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

Could Evolutionary Psychology’s Critics Pass Evolutionary Psychology’s Midterms?

Published 17 February, 2012

Back in October of last year, Larry Moran wrote a critique of an article about domestic abuse, which I subsequently responded to, pointing out an error in Moran’s post. Moran later responded in turn on his blog, writing, in part:

Robert Kurzban was upset by my critique of science journalism and evolutionary psychology [Evolutionary Psychology Crap in New Scientist]. You might recall that my criticism is based on many common features of evolutionary psychology but the most important are the unwarranted assumptions that: (1) a particular specific behavior has a strong genetic component. (2) that the behavior is adaptive, and (3) that we know how our ancestors behaved.

Remarks in the comments were salty. From his reading of my web site, for instance, he draws the inference that I am not a genuine scientist, but he helpfully tells me how I could become one, which it turns out has to do with picking the right collaborators, writing:

… evolutionary psychologists seem to avoid doing real science. They prefer to just assume that their model is correct and look for good stories to “confirm ” it.

Robert Kurzban’s website is a good example of that. A scientist would write ….

We are interested in testing whether certain human behaviors have a strong genetic component and, if so, whether the behavior is adaptive. If the answers to those question are “yes” then we’d like to do some work to find out when such traits might have evolved. 

We are collaborating with geneticists to identify potential adaptive behavior alleles and to see if there’s any evidence of a selective sweep of the corresponding region of the genome.

With that as background, my interest is that at the time I read Moran’s post, I recall being struck by his claims about the three assumptions that characterize the field. Not only were they wrong, but they were wrong in such a basic way that it seemed  to me that he probably hadn’t read anything at all about the field.

This semester I am teaching Psychology 272, Evolutionary Psychology, to about 100 University of Pennsylvania undergraduates. Their first exam was last week, so I thought I would put my guess to the test, presenting Moran’s assumptions as the topic of an essay question.

I had to edit slightly, but I preserved his actual words as well as I could. Here is the essay question as my students saw it on the exam:

Recently, someone writing about evolutionary psychology wrote that the field makes a set of assumptions. In particular, the writer claimed that evolutionary psychologists who are studying a particular behavior assume that (1) the behavior “has a strong genetic component,” (2) the behavior “is adaptive,” and (3) we know how our ancestors behaved.

For TWO of the three assumptions above (5 points for each), based on your readings and the material presented in lecture, indicate whether or not each of the three assumptions is indeed made by evolutionary psychologists. If the assumption is correct, provide a justification for the assumption. If it is not, explain why it is wrong and how you would change the assumption to make it correct.

My interest was in measuring how much instruction someone would need to be able to identify (and therefore not make) the errors in Moran’s post. At the time of the exam, my students had had 8 lectures of 1 hour and 20 minutes, or about 11 hours total. (I put the readings that were assigned at the end of this post.) This is an undergraduate class, with Sophomores, Juniors, and Seniors. The only prerequisite is introductory psychology.

Before I give the results, I want to be clear that my argument here isn’t about whether the assumptions are themselves correct; my interest is in what evolutionary psychology as a field assumes. How much time and effort would it take to learn enough about the field to avoid making the mistakes that Moran makes, even if it turns out that the assumptions themselves are problematic?

Here are the data. The results were that 53 of 76, or 70% answers to assumption (1) indicated that the assumption was false. For the second and third assumptions these numbers were 30 of 40 (74%) and 33 of 41 (82%). To summarize, a clear majority of my students, with four weeks of instruction in my undergraduate course, were able to recognize that Moran’s claims about what evolutionary psychology assumes were wrong.

These values actually underestimate a little bit. In the case of the first assumption, many students who said that the assumption was right reinterpreted the statement to make it more reasonable, emphasizing that all traits are jointly caused by genes interacting with the environment. (This is not to say that some students did not get it wrong, just that 70% doesn’t properly capture the fraction that got it right.) Also, I want to sound a note of thanks to Jennifer DeSantis, my superlative TA, who, I should say, actually did all the heavy lifting on the grading of the essays.

To give a sense of what they said, here are some excerpts from their essays. (I received permission to post from the authors of the answers.)

