Monday, October 15, 2007

Why Pigs Don't Have Wings

 
Jerry Fodor publishes a critique of adaptationism in London Review of Books. The title is Why Pigs Don’t Have Wings and it's an excellent read. I wish I could write like this ...
In fact, an appreciable number of perfectly reasonable biologists are coming to think that the theory of natural selection can no longer be taken for granted. This is, so far, mostly straws in the wind; but it’s not out of the question that a scientific revolution – no less than a major revision of evolutionary theory – is in the offing. Unlike the story about our minds being anachronistic adaptations, this new twist doesn’t seem to have been widely noticed outside professional circles. The ironic upshot is that at a time when the theory of natural selection has become an article of pop culture, it is faced with what may be the most serious challenge it has had so far. Darwinists have been known to say that adaptationism is the best idea that anybody has ever had. It would be a good joke if the best idea that anybody has ever had turned out not to be true. A lot of the history of science consists of the world playing that sort of joke on our most cherished theories.
UPDATE: Read Jason Rosenhouse's take on the Foder essay [Fodor on Natural Selection]. Jason makes some good points but I think he misses the main idea; namely that many scientists (and philosophers) have an inordinate confidence in natural selection as the explanation for almost everything in biology that's important (to them).


[Hat Tip: Andrew Brown at Helmintholog: Adaptationism contested. Andrew is the author of "The Darwin Wars."]

[Photo Credit: Uncyclopedia.]

35 comments :

  1. I've been reading these blog posts on the adaptationism debate for a while now and I still don't see what the fuss is all about. The proportion of changes that are due to adaptation (call it p) is a number between 0 and 1. Everyone agrees that p is larger than 0, and everyone (surely?) agrees that it is smaller than 0.5. So the entire debate is just a matter of speculation about the exact value of a parameter (which we don't have enough data to estimate accurately, and which surely varies hugely over time and between species) in a fairly narrow range. What am I missing?

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  2. I didn't care for Fodor's writing. I had to get at least a third of the way through before he managed to maintain my attention. You can probably guess that I am not an opera fan.

    Anyway, when he says "adaptationism," he seems to mean pan-adaptationism. Everyone one of his "alternatives" still involves adaptation. Evo-Devo? You're still selecting for something, you're just adding a mechanism for how that something comes about. Free-riding? Something still has to be selected for to be free-ridden on. Natural selection is not going away. Certainly other things will be added to it, but there's no way it will be discarded.

    I didn't think his rejection of the comparison of natural to artificial selection was as deep as he seems to think it is. Does it matter so much whether the selective criteria are the result of a mind or not? Not from the point of view of the organisms being selected. It certainly has some benefit from the point of view of the one doing hte selection, because you can select from a broader range of traits; things without survival value or things with an evolutionary path ('channeling' seems like a bad word for this) tha tmight not otherwise occur.

    And he never really gets to the nitty-gritty of his title metaphor: pigs don't have wings because they, like us, are trapped in the tetrapod body plan.

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  3. Fodor:"...if the theory of natural selection turned out not to be true...If phenotypes aren’t selected at all...," and he's working on a book about "evolution without adaptation"? You seriously link approvingly to this pseudo-gutting of a bunch of pure straw men?

    Jason's right. This is a knee-jerk, reactionary response to the excesses of evolutionary psychology (for which I do not carry water). It has little to do with the way real "adaptationists" actually think.

    And your summary of the essay's main idea: "that many scientists (and philosophers) have an inordinate confidence in natural selection as the explanation for almost everything in biology that's important (to them)" is, of course, your own oft-expressed opinion, but Fodor goes way, way beyond this.

    Speaking for myself, my confidence in natural selection is as an explanation for adaptation, which I insist is empirical. If you argue with that, I conclude that either you doubt that adaptation is prevalent in real organisms (which would suggest to me that you are armchair- or lab-bench-bound and have little knowledge of organisms and environments) or you think that there is some process other than selection that can result in adaptation (in which case you should hurry up and publish, since nobody else has a good idea).

    And now I'm done taking the bait here at Sandwalk.

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  4. "natural selection is as an explanation for adaptation, which I insist is empirical"

    That's BS. You have failed to provide a single empirical case in which directional selection is found to be the main responsible for the origin fo an adpatation.

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  5. konrad asks,

    What am I missing?

    What you're missing is the way one looks at the process of evolution. One group tends to see everything important as an adaptation while the other group struggles with the idea that lots of things may be accidents.

