This is inspired by a discussion I had over on Evolving Thoughts.
Perhaps one way to approach part of Fodor’s argument against natural selection is to focus on the lack of a “free-rider” type problem in other areas of science. I’m curious what others think of this.
So, define a selection free-rider as a phenotypic trait that was not “selected for” in some particular instance, and is correlated with a trait that was selected for. Further, the free-rider could have been selected for (making the correlated trait the free-rider), either actually in some other species or population, or by some possible biological scenario. For instance, the brownness of fur might be a free-rider in one species, because it is correlated with the fur having the insulating properties that it does, which is what was actually selected for. But in another species (or maybe even in another population of the same species), it is the insulating properties that free-ride, because the brownness is selected for (because it provides camouflage, or whatever). If we think of selection as a mechanism or force (which is not uncommon in evolutionary biology), we might say that if selection does not act on a trait T1, but does act on a correlated trait T2, then T1 is a free-rider. If selection had acted on T1, then T2 would be the free-rider.
Now it seems to me that there is nothing like a free-rider problem in sciences such as physics or chemistry. Consider gravity (and I’ll stick to Newtonian mechanics just for simplicity): we know that gravity acts on things with mass, and not on things without mass. So we might think that the massless properties of objects are gravity free-riders, because they ride free on gravity. Maybe color is a gravity free-rider: each of my 2kg red books fall exactly the same when dropped from the same height. But this can’t be right: we already knew that gravity only acts on mass, nothing else. Gravity doesn’t act on mass in some contexts, but not in others.
The problem then is that selection sometimes acts on brown fur and sometimes doesn’t, and this is true for every phenotypic trait. But gravity always acts on mass, magnetic forces always act on iron-containing things, and so on. I take this to be closely related, if not identical to, Fodor’s complaint that there aren’t laws of selection. Because gravity doesn’t have free-riders, I can tell you exactly how it will act on some object if you tell me its mass, which is just applying the Newtonian theory of gravity. But if you tell me all the traits that an organism has, I can’t tell you which one (or ones) selection acted upon. I can’t even generate a list of traits that selection will always act upon. Of course, in one particular case, I may be able to actually figure it out, but that’s not because of the application of theory. The theory simply tells me that some one (or more) of those traits was acted upon by selection.
The above is pretty sketchy, but as I said, I’m curious of what others think. Even if Fodor draws the wrong conclusion, this does seem like an interesting difference between biology and other sciences. Are there examples of free-riders in other sciences that I’m just not thinking of? There are lots of examples where one has to mind the difference between correlation and causation, but the selection free-rider problem seems like a special case: causes and correlations can be switched around depending on context.