Saturday, 8 December 2012

Debunking Evolutionary Psychology

I wanted to discuss this topic because recently there have been a few disgruntled comments made about Rebecca Watson's talk at the "Skepticon" conference called: "How Girls Evolved to Shop" where she brings up a number of dodgy claims made by researchers in the field as well as how they're presented in the media. The main focus of her discussion, from my point of view at least, was on how we should be skeptical of the main assumptions of evolutionary psychology, how we should question how science is presented in the media, and also a good discussion on the effect that sexist and misogynistic attitudes have on the direction of some research in the field. Some of the criticisms against Watson are just plain silly, like the idea that since she is not an evolutionary psychologist then she should just remain quiet on the topic (or, "Shut Up and Sing", as P.Z. Myers puts it), but some arguably carry a little more substance.

An argument which is potentially more troubling is one presented by Ed Clint here which suggests that Watson's talk was an attack on the entire field of evolutionary psychology, and is thus an example of science denialism. This characterisation of her position seems unfair to me given that it seemed that she was attacking the bad science, not the entire field, but I thought it might be a good idea to discuss why the field of evolutionary psychology is often dismissed and what distinguishes the good science from the bad.
The latest deadweight dragging us (evolutionary biology) closer to phrenology is evolutionary psychology, or the science formerly known as sociobiology. If evolutionary biology is a soft science, then evolutionary psychology is its flabby underbelly. - Jerry Coyne1.
Given the somewhat controversial title of this essay, it is perhaps necessary for me to preface it with a few disclaimers. Firstly, I am not a creationist and, for all intents and purposes, evolution is TrueTM. Secondly, whenever somebody voices their skepticism over the veracity of evolutionary psychology, they are often met with the retort, “Do you not believe that the brain is a product of evolution?” with the implication that since behaviors are the product of the brain, and the brain is a product of evolution, then behaviors are the product of evolution. This logic, however, is flawed for reasons I will discuss later but I do accept that the brain is an evolved organ with implications for resulting behaviors. And thirdly, this is not a broad scale attack on evolutionary psychology – instead, my focus is on the particular approach to evolutionary psychology known as the “Santa Barbara church of psychology”2.

To distinguish between the two approaches, I will follow the nomenclature used by Gray, Heaney and Fairhall3 where they refer to this approach as Evolutionary Psychology (EP). This approach (used by popular authors like Steven Pinker in his “How the Mind Works”) attempts to explain a wide range of human behaviors, like whether we have an evolutionary preference for green lawns, with an emphasis on the concept of a modular mind, and utilises a cartoonish view of the Pleistocene – with all considered, we have to wonder whether it should be rebranded as the “Hanna-Barbera church of psychology”.


The standard tool in this area is the explanatory strategy called “reverse engineering”4. While ‘normal’ engineering attempts to design solutions to problems, Evolutionary Psychologists argue that current features of the human mind can be explained as solutions to problems presented in our Environment of Evolutionary Adaptedness5. For this to be a valid explanatory strategy, Gray et al. argue that three criteria must be met:
  1. all traits are adaptations
  2. the traits to be given an adaptive explanation can be easily characterized
  3. plausible adaptive explanations are difficult to come by.
As we would expect, these assumptions are frequently violated. Given what we now know about evolutionary processes, the first is perhaps the easiest to refute as it is obvious that not all traits come about as a result of natural selection. Ignoring the more complicated issues of genetic drift, pleiotropy, and epistasis, a perfect example of why we should be skeptical of this claim is Gould and Lewontin’s6 concept of the spandrel which, in simple terms, is a byproduct of the selection of another trait. In this sense, asking for the adaptive explanation for some behaviors is akin to asking what the selection pressure was that caused blood to be red.