    The difference is reflected in how you form hypotheses. The adaptationists tend to formulate hypotheses based on natural selection of a characteristic. The problem is not that such hypotheses are formulated, it's that they are frequently assumed to be the correct explanation. It's almost as if once a plausible adaptationist explanation is created that's the end of the investigation.

    Let me give you an example. If someone were to ask you why women go through menopause, chances are you'd reply with some version of the grandmother theory. Once there was an adaptationist explanation—thanks to Hamilton—it's almost as if all non-adaptationist explanations disappear.

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  6. Sven DiMilo says,

    Fodor:"...if the theory of natural selection turned out not to be true...If phenotypes aren’t selected at all...," and he's working on a book about "evolution without adaptation"? You seriously link approvingly to this pseudo-gutting of a bunch of pure straw men?

    The title of my book is "Evolution by Accident." As you might guess, I share some of the same concerns as Fodor, even though I admit that he exaggerates. Frankly, I find his hyperbole a bit annoying but then I also find the hyperbole of Dawkins and Dennett annoying. Isn't it interesting that adaptionists are very selective concerning the kinds of exaggerations that annoy them?

    This is a knee-jerk, reactionary response to the excesses of evolutionary psychology (for which I do not carry water). It has little to do with the way real "adaptationists" actually think.

    Out of curiosity, why do you think that adaptationists like Dawkins and Dennett haven't been vocal in their criticism of evolutionary psychology?

    Speaking for myself, my confidence in natural selection is as an explanation for adaptation, which I insist is empirical. If you argue with that, I conclude that either you doubt that adaptation is prevalent in real organisms (which would suggest to me that you are armchair- or lab-bench-bound and have little knowledge of organisms and environments) or you think that there is some process other than selection that can result in adaptation (in which case you should hurry up and publish, since nobody else has a good idea).

    There's not a pluralist in the world that would disagree with you. Natural selection is the only viable explanation for adaptation. The fact that you would even ask this question shows me that you have no idea what this debate is all about.

    Let me give you a quick summary of what you've missed. The question is not what is responsible for something that is clearly an adaptation. The question in many cases is whether a given characteristic is an adaptation.

    The adaptationists tend to the belief that most phenotypic characters are adaptations and then they leap directly to the explanation, which of course involves natural selection. The pluralists do not make that initial assumption unless it's warranted. Consequently the non-adaptationist explanations remain in play instead of being dismissed a priori.

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  7. Adaptationists convince themselves that NS is sufficient to explain complex adaptations, when actually, it isn't. I think this is very clear in the way they mishandle Gould and Vrba's insight abut exaptation, by:

    1) Believing that natural selection is indeed sufficinet to explain complexity and adaptation. False! You REALLY can't go much far in explaining without exaptation

    2) That natural selection is the only GOOD explanation of adaptation and complexity. Exaptation basically just doesn't exist for them

    I think any person taht has ever SERIOUSLY researched actual cases knows how important exapatation actually is in the origin of complex adaptaions.

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  8. "Natural selection is the only viable explanation for adaptation"

    Nonsense.

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  9. suffice it to point out how much adaptation is epigenetic; and how much adaptation is the result of that fortunate coincidence (chance) we call exaptation.

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  10. I will grant that not all biological adaptation (order, fit, regulation) is due to selection at the individual level. Some of it is the result of selection at other levels - intra-genomic, cellular, social group, inter-species symbiont, constructed niche.

    Hamilton, Williams, and Trivers certainly didn't figure everything out, but they cleared a lot of hand-waving deadwood and they got evolutionary biology back on a firming theoretical footing, from which workers like Nowak, Deacon, West-Eberhard and others could take it in new directions.

    Tupaia

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  11. Yes, when Jerry Fodor adapted philosophy to evolutionary psychology, he made a terrible mistake by designing an accident.

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  12. "The fact that you would even ask this question shows me that you have no idea what this debate is all about."
    I am well aware of your reluctance to assume that a phenotypic trait is an adaptation. I'll even grant that in the absence of data, that's often a judgment call. Maybe that is what "this debate" is about, for you. But that is decidedly NOT the context of this particular bout of the debate; we were talking about about what Fodor wrote, not what you think. I asked the question in direct response to the article to which you originally linked approvingly, as an "excellent read" (no indication that you thought it "exaggerated" or "annoying" until now, in comments). If you bait the hook with a worm and catch a fish it's disingenuous to castigate the fish for not biting on a minnow instead. If that makes sense.

    As I read Fodor's essay, he is going well beyond what a reasonable and informed pluralist like yourself (as opposed to, say, sanders) should be willing to agree with. Hence my perhaps intemperate response.

