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

New Paper Concludes Evolutionary Psychology is not “Unfeasible”

Published 21 July, 2011

I was relieved by the time I got to the conclusion of a paper by Bolhuis et al., just published at PLoS Biology; they concluded that problems with evolutionary psychology do not, in fact, render the field “unfeasible.” Whew!

The theme of the paper is that the “key tenets” of evolutionary psychology require updating in light of modern findings. In some sense, it’s a bit hard to argue with their conclusion that the field should make use of ideas and findings from other disciplines. Hard to argue with that. In fact, as far as I know, it’s so hard to argue with that that no one has actually done so. Raise your hand if you think evolutionary psychologists shouldn’t make use of all the relevant ideas that surround the discipline… I’ll return to this…

So, while I think that finding value in the paper is not unfeasible, the worries they articulate about the discipline had an oddly familiar feel to them, and occasionally while reading I experienced more than a little bit of déjà vu

Take, for instance, the way that they construe the field’s view of development. For some reason, they seem to think that evolutionary psychologists think that all behavior is due to “genetically pre-specified strategies” (p. 2). They, in contrast, urge a more sophisticated view of development:

The development of an organism, including the characteristics of its brain, involves a complex interaction between genetically inherited information, epigenetic influences, and learning in response to constructed features of the physical and social environment.

This criticism is useful to the extent that it reflects a new view of development. Less so to the extent that the field has had precisely this view from the start, relying on the idea that development was a complex interaction between the organism’s genes and the environment – including everything in the world that impinges on it. (The authors specifically identity UCSB as their target at the beginning of the article. They are urging an update in the principles developed by the Santa Barbara school, so I’ll draw on and refer to work by Tooby and Cosmides and, ahem, a couple of their students, with apologies to those whose work I don’t mention.) So, did Tooby and Cosmides make any remarks that resemble their view of development twenty years ago? Well, there’s 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. (Tooby & Cosmides, 1992, p. 83).

More generally, Bolhuis et al. repeat the tired trope that evolutionary psychologists are more or less genetic determinists. Yawn.

Speaking of the environment, they also have some remarks to make about the EEA, the environment of evolutionary adaptedness, which Tooby and Cosmides (1990) gloss as “a  statistical  composite  of the  adaptation-relevant  properties  of  the  ancestral  environments  encountered  by  members  of  ancestral  populations,  weighted  by  their  frequency  and fitness-consequences.” This EEA concept includes all these properties, including physical properties such as the force and direction of gravity, the wavelengths of light that hit the planet, and any number of invariances stated at any level of abstraction. Tooby and Cosmides (1990), indeed, use a somewhat whimsical example of a statistical invariance: “…predation  on kangaroo  rats  by  shrikes  is  17.6%  more  likely  during  a  cloudless  full  moon than  during  a  new  moon  during  the  first  60  days  after  the  winter  solstice  if  one  exhibits  adult  male  ranging  patterns…” (p. 389). While this example is whimsical, it illustrates that selection can operate given stability of any feature of the environment, independent of how abstract it is. This example also illustrates a key point which the less attentive might have missed, that the first “E” in EEA emphatically does not mean the same thing as it does when you talk about, for instance, “environmental studies,” which is about climate and that sort of thing. The EEA concept is much broader. I’m emphasizing this because the authors’ critique of the EEA concept is that the Pleistocene was “far from stable,” and to support this claim, they cite two papers about… the weather. Yes, the weather varied, and of course weather matters. That doesn’t mean that there were not environmental invariances against which selection could act.

(A couple little asides. In Box 1, they suggest that the EEA concept has been updated – they cite Tooby and Cosmides’ (2005) Handbook chapter – from its original. They say that “the more recent formulation of the EEA concept presents a broader, less specific theoretical landscape of our past lives, based on an abstract statistical composite of all relevant past selective environments.” Compare the 1990 version, quoted above, with their gloss of the 2005 version. I’m uncertain what they think was updated. As another aside, the claim about development is in the context of a remark about what they call “universalism.” They say that the view from evolutionary psychology, that there is a human nature, “led to the view that undergraduates at Western university constitute a representative sample of human nature.” I was unable to find any documentation for the claim that evolutionary psychologists think that these (admittedly convenience) samples are “representative.” Indeed, though I have not done any research on the topic, my guess that if you compared evolutionary psychologists with social psychologists, you would find that there is more, not less emphasis on gathering data cross-culturally.)

