November 10, 2007
Why Pigs Don't Have Wings, Mark II
Jerry Coyne and Philip Kitcher respond to Jerry Fodor's piece in the LRB:
As does Daniel Dennett:Jerry Fodor makes the striking claim that evolutionary biologists are abandoning natural selection as the principal, or even an important, cause of evolutionary change, and that ‘it’s not out of the question that a scientific revolution – no less than a major revision of evolutionary theory – is in the offing’ (LRB, 18 October). This is news to us, and, we believe, will be news to most knowledgeable people as well. The idea of natural selection is, in fact, alive and well, and remains the only viable explanation of the apparent ‘design’ of organisms – the remarkable fit between them and their environments and lifestyles – that once was ascribed to the divine.
He does provide two of his favourite foretastes, however: evo-devo and the famous case of the domesticated Russian foxes. These interesting developments both fit handsomely within our ever-growing understanding of how evolution by natural selection works. Briefly, evo-devo drives home the importance of the fact that in addition to the information in the genes (the ‘recipes’ for making offspring), there is information in the developmental processes (the ‘readers’ of the recipes), and both together need to be considered in a good explanation of the resulting phenotypes, since the interactions between them can be surprising. Of course the information in the developmental processes is itself all a product of earlier natural selection, not a gift from God or some otherwise inexplicable contribution. The foxes are a striking instance of how selection acting on one trait can bring other traits along with it – which may then be subject to further selection.
And Steven Rose, Colin Tudge, and Kit Evans.
Posted by Robin Varghese at 11:00 AM | Permalink
Comments
Dennett and Rose are even on the same side on this one (one of the biggest feuds in science is between the Dawkins-Dennett-Pinker side VS Gould-Rose-Lew).
Jerry Fodor's argument has been shot full of holes, even from bitter enemies fighting each other.
At least he he a force for galvanizing reason among fighting forces.
Posted by: Dave Ranning | Nov 10, 2007 12:30:34 PM
And I'm sure they are both thrilled to have common cause with Tudge.
Posted by: Carlos | Nov 10, 2007 2:00:08 PM
Dennett and Rose are not on the same side on this one. Rose's letter compliments Fodor on his critique of ev. psych. and even of natural selection in biology. He just wants to save the Darwinian baby from the pan-adaptationist bathwater. This is much closer to Fodor than it is to Dennett, as Rose says in the very first sentence of his letter.
Posted by: Jonathan | Nov 10, 2007 2:31:46 PM
I think Cosma Shalizi writes pretty sensibly on why things like self-organization in embryological development cannot truly replace Darwinian explanation, although it can supplement it, in this review of Philip Ball's 'The Self-Made Tapestry':
Enter snowflakes. Enter, also, D'Arcy Wentworth Thompson, who in 1917 published a book, On Growth and Form, which has haunted all discussion of these matters ever since. Thompson's aimed to show that huge chunks of biology are simply the consequences of physics and (less often) chemistry. When he wrote that "the form of an object is a `diagram of forces,' in this sense at least, that from it we can judge of or deduce the forces that are acting or have acted upon it," he meant forces. His accounts of the physics behind morphogenesis were ingenious, extremely elegant, very convincing and, significantly, aimed at very large features of the organism: the architecture of the skeleton, the curve of horns or shells, the outline of the organism as a whole. Most of us are resigned to abandoning biochemical details to crawling molecular chaos, but these are supposed to be more mysterious and inspiring affairs. Thompson tried to explain them using little that a second-year physics undergrad wouldn't know. (Thompson's anti-reductionist admirers seldom put it this way.) In particular, Thompson made a point of not invoking natural selection, indeed of leaving any kind of history out of the story. "A snow-crystal is the same today as when the first snows fell": so, too, the basic forces acting upon organisms, so why bring history into it? The early years of this century are littered with biologists with little use for natural selection; they are now almost all deservedly forgotten. Thompson owes his continuing influence to the fact that his alternative doesn't beg questions at every turn. (Also, of course, he wrote beautifully, better than the poets of his day.)
Since Thompson's day, then, there has been a tension in the study of morphogenesis between evolution and (other kinds of?) self-organization, and this is one of Ball's themes, though not the leading one. Partly it is an argument about logical and theoretical questions --- what is natural selection competent to explain? what features of organisms could not be modified by selection? to what extent is self-organization unavoidable? --- and partly it's about where the balance between self-organization and evolution lies in actually existing organisms.