    As to why "adaptationists like Dawkins and Dennett haven't been vocal in their criticism of evolutionary psychology," you'd have to ask them. Personally, I think there is a plausible grain of truth to the whole thing...it's not all excess.

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  13. We have been here before, and I don't see any new arguments. Nor do I see why adaptionists can't follow their own research strategy, as long as they are willing to test their models.

    pigs don't have wings because they, like us, are trapped in the tetrapod body plan.

    Surely an adaptionist would first go "why would they"..., um, no, that didn't come out right, I mean "what is the selective pressure"? :-P (Actually I would hitch on to Larry's complaint here, why are we trapped? Birds and bats circumvented this. It may be correct in the discussed cases, but it is an insufficient description for this poor layman.)

    It is slightly wrong too, unfortunately there is a profusion of such creatures fouling the streets, renamed as "pigeons". :-\

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  14. That's right. You cannot label me Gouldian.
    I do not simply IGNORE epigenetic adaptation, for one. And I disagree: I don't think selection is the main mechanism that explains adaptations, like Gould did. Gould's point becomes the mere observation that neutral traits are possible, yet because adaptation IS fundamental, by conceding this point he ultimatly gives away the entire "battle" as a mere anecdote, a footnote to the really good stuff: you know it. Natural selection!!!!

    Gould was, in fact, too much of selectionist. After all, he ambitiously wanted to extend the levels for selection to several other supraorganismal units, including clades...hmmmmmm....

    I don't know abut you guys but I tend to be more picky about what actually qualifies as a unit of selection

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  15. Sanders: "[Gould] to extend the levels for selection to several other supraorganismal units, including clades"

    Dawkins, Gerhart & Kirschner also think clade selection is important. For intra-organismic (somatic) selection, see for example Stearns on selection arenas, many others on selection in brain, adaptive immunity, gametes, cancer. (e.g. Cziko on universal darwinism.) Multilevel selection is related to major evolutionary transitions (Nowak, Jablonka & Lamb).

    http://www.dialogonleadership.org/Varela.html

    Francisco Varela: "...evolution doesn't have one single unit of selection, but is multiple. …So if you don't have multiple levels of selection, you don't understand evolution at all"

    Tupaia

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  16. Maybe you would like to read what Varela thought about what the theory of clonal selection CANNOT explain about the immune system. The problem of the distinction of self from non-self.

    You know that both selection as a developmental theory, as well as the idea of "higher" units of selection, are still far from being mainstream "facts", to put it VERY kindly.

    At any level, we must be clear about exactly what is selection supposed to explain. For example, does anyone think that clade selection can "produce" evolvability? There are intrinsic limits to what a "selection" framework can offer at ANY level. Unless certain very specific conditions are met (as in artificial selection in sexual organisms), selection is not at all as wondrously powerful as some would have it.

    Selection has been proposed for everything, from genes to organisms to demes, clades, rnas, even cosmological units of selection. The "great importance" of selection to the evolutionary process is NOT demonstrated by such "versatility" of the framework. If anything it suggests that selection has been abused, that is, it has been falsely extended beyond the actual limits within which it remains a useful concept.

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  17. I can't imagine why varela could suddenly think that selection at all levels was something so wonderfully explicative...I guess he wished to emphasize the fact that there are "higher grade" autonomous systems, but he should KNOW that bowing down to the selectionist perspective completely undermines the relevance of a a truly systemic outlook. Selectionist thinking is NOT the systemic way of explaining the evolution, neither of organism nor of any other biologicla units.

    Where did you get that varela quote from?

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  18. The url for the quote is right there in the post.

    "Selection has been proposed for everything, from genes to organisms to demes, clades, rnas, even cosmological units of selection."

    Don't forget quantum darwinism, memetics, evolutionary archaeology...

    Different levels in the biological hierarchy and various inheritance systems have unique characteristics that affect the role of selection and other processes involved in the construction of form and function.

    Varela and Maturana, 'Autopoiesis and Cognition,' 1980. Do a search on "selection"
    http://tinyurl.com/3yaubq

    Tupaia

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  19. On pigs and wings: It's probably easier to lose a body segment than gain one. (For example, trends in arthropod evolution.) Hence birds and bats don't have forelimbs in addition to wings.

    Tupaia

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  20. ...because they didn't change their body plan by adding or losing a segment.

    Tupaia

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  21. larry moran said: "What you're missing is the way one looks at the process of evolution. One group tends to see everything important as an adaptation..."

