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Fodor on Natural Selection
16 Oct, 2007 11:50 am
Philosopher Jerry Fodor offers up the latest example of a familiar genre: essays declaring the forthcoming demise of natural selection, coupled with very little in the way of supporting argument. He is writing in the London Review of Books. There's quite a bit I find wrong with Fodor's essay. In this post, however, I will focus solely on what I take his main argument to be, and explain why I find it inadequate
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.
We should also note Fodor's version of “the theory of natural selection:”
But Darwin's theory of evolution has two parts. One is its familiar historical account of our phylogeny; the other is the theory of natural selection, which purports to characterise the mechanism not just of the formation of species, but of all evolutionary changes in the innate properties of organisms. According to selection theory, a creature's 'phenotype' - the inventory of its heritable traits, including, notably, its heritable mental traits - is an adaptation to the demands of its ecological situation. Adaptation is a name for the process by which environmental variables select among the creatures in a population the ones whose heritable properties are most fit for survival and reproduction. So environmental selection for fitness is (perhaps plus or minus a bit) the process par excellence that prunes the evolutionary tree.
Now, these are a confusing couple of paragraphs. They seem to conflate several key ideas for the purpose of creating a straw man. First, I assume that by “innate properties” of organisms Fodor means their genetic endowments, as otherwise I can make no sense of this at all. Natural selection is a process that affects gene frequencies in populations of animals over many generations. If Fodor has in mind innate properties that are not genetic, then I do not think that natural selection is offered by anyone as an explanation for them.
Second, I am not aware of anyone who seriously argues that natural selection is the sole explanation for the innate properties of organisms. Fodor gives no examples of anyone actually defending that view. The names usually associated with adapationism, such as Richard Dawkins, George Williams, Daniel Dennett, and John Maynard Smith certainly do not (or did not in Maynard Smith's case) believe any such thing. This looks like a pretty blatant strawman to me.
But the really egregious part of these paragraphs is the conflation of natural selection as the explanation for adaptations on the one hand, with the idea of adaptionism on the other. The former is, as far as I know, entirely unquestioned among biologists, while the latter is a derogatory term used by some critics (Stephen Jay Gould most famously) to describe an approach to certain biological problems thought by the critics to rest on faulty assumptions.
Fodor is, presumably, referring to Daniel Dennett when he talks about Darwinists saying that “adaptationism is the best idea anyone has ever had.” The trouble is that neither Dennett nor anyone else has ever said any such thing. Here is the full quote, from Dennett's book Darwin's Dangerous Idea:
Let me lay my cards on the table. If I were to give an award for the single best idea anyone has ever had, I'd give it to Darwin, ahead of Newton and Einstein and everyone else. In a single stroke, the idea of evolution by natural selection unifies the realm of life, meaning, and purpose with the realm of space and time, cause and effect, mechanism and physical law.
Elsewhere in his essay Fodor quotes the latter part of this statement, for the purpose of ridiculing it, albeit without crediting Dennett. So plainly he knows the full context of Dennett's statement. Either Fodor is guilty of an egregious misrepresentation of Dennett's views, or he has wrongly conflated “evolution by natural selection” with “adaptaionism.”
Whenever someone, especially a philosopher, starts claiming that there are major conceptual problems with natural selection or that selection is on its way out among biologists, I always like to bring it back to specific adaptations. The eye, for example. The usual account says that eyes evolved gradually through numerous intermediate steps, each one attainable from the one before by a chance genetic variation, with natural selection preserving the intermediate steps while waiting for the next variation to arise. That natural selection has such creative power is the really bold claim of Darwinian theory. If some reputable person is arguing that the usual account is wrong, not just in the details but in the fundamentals, then I will raise an eyebrow and listen with interest to what the fellow is saying.