The case for the self-organizers can be put very strongly, at least for multicellular organisms, for metazoans. These are not bloated sacks of protoplasm but (as the biologist say) "differentiated" --- there are different chemicals in different parts of the body. This in itself could be achieved without much effort; shake up a bunch of marbles in a box and there will be more of one color of marble in one corner, more of a different color in another corner. But mere chance won't give us enough differentiation, and it won't give us a reliable pattern of differentiation; it would be as though every fertilized egg was equally liable to turn into a frog, an oak, Bilharzia or something out of Lovecraft. So there has to be some particular differentiating influence. It cannot be the genes (on which natural selection acts), since genes only encode information about proteins, i.e. about what chemicals to make, not where to put them. So it would seem that differentiation, morphogenesis, must be due to some internal process, some reaction of the proteins and their associated chemicals which sorts out what goes where; but this is to say that there needs to be spontaneous pattern formation, that development must be self-organizing.
It may, admittedly, look like we're in trouble with some obvious facts, that this argument leaves genes and natural selection with no purchase at all on morphogenesis. But not even the most enthusiastic of the self-organizers, the ones with the least use for Darwin (e.g., Brian Goodwin) goes that far. It's very clear that developmental traits can be inherited. Individual mutations can cause the organism to grow six well-formed fingers on each hand (in human beings), or legs in place of antennae (in fruit flies); somehow changes in one protein have to ratchet up into large modifications of the organism. One way to achieve this is to recognize that the same mechanism can form many different patterns depending on its parameters, which, in the case of morphogenesis, will involve the chemical properties of the proteins and protein-products in the embryo, which are just what the genes control. The genes twiddle the knobs, so to speak, and then let self-organization do its voodoo.
This is a pretty convincing line of argument; at least, I'd like to think so, since it convinced me for years. No longer; let me try to say why with a fairly concrete example. There is, as I mentioned, a very nice theory about the markings of mammalian coats, developed by Hans Meinhardt and his collaborators. It explains them through spontaneous pattern formation, using some ideas invented by Alan Turing in the 1950s, and, depending on the parameters of these "activator-inhibitor" systems, they can give you tiger-stripes, or leopard-spots, or even giraffe-blotches, with controllable size, density, wiggliness, etc. Suppose we established that this is really the mechanism at work; could we then finally close the books on how the leopard got its spots? No: it is a conspicuous fact (or, rather, an inconspicuous one) that tigers are tiger-striped, while leopards and leopard-spotted, and there is nothing in the activator-inhibitor story to say why this should be so. It's not enough for a pattern to form, it must also function. Pattern formation is in general unable to create adaptations, to produce something which fits with the organism's environment. The case of tiger-stripes and leopard-spots could be resolved by appealing to parameter-tuning, as above, but this doesn't go far enough. There are, after all, many, many different pattern-forming mechanisms, producing many different sorts of patterns. Assuming an organism employs such a mechanism, why that one rather than another, producing very different patterns? The only answer, so far as I can see, is that, in the organism's environment, the patterns it makes are more adaptive than those of rival mechanism. (Lipids are just as capable of forming open "plumber's nightmare" surfaces as closed vesicles; cell walls are vesicles because it helps an organism if it doesn't leak all over creation.) So even the kind of self-organization which happens in morphogenesis is under evolutionary control.
So, I think Shalizi would agree with Rose's basic point that "The idea of natural selection is, in fact, alive and well, and remains the only viable explanation of the apparent ‘design’ of organisms – the remarkable fit between them and their environments and lifestyles – that once was ascribed to the divine." (and I'm sure that Dennett would agree with this sentence too).
Posted by: Jesse M. | Nov 11, 2007 12:23:16 AM
Jona---
Rose, coming from a Marxist tradition, is clinging to a "Blank Slate" view that Dennett and Pinker have crushed. Believe me, having come out of the same background, I was hoping for their analysis to prevail under observation.
But even Rose can see the danger Fordor presents to science, and cannot, even under ideological commitment, embrace Fordor.
Having a Buddhist and Marxis background dependent on the "Blank Slate" of the human mind, it is disheartening to see these ideas crushed by neuroscience.
But I agree, if he could get away with it, Rose would fully sopport Fodor.
Posted by: Dave Ranning | Nov 11, 2007 12:28:46 AM
Dave,
To complicate matters, Fodor is a die-hard nativist on matters of the mind. He's even more opposed to the idea of the blank slate than Pinker. He just doesn't buy into ev. psych at all.
Posted by: Jonathan | Nov 11, 2007 11:21:34 AM
Jona--
What they both fear is Sociobiology and Determinism, the ultimate deflation of the human ego. Both can't even take a peak at the process without uncontrolled resistance and reaction. Which proves their nemesis's point.
Posted by: Dave Ranning | Nov 11, 2007 11:57:51 AM
But the most important thing is that nothing be a gift from God. Can't we all agree on that?
Posted by: Lloyd Mintern | Nov 11, 2007 5:30:46 PM
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