    I think I'm starting to get it. This debate doesn't exist in molecular evolution, because everyone knows the majority of changes at the DNA level are not adaptive. But in phenotypic evolution (a field I'm not familiar with - hence my attempt at trying to educate myself here) the assumption is that the majority of neutral changes are never observed, so we have no idea how many of the so-called "important" (to whom?) changes are adaptive. This depends entirely on the definition of "important" - we could resolve the debate trivially by defining it to refer only to adaptive changes - is that what some adaptationists do implicitly?

    Assuming that no one is about to agree on what does or does not qualify as "important", we clearly need to look at some other criterion for which are the phenotypic changes to study. Substituting "observable" for "important" won't do, because molecular changes are also observable (so for "observable" changes the debate is already resolved). One could presumably come up with some definition based on observable quantitative traits, but the point is that surely the degree of preponderance of adaptation is critically dependent on what one is looking at (which is a function of the available technology). If one looks at low levels (close to the molecular level), one will presumably see a preponderance of non-adaptive changes; at higher levels there is more room for postulating adaptive explanations. But until there is a way of quantifying this there can be no proper way of measuring the preponderance of adaptive changes, in which case the debate is just non-quantitative pseudo-science, right?

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  22. "my confidence in natural selection is as an explanation for adaptation, which I insist is empirical"

    "Natural selection is the only viable explanation for adaptation"

    Could someone please define "natural selection" and "adaptation" in this context? I thought adaptation refers specifically to changes that have risen to fixation under the influence of positive selection, but that is clearly not the way the term is being used here.

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  23. Another question (I'm trying to convince myself that it makes sense to consider the selective pressure on a large set of molecular changes that are fixed in succession as if the whole set is a single change - if not, does any of the terminology in phenotypic evolution make sense?):

    Suppose a given phenotypic change is caused by 100 molecular changes, 95 of which are neutral and 5 of which are adaptive. Is the phenotypic change said to be adaptive? Is there consensus on this?

    What about a phenotypic change caused by 1000 molecular changes, 999 of which are neutral while the remaining one is arguably adaptive with very slight selective pressure?

    (For simplicity, let's assume that the changes happen in a fixed order, so that epistatic effects don't have to be considered separately. Also, I'm assuming that the definition need not be a function of when in the sequence of changes the adaptive change(s) occur.)

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  24. (Actually I would hitch on to Larry's complaint here, why are we trapped? Birds and bats circumvented this.

    Birds and bats managed to get wings by giving up usable arms. They are still tetrapods. Six or more limbs would be an obvious improvement, this is the way that angels and pegasi are drawn.

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  25. Nobody can confuse that M&V quote with an apology for the central role of selection. Maturana and Mpodozis therefater made it clear that selection does not guide evolution.
    I myself have never denied that selection is an important part of the evolutionary process. However, it is by no means the only viable explanation to adaptation.
    Quite on the contrary, the precise relation of selection to adaptation is debatable since we lack adequate empirical grounds for the claim that natural selection is the main mechanism behind the origin of new adaptations, wheres we have abundant evidence for other mechanisms giving origin to adaptations ("monsters", exaptation, epigenetic)

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  26. M&V, 'Autopoiesis and Cognition' 1980, p.111:

    "it is to be expected that if the proper contingencies are given, higher order autopoietic unities will be formed through selection."

    Note: M&V are referring to evolutionary transition; they give the example of origin of multicellularity.

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  27. Yes: M& V were much more selectionist at the beggining; you know, they were born out of this darwinian world, like everyone else. Varela did not concern himself as much with evolution as Maturana did. Maturana substantially removed himself from selectionism thereafter.

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  28. This review article is a useful resource on adaptation through natural selection and a critique of Maturana:

    Evolution by natural selection: more evidence than ever before
    RF Nespolo
    Revista Chilena de Historia Natural

    http://www.scielo.cl/scielo.php?pid=S0716-078X2003000400012&script=sci_arttext

    Tupaia

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  29. Believe me; Nespolo's article is much more useful as a resource on adaptation by natural selection, than as a critique of Maturana.
    Nespolo does not understand the first thing about Maturana. His critique reflects that quite clearly.

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  30. Jason Rosenhouse is censoring me on his blog. For no good reason, of course. I guess he felt his faith in selection shaken and got scared haha. Freakin sleectionist amateur.
    Scienceblogs suck...long live the sandwalk, haven for the lonesome antiadaptationist.

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  31. Let me give you an example. If someone were to ask you why women go through menopause, chances are you'd reply with some version of the grandmother theory. Once there was an adaptationist explanation—thanks to Hamilton—it's almost as if all non-adaptationist explanations disappear.

    Yes, it's almost as if there hasn't been a huge discussion in the literature, back and forth, pro and con, after Hamilton, with lately several studies demonstrating the grandmother effect in real demographic data from human populations. Or maybe a certain prof Moran has simply not bothered to read said literature because of his preconceptions. For shame.