Gray et al. discuss the latter two issues in more detail but essentially the second claim is problematic given the lack of discrete boundaries for certain traits and they use Lewontin’s7 example of the “chin” to demonstrate this. They also extensively dissect the third criterion but a successful rebuttal of this is perhaps exemplified by Rosen’s8 suggestion that the only two constraints on adaptive explanations are the inventiveness of the author and the gullibility of the audience. It is important to note that I am not suggesting that we should abandon attempts to describe behaviors using adaptive explanations, nor am I saying that all behaviors are spandrels or the result of obscure evolutionary processes, but rather I am highlighting the fact that a plausible story is not evidence in itself. This position is described by Williams9 thusly:
The ground rule - or perhaps doctrine would be a better term - is that adaptation is a special and onerous concept that should be used only where it is really necessary.
As is clear to most evolutionary biologists, and other interested skeptical parties who are less than enamoured by the efforts of Evolutionary Psychologists, the approach described by Williams above is rarely followed and instead these scientists appear to fire off adaptive explanations with reckless abandon, with their work often consisting of nothing more than folk wisdom and a post hoc just-so story explanation. To attempt to circumvent this, Gray et al. propose two “common sense” tests: The Grandparent Test, and the Lesser-Spotted Brown Gerbil Test. The first asks us to consider, “Does this work give us any insight into human behavior and cognition beyond popular knowledge?” and the latter asks, “Would this research be publishable in major international journals if the species was a small noncharismatic mammal rather than our own?”. Although these ‘tests’ are only guides and should not be used as definitive tools for ruling out instances of research, it is interesting to note that most examples of EP found in journals fail these basic tests. However, picking examples of this kind to discuss here would be like shooting fish in a barrel, so instead I will look at research behind the evolutionary explanations for cheater detection.


Cosmides10 proposed the “social exchange algorithm” which argues that for cooperation to be maintained in a society, we must be able to detect cheaters – with this consistent selection pressure present, humans must have evolved a cognitive mechanism to do this. This idea began with the research using the Wason Card Selection Task which utilises a generalised if P, then Q rule.

The task is straightforward: Given the cards presented in the image above, which cards should you turn over to test the claim that 'if a card shows an even number on one face, then its reverse side will be red'? The correct solution is that you should turn over the

Despite the apparent simplicity of this task, Wason11 found that only 10% of his subjects answered this correctly. However, the interesting twist on this logical conundrum is that when the context of the problem is framed in a way that is socially relevant, people tend to perform far better. That is, accuracy increases if we change the proposition to: “if you are drinking alcohol then you must be over 18”, and we changed the cards above so that they read “17”, “Beer”, “22” and “Coke”, where the correct cards to turn over are “17” and “beer”12. This means that when we replace the abstract logical notions with a real world example of the same relationship, but with the inclusion of a possible "cheater" (i.e. 17 year olds drinking beer) then we can successfully solve the task by hunting out the cheater. From this, Cosmides predicts that cheater detection is an evolved trait that should only be evoked in social exchange situations, where there is a requirement, benefit and cheater (in accordance with the assumptions of game theory). So here we have a theory that provides novel insight into human cognition and surpasses our folk wisdom, and clearly passes the Grandparent and Lesser-Spotted Brown Gerbil tests. Can we then be confident in our knowledge that this is an evolutionary adaptation? Unfortunately, not yet.

The alternative explanation suggested by Sperber, Cara and Girotto13 is that specific properties of the cheater detection scenario employ a more general “exception-testing” rule – this would account for the results in the cheater detection scenarios but it would not support an evolved mechanism that was responsible for cheater detection. If these “properties” could be identified and removed from the cheater detection task, and this resulted in the effect disappearing, then the empirical support for Cosmides’ theory would also disappear. To test this they developed a three-part recipe to ensure correct card selection:

  1. the P-and-not-Q case is easier to mentally represent than the P-and-Q case (underage drinkers versus legal-age drinkers);
  2. the P-and-not-Q case should be of more importance than P-and-Q case (breakers of the law versus followers of the law)
  3. the rule should be clear and unidirectional (there is no implication that legal-age drinkers should be drinking beer).
When looking at Cosmides’ culture-specific form of the test (where the rule was “If a man eats cassava root, then he must have a tattoo on his face” and the options “Eats cassava root”, “No tattoo”, “Eats molo nuts”, and “Tattoo” were presented - with the "cheater" being the non-tattooed man eating cassava root), Liberman and Klar14 noted some inconsistencies between the cheater and non-cheater scenarios. Firstly, in the noncheating scenario there is no specific violating rule (e.g. a man with no tattoo eating a cassava root), secondly, the rule for cheating is strict and exclusive, whereas the non-cheating scenario has reduced importance through the use of qualifiers such as “usually” and “primarily”, and thirdly the non-cheating rule is more easily interpreted as being bidirectional.

