Abstract
Causalism is the thesis that natural selection can cause evolution. A standard argument for causalism involves showing that a hypothetical intervention on some population-level property that is identified with natural selection (e.g., variation in fitness) will result in evolution. In a pair of articles, one of which recently appeared in the pages of this journal, Jun Otsuka has put forward a quite different argument for causalism. Otsuka attempts to show that natural selection can cause evolution by considering a hypothetical intervention on an individual-level property. Specifically, Otsuka identifies natural selection with the causal relationship between a trait and fitness, claims an intervention on the strength of this relationship can cause evolution, then concludes that natural selection can cause evolution. Below I describe why Otsuka’s argument for causalism is unconvincing. Central to my criticism is that Otsuka’s argument works only if one adopts an indefensible account of natural selection, according to which natural selection can occur in the absence of trait or fitness variation. I go on to explain why any attempt to demonstrate the truth of causalism via a hypothetical intervention on an individual-level property would appear to require one to adopt an account of natural selection that is inadequate for the same reason. This in turn means the plausibility of causalism does indeed depend on the plausibility of the claim that population-level properties, which supervene on the properties of the individuals in the population, can be causally efficacious.
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Notes
One could attach subscripts to β to indicate that it represents the causal influence of Z on W. Since I do not use β for any other purpose in this paper, I will leave these subscripts out.
Since I, along with the majority of other participants in the debate over causalism and statisticalism, endorse roughly this account of causation, I will not provide a more in depth description or defense of it. The unfamiliar reader should consult Woodward (2003) and Pearl (2009) for particularly illuminating exegeses.
Otsuka’s description of natural selection may remind some readers of descriptions of “selection for.” But the similarities only go so far; “selection for” is typically understood to occur only when there is trait and fitness variation (Sober 1984a). See also Lewens (2010) for discussion of these issues.
One potential objection to Otsuka’s discussion of an intervention on β is that interventions are typically understood to be carried out on variables, not parameters. I will not consider that objection here.
See McLoone (2015) for a discussion of how this issue relates to the definition of "group selection" articulated by some proponents of the "contextual approach" to multilevel selection.
See Sober (1984b) for a related discussion, though his is focused on the difference between type- and token-level causal claims.
Matthen and Ariew write that they “assume Sober’s fairly orthodox treatment” of natural selection, namely, “natural selection is evolution due to heritable variation in fitness” (Matthen and Ariew 2009, p. 204). In fact, this is not Sober’s account of natural selection. The part of Sober’s book that Matthen and Ariew explicitly reference says this: “If the organisms in a population differ in their ability to survive and reproduce, and if the characteristics that affect these abilities are transmitted from parents to offspring, then the population will evolve” (1984a, b pp. 21–22). This is different than saying, “natural selection is evolution due to heritable variation in fitness,” which is the interpretation Matthen and Ariew ascribe to the passage. Later in that same chapter, Sober also provides a case that he explicitly and plausibly describes as one in which there is selection but not evolution (Ibid., pp. 40–41). Sober writes later in that book, “selection doesn’t imply evolution…Selection implies evolution only when no other evolutionary force counteracts it and the trait being selected is heritable” (Ibid., p. 151, emphasis in original).
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Acknowledgements
I would like to thank Robert Brandon, Bruce Glymour, Jun Otsuka, Elliott Sober, and two anonymous referees for providing helpful comments on earlier versions of this manuscript.
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McLoone, B. Why a convincing argument for causalism cannot entirely eschew population-level properties: discussion of Otsuka. Biol Philos 33, 11 (2018). https://doi.org/10.1007/s10539-018-9620-8
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DOI: https://doi.org/10.1007/s10539-018-9620-8