On the first assumption, Kathryn Raynor writes: “When studying a particular behavior, evolutionary psychologists do not make the assumption that the behavior has a strong genetic component. This would be an example of the gene vs. environment [dichotomy] that evolutionary psychologists try to avoid. The notion of genes vs. environment is a bad dichotomy because each heavily influences the other. An organism’s behavior results from the complex interplay between genes and environment…”

On the second assumption, that behavior is “adaptive,” Kathryn Raynor, again, writes: “Evolutionary psychologists also do not [her underline] automatically make the assumption that a particular behavior is adaptive. This  is a very strong claim; in order to assert that some behavior is adaptive, there must be evidence that the behavior serves a function, that is, it solves an adaptive problem, AND that it is specialized or well-designed to perform that function….” Laura Micu similarly penned: “Evolutionary psychologists don’t assume that a behavior is an adaptation, they study it to find out whether it is an adaptation, a by-product or a ‘cheap’ left-over…”

Finally, on the third assumption, Laura Micu, again, writes “…we don’t know, or are able to say for sure, what our ancestors’ behavior might have been. We can only speculate given historical and present-day social observations, as well as observations of animals that are closely related to us…” Similarly, Geoffrey Bass writes: “The above assumption is incorrect. It would be absurd to assume that we could determine with a great deal of accuracy how our prehistorical ancestors actually behaved, and evolutionary psychologists make no such claim. They are interested,  to some extent, in the origin and development of adaptive behaviors… it requires that we can identify or speculate about specific challenges our ancestors might have faced…”

Again, I want to be clear that the issue for this purpose is not whether the assumptions are good ones. Perhaps there is a logical flaw in the adaptationist analysis that I asked my students to entertain. Perhaps we can know for sure what our ancestors did. What I’m saying is that my students, by and large, correctly identified the assumptions of the discipline, a feat that Moran was unable to accomplish.

The broader point is that Moran is only one instance of a larger phenomenon, and critics of evolutionary psychology frequently demonstrate innocence of the field’s basic assumptions and theoretical commitments. As I’ve said in the past, an interesting question is why critics feel comfortable voicing such strong objections to the field, given their lack of background, even to the point, as in this case, of accusations of the discipline not being a science. I don’t pretend to understand the motives, but it’s an area that merits closer study. I’m afraid that we can be confident that there will be plenty of additional data along the same lines from our voluble critics of evolutionary psychology.

Required Reading for Psychology 272, through Week 4

Cartwright (2008), pp. 1-91, 145-170, 191-228, Dawkins (2006), pp. 1-165; Miller (2007); Kurzban, 2010, Chapter 2; Tooby & Cosmides (2005)

Cartwright, J. (2008). Evolution and Human Behavior: Darwinian perspectives on human nature (2nd ed.).Cambridge,MA: MIT Press.

Dawkins, R. (2006). The Selfish Gene: 30th Anniversary Edition. Oxford: Oxford University Press.

Kurzban, R. (2010). Why everyone (else) is a hypocrite: Evolution and the modular mind. Princeton, NJ: Princeton University Press.

Miller, G. F. (2007). Sexual selection for moral virtues. Quarterly Review of Biology, 82(2), 97-125.

Tooby, J. & Cosmides, L. (2005). Conceptual foundations of evolutionary psychology. In D. M. Buss (Ed.), The Handbook of Evolutionary Psychology (pp. 5-67). Hoboken, NJ: Wiley.

  • Alex Shaw

    But Rob… clearly every trait in human beings has to have a gene associated with it. For example, there must be a heart gene, an arm gene, ect. It would be really useful to do some behavioral genetics to examine the heritability of these traits… surely the presence or absence of a heart, arm, and most traits that underlie important brain functions must be highly heritable and thus we can learn so much from first doing our proper homework and looking for these genes. It is good that Moran can educate us evolutionary psychologists.

    Additionally, why make hypotheses about an adaptive function unless you have evidence ahead of time that it is definitely an adaptation. No scientific discoveries have EVER resulted from making hypotheses first and then seeking out evidence to confirm or falsify those hypotheses… that is just not how science works. Again, thanks Moran.

    Finally, he is right that thinking about the constraints that faced our ancestors is a complete waste of time… we just have no idea. The EEA might have included ipods, Justin Bieber, and flying cars. Based on our lack of knowledge we should again not use this logic to constrain possible hypotheses about how the mind works and should instead run experiments in a guess and check fashion. Again, we thank Moran for this correction.