Their point about the EEA is largely in the service of the idea that attention needs to be paid to recent evidence of fast genetic change. Probably one of the best known sources regarding this is the Cochran and Harpending book, and these authors specifically address the claim that Tooby and Cosmides made, which turns heavily on the distinction between complex adaptations – which require many changes across substantial numbers of genetic loci – and simple adaptations, which require changes in few, or one. Cochran and Harpending themselves acknowledge the logic of this argument, though of course they emphasize that changes in simple adaptations can be important, too, and certainly rapid genetic changes affecting lactose intolerance is important to people who can’t tolerate lactose. There is an important sense, then, in which one might retain the view that modern skulls house a stone age mind – particularly with respect to complex cognitive adapations, the focus of evolutionary psychology – while being happy to concede that there is an important sense in which our bellies don’t house a stone age digestive tract.

I try to keep these posts relatively brief, and there is much more to say about this paper, but since so much of the territory they cover is well worn, I’ll restrict myself to just a few brief remarks to conclude, and suggest that interested readers have a look at the original paper; a nice feature of PLOS is that access is free.

The authors critique “massive modularity,” and their main arguments against the idea are, first, that there are associative learning mechanisms and that second, quoting now, “there is broad involvement of diverse neural structures in many psychological processes, and there is feedback even to the most basic perceptual processing” (p. 3). On the second point, I have no idea why these observations undermine modularity, so I can’t speak to it. Sure, many processes require the action of many modular structures, and some modules take input from other modules, including low level modules. It’s unclear to me what the problem is supposed to be. On the first point, there was a rejoinder to this argument in a section called “Domain-general abilities” in a paper by two evolutionary psychologists writing about modularity, but their arguments are not addressed here, and the paper in which it appears is uncited, possibly because it was hidden in an obscure journal called Psychological Review.

Probably the most aggravating part of the paper is the section entitled “Towards a New Science of the Evolution of the Mind,” which begins with the idea that evolutionary psychology needs to expand its focus to include – wait for it – Tinbergen’s four questions. This would be an important critique as long as it weren’t the case, and generally acknowledged, that these questions already constituted the basic framework for the discipline. Whether it is or not I suppose is somewhat debatable, but here’s what Wikipedia thinks… “[Tinbergen’s] schema constitutes a basic framework of the overlapping behavioral fields of ethology, behavioral ecology, sociobiology, evolutionary psychology, and comparative psychology.” I note, by the way, that social psychology is not on the list, so if the authors of this paper thought that a discipline needed some schooling, it seems to me they picked the wrong one…  Indeed, one could make the claim that it was, in fact, evolutionary psychologists who introduced these ideas as important – even key – to doing good social science. Somehow, the field never gets thanked for this…

And, of course, what paper on the field would be complete without the insinuation that evolutionary psychologists are just telling stories? The authors helpfully inform readers that evolutionary analyses “are best regarded as hypotheses, not established explanations, that need to be tested empirically,” and they carefully use the word “sometimes” to make the claim simultaneously technically correct and irritating: “Evolutionary psychologists commonly seek to study how the human mind works by using knowledge of evolution to formulate, and sometimes test, hypotheses concerning the function of cognitive architecture…” (p. 4).

To return to their conclusion, where I began, they write:

A modern EP would embrace a broader, more open, and multidisciplinary theoretical framework, drawing on, rather than being isolated from, the full repertoire of knowledge and tools available in adjacent disciplines.

Substitute any field you want for EP in there, and is this deep conclusion ever going to be false? The remark is vacuous in general, but vexing when applied to evolutionary psychology. Sure, what social science really needs is some sort of, I don’t know, Integrated Causal Model, one that uses principles from the natural sciences to inform the study of human (and non-human) behavior. Social scientists should be looking to anthropology, biology, and economics… If only someone had proposed something like that twenty years ago.

Coda: Exercise for the reader. How many of the five usual critiques appear in this paper?

  • Jesse Marczyk

    I’m about ready to start writing a paper about how researchers in behavior genetics need to start considering the impact of the environment in shaping behavior, but the endeavor isn’t otherwise bankrupt. Clearly, it’ll be publishable.

