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The Problem of Evolutionary Psychology

I’m not a biologist, so I welcome comment from real biologists in what follows here. It’s my understanding, however, that evolutionary biology really tries hard to avoid the “just-so” stories of many popular accounts. Example: you may read that giraffes evolved their long necks because they helped the animals reach leaves other browsers couldn’t. But that’s a post-hoc explanation: we know giraffes use their necks that way, but we can’t know what the original evolutionary “reason” was, or whether the browsing is a side effect from some other advantage, like mate selection. I imagine it’s a strong temptation to tell explanatory stories (and I’m sure I’ve done it myself), but it’s not really scientific to do so.  As with anecdotal evidence, “just-so” stories may be true or false, but there’s no way to evaluate their correctness without additional information.

Which leads me to this article in Slate, citing a study that claims women walk in a less sexy manner and have greater hand strength during ovulation to help prevent rape. Several people have already done comprehensive take-downs of this article and the study it’s based on (by Jerry Coyne, PZ Myers, Amanda Marcotte, and I’m sure many others), so I’ll just summarize what they’ve already said:

  • The study is based on a small sample without much in the way of controls, so it’s a little untrustworthy from the outset. There’s also some question about whether the results are consistent with other studies.
  • Even if the immediate result (women walk in a less sexy manner and have greater hand strength during ovulation) is true and universal, extrapolating it to an evolutionary rape-prevention strategy is questionable, since it’s no better than a “just-so” story.
  • A logical consequence of the study would then be that women are OK with assault when they aren’t ovulating, which doesn’t make any sense.
  • Finally, many other studies have shown definitively that rape in humans is not about sex or reproduction, but about the power the rapist exerts over the victim.

So much for the Slate article and the study it summarizes. It does highlight in its extremity many of the problems with evolutionary psychology, the field that tries to understand the human psyche (language, social behaviors, etc.) using the tools of evolutionary biology. By itself, this is a honorable undertaking, but it’s fraught with danger: so many human behaviors are culturally weighted, so it’s difficult to disentangle what is innate from what is contextual. As the late great Stephen Jay Gould was fond of pointing out, natural evolution is Darwinian—characteristics acquired by adults aren’t transmitted to offspring, while cultural evolution is Lamarckian—we teach our children, and knowledge is cumulative over time. So little girls’ preference for the color pink in the US is culturally-defined (and hasn’t always been true!), not innate, but occasionally evolutionary psychologists will present studies attempting to show the opposite.

The problems of evolutionary psychology in the end will be corrected by scientific methodology. If they can be tested by experiment or other kinds of hard evidence, as opposed to “just-so” stories,  specific claims of evolutionary psychology will be vindicated or invalidated as with any other scientific endeavor. However, as long as so many evolutionary psychology studies seem to be focused on finding evolutionary explanations for some of humankind’s worst behaviors (rape, genocide, racism, etc.) and failing to back them up with good evidence, it’s irresponsible for the media to report stories that are actually pseudoscience. Doing so damages legitimate evolutionary psychologists’ reputations, and harms the reputation of science itself in the eyes of the public.

(Slight edit: I misspelled PZ Myers’ name in the original post.)

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8 Responses to “The Problem of Evolutionary Psychology”


  1. 1 revrichard59 January 19, 2011 at 17:48

    As as non-scientist I get frustrated when a news report jumps the gun, giving as a “result” something that is a prelminary study based on a small sample.

  2. 2 Caudoviral January 19, 2011 at 18:48

    Very nice post! And thank you for helping spread the word about this terrible study.

    “it’s irresponsible for the media to report stories that are actually pseudoscience”

    The sad thing is that if that doesn’t stop them from doing so with the woo associated with every other branch of science, that isn’t going to stop them with evolutionary psych. Responsibility seems significantly less than readership in the media’s eye.

  3. 3 criener January 19, 2011 at 19:26

    I’ll go ahead and play (sort-of) devil’s (sort-of) advocate.
    I am actually a fan of Jesse Bering’s stuff in general, but it is very speculative, as most of evo psych is. This doesn’t necessarily invalidate everything in the method section, but the discussion sections can be real hilarious.

    First, a few things: popular science writing focuses on bleeding edge science (science that is happening right now! breaking science news!) at the expense of consensus science. Further, in the interests of grabbing eyeballs, they blur this line. This is not a good way to explain science to the lay public, because the bleeding edge is often the most speculative. So, that’s bad.
    But I am not sure that evo psych is particularly and uniquely bad, or that different from saying “Hey! there’s arsenic-based life forms!”

    So, here are what I see as some major subclaims to the article:
    1) There are a number of women’s behaviors and psychological responses that change across the ovulatory cycle. I’d say that there is a fair amount of evidence for this. Whether attractiveness ratings, or hand strength, or even number of phone calls made to dad (really), there are interesting and meaningful psychological measures that change across the month for women, and not so much for men.
    2) Several of these measures (hand strength, differential attraction, increased racism) can be grouped into a “rape protection” adaptation. This I find ridiculous and speculative (and, I am quite sure, profitable).

    So, I think that the big message is that our behavior is influenced by our biology (hormones) and women’s hormones vary across the month. Of course this affects their behavior. Why does it is subject to speculation.
    If evo psych in the popular media were more: here are a bunch of studies which have documented changes in behavior across the month. Huh. Isn’t that interesting. Then, if they presented several alternative hypotheses, and the experiments that could contribute, I would be much happier. As it is, science journalism works very hard for the entertainment value and not so hard for the educational value. Unfortunately, this approach turns out to be effective in dollars, but not in sense.

    • 4 Matthew R. Francis January 19, 2011 at 20:11

      The critics aren’t denying that there are variations over the course of an ovulation cycle, as far as I can tell. To correlate so many things strictly to ovulation alone almost reduces a woman to one aspect of her physiology, which is pretty ridiculous. (Most of us, women and men, seem to be more strongly influenced by sleep and/or caffeine cycles.)

      I note that even though you’re playing “devil’s advocate”, you actually are more cynical about the study than I was!

      • 5 criener January 19, 2011 at 20:40

        It is funny that so many of these science writers have not found a way to write honestly about effect sizes.
        Yes, all these things affect us (sleep, caffeine, hormones) but how much? Neither the articles nor the criticisms touch on this.
        What I find a bit distasteful about the critics is that they often say “small study, psychology undergrads, hasn’t been replicated” and don’t bother to actually read any of the studies and interpret their statistics.
        Basically, every single claim made in these articles is a probabilistic one, and journalists often make the (much clearer and better writing) straightforward claim, rather than the (on average, 5% extra risky behavior, as assessed on this questionnaire… that it is hard to explain, but has been used a lot of times, but might inflate this a little bit, or that a little bit…)


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