But if the person is granting the basic accuracy of the usual account, and by extension accepting natural selection's role in crafting every other complex adaptation in nature, then I am afraid that whatever he is arguing for is something a great deal less than a scientific revolution. If you are conceding that natural selection is the explanation for complex systems, then you are automatically conceding that natural selection is the most important of evolutionary mechanisms.
In saying this I don't think I am merely expressing a personal preference for certain kinds of biological problems (explaining biological adaptations) over other kinds (explaining traits of organisms that are not obviously adaptations). I think it is fair to say that the main stumbling block in the acceptance of evolution, not just for creationists but for everyone, is the problem of complex systems. There's a reason Paley's argument was so convincing when he first devised it. Once you provide a naturalistic explanation for such complexity, everything else is a detail.
At any rate, I see nothing in this essay to suggest that Fodor is rejecting the usual account. He discusses some philosophical issues concerning the proper definition of the notion of “selection for,” but it looks to me like if you asked him where eyes come from, he would answer essentially like Richard Dawkins. For the record, I am not impressed by his arguments here (what he describes as “the conceptual issue” threatening the centrality of natural selection) but I will not address them here.
Fodor later turns to “the empirical issue:”
Even the hardest core Darwinists agree that environmental effects on a creature's phenotype are mediated by their effects on the creature's genes: its 'genome'. Indeed, in the typical case, the environment selects a phenotype by selecting a genome that the phenotype expresses. Once in place, this sort of reasoning spreads to other endogenous factors. Phenotypic structure carries information about genetic structure. And genotypic structure carries information about the biochemistry of genes. And the biochemical structure of genes carries information about their physical structure. And so on down to quantum mechanics for all I know. It is, in short, an entirely empirical question to what extent exogenous variables are what shape phenotypes; and it's entirely possible that adaptationism is the wrong answer.
This is a prelude to an argument that it is internal developmental constraints, as opposed to natural selection, that really drives evolution, but once again Fodor's phrasing is terribly confusing. “Adaptationism” is not a proposed answer to the question of the extent to which external, as opposed to internal, factors influence the phenotypes of organisms. Rather, it is an approach to biology that argues that in trying to explain the origin of some trait in an organism you should hypothesize that it is an adaptation and then use that hypothesis to formulate testable conjectures. Note that the hypothesis is the beginning, not the end, of the investigation, contrary to what some critics of adaptionism suggest. This approach has notched up far too many successes to be discarded cavalierly.
Presumably Fodor's point is that adaptationists accept a low standard of evidence in describing various traits as adaptions, thereby ignoring other possible mechanisms. He writes:
When you ask Darwin's question - why are phenotypes often similar? - you do indeed get Darwin's answer. But if you ask instead why it is that some phenotypes don't occur, an adaptationist explanation often sounds somewhere between implausible and preposterous. For example, nobody, not even the most ravening of adaptationists, would seek to explain the absence of winged pigs by claiming that, though there used to be some, the wings proved to be a liability so nature selected against them. Nobody expects to find fossils of a species of winged pig that has now gone extinct. Rather, pigs lack wings because there's no place on pigs to put them. To add wings to a pig, you'd also have to tinker with lots of other things. In fact, you'd have to rebuild the pig whole hog: less weight, appropriate musculature, an appropriate metabolism, an apparatus for navigating in three dimensions, a streamlined silhouette and god only knows what else; not to mention feathers. The moral is that if you want them to have wings, you will have to redesign pigs radically. But natural selection, since it is incremental and cumulative, can't do that sort of thing. Evolution by natural selection is inherently a conservative process, and once you're well along the evolutionary route to being a pig, your further options are considerably constrained; you can't, for example, go back and retrofit feathers.
That all seems reasonable on the face of it; but notice that this sort of 'channelling' imposes kinds of constraint on what phenotypes can evolve that aren't explained by natural selection. Winged pigs were never on the cards, so nature never had to select against them. How many such cases are there? How often does a phenotype carry information not about a creature's environment but about aspects of its endogenous structure? Nobody knows.