    While I’m at it, I may also write a paper suggesting to hungry people that they consider eating to deal with their problem.

  • gcochran

    “There is an important sense, then, in which one might retain the view that modern skulls house a stone age mind ”

    I have a special insight into the thinking of those authors. and I assure you that they would disagree. Not entirely: obviously, all adaptations are to the past, rather than to the present. But there is every reason to think that natural selection has changed people’s psychology over the past few thousand years. There is also every reason to think that widely separated populations experienced
    significantly different selection pressures over far longer periods, well before the Neolithic: people didn’t all experience the _same_ stone ages. In fact, it now looks as if some populations (like Bushmen) have been genetically separated from from the rest of the human race for 150,000 years – or maybe longer, if the new low estimates of the human mutation rate hold up.

    That’s not even considering the fact that some populations have as much as 10% archaic ancestry (Neanderthal and Denisovan) – what does that say about ancient co-adapted gene complexes?

    • Robert Kurzban

      Thanks for taking the time to comment. My remark that you quote was a claim about the conjunction – that is, one could (in principle) have different beliefs about the time scale with respect to different adaptations – rather than attributing a position to you beyond your remark in the book, which I’ll quote here, just for completeness: “We think that this argument concerning the evolution of complex adaptations is correct, but it underestimates the importance of simple adaptations, those that involve changes in one or a few genes” (p. 10). As you say, people can differ on the weight that they place on these issues, and I certainly take that point. If people want to apply adaptationist logic to human psychology, and include more recent (and varied) human environments in their guesses about the features that selected for the design of human psychology, I certainly would have no objection to that.

  • john liddle

    Liked the article. Not so sure about 1 of the responses. Concerning hungry people

    • Jesse Marczyk

      It’s a sarcastic metaphor for trying to tell someone something they already know and passing it off as genuine insight.

  • David Pinsof

    Interesting point that if any discipline is in need of revision it is social psychology, not evolutionary psychology. Yet the number of anti-social psychology papers is, to my knowledge, zero, and the number of anti-evo psych papers is quite large. Of course, this is partly due to the marginalization of evo psych, but I think there is another reason: social psych doesn’t actually have a foundation. If I wanted to attack social psych, I wouldn’t know where to begin. There are no unifying principles, no overarching theories, no central tenets: it is just a hodge-podge of disconnected findings with superficial explanations. One simply cannot attack something as amorphous and disorganized as social psych. This is a problem. The fact that it is actually possible to critique the tenets of EP (however unconvincingly) reveals its strength as a discipline. The fact that social psychology cannot be critiqued in this manner reveals its weakness as a discipline. Of course, I doubt this line of reasoning will mollify any of EP’s detractors, but it’s worth putting out there.

    • Justin Weinhardt

      Not only is the this argument worthy of putting out there I believe that you should formally (a paper) use these exact same arguments as a critique of the field.

      For a better by not flawless (are they ever?) paper on unifying behavioral science those interested should check out a behavioral and brain sciences by Herbert Gintis’s “A Framework for the unification of the behavioral sciences” which incorporates evolutionary theory, game theory and decision theory.

  • http://www.ling.ed.ac.uk/~tsphilli/index.htm Thom Scott-Phillips

    It’s tragic how often EP is misrepresented by its critics. It often happens in person too. The strawmen have been dealt with multiple times before, so it’s not so interesting to go over them every time. What’s more interesting is to ask why EP comes in for this treatment. Why do so many scholars have fundamental misunderstandings of the basic premises? I don’t know the answer to that question, but I would welcome everybody’s thoughts.

  • skunk1980

    Over and over on this blog we read of attacks on EP, especially this lie of “just so” stories. I mean what the hell is this nonsense? How can any intelligent individual honestly think that EP is not a valid field of research? And that, somehow, unlike any other science, it doesnt update its theories, methods, and findings as time goes on? This is just ridiculous. Its crazy to me how EP is treated as dogmatic when it is anything but that. Why the heck is this?

  • Charlie D.

    Dear skunk1980,
    Did you read the original PLoS Biol article? Do you think that ‘new opportunities for EP’ sound like an attack on EP? The article is much more positive and constructive than you seem to think.

