Tuesday, May 12, 2009

Jason Rosenhouse Doesn't Understand Pluralists

 
Jason Rosenhouse has posted some comments on a recent book review by Richard Lewontin. In that book review, Lewontin—who along with Gould is the co-author of the spandrels paper—questions the emphasis on natural selection and the use pf "Darwinism" as a synonym for evolution. Read Lewontin on Darwin to see what Jason thinks of the book review.

I want to focus on a specific question that Jason Rosenhouse asks.
I've never really understood what it is exactly that anti-selectionists are complaining about. If they agree that complex adapations arise as the result of gradual accretion mediated by natural selection, then I fail to see how they are really so different from people like Richard Dawkins or Daniel Dennett (two people often described as being beknighted uber-selectionists). If they do not agree then I would like to hear their proposed alternative mechanism.
The original paper by Gould and Lewontin, The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme, explains the problem very well. The authors begin their criticism with ...
We wish to question a deeply engrained habit of thinking among students of evolution. We call it the adaptationist programme, or the Panglossian paradigm. It is rooted in a notion popularized by A.R. Wallace and A. Weismann, (but not, as we shall see, by Darwin) toward the end of the nineteenth century: the near omnipotence of natural selection in forging organic design and fashioning the best among possible worlds. This programme regards natural selection as so powerful and the constraints upon it so few that direct production of adaptation through its operation becomes the primary cause of nearly all organic form, function, and behavior. Constraints upon the pervasive power of natural selection are recognized of course (phyletic inertia primarily among them, although immediate architectural constraints, as discussed in the last section, are rarely acknowledged). But they are usually dismissed as unimportant or else, and more frustratingly, simply acknowledged and then not taken to heart and invoked.
The anti-selectionists—I am one—do not question the fact that adaptations are produced by natural selection. What we question is whether everything in evolution is an adaptation. We question those who think that "evolution" and "natural selection" are synonyms. And since "Darwinism" is equivalent to evolution by natural selection we question whether evolution is the same as Darwinism.

We pluralists like to point out that much of evolution is due to random genetic drift. Since Darwin's name is not associated with the theory of evolution by random genetic drift, it is inappropriate to say that all of evolution is Darwinist.

It's not that complicated. It was all explained in the classic spandrels paper published 30 years ago. Complex biological structures may be due entirely to adaptation, or they may be mostly an accident that's arisen by random genetic drift, or they may be due to combinations of drift and selection.


8 comments :

  1. On this topic, see Jerry Coyne's May 12 post on Richard Lewontin’s review of Coyne's book Why Evolution Is True at
    whyevolutionistrue.wordpress.com

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  2. Thanks for the post. Let me point out that I also wrote this:

    “Given Lewontin's past writing (most notably his spandrels paper with Stephen Jay Gould) I would guess that his point is that some biologists are too quick to attribute some anatomical feature of some organism to the prolonged working of natural selection.
    This also seems to be the point you are making here.

    My concern is that in making this point some on your side of this use rhetoric that can easily be misconstrued. I think someone could read Lewontin's essay and come away thinking that natural selection is relatively insignificant in evolution. For exaple, Lewontin writes

    “Where he [Jerry Coyne] is less successful, as all other commentators have been, is in his insistence that the evidence for natural selection as the driving force of evolution is of the same inferential strength as the evidence that evolution has occurred.”I am sure I will be hearing that line at the next creationist conference I attend. I would feel better if Lewontin had added a line such as, “Certainly natural selection is a compelling explanation for complex structures like bird wings and immune systems, but there is much more to evolution than that.”

    At any rate, you would know better than I whether out of control adaptive thinking is a problem for biological research. My impression, though, was that Gould and Lewontin were really exaggerating the extent to which Just-So stories dominate the discourse.

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  3. Viruses have lots of easy-to-understand examples of "its not adaption, sometimes shit just happens." Sure, influenza makes you sneeze and polio makes you poop and chicken pox make you all blistery so these viruses can be transmitted person-to-person.

    But there is no evolutionary advantage to HPV causing cervical cancer. Sometimes, shit just happens.

    There is no evolutionary advantage to polio causing paralysis. Sometimes, shit just happens.

    There is no evolutionary advantage to HSV-1 causing blindness. Sometimes, shit just happens.

