang-up.

        As for what culture IS, I think the best theoretical paper on the topic to date is Kathryn Coe’s “Ancestor-descendant conflict”. It’s exactly what I was looking for: the end of memetic and group explanations.

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