    Dear Dr. Kurzban,
    It is not clear why you found the ‘Tinbergen’ part of the paper ‘most aggravating’. I actually thought that was the best bit of the article! Not sure what a wikipedia quote has to do with all this, btw. Isn’t it true that EP is using evolutionary considerations to explain the way the human mind works? I.e. isnt’ EP confounding two of Tinbergen’s questions? In fact, isn’t that the essence of EP?
    That is what makes it different from cognitive psychology and evolutionary biology, isn’t it? I thought the authors discussed that quite clearly – it certainly made me think.

    • Alex

      I don’t understand the suggestion of conflation. Are you suggesting that EP does not understand Tinbergen’s distinctions because it uses ultimate explanations in order to investigate proximate mechanisms? I mean it is true that these are two different levels of analysis, but I learned even in intro biology that these are complimentary levels of analysis–i.e. proximate mechanisms can often give one insights into ultimate function and ultimate explanations can help constrain one’s investigations of proximate mechanisms… Is that the beef?

  • Mars

    1) I think the main point of the article is that if evolutionary psychologists really think human behavior results from the same evolutionary processes as behavior in other organisms, then maybe they should use the full range of techniques that other evolutionary biologists use for other species. Observing behavior in one-shot laboratory experiments (with subjects who have already undergone substantial development, learning, and enculturation), is probably not going to help you compare the origins of that behavior.

    2) Fewer and fewer evolutionary biologists or population biologists do null hypothesis testing. They make a good point that EP might want to follow their lead and start using statistics that compare competing hypotheses instead of endlessly claiming that such-and-such behavior is “compatible” with some favored hypothesis. Especially in cases when such-and-such behavior is “compatible” with much different hypotheses.

    3) Maybe everyone agrees that this is a good idea. Their point is probably more like “even though everyone agrees this is a good idea, few people are acting on it.”

    4) How many EPs have a good core coursework in quatitative population biology – quantitative population genetics, evolutionary game theory (making and analyzing analytical models), etc.? The basic core that other evolutionary biologists are trained in. That would be a good start, I think.

    5) People who study brain structure, development and function for a living seem to get by perfectly well without reference to modules. The only people who use the word (as far as I know) are evolutionary psychologists. Might it avoid confusion, to just adopt to the terminology of the people who study these full-time. Instead of inventing or reinventing the wheel. Frankly, the term “modularity” is confusing to many people, as you are no doubt aware, and I am not sure what it gains EP above just using existing concepts and terms.

    6) I think the defense that “at least we’re better than social psychology” is sort of sad. It’s as if the fact that as long as EPs think more about evolution than SPs all is right in the world.

    7) At least the article pointed out at the Trivers 1972 was wrong. Theorists have only known this for over 30 years. Maybe this article will discourage more people from citing Trivers. But probably not.

    • paul turke

      I see little to agree with in this laundry list, but point five is particularly wide of the mark.

      “Modularity” is in fact fundamental to development (it manages pleiotropies, for example); the concept is critical to the evolution complexity, and therefore it is widely discussed in this literature (see, e.g., Wagner, G. and Altenberg, L, 1996, Perspective: complex adaptations and the evolution of evolvability, Evolution 50 (3):967-076; Turke, 2008, Williams’s theory of the evolution of senescence: still useful at fifty. Quarterly Review of biology 83 (3):243-256).

      Being comprised of complex adaptations, brains must have modular organization.

  • Charlie D.

    Dear Alex,
    I think the PLoS authors are saying the same thing as you here, namely that evolutionary considerations can be used to generate hypotheses about mechanisms (and vice versa). That is quite different from trying to EXPLAIN mechanisms with evolutionary considerations – and that is what the authors suggest is the essence of EP. It looks to me that the authors are arguing that to study the mechanisms of the mind (as it were), one needs methods from cognitive psychology and neuroscience. In order to study the evolutionary history of human cognition, one needs evolutionary methods. This sounds perfectly sensible to me. Reading the PloS paper made me look up their first ref, where this point is made rather succinctly: ‘Can evolution explain how minds work?’. The answer to this q seems to be ‘no’ in both papers.

    • Alex

      Not to be offensive… but that distinction seems more semantic than substantive to me. It seems that people who do EP well do respect the distinction between ultimate explanations and proximate mechanisms and investigate them as separate (but complimentary) considerations.