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  32. Windy,

    I read the literature. Here's an example from Jamison et al. 2002.

    An unresolved question arising from human evolutionary research relates to the function of the postreproductive period in human females. If menopause is not merely an artifact resulting from the benefits of civilization, there must be an adaptive mechanism favoring the offspring of women who continue to thrive well past the time of their last ovulation. The "grandmother hypothesis" was developed on the basis of the original suggestion by Williams (1957 Evolution 11:32-39) that "stopping early" would benefit already-born children. This idea, combined with the concepts of kin selection (Hamilton 1964 J Theor Biol 7:1-52) and parental investment (Trivers 1972 Sexual Selection and the Descent of Man, Chicago: Aldine, p. 136-179), was expanded to suggest that postreproductive women (in contrast to males) contribute to their inclusive fitness by extending support to their grandchildren. We used discrete time event history analysis (Allison [1984] Event History Analysis, Newbury Park: Sage; Allison [1995] Survival Analysis, Cary, NC: SAS Institute) and logistic regression on data provided in population registers (Shūmon Aratame Chō, or SAC) from a village in central Japan, covering the period from 1671-1871, in a preliminary investigation of the effects of household grandparental presence on the probability of a child's death. We found that after accounting for the presence of other household members, the only grandparent whose presence exerted a consistent negative effect on the likelihood of a child's death was the mother's mother. Due to the small sample size of households that contained maternal grandmothers, these results failed to achieve statistical significance.

    There are other studies that show a more positive correlation between the presence of a grandmother and survivability of grandchildren but then there are also correlations between infant survivability and the presence of an older sibling or a maternal aunt.

    In most cases that I have read about the percentage of grandmothers who are available to fill this role is quite small. This is important when you're thinking about selecting for this role in a large population.

    What you seem to be missing is the connection between these observations and the explanation of menopause in our primitive hunter-gatherer societies. Just because the presence of grandmothers (without grandfathers) can be a help to a small number of mothers does not prove that the effect was significant enough in the past to select for menopause.

    Maybe there was selection for getting rid of grandfathers since that's the best way to ensure that a maternal grandmother will be available to help out with the grandchildren! :-)

    (Note that in the absence of grandfathers, there's not much need for menopause to avoid pregnancy. Unless, of course, you imagine that our ancient grandmothers were a lot more promiscuous than modern grandmothers.)

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  33. Interesting that you stopped quoting there. This is what the rest of the abstract says:

    "Due to the small sample size of households that contained maternal grandmothers, these results failed to achieve statistical significance. Their importance, however, is in what they suggest about future research, i.e., census data from preindustrial societies can provide a basis for testing evolutionary proposals, including the "grandmother hypothesis.""

    So, a single study with too small sample size to draw conclusions, but suggesting avenues for further research! I wonder why you think this furthers your point, if there are other studies showing a "more positive correlation". What about the more recent work of Virpi Lummaa in Finland and the work in Gambia? What about menopause in whales?

    "...there are also correlations between infant survivability and the presence of an older sibling or a maternal aunt."

    Great, so maybe there was kin selection for a wider range of interactions. A more complex situation does not negate the possibility of an adaptive explanation.

    "In most cases that I have read about the percentage of grandmothers who are available to fill this role is quite small."

    If you mean that people generally did not live long enough: not according to Hawkes.

    "Just because the presence of grandmothers (without grandfathers)"

    Where do you get that grandfathers need to be "absent"? My grandmothers, at least, managed to contribute to the grandchildren in the presence of grandfathers.

    "Unless, of course, you imagine that our ancient grandmothers were a lot more promiscuous than modern grandmothers."

    If we go back to the LCA with chimps, I can certainly imagine that.

    But, whatever the results further research provides, your assertion that the grandmother hypothesis caused all other explanations to "disappear" is false. In addition, you imply that people choose the grandmother explanation because of myopia, not because they have been convinced by the evidence.

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  34. As you know, windy, that's Dr. Moran's MO: Somebody suggests a hypothesis of adaptation for some trait, he waves around a copy of Gould and Lewontin and says "it might not be!," and then expresses his personal incredulity as if it's more rigorous than the original hypothesis.
    *shrug* It gets old.

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  35. The Gould-waving seems to get especially vigorous if we are talking about behavioural adaptations in a certain great ape :) Oh well, just putting in a good word for the work of fellow Finns like Lahdenperä, Lummaa and Westermarck (the latter's classic work got also dissed here as just-so stories.)

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