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Are natural selection explanatory models a priori?

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Abstract

The epistemic status of Natural Selection (NS) has seemed intriguing to biologists and philosophers since the very beginning of the theory to our present times. One prominent contemporary example is Elliott Sober, who claims that NS, and some other theories in biology, and maybe in economics, are peculiar in including explanatory models/conditionals that are a priori in a sense in which explanatory models/conditionals in Classical Mechanics (CM) and most other standard theories are not. Sober’s argument focuses on some “would promote” sentences that according to him, play a central role in NS explanations and are both causal and a priori. Lange and Rosenberg criticize Sober arguing that, though there may be some unspecific a priori causal claims, there are not a priori causal claims that specify particular causal factors. Although we basically agree with Lange and Rosenberg’s criticism, we think it remains silent about a second important element in Sober’s dialectics, namely his claim that, contrary to what happens in mechanics, in NS explanatory conditionals are a priori, and that this is so in quite specific explanatory models. In this paper we criticize this second element of Sober’s argument by analyzing what we take to be the four possible interpretations of Sober’s claim, and argue that, terminological preferences aside, the possible senses in which explanatory models in NS can qualify, or include elements that can qualify, as a priori, also apply to CM and other standard, highly unified theories. We conclude that this second claim is unsound, or at least that more needs to be said in order to sustain that NS explanatory models are a priori in a sense in which CM models are not.

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Notes

  1. Following Sober, we take explanatory models as summarized by conditionals with the explanans as the antecedent and the explanandum as the consequent. We ignore here the rich recent literature and discussion on models, explanation, and explanatory models in science, for nothing in this paper hinges on this simplification (see Díez 2014 for a model-theoretic account we favour).

  2. Sober (personal communication) would write (4) as “a mother’s fitness is her expected number of grandoffspring”; although we find this formulation also acceptable, given the huge discussion about the meaning of ‘fitness’, we prefer to avoid to use the term when possible.

  3. Sober may reply that all models use the concepts of fitness and heritability (personal communication). We agree that some of these non IB conditions may be rephrased in terms of fitness (in one of its meanings), and that they also use the notion of heritability, but sharing concepts does not suffice for answering Fodor’s charge, it is also essential that the contents/facts expressed by these concepts have something adaptive relevant in common. Our proposal below specifies what this content is.

  4. One might try to argue (Sober, personal communication) that the penultimate component of the antecedents (SexRatio (4), ZebraLion (3), BlakMoths (4), etc.) are empirical, general and with modal import, but also qualify as initial conditions. Yet, if (departing from what we think is standard) one reshapes the notion of initial condition for it to include empirical modal regularities of this kind, then the same move could be done in CM.

  5. This is so even in sex ratio models. The relation, in different fecundity models, between increasing the number of offspring and long term differential reproduction is far from a priori, and actually in some cases having fewer offspring (Fialkowski 1987), or sacrificing some (Einum et al. 2000), is more fecundity-adaptive.

  6. The comparison in this section between NS and CM focuses on NS general adaptive principle and Newton’s Second Law, and is completely independent of other comparison made, and discussed, in the literature between NS and Newtonian theory focusing in so-called “zero-force laws” (Sober 1984; Matthen and Ariew 2002; Walsh et al. 2002; Stephens 2004; Brandon 2006, 2010; McShea and Brandon 2010; Brandon and McShea 2012, Barrett et al. 2012).

  7. ‘Fitter’ not in the sense of having greater probabilistic propensity to expand, but in the above mentioned sense, i.e. solving ecological problems (Lange and Rosenberg 2011: 595–596, make a similar distinction).

  8. For other, related versions of the principle, see e.g. Sober (1984, 1993), Brandon (1980, 1996), Kitcher (1993, § 2.4), Rosenberg and McShea (2008), Ginnobili (2010).

  9. In ZebraLion, the trait t is high speed, (3) specifies the function facilitated by the trait, in this case escaping predators, which makes this explanation a case, not of the “fecundity” sub-type like SexRatio, but of the “survival” one; and (4) specifies that such a function is, in the context, beneficial for differential reproduction. Thus ZebraLion (3)–(4) express the particular specification of NSGP for the particular explanandum in point. Likewise with BlackMoths (4)–(5), also a survival-by-escaping-predators case, though here performed not by running but by camouflaging. And similarly the giraffe’s neck (with a feeding function), the peacock’s tail (with a partner attraction function), or other more interesting cases like predator–prey models, or even more complex cases involving more than one function, like the explanation of color patterns in poeciliid fishes (cf. Endler 1983).