      I think the problem is that EP’s agree with the paper too… in that what the paper is suggesting is that we endorse ideas that most people who do EP already agree with.

  • Charlie D.

    Dear Alex,
    No you’re not being offensive, but not very consistent either. Earlier you said that ‘ultimate explanations’ and ‘proximate mechanisms’ are ‘two different levels of analysis’; and now you argue that the ‘distinction seems more semantic than substantive’. So, which is it, then? It would seem that two explanations at ‘different levels of analysis’ would be substantially different ones, or as the PloS authors put it (p. 4) ‘logically distinct questions’.
    It would be nice if, as you say, the ‘problem’ is that most people in EP already agree with the PLoS paper. Then there would be no problem! Only snag is though, that the PLoS paper seems to say that EP is confounding ‘ultimate’ explanations with ‘proximate’ ones, and I think they’re right.
    After all, if EP would indeed investigate the history of the mind using evolutionary methods, and the mechanisms of the mind using methods from cognitive psychology and neuroscience, what’s new about EP compared to these established disciplines?
    Not wanting to be offensive, of course……

    • Jesse Marczyk

      I’ve never seen evolutionary psychology papers confusing proximate and ultimate causation, much less a trend of evolutionary minded researchers doing that. I’ve seen cases of people (non-evolutionary) using proximate explanations as ultimate ones, (people like sex because sex feels good), and I’ve seen cases of people arguing against EP conflating the two (I don’t have sex because I want children; I have sex because it feels good).

      What’s new about EP is that it provides a solid theoretical foundation that was previously missing from a lot of research. It informs people as to “why” and better directs research into the “how” question.

    • Alex

      What I meant about it being semantic is that you are quoting something that you feel blurs the lines of the two levels of analysis. I was saying that while you can do that and try to nail EP’s for that this seems like semantics to me since in practice people who do evolutionary psychology are very aware of this distinction and their research programs reflect an understanding of this distinction.

  • Charlie D.

    Dear Alex,
    Ok let’s assume that EPs appreciate the distinction between the two, and they don’t confound the two. What then distinguishes EP from evolutionary biology on the one hand, and cognitive psychology & cognitive neuroscience on the other? Exactly, in that case, it’s not EP anymore, because the crux of EP is that it combines the 2 ‘levels of analysis’.

    Dear Jesse,

    You say ‘It [EP] informs people as to “why” and better directs research into the “how” question.’ I presume that out of Tinbergen’s 4 whys you are alluding to the question of function. That is behavioral ecology, then, (not evolution) isn’t it? Whichever q it is, this simple reitterates what the PLoS authors said, namely that evolutionary (or functional) considerations can generate hypotheses as to what you call the ‘how’ question. But I think EPs would argue that their field goes further than just generating hypotheses about mechanisms. Just ask them.

    • Alex

      I’m always a fan of saying that everyone should be an evolutionary psychologist (a friend of mine says the flipside of this which is that there should be no evolutionary psychologists)–both of these mean the same thing. I agree that evolutionary psychologists are simply psychologists who use the tool boxes of many disciplines–using the tools of cognitive psychology, neuroscience, economics, evolutionary biology, modeling, ect to investigate how the mind works. In a perfect world we would not need a label like evolutionary psychologists because everyone would use all of these important tools. But being that we live in this world, the label is still necessary to differentiate us from psychologists who do not use all of these tools.

      As for the issue of combining the two…. what the means is that we, you know, actually pay attention to ultimate causation. To quote Rob’s Alas poor evolutionary psychology paper:

      “Providing a proximal explanation neither invalidates an ultimate explanation nor replaces it. A biomechanical explanation of how the heart works doesn’t make it any less a blood-pump. And knowing that it’s a pump can guide the search for other features of the heart. One can go about doing physiology and psychology without care for ultimate explanations. Indeed, scientists who reject the evolutionary approach are free to derive hypotheses from whatever other sources they wish, including intuition, observation, or psychic cats. But if “insisting” on a more thorough explanation for psychological phenomena is a crime, then evolutionary psychologists are guilty as charged.”

      I think that is what EP’s mean by “combining the two”… we use BOTH ultimate and proximate causes as two complimentary levels of analysis.