    Yay :P

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  4. "I've never really understood what it is exactly that anti-selectionists are complaining about. If they agree that complex adapations arise as the result of gradual accretion mediated by natural selection, then I fail to see how they are really so different from people like Richard Dawkins or Daniel Dennett. If they do not agree then I would like to hear their proposed alternative mechanism"

    Jason is right. So let me be clear about this: I do not agree that adaptations (complex or npn-complex) are mainly the result of natural selection.

    Phenotypic plasticity and exaptation are two important mechanisms other than selection that are involved in the origin of adaptations (complex, and non-complex). Larry likes to ignore phenotypic plasticty but it is right there in the spandrel's paper that he supposedly has read so deeply.

    “Certainly natural selection is a compelling explanation for complex structures like bird wings and immune systems"

    Biologists are not concerned about the "compellingness" but about the scientific usefulness of an explanation. To say "the bird wing is the result of natural selection" is as vacuous a statement as can be made about the evolution of the wing. It is further patently unrealistic, since natural selection is only a fraction of what is needed to understand the evolution of things like bird wings and immune systems. I can discuss a lot about the evolution of the bird wing, and I can tell you, what you're doing is not science, it's butchery.

    The only reason I can see some people still clinging on to this "selection explains complex adaptation" thing is not for any great empirical documentation or true scientific support of such a thing. They do it to merely becuase this was the way Darwin understood natural selection as an alternative to paleys ( crappy) argument for design.

    The reasons, of course, for rejecting intelligent design reside in making the distinction of scientific or non-scientific explanations, and does not reside in any specific evolutionary mechanism. Maybe if neoatehists were smart enough to realize this they would stop trying to squish the entirety of evolutionary biology into the narrow box of "natural selection".

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  5. So, to summarize the debate as I've read it here and there:

    "pluralists" acknowledge that selection is important, but doesn't explain everything.

    "ultra-selectionists" acknowledge that constraints are important, but don't explain everything.

    And the point is? Oh yeah, there's a major difference in that each acknowledge many influences over evolution, but that the others disregard their favourite explanation.

    Eventually, "pluralist" is a poor wording because it implies the others are not, which is simply a strawman.

    Now, the debate runs alike:
    "Selectionist": Horns in rhinos were probably selected because it provided a useful defense against enemies, this is adaptive!
    "Pluralist": You're wrong, two horns or a single one is a developmental constraint because it does not make any difference in fitness.
    "Ultra-Meist": Hum, and what about sexual selection? Two horns are quite cool, don't you think?
    "Post-Pluralist": Okay, it just looks like horns are useful as defensive weapons today, in that sense these are possibly developmentally constrained exaptive adaptations, but you know base ball, don't you? It is thus possible that pre-horns in a distant past were used as efficient sexual displays and increased fitness via attractiveness but they are still evolutionary constraints because you know, rhinos don't fly.

    (Chirping rumours of battle).

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  6. Laurent, Jason gets it, but you don't. This is a question about whether adaptation rises only by natural selection. Everyone agrees that both adpatiove and non-adpatove traits exist. But when you see and adpataion, is it immediately proof that it is the result of natural selection? (the answer: of course not)

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  7. Not much changes around here, I see. Adaptation at the population level is the product of selection, period. Phenotypic plasticity, is itself an adaptation (show me a case of plasticity that mismatches phenotypes to environments and I'll change my mind). Exaptations are structures that acquire a new function; the spread of the new function (and subsequent modifications to the original structure) occurs by selection. Most evolution occurs by drift at the genotype level; the conceptual leap to phenotype is dubious. Complex biological structures may "arise" by drift, but they must be maintained in populations by selection. If there is a cost to making and maintaining them (as is implied in "complex") then they are not "neutral."

    *shrug* So there's my opinion--it hasn't changed either.

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  8. "Adaptation at the population level"

    That may have nothing to do with the origin of biological structures. For instance, the fitness of a population can change with no new phenotypes involved. We're talking about the origin of organic structures here.

    "show me a case of plasticity that mismatches phenotypes to environments and I'll change my mind"

    Say we have environmental exposure to a teratogen, and we get several malformations. Not necessarily a "fit to environment" huh.

    "Most evolution occurs by drift at the genotype level; the conceptual leap to phenotype is dubious"

    What the hell do you mean? Obviously mutations producing non-adapative phenotypic traits exist.

    "Complex biological structures may "arise" by drift, but they must be maintained in populations by selection"

    In any case, selection is insufficient.

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