    • Anonymous

      I think you forgot to add #sarcasm, just in case anyone was confused…

      • Alex

        I hoped at least that the sarcasm was clear. The sad thing about Moran’s comments is that it is not just that he misunderstands Evolutionary Psychology, but he exhibits a college freshman’s understanding of biology and genetics. To quote Wikapedia’s page on “norms of reaction:

        “Popular non-scientific or lay-scientific audiences frequently misunderstand or simply fail to recognize the existence of norms of reaction. A widespread conception is that each genotype gives a certain range of possible phenotypic expressions. In popular conception, something which is “more genetic” gives a narrower range, while something which is “less genetic (more environmental)” gives a wider range of phenotypic possibilities. This limited conceptual framework is especially prevalent in discussions of human traits such as IQ, Sexual orientation, altruism, or schizophrenia”

    • https://sites.google.com/site/pleeplab/ Robert Kurzban

      I think you forgot to add , just in case anyone was confused…

  • Anonymous

    And evo psy becomes even less testable. How is something selected for if it has no underlying genetic basis?

    • Dan Conroy-Beam

      Wow, I didn’t see the part where anyone said anything about adaptations having no underlying genetic bases. I’d really appreciate it if you could point it out to me. It would be really stupid of me to fail to understand something really straightforward. Perhaps I should give up on engaging honestly with what I read?

    • http://pulse.yahoo.com/_WADSITAJWDFEJU3TKJOFY54BWY Jeffer J

      Read the article next time.

  • Nietzsche

    Moran belongs to the ‘Evolutionary-Psychology-Isn’t-Science’ School. This school is populated by intellectuals whose chief ‘argument’/rhetorical gambit contra evolutionary psychology is to employ a methodological and epistemological double standard: Evolutionary psychology as a lens with which to investigate and explain human cognition and behavior fails insofar as it cannot satisfy the methodological and evidential desiderata that the ‘Evolutionary-Psychology-Isn’t-Science’ School sets forth. (Typically this ‘school’ of intellectuals is hostile to adaptationism more generally, but the hostility becomes more apparent and amplified whenever we’re dealing with you know what.)

    It’s very convenient for the ‘Evolutionary-Psychology-Isn’t-Science’ School that their ‘criteria’ safely (and ever-so ironically) places evolutionary-psychological hypotheses outside the reach of what they would consider ‘valid’ and ‘corroborated’ science. If one were to truly adhere to their quaint criteria, however, eyes and ears, along with pretty much any other complex trait, could not be asserted to be adaptations until you put them through such stringent tests, on pain that the assertions would fall short of ‘valid’ and ‘corroborated’ science. Yet they almost always have no qualms with those sorts of adaptations.

    Change the topic to jealousy or rape avoidance or cheater detection or mate preferences, and so on, and their tune changes quickly. Suddenly their refrain becomes “show us the genes;” “test for fitness advantages;” “we cannot reconstruct our ancestral past;” “reverse-engineering is an unworkable methodology;” etc.

    I had responded to Moran’s post and even invited to give him an informal tutorial on the foundations of the field (we both happen to live in the same city). Apparently he didn’t bite on the offer. I don’t think he’s really interested in learning about the field.

    No question, a brief perusal of his blog confirms that he is an anti-adaptationist (and a frequent invoker of Gould, to boot). I’m not sure whether it’s just Moran’s hostility to adaptationism that fuels his principled nay-saying of evolutionary psychology, or whether it’s more based in ideological resistance (which unfortunately is common amongst many academics who don’t like the field).

    Given that he’s a science blogger invested in the public debate against intelligent design creationism, I think that he undercuts adaptationism at his peril.

    • Anonymous

      Thanks for your remarks. These strike me as reasonable points. The potential inconsistency you point out is one reason that I think it’s important to try to get critics to articulate what they take to be evidence of adaptation. I think Gould fans would do well to recall that he in addition to his frequent remarks about side-effects, he also wrote (in “Darwinian Fundamentalism”) that “eyes are for seeing and feet are for moving. And, yes again, I know of no scientific mechanism other than natural selection with the proven power to build structures of such eminently workable design.”

  • Clarence Williams

    While Moran’s first statement characterizing EP, “a particular specific behavior has a strong genetic component,” undoubtedly needs clarification, I cannot view it as being “false.” EP postulates that many human behaviors are adapted, which, by definition, means “they are shaped by evolution.” The former quote is from your book, Why everyone (else) is a hypocrite, and is specifically this: “Modules, shaped by evolution, are designed to implement strategies that are appropriate for the relevant problem” (p. 65). Thus, Cosmides’ cheater detector module is shaped by evolution, and evolution requires “a strong genetic component.” That is, one or more genetic mutations in some distant relative eventually resulted in behavior that provided a unique, improved skill at detecting a good coalition partner, thus endowing a fitness advantage.