      • Alex

        As a common sense example… I can win a fight by using a right handed punch of a left handed punch. However, it would be much more effective to use a combination of rights and lefts. In fact the two can nicely compliment each other. Advocating such a combination would not mean that I confuse my right with my left.

  • http://deleted Charlie D.

    Dear Alex,
    Your point about the complementary use of left and right is obviously true, and any decent scientist would agree with that. And, as the PLoS authors actually state, considerations from one domain (or ‘level of analysis’) can inform the other. But EP is going (much) further, as exemplified by your expression ‘ultimate causation’. Presumably that means that evolution is a causal factor in the way humans think. That is indeed the essence of EP: ‘Our modern skulls house a Stone Age mind’. That is the crucial fallacy of EP that I think the PLoS authors are addressing in the ‘Tinbergen’ section of their paper. I just re-read that bit, and I must say they are spot on when they state: “accounts of the evolution of brain and cognition cannot in themselves explain the brain’s underlying working mechanisms [1], since these are logically distinct questions. While evolutionary analyses may generate clues as to the mechanisms of human cognition, these are best regarded as hypotheses, not established explanations, that need to be tested empirically [1,64,79], and there are instances where such evolutionary hypotheses about mechanisms have had to be rejected [1].”. You quote Rob when he says: “But if “insisting” on a more thorough explanation for psychological phenomena is a crime, then evolutionary psychologists are guilty as charged.” Well, QED, I would say. Using evolution as an ‘ultimate’ causal factor is not ‘a more thorough explanation’ (a bit presumptuous, wouldn’t you say?), it is just plain wrong. Maybe that is the ‘ultimate’ fallacy of EP.

    • David Pinsof

      I fear this discussion is more about semantics than about any substantive disagreement, but allow me to take a shot at clarifying things. You presumably think that injecting the concept of “causality” into any ultimate-level analysis is misguided. On the one hand, it does seem a bit strange to say that evolution “causes” or “explains” a particular aspect of our psychology. But when you get right down to the logic of it, this statement is inescapable. After all, if A caused B and B caused C, it seems obvious to say that A played a “causal” role in C (I’d be interested in an argument against this contention). Similarly, if many generations of selection caused a mechanism to evolve, and that mechanism caused a behavior pattern, it makes sense to say that selection played a causal role in that behavior pattern. Of course, the mechanism itself caused the behavior pattern more directly than did selection, but this does not nullify the causal role of selection. Thus, referring to proximate and ultimate “causation” is no more problematic than referring to both the cue stick and the cue ball in explaining the trajectory of the eight ball.

      • Alex

        For the cue ball analogy I think the debate would be more akin to arguing that it was not my arm moving that caused the 8 ball to move, but it was the contact between the balls.

    • Alex

      I get how this works… we keep agreeing on what is the right thing to do, but you keep saying that we don’t do those things and I keep insisting that those are the things we do. You’ve already agreed above that you can use ultimate explanations to search for proximate mechanisms and vice versa. That is all evolutionary psychologists do. This step further you are suggesting is a straw man and seems to suggest that EP’s do not generate hypotheses and, like, test them. Again to quote Rob (it’s so sad that these criticisms are so recycled that Rob’s paper from almost 10 years ago addresses these criticisms):

      “Evolutionary psychologists use our limited knowledge about the past to generate hypotheses. However, as others have pointed out, evolutionary psychologists’ hypotheses about human psychology can be tested in the very same way that other hypotheses about human psychology can be evaluated. ”

      If you can find me an evolutionary psychologist who does not actually test their claims empirically… they would not be an evolutionary psychologist.

      Also, regarding the semantics about causation, see David’s post. Obviously evolution (or noise) causes human cognition…that does not mean we stop with ultimate causes or spend our time trying to affirm our view of ultimate causation. We are scientists like anyone else.. we choose to use the nifty tool of adaptive analysis to generate hypotheses.

  • http://deleted Charlie D.