To eliminate these confounds, Liberman and Klar reversed the conditions whilst maintaining the basic cheater detection structure and found that detection of non-cheating was at 70%, whereas cheater detection was at 30% - a perfect reversal of the results found in typical cheater detection scenarios. In other words, even though there were still cheaters in the design (non-tattooed men eating cassava root), by removing the biases from the setup so that "cheater detection" was no longer the less difficult task, subjects were less likely to search for them. With the effect completely disappearing under these conditions, it becomes clear that the effect is not a result of social relevance like Cosmides suggested, but is instead simply an effect produced by experimental confounds. In other words, cheater detection is a result of the “saliency” of the cheater in these experiments, and it is this saliency that gives people the correct result, and not the presence of a “cheater”.


This failure to properly adjust variables in an experiment (thus reliably establishing causality) seems to be regular feature of Evolutionary Psychology research, even when they meet the common sense tests suggested above, so why do these factoids spread so quickly and become cemented in popular thought? Do we have an evolved ability to be gullible of EP claims? Most people would reject such an idea, so what is it that separates these “ridiculous” claims from the ridiculous claims made by EP proponents?

It could be the persuasive logic and rhetoric that is often employed as support for their theories, in particular are the two claims that these behavioural traits are; 1) independent of global processes, automatic and often not part of conscious thought, and 2) universal across cultures. On the surface these two arguments appear to give us good reason to believe that a behavior is a result of evolutionary processes, as both points imply that it is instinctual or innate, and even though organisms have the ability to adapt over their lifetime, there is the hidden assumption that such traits are too “complex” to have been learnt. However, these arguments do nothing to support their claims.

The first argument is countered by Gray et al. with the example of riding a bike; it is clearly a specific process that functions independently from global processes and generally we do not need to consciously operate our bodies in order to successfully ride a bike. As a demonstration of this, ask yourself what you would do if your bike started to tip to one side. Most people reply that they would lean to the opposite side to right themselves but this is incorrect as it would result in the person falling off their bike – instead, when this happens the rider will turn the handlebars which corrects their centre of gravity. This meets the requirements of criterion (1), but surely nobody would think that riding a bike is an evolved trait. Part of the reason why we can easily reject such a claim is that the learning period is obvious and when this learning phase is more subtle (like with language or walking) we are sometimes fooled into reaching the wrong, or premature, conclusions.

Now we need to consider the second argument – that if something is universal across cultures, then it cannot possibly be learnt. Is this true? Of course not. Whilst it is necessarily true that an evolutionary behavior would be universal across cultures, it is not true that a universal behavior is an evolutionary behavior. This is because species-specific behaviors can either be a result of an innate trait, or the result of shared species-specific patterns of experience. In other words, if the environmental factor that produces a particular learning experience is present across all individuals of the species, then we would expect them all to learn the same behavior. Again I turn to Gray et al. for an example, where they point out that all humans, no matter what culture you look at, will eat soup from a bowl and not a plate. The common environmental variable here is gravity and it gives us a universal behavior – however, the literature on the evolved “eating soup from a bowl” behavior is relatively scarce in the EP journals.


The common misconception spread by bad Evolutionary Psychology is that we have any significant understanding of evolved behaviors in humans. This belief is pushed out year after year in books by Pinker, Buss, Tooby and others, and it has now become more of an exercise in politics rather than attracting interest in science and rational thinking. Consistently these EP journals print articles discussing how women prefer the colour pink because it reminds them of red berries from the hunter-gatherer times of our ancestors15, ignoring the fact that the preference for pink in women is an extremely recent trend from the last few centuries (traditionally baby boys were dressed in pink and girls in blue), and ignoring the fact that hunter-gatherer roles were not separated by sex; or articles about how men are attracted to red lipstick because they look like vaginas16. Even the more credible claims like cheater detection, or men being attracted to women with low weight-to-hip ratios17, are plagued by poorly thought out methodological designs and an over-eagerness to ignore the relevant literature on possible learning mechanisms that could account for the data – so much so that they earn themselves the reputation of being ‘behavioral creationists’.