  10.  For a standard and totally precise exposition, and application to CM, Thermodynamics and other theories cf. Balzer et al. (1987). For a more informal presentation, see Moulines (2002). The program originates in Sneed (1971), and Kuhn (1976) acknowledges that it is the approach that captures his proposal best. The expression ‘guiding principle’ is coined in Moulines (1984).

  11. It is in this regard that, as we noted at the beginning, the specialization relation is more similar to the determinable-determined relation than to Lange and Rosenberg’s second order-first order realizers one. In both interpretations general principles are empirically unspecific and characterize only very abstractly the conceptual role theoretical entities, but it is essential to guiding principles that they mention at least the kind of thing one has to look for in the specializations, a feature that is not captured by a purely second order characterization.

  12. Note that what makes something a guiding principle worth to occupy the top of the net, is not simply that it is “general”, but that it possesses the kind of generality that unifies the different applications of the theory by having open parameters that different specializations specify step by step. This is why some general adaptive principles (such as the so-called Fisher’s Fundamental Theorem, the Hardy–Weinberg Law, or some general mathematical models developed by Haldane and Wright) do not qualify as guiding principles for the whole NS theory-net, although they may perfectly well be the dominating principle in some sub-branch.

  13. Some functions, such as camouflaging, may serve different adaptive needs, such as escaping predators (e.g. black moths) and food supply (e.g. chameleons). We will not enter into these complications here.

  14. Kuhn himself claims that his generalization-sketches have a peculiar epistemic status, which he characterizes by using the expressions quasi-analytic (cf. Kuhn 1970: 304 n. 14; 1976: 198 n. 9) and even synthetic a priori (cf. 1989: 22 n. 19; 1990: 317 n. 17); we think that the idea is similar to ours (cf. also Earman and Friedman 1973 for a classical discussion about the epistemic/empirical status of Newton’s Second Law and other mechanical laws).

  15. We do not aim to make here even a brief overview of the vast literature and discussion on apriority, conceivability and related notions. The following comments are confined to our NS vs CM case and apply only in this respect.

  16. It is worth emphasizing that, though heuristic, they are not intended to apply everywhere. There are trajectories that CMGP does not aim to apply to; for instance the movement of a pen in somebody’s hand at will; or more interestingly the trajectory of light beams (which for a while was considered to be a mechanical trajectory to be explained with its special law, but finally it was expelled out as a non-mechanical explanandum). Likewise there are “trait trajectories” that are not intended to be explained adaptively, e.g. series of mice with tails cut at somebody’s will; or more interestingly, genetic drift or horizontal transmission phenomena.

  17. We have looked for interpretations that make the relevant conditionals (in NS but not in CM) a priori. One could argue that what Sober qualifies as a priori is not the relation between the antecedent/explanans and the consequent/explanandum, but the relation between the conditional as a whole and something else (we thank an anonymous referee for this suggestion). We have not found in Sober’s works textual evidence for this interpretation. In absence of Sober’s specification of what this relation could be, it is not possible to check whether it would distinguish NS from CM as Sober intends.

  18. The same applies to the application of Freq across generations in order to “explain” the substitution of one trait by another.

  19. This answer is related to the one given by Lange and Rosenberg (2011: 594) when they claim that “The mother failed in distributing evenly (and without cutting them) the strawberries among her children because she had 23 strawberries and three children” is not a causal explanation at all. Although there is a kind of explanation involved, there is nothing relevantly causal involved. It is a purely mathematical explanation like “There remain three berries because there were five and I ate two”. Note also that (terminological infelicity aside) this would not serve to Sober’s goals either, for it is as easy to apply this to evolutionary concepts as to mechanical concepts. There is nothing specific “strawberry-al”, evolutionary or mechanical in them, the explanation is purely mathematical.

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Acknowledgments

This paper develops and, introducing essential new elements, elaborates in detail an objection very briefly sketched in Díez and Lorenzano 2013. We want to thank D. Blanco, S. Ginnobili, C. Hoefer, E. Sober, A. Sole and two anonymous referees for their helpful comments on previous versions of this paper, and the research projects FFI2012-37354/CONSOLIDER INGENIO CSD2009-0056 (Spain), FFI2013-41415-P (Spain), PICT-2012 No. 2662 (ANPCyT, Argentina) and PIP No. 112-201101-01135 (CONICET, Argentina) for financial support.

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  1. LOGOS Research Group, University of Barcelona, Barcelona, Spain

    José Díez

  2. National University of Quilmes/CONICET, Bernal, Argentina

    Pablo Lorenzano

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  1. José Díez
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  2. Pablo Lorenzano
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Correspondence to José Díez.

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Díez, J., Lorenzano, P. Are natural selection explanatory models a priori?. Biol Philos 30, 787–809 (2015). https://doi.org/10.1007/s10539-015-9498-7

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