    Dear David and Alex,
    If generating and testing hypotheses about mechanisms is all that EP does, then I have no qualms with it (and neither would the PLoS authors, I reckon). What do the PLoS authors (because we are discussing their paper, right?) say about this? They agree with you that EP is testing hypotheses, but obviously evolutionary inspired hypotheses. I quote: “Generally these hypotheses have a functional perspective—that is, EP proposes that a particular mechanism functioned to enhance reproductive success in our ancestors.”. Do I understand you correctly, then, that EP is particularly testing evolutionary hypotheses about cognitive mechanisms? So, ‘Our modern skulls house Stone Age minds’ is merely a hypothesis that is being tested by EPs?

    Regarding the issue of ‘ultimate’ vs ‘proximate’ causation, this goes back all the way to Aristotle, who distinguished 4 different ’causes’ to describe one and the same thing. For instance, a chair has a material cause (made of wood), an efficient cause (made in such and such a way by Mr. Carpenter), a formal cause (it has four legs, a seat and a back), and a final cause (it’s used to sit in). Roughly speaking, what you call ‘ultimate causation’ concerns final causes, while ‘proximate causation’ concerns efficient causes. Note that Aristotle’s final cause isn’t a cause at all, but a CONSEQUENCE or a function. The function of a chair is that you can sit in it; no one would say that that is the (efficient) cause of it. In the same way, what you call ‘ultimate causation’ isn’t causation at all. EP is about adaptive value, particularly about the adaptive value of cognitive systems in our ancestral environment. Thus, the statement that ‘evolution causes human cognition’ is wrong. I don’t even know how to translate that to Aristotle’s chair. Something like ‘This chair is caused by the fact that over generations people could sit in chairs’. Evolution is a process, and as such cannot be the cause of anything. There is a causal factor for the PROCESS of evolution, namely – you’ve guessed it – natural selection. Presumably, in the Stone Age there was variation in cognitive mechanisms that our hunter-gatherer ancestors had at their disposal. Some of these mechanisms were better adapted to the EEA than others, and so natural selection determined which ones disappeared and which ones survived. As such, you might say that natural selection is a causal factor in the process of evolution. But, clearly, the different cognitive systems in the Stone Age all had their own causal factors, and natural selection simply intervened in the resulting variation. Natural selection didn’t ’cause’ those different cognitive systems, it only selected among them. In the same way, natural selection (let alone ‘evolution’) didn’t cause human cognition. This is not a ‘semantic’ discussion (as if ‘semantic’ is the same as ‘trivial’…), I think, but a crucial logical issue.

    • Alex

      The Stone aged mine thing is an assumption though one with logical support… we assume that our minds are the products of natural selection and so we constrain the types of hypotheses we generate–i.e. having a hypotheses about fingers being designed for texting seems implausible.

      You are right that the answer to the question “why is there X cognitive mechanism” is not caused by natural selection it is caused by random variation. But if you question is why did X mechanism propagate and become prevalent in a population… then I would say that natural selection is the cause or more specifically that the mechanism resulted from the non-random survival of randomly varying replicators–i.e. evolution. Therefore I don’t find is weird to say that evolution caused this trait to propagate anymore then I think it is weird to say that a if I drop a piano off a roof that gravity was a cause of the person’s death. That would not be the best way to describe the cause… but still a cause no less. Therefore I think you lose even the semantic debate.

      But lets say I lose that. Your argument seem semantic (boring) to me unless you can explain to me how this would change the way that EP’s do their work. It seems like all the things you recommend (and this paper recommends) are things that evolutionary psychologists already do. Even if evolution or natural selection were not a cause, it would not change the way EP is practiced. I am personally tired of being told by others like Gould that we don’t understand by-products, ect. There are only so many times we can be perfectly clear about what we do and then have condescending others tell us that we should we doing what we already do.

      I honestly have to stop this conversation because I no longer understand what you are arguing. You said that it was cool to use evolutionary explanations to constrain our hypotheses and inform the types

      Whenever I say we do X… you say ok X is cool, but you don’t do X based on a quote from a paper that is critical of your view without quoting actual EPers.

  • David Pinsof

    Dear Charlie,

    All EP does, at least as I see it, is use evolutionary theory to generate hypotheses about human behavior and cognition. So I’m not sure what it is about the statement “our modern skulls house a stone age mind” that bothers you. I take this statement as nothing more than a (colorfully-written) rule of thumb for generating hypotheses. For instance, we are unlikely to find complex psychological adaptations suited for modern life, and so looking for “contraception avoidance” mechanisms is bound to be a waste of time. Similarly, it might prove fruitful to look for “snake avoidance” mechanisms, even though in today’s environment snake bites account for a negligible number of deaths.