I started this post with the disclaimer that this is not a broad attack on evolutionary psychology, and it is not a denial of the fact that the brain is an evolved organ, and I want to reiterate those points. The intention of this post is to highlight the flaws and inconsistencies in the field, not to convince people to reject it wholesale but instead to increase the skepticism surrounding this field. If a claim is made to the effect of “We evolved to do X/ prefer Y/ etc” then the question we should ask is “What research experimentally separated the learnt effects from evolved processes?”. The misconception is not that behaviors can, or have, developed in organisms as the result of evolutionary processes, but rather the belief that we can prematurely accept these conclusions based on faulty logic and an overreliance on (and misapplication of) evolutionary principles.


1. Coyne, J.A. (2000). The fairy tales of evolutionary psychology: Of vice and men. The New Republic, 3 April, pp. 27-34.

2. Laland, K.N., & Brown, G.R. (2002). Sense and nonsense: Evolutionary perspectives on human behavior. Oxford, UK: Oxford University Press.

3. Gray, R. D., Heaney, M., & Fairhall, S. (2003). Evolutionary psychology and the challenge of adaptive explanation. In J. Fitness & K. Sterelny (Eds.), From Mating to Mentality (pp. 247-268).

4. Pinker, S. (1997). How the mind works. London: Allen Lane.

5. Tooby, J., & Cosmides, L. (Eds.). (1992). The psychological foundations of culture. In, J.H. Barkow, L., Cosmides, & J. Tooby, (Eds.), The Adapted Mind: Evolutionary Psychology and the Generation of Culture, (pp. 19-136). Oxford: Oxford University Press.

6. Gould, S.J., & Lewontin, R.C. (1979). The spandrels of San Marco and the Panglossian paradigm: a critique of the adaptationist progam. Proceedings of the Royal Society of London B, 205, 581-598.

7. Lewontin, R.C. (1978). Adaptation. Scientific American, 293, 212-228.

8. Rosen, D.E. (1982). Teleostean interrelationships, morphological function and evolutionary inference. American Zoologist, 22, 261-273.

9. Williams, G.C. (1966). Adaptation and Natural Selection. Princeton University Press, Princeton, N.J.

10. Cosmides, L. (1989). The logic of social exchange: Has natural selection shaped how humans reason? Studies with the Wason selection task. Cognition, 31, 187-276.

11. Wason, P. (1966). Reasoning. In, B.M. Foss (Ed.), New horizons in psychology. Harmondsworth, UK: Penguin.

12. Griggs, R. & Cox, R. (1982). The elusive thematic material effect in Wason’s selection task. British Journal of Psychology, 73, 407-420.

13. Sperber, D., Cara, F., & Girotto, V. (1995). Relevance theory explains the selection task. Cognition, 57, 31-95.

14. Liberman, N., & Klar, Y. (1996). Hypothesis testing in Wason’s selection task: social exchange cheating detection or task understanding. Cognition, 58, 127-156.

15. Hurlbert, A. & Ling, Y. (2007). Biological components of sex differences in color preference. Current Biology, 17, 623-625.

16. Elliot, A. J., & Niesta, D. (2008). Romantic red: Redenhances men's attraction to women. Journal of Personality and Social Psychology, 95, 1150-1164.

17. Singh, D. (1993). Adaptive significance of female physicalattractiveness: Role of waist-to-hip ratio. Journal of Personality and Social Psychology, 65(2), 293-307.


  1. A good critique! Though I like several individuas in the field, I am amazed at how bad typical EP work is. A particular pet peeve, common in the literature, is the introduction of evolutionary story telling to justify a hypothesis that in no way require babbling about evolution. Often the hypotheses come out of folk psychology, and you could just say "people think X" so we investigated it, with nothing further needed.

    For thoughts on how EP can be done right... Can you get through to this paper?

    1. Yes, I agree about how evo psych explanations are sometimes used as basically 'fillers' or even ways of selling research ideas, when (as you say) this isn't necessary at all.