    • Anonymous

      Thanks for your comment. I don’t think that “shaped by evolution” and “has a strong genetic component” are synonyms, which I think might be what you’re saying. The crux of the issue is whether it is sensible to think of traits as having genetic components and some other (learned? cultural? environmental?) component. At the risk of inserting an overly long quotation, I’m fond of Tooby & Cosmides (1992) rendering of this: “…every feature of every phenotype is fully and equally codetermined by the interaction of the organism’s genes (embedded in its initial package of zygotic cellular machinery) and its ontogenetic environments-meaning everything else that impinges on it. By changing either the genes or the environment any outcome can be changed, so the interaction of the two is always part of every complete explanation of any human phenomenon. As with all interactions, the product simply cannot be sensibly analyzed into separate genetically determined and environmentally determined components or degrees of influence. For this reason, everylhing, from the most delicate nuance of Richard Strauss’s last performance of Beethoven’s Fifth Symphony to the presence of calcium salts in his bones at birth, is totally and to exactly the same extent genetically and environmentally codetermined. “Biology” cannot be segregated off into some traits and not others.” (Tooby & Cosmides, 1992, p. 83).

      • Clarence Williams

        Thanks, Robert, and thanks in advance for bearing with me as I continue to argue the point.

        Your explanation here reveals why I would still answer, “True, EP believes [adapted] behavior ‘has a strong genetic component.’” The revelation: We disagree on the crux of the question, although not the crux of the matter.

        You’ve quoted enough to note the matter, to which I fully agree. The crux of the question, however, is to draw the very distinction Barkow, Cosmides and Tooby (1992) make after your excerpt: “Nevertheless, one could understand and acknowledge that all human phenomena are generated by gene-environment interactions, yet believe that the existence and participation of the environment in such interactions insulates human phenomena from interesting evolutionary patterning” (p. 84). Humans are not insulated from interesting evolutionary patterning, which is next explained to incorporate the genetic component. In other words, answering, “False, EP does not believe [adapted] behavior has a strong genetic component,” falls into that misunderstanding (warning) characterized by Barkow et al (as I’ve just quoted).
        More importantly, though, I am opposed to this seeming flight from the genetic essence (that word does not presuppose either “weak” or “strong,” but maybe there’s a better one) of EP-postulated adapted behavior. The gene(s) that channel the adapted behavior as opposed to the pre-mutation behavior most assuredly exist. This is true whether they are ever found or not, and we should not shy away from that biological fact.

        For instance, at one point in human history the population was characterized by a weak “cheater detection” mechanism (much like that of chimps). A genetic mutation is postulated to have channeled the development of an ever so slightly different module used to gauge social exchanges, giving the possessor an improved ability in social exchanges. The rest is history, and human now possess a “cheater detection module” that is superior for solving problems in the social domain or framed in social terms (we are still stuck with an inferior module for solving problems when presented in abstract form). A genetic change resulted in the posited adaptation. Will we find those genes? Maybe not, but that’s beside the point.

        I understand the need to divorce ourselves from genetic determinism, but sometimes (as in this case) we go too far.

        • Alex

          I think your point is reasonable but could it be a matter of pragmatics? By saying that EP’s believe in a strong genetic component the “strong” must mean something more than just “gene’s play a role”, otherwise Moran would just have said that EPs think behavior has a genetic component. I think the accusation of the “strong genetic component” implies to an audience something more like genetic determinism–though that is clearly an empirical question that could be answered on mturk.

          • Clarence Williams

            Yes, Alex, it probably is more a semantic issue than anthing of substance…from an EPer’s standpoint. For all I know, Moran may be an environmental determinist, so I can’t speak for him. That’s why it’s critical to avoid “sound bites” and declare someone wrong if they answer Moran’s question either way.

            I am sensitive to the issue because I think it illustrates the near-panic flight away from genetic underpinnings that characterizes many EPer’s explanation of genes and environment. There is an altered genetic foundation to the “cheater detection module” (to continue my same example), a gene (or several genes) that bestow a special skill, and it probably arose in the face of diverse social environments. Yes, it developed in the face of the environment (but probably several) and, therefore, it might be said that it cannot be separated from the environment, but leaving it at that creates a misunderstanding about what is meant by an adaptation.