    As far as the proximate vs. ultimate distinction, I see this as both semantic and trivial. Whether or not a ‘process’ can be a ’cause’ seems of little importance to me. If there are some negative consequences of me thinking that processes like natural selection can ’cause’ a particular adaptation to arise, then please let me know. Otherwise, I see this issue as unworthy of additional finger-muscle exertion.

  • http://deleted Charlie D.

    Dear Alex,

    I think you’re right, that we should end this conversation – it doesn’t seem to evolve, as it were. I’m just puzzled by your inconsistencies. First you say that “we assume that our minds are the products of natural selection” and a little later you say that “You are right that the answer to the question “why is there X cognitive mechanism” is not caused by natural selection”. Talking about ‘logical support’, eh? Then you top it off by concluding that our cognitive mechanisms are “caused by random variation”. This doesn’t make any sense to me, so no wonder I am ‘losing even the semantic debate’….

    • Alex

      I was watching baseball and sent off the last response before I was finished editing it… hence why it was full of typos and trailed off at the end there. By random variation I meant “random mutations”–mutations are what cause the existence of the mental machinery and natural selection is the cause of said traits propagation. I’d like to note that you seem to keep going back to the well with this semantic debate over the word cause and ignore my request that you explain how this pedantic point would change the way we do our science. I’m don’t think you are right about the cause thing at all, but I also don’t care about being right about that. I need to learn not to engage in this sort of thing:

  • D Ruhl

    Hello Dr Kurzban,
    Maybe I’m missing something obvious here, as I haven’t paid much attention to EP since undergrad, but I don’t see how your argument about simple vs. complex adaptations addresses the point about recent selection made in the paper. Yes, much (maybe most) of the recent selection reported may involve “simple” non-cognitive traits (lactose tolerance, skin melanin, etc), but – as the PLOS authors point out – much of it is also concentrated in neurally-expressed genes. To me this just doesn’t jibe with a declaration that psychological adaptations were “complex” and too gradual to have changed much lately. Presumably, these neurally-expressed genes were swept to fixation because they had some substantive effect on behavior/cognition. How does this NOT undermine the “modern skulls house a stone-age mind” notion – or at the very least make the extrapolation of current behavior to Pleistocene causes imprudent? Put differently, if evidence of recent (and potentially accelerating, see SI of Hawks et al 2007) selection on neurobiologically-relevant genes does not undercut the “stone-age mind” concept… what set of data would? Hypothetically, how COULD it be falsified? The question isn’t meant facetiously, nor do I have some anti-EP axe to grind; it’s just that, from the outside looking in, one gets the impression that certain tenets are less hypotheses to be tested than doctrines to be defended. I’d be happy to be proven wrong on that point.
    Thanks, and enjoyed the blog.

  • http://deleted Charlie D.

    Dear Alex,
    I think we’re making progress here. You are absolutely right that random mutations are the historical ’causes’ of cognitive mechanisms, but that automatically makes evolutionary theory useless for studying these mechanisms. (but it’s absolutely wonderful for studying evolution, of course!). So, you’ve hit the ’cause thing’ on the head, and I wish you and your fellow EPs all the best with continuing attempts at unravelling the human mind. I’d hate to be ‘pedantic’, so I will follow your earlier suggestion to terminate this debate, and leave you in the very capable hands of David Ruhl. Oh yes, my wife thought that cartoon was spot on…..

    • Alex

      Well it’s good we found something to agree on (the cartoon). Also, above you agreed that you can look at ultimate explanations to constrain your hypotheses about proximate mechanisms so it seems like we actually both agree that using natural selection can inform hypotheses about the mind. The reason for this of course goes back to what I said above.

      When I say that natural selection caused the trait to be present in human beings, I mean that it is the reason the trait in question has stuck around. Fortunately for us EPs natural selection is much like George Costanza–it is very very frugal and therefore most traits that are still present today are there for a purpose. That is what makes natural selection such such a useful tool for asking how the mind works computationally. Though it is a pretty crummy tool for answering the question how a gene would mutate to produce a trait to begin with… but then again that is not the question we EPS are trying to answer.

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