Thursday, November 29, 2007

Crazy Jerry (I)

I’m gonna do something pretty stupid and weigh in on the controversy surrounding Fodor’s recent salvos against ‘Darwinism.’ Fodor has argued that adaptationism is wrong, and that the theory of natural selection is in the midst of a crisis. Figures in the field now seem to be wondering whether Fodor has merely gone bonkers, or whether he has finally come out as a Dark Lord. To make matters worse, the few positive reviews have been from places like this.

On the other hand, I managed to re-read his latest essay this morning, and I’m just not seeing what all the fracas is about. So this is my attempt to clarify the issues as I understand them:

Contrary to what has sometimes been implied, Fodor is not dismissing most of what we understand by the concept ‘evolution.’ This is how he concludes his most recent essay ‘Against Darwinism’:

“None of this should, however, lighten the heart of anybody in Kansas; not even a little. In particular, I’ve provided not the slightest reason to doubt the central Darwinist theses of the common origin and mutability of species. Nor have I offered the slightest reason to doubt that we and chimpanzees had (relatively) recent common ancestors. Nor I do suppose that the intentions of a designer, intelligent or otherwise, are among the causally sufficient conditions that good historical narratives would appeal to in order to explain why a certain kind of creature has the phenotypic traits it does…It is, in short, one thing to wonder whether evolution happens; it’s quite another thing to wonder whether adaptation is the mechanism by which evolution happens.” ('Against Darwinism')

So Fodor does not think that he is arguing against Darwinism per se, or against evolution, or against the idea that species adapt themselves over time to their environment. His thesis, rather, is the following: “the theory of natural selection can’t explain the distribution of phenotypes in biological populations.” This is a bold claim, probably too cavalier, and most likely wrong…but it’s not crazy. His beef is about how, not whether evolution happens.

So, what then is Fodor’s problem with adaptationism? As far as I can tell, it has less to do with the idea that species adapt over time to their environment and more to do with the notion that phenotypes are selected for (an important term of art) in a lawful way. Here in skeletal form is the argument:

1) Natural selection via adaptationism is plausible only if it can distinguish between the selection of creatures that happen to express some phenotype, and those that are selected for expressing some phenotype.

Why (1)? The argument is long, but it boils down to the fact that nature has no way of making the distinction. And yet, according to adaptationism, natural selection determines that certain phenotypes persist while others die out by selecting for the former against the latter. More on this below.

2) This distinction rides on the plausibility of relevant counterfactuals.

If we confine ourselves only to the actual world, we will never know whether our large brains were selected for the robust social cognition they allow, or whether those among our ancestors who happened to have big brains were selected for some other reason, and enhanced social cognition is a just a(n) (un)fortuitous byproduct. Or a different example: our elongated jawbones were selected for (some purpose), while our chins we get for free because they are the necessary result of an elongated jawbone. Hence, to distinguish selection from selection for, we need to consider the relevant counterfactuals: would large brains have resulted iff brain size played no role in social cognition; if social cognition played no role in fitness, would large brains have developed anyway? And so on…

3) There are only(!) two suggested ways to make sense of such counterfactuals: a) taking the phrase ‘mother nature’ quite literally; or b) positing laws of selection.

Fodor just asserts that these are the two options, but I’ve not found anyone disputing this. Now, 3a can’t be right, because there is no mind governing selection (again, this is just an assumption, but it’s surely right). To use Fodor’s example: Granny sells zinnias at the market, and selects them for their high prices. The high-priced zinnias happen to come with large roots. If we want to decide whether large roots, or high prices, are selected for, we just ask ourselves whether Granny would sell high priced plants with small roots. Of course she would. Thus, high-price is selected for, and large roots (in this world) just happen to be selected. This is all fine and well only because Granny has a mind, and she is making the choices. But nature does not have a mind, so 3a can’t be right.

3b is where we hit the rub. Things hinge on how we should understand ‘law,’ because Fodor’s claim, remember, is not that evolution does not happen, but rather is that there are no laws that govern of natural selection. Fodor argues that if there were laws of natural selection, then we would be able to decide lawfully whether, given any two phenotypes, P1 and P2, which one wins out. But there is no way to do this, because no phenotype in and of itself is fit; it is only fit within a certain environment. As Fodor puts it, the fitness of a phenotype is “massively context dependent.” In other words, Fodor’s point seems to be that there is no law concerning the fitness (selection for) P1 and P2 per se, because P1 wins out over P2 (or vice versa) only within some environment.

Eliot Sober asks, why is this a problem? Once we do control for environment, isn’t there a necessary answer for which one wins out? The contention between Fodor and Sober seems to be on the role and status of laws in science. For instance, economists might argue that, all things being equal, an increase in the money supply will lead to inflation. Of course, there are so many intervening variables in the real world that this correlation rarely if ever holds, and when it does hold, there is always someone who can argue that the correlation is accidental, not lawful. In other words, all things are never equal, so in what sense can we call this a ‘law’ that relates increases in the money supply to inflation? At this point, I think that the debate becomes somewhat ad hoc. Economists will respond, as Sober does, by saying that they are constructing models, that the models help both to predict and explain phenomena, and that whether you want to call the rule-sets that govern variables in a model ‘laws’ or not is just a function of how strongly you want to interpret ‘natural law.’So, the contention seems to be, when we can something determinate in terms of natural selection only by specifying a context, whether we should count this a law or not, and this in term seems to ride upon how 'universal' you want your 'laws of nature' to be. For something to be a law, must it hold unconditionally across the entire universe, or can may one still speak of a law even when conditions and contexts have to be set? It's a very interesting question--it seems to me that most sciences now are fine talking about models rather than laws--but I don't think that one is crazy for coming down either way.

1 comment:

  1. I have a reply to Fodor here. Comments are welcome!

    ReplyDelete