            It’s exceptionally difficult to explain what EP means in regard to an evolved adaptation, so I stand ready to reword my understanding of gene/environment interaction. I am not prepared, however, to avoid the fact that adaptations have a genetic basis that is wholly different than the genes underlying learning.

          • Alex

            I guess I don’t see this as much as being about something being genetic (strongly or not) or environment… it sounds more like you are discussing the distinction that every EPer is on board with which is the distinction between domain specificity and generality.

            As an EPer I think making the claim that X has a basis in the genes is a meaningless statement. Being able to make videos parodying A-Rod for thinking he is a Centaur is surely in the genes, but I don’t think there is an ACC (A-rod comedy Centaur) system that arose as an adaptation. It seems like this domain general versus specific distinction is more of what you are getting at.

            So the question isn’t whether cheater detection has a genetic based (it does), it is a question of how specific that putative system is.. . is it a general reasoning system? Is it cheater’s it is picking our or just people who do things that are socially abnormal? Ect… These things seem to be the real question of interest.

          • Clarence Williams

            At the risk of beating a dead horse, let me repeat my assertion: someone saying that EP believes behavior has a strong genetic component is not wrong. When an adaptation is posited, say, a cheater detection module, we are, of course, saying that a genetic mutation occurred in some ancient past environment. It is as appropriate to discuss and separately investigate that gene (or genes) as it was for the PKU gene. The latter decimates the child’s brain while the former endows adaptive social behavior. Fortunately, geneticists ignored Barkow, Cosmides and Tooby’s (1992) advice that “the product cannot be sensibly analyzed into separate genetically determined and environmentally determined components or degrees of influence.” Geneticists studied the disease separately. Environmental manipulation (diet control) denudes the PKU gene, revealing the indelible link between genes and environment, but nonetheless the two can and are separate components with potentially different degrees of influence.

          • Alex

            See my above point. I argued that it is wrong to say “strong genetic component” if a normal audience will read that as implying determinism (and I am pretty sure that is what Moran meant by this term also), which I take it you disagree with. We could settle that argument by running a study on Mturk about how people interpret that sentence, so I don’t see the merits in debating that empirical question.

            As for the geneticists you mentioned I don’t see how they are ignoring Barkow, Cosmides and Tooby’s (1992) suggestion… I’m guessing they did not really study environment separately as you suggest. That is, they did not test how non-genetic material responds to diet control, which is what it would mean to really ignore their suggestion. They instead tested how this genetic material responded to an environmental change.

            *Obviously there are some cases where genes are close to deterministic–in extreme cases of severe deleterious mutations where there is almost no known environmental factors that can change how this gene is expressed.

          • http://popsych.blogspot.com/ Jesse Marczyk

            Moran definitely meant it to imply determinism. His understanding of genetics seems terrible, perhaps unsurprisingly:

            “Let’s imagine a time back in hunter-gather days when there were two groups of men who differed in their violence-against-women alleles. One group was kind and considerate toward their female companions. They treated them with respect. The other group treated women as property and often beat them in order to prevent imagined infidelity. Somehow the violent group managed to mate more frequently and/or have more children than the kind group so the allele for kindness and respect was eliminated from the population. “

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  • Doug Drake

    Here’s a data point that might help in your search for a motive. It comes from an essay by (once famous) psychologist Geoffrey Gorer, published in 1956, entitled, “The Remaking of Man.” Gorer writes,

    “One of the most urgent problems – perhaps the most urgent problem – facing the world today is how to change the character and behavior of adult human beings within a single generation. This problem of rapid transformation has underlaid every revolution (as opposed to coups d’etat) at least from the time of the English Revolution in the seventeenth century, which sought to establish the Rule of the Saints by some modifications in the governing institutions and the laws they promulgated; and from this point of view every revolution has failed… the character of the mass of the population, their attitudes and expectations, change apparently very little.”

    “Up till the present century revolutions were typically concerned with the internal arrangements of one political unit, one country; but the nearly simultaneous development of world-wide communications and world-wide ideologies – democracy, socialism, communism – has posed the problem not merely of how to transform ourselves – whoever ‘ourselves’ may be – but how to transform others.”

    Gorer was a friend of George Orwell, and helped him get his first book published. Both were socialists.

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