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"Teleofunction, Natural Selection and Counterfactuals"

Putnam objects to teleofunctional accounts of meaning on the ground that the natural-selective explanations they require "all ... involve counterfactual conditionals at one point or another." For example, suppose we say that black pigmentation in the peppered moth was selected for in industrial towns in 19th-Century Britain because black color camouflages the moth when it lands on soot-darkened surfaces.⁽¹⁾ What we mean, according to Putnam, is that the moths need to escape certain predators if they are to survive and reproduce; that moths with the genotype responsible for black color, and thereby for the color's effect of camouflage, lived to reproduce in greater numbers;

and finally -- we have to add -- that they would not have survived in greater numbers if they had not [been camouflaged]... [W]ithout this addition the possibility is not ruled out that the genotype that is responsible for [black color] was selected for some reason other than [the effect of camouflage] that accompanies its presence.⁽²⁾

Dub this counterfactual -- 'The moths would not have survived if they had not been camouflaged' -- Putnam's counterfactual. Such counterfactuals, he says, are what "'do the work' in powering explanations by natural selection." But the counterfactuals, at least when applied to cases that might involve mapping, smuggle in both the intensionality and the intentionality that was to be explained. "The whole idea of a unique correspondence ... is an illusion, an artifact of the way we describe the situation."⁽³⁾

The most egregious problem with this curious line is the unargued assumption that without Putnam's counterfactual, the possibility is not ruled out that the genotype responsible for black color was selected for not because of the color's effect of camouflage but because of some other effect. From the point of view of natural selection, there is no such thing as being simply "not camouflaged" (not that Putnam is necessarily suggesting the contrary). Something that is only not camouflaged need have no effect at all, hence none on which selection could operate. Selection can operate only on some definite positive alternative to being camouflaged, some actual effect of a trait actually in the population. Negation in this context is not exclusion negation but choice negation: to say that the genotype responsible for black color was selected for not because of its effect of camouflage is to say that it was selected for because of some specific positive alternative effect E (as Putnam seems to mean). For example, it might be to say that it was selected for because black moths are faintly warmer in sunlight than gray moths (the black color absorbing light at more wavelengths than gray).

It follows that the possibility that the genotype responsible for black color was selected for not because of its effect of camouflage can be ruled out by ruling out each of the relevant alternative positive claims that it was selected for because of specific positive effect E -- say the effect of faint warming in sunlight -- where E is an effect of a trait present in the population. That is, for each relevant positive alternative effect E, one rules out the claim that the responsible genotype was selected for because of E. Indeed this is how biologists actually proceed. In the case where E is the faint warming effect, they would cite evidence against the claim that the faint warming caused the observed differential in reproductive rates (between black moths and gray). Most of the evidence comes from their background knowledge of the lives of moths, moth predators and environments, and of the relative significance of various causal processes at work among them. Such "actualist" evidence reveals that there is no plausible causal story according to which the faint warming effect was the reason for the survival of the black moths in greater numbers than their gray brethren.

Furthermore, merely to rule out -- merely to deny -- the causal statement that the faint warming is responsible for the survival does not entail Putnam's counterfactual that the moths would not have survived if they had not been camouflaged. Indeed the mere negation of a causal statement, which has the form "It is not the case that A caused B," entails no counterfactual at all. It follows that for each of the relevant alternatives E to camouflage's being the effect responsible for survival, the claim that E was responsible can be ruled out, all without entailing Putnam's counterfactual. True, the remaining use of a causal notion -- as in "Camouflage caused the survival" -- may imply a counterfactual, but this counterfactual contains no negative predicate (such as 'not camouflaged'). Furthermore, since the causal processes involved are all determined by physical causal processes, the counterfactual amounts to a "strict counterfactual" whose truth Putnam allows.⁽⁴⁾

1. Putnam (1992), 26. I've changed his example to a parallel one, for clarity.

2. Putnam (1992), 26.

3. Putnam (1992), 31.

4. Putnam (1992), 51-52.

References

Putnam, Hilary (1992). Renewing Philosophy (Cambridge: Harvard University Press)