Functions are historical, so there

Justin Garson, Putting History Back into Mechanisms (forthcoming, BJPS)

This is in large part a forceful reassertion of the role of history in functions, and thus in biological mechanisms—which are functional in that they are mechanisms for things.[1] I’m very sympathetic.

The main argument is the familiar one from malfunction. An item’s function can’t just be what it does, since then malfunctioning—having a function but not performing it—would be impossible. That means you have to look beyond something's current operations to determine its function, and the obvious candidate is its past operations. Garson points out that the main alternative, appealing to its current operation in other organisms—such as Boorse’s “species-typical” operation—is blocked by Neander’s “pandemic” problem. If some disease blinded the entire human species for a few days, we would still (especially!) want to say our eyes were all malfunctioning. As Boorse acknowledges, the only solution is to appeal to species-typical operation across time, which makes history relevant again.

Garson draws two morals. One is epistemic: there's no escaping the need to look back in time to determine functions. That doesn’t mean looking all the way back to the (likely obscure) evolutionary origins of mechanisms; on Boorse’s view, it may only involve looking back a little way. 

The second is metaphysical: one shouldnt equate mechanistic explanation with constitutive explanation. Mechanistic decomposition looks very much like a constitutive explanation, but the historical element in mechanisms means one needs to take care. Garson bites the Swampman bullet—if the world were five minutes old, nothing would have a function (p.27). So mechanistic explanations don’t involve instantaneous supervenience.

Just two thoughts from me. One is that all of this follows from a concern for malfunction. If one is sceptical of the normative in biology, one might do without that. Garson thinks the pluralist views of people like Godfrey-Smith are vulnerable to the pandemic objection. But granted the courage of one's interest-relativist convictions, one could maintain that while eyes are interesting to us because they used to see (or would be able to see, but for...), that’s a feature of us, not them. I don’t like that approach, because I think we need normativity for semantics and so for being interested in things, but for all Garson says it seems to be available.

The other is what I take to be the superiority of Boorse’s causal contribution aproach to function, even in its historical version, to one based on selected effects. A weakness of selected-effect function has always been the possibility that the effect in question was never actually selected. Has there really been selective competition between members of a species with and without hearts? Probably not, since once you get to the point of having hearts at all, you tend to need them. Boorse’s approach avoids that problem, by (implicitly at least) appealing to counterfactuals. If your ancestors had been missing hearts, it would not have been good for their reproductive potential.[2]

I’m glad to see this paper, and I hope its lesson is taken to heart.

[1] This sense is to be distinguished from a broader sense, familiar from other sciences with no normative notion of function, which roughly just means causal chain. Perhaps I am reluctant to accept correlational evidence that, say, gum infections cause Alzheimer's until I am presented with at least a plausible mechanism for it to do so; that’s the purely causal sense of the word, since nothing has the proper function of causing Alzheimer’s.

[2] In fact there is often such selection, it’s just so effective we don’t notice. Anencephalic babies don’t reproduce; that’s intra-species selection for cerebra. But it would be odd for assignments of function to turn on whether such defects actually occur.