      Thanks for the link to your paper. I've been reading through it today and I'm pretty sure I read it years ago and it contributed to my current standing on the field. I liked the way you divided the approaches up as essentially being evolutionary explanations vs evolutionary hypotheses and I think that's a great way of looking at it. What did you think of Gray's argument that the approaches can be summed up as 'Evolutionary Psychology' vs 'evolutionary psychology'? Is it a similar characterisation of the issue as what you presented?

    2. Probably pretty similar. The problem is in finding a way to talk about the stuff of the last few decades without privileging it in some undue way (for example, by letting it have the capital letters). There has been continuous work integrating psychology and evolutionary thinking since Darwin, and frankly there was at least some before that. At some point psychologists need to start being more strict about what we let people get away with when labeling their systems.

      Buss et al should NEVER have been allowed to arrogate the term "evolutionary psychology" to mean only the things they were working on.

  2. I was glad to see you comment on this. I've always found EP a little hard to deal with since the proponents mine multiple disciplines. In spite of EP's name, as an anthropologist and due to disciplinary filters, I have always experienced EP as an anthropological problem, although one that bleeds out into other fields. Obviously Tooby is an anthro, and there is a long-standing streak of hyper-adaptationism in anthropology that contributed to EP. Even here, Ed Clint is in the process of launching himself into an anthropology career (although he was a psychology undergrad). I can deal with the various fields of anthropology, but the discussions tend to squeeze out into experimental psychology, evolutionary biology, neurobiology, sociology, etc. So it's definitely been informative to see the responses to Clint from people in different disciplines.

    I feel for you in the evolutionary *psychology* complaint, but I am sort of relieved--I wonder if anthropologists only dodged that mud pie because "evolutionary anthropology" was already taken.

    1. Thanks for the comment, Apxeo. The info on anthropology is interesting and I wasn't aware of the hyper-adaptationism in the field, although it does make sense after thinking about it. I think Clint is a classic example of one of the biggest problems in evo psych - people with a psychology degree and no understanding of biology trying to discuss the evolution of certain behaviors (or, perhaps worse, biologists with no understanding of psychology try to discuss the evolution of behaviors).

      And you're right, psychology definitely drew the short straw by having its name attached to the evo psych research...

    2. I don't know the current state of Anthro, but I know "Evolutionary Psychology" used to mean something a bit different for them. Louise Barrett had a textbook with that title a while ago, which was really a behavioral-ecology-of-humans book; i.e., there wasn't much in it to qualify as psychology proper. However, unlike those mucking around in psych, at least it was deeply grounded in evolution. (Incidentally, that is the same Barrett whose more recent book I have been gushing about recently, starting here.)


    It seems Jerry Coyne is actually quite the fan of evo psych.

    1. Coyne's position has definitely softened over the last year or so, and he's stepped away from the extreme position that rejected all of evolutionary psychology and so now his position is not too dissimilar from the one I outlined in my post.

      With that said, I think Coyne may go a little further than me in that he seems to uncritically accept some controversial findings within evolutionary psychology, like the innate features of language, fear responses, and incest avoidance, and even attributes some non-evo psych findings to evolutionary psychology, like physical differences between races, sexual dimorphisms, and the development of lactose intolerance.

      Regardless of his personal position on the issue, my arguments don't stand or fall on the comments of a single evolutionary biologist. That is, he could come out and claim that every finding within evolutionary psychology was valid and perfect, and it still wouldn't affect the validity of the arguments I discuss above.

      Thanks for the comment.

  4. Another great article.

    I was wondering if you have read Sesardic (2003) and if so, what you thought of his own 3 criteria for a valid EP hypothesis. They seem to be based on Griffiths' criteria but are much more rigorous (as far as I can make out) i.e. they resolve all of the problems put to Griffiths'.

    1. I read the article a few years ago and I think he makes a decent case for deciding whether something is a just-so story or a valid scientific hypothesis. If an hypothesis is presented with a viable recognised mechanism, makes predictions, and survives attempts to falsify it through the testing of possible confounds, then it can't be a just-so story.

      With that said though, that doesn't mean it's a valid or true hypothesis (as I think Sesardic himself says) and that's where I think the Grey criteria come into play.