In the opening sentence of this quotation, Fodor is referring to common ancestry, not natural selection, as “Darwin's answer.”
Fodor is very taken with his winged pig example. His essay is titled, “Why Pigs Don't Have Wings.” And I agree that if the question is why we don't find various hypothetical phenotypes, then it is often implausible to say that at one time those phenotypes existed but then lost out in competition with other phenotypes.
But Fodor's question just is not one that biologists dwell on much. They're too busy trying to sort out the proper relationships among modern species, or trying to ferret out the intermediate steps of complex systems. They concern themselves with questions like, “BIllions of years ago there were no eyes. Today, there are lots of eyes. Where did those eyes come from?”
If the devotees of developmental constraints want to claim the lack of winged pigs as a victory for their side then they are welcome to it. The supporters of selection can still claim eyes, bird wings, flagellae, blood clotting cascades and every other complex system over which everyone gets so excited.
In addition to developmetnal constraints Fodor points to the possibility of linkages between certain traits. This is the spandrel idea popularized by Gould and Lewontin. The idea is that trait X might persist in a population not because it triumphed in Darwinian competition with various not X's, but because it is genetically linked with trait Y which itself was favored by selection. This, too, is hardly a new idea, and it is not one evolutionists inclined towards adaptationism have been ignoring.
In short, Fodor has rehashed some very familiar practical issues in teasing apart which parts of an organism are the products of selection and which parts arose from other evolutionary mechanisms. Yes, of course, it can be difficult to recreate precisely the evolutionary history of a modern species. But he has offered nothing to challenge the centrality of natural selection in explaining complex adaptations, and he certainly has offered nothing that augurs for a revolution in biology.
In the final paragraphs of the essay Fodor tells us what is really bothering him. Evolutionary psychology:
But I think there's also a moral about what attitude we should take towards our science. The years after Darwin witnessed a remarkable proliferation of other theories, each seeking to co-opt natural selection for purposes of its own. Evolutionary psychology is currently the salient instance, but examples have been legion. They're to be found in more or less all of the behavioural sciences, to say nothing of epistemology, semantics, theology, the philosophy of history, ethics, sociology, political theory, eugenics and even aesthetics. What they have in common is that they attempt to explain why we are so-and-so by reference to what being so-and-so buys for us, or what it would have bought for our ancestors.
From here Fodor dives into a litany of various evolutionary psychology explanations he presumably has seen somewhere or other. He is careful not to provide a single citation, which would make it possible to look into the details of the hypotheses he describes so callously. I suspect there's some serious oversimplifying going on here.
That aside, once again it is unclear what Fodor is suggesting. Is he saying that natural selection is not the primary explanation for why our brains have the structure and characteristics that they do? Does he think that such a complex, functional organ can come about by some mechanism other than natural selection? If he does, then I would like very much to hear his proposed explanation.
But it seems more likely that he is making the entirely conventional point that it is a difficult practical problem to tease apart which aspects of the brain were the targets of selection and which parts piggy-backed on those fitness enhancing traits. This, however, is not a claim that merits Fodor's melodramatic language about revolutions and the demise of natural selection.
Fodor's essay is quite long and I have only replied to a few brief excerpts. It is probably worth another blog entry discussing some of Fodor's more philosophical points. But for now it looks to me like Fodor has merely erected a familiar straw man version of adaptationism, and has rehashed a lot of cliched arguments against it. Worst of all, I find virtually nothing in this essay that is in any way new (a description of an interesting experiment on trait linkages in foxes being a notable exception), and nothing that comes close to justifying Fodor's strident language.
Fodor and Dennett have a history of tendentious disagreements. In one exchange, Dennett wrote of Fodor:
Now this really is absurd. Silly absurd. Preposterous. It is conclusions like this, built upon such comically slender stilts, that give philosophy a bad name among many scientists.
Based on this essay, I agree with Dennett's assessment.
Originally published on EvolutionBlog