Is Natural Selection a Population-Level Causal Process?

Abstract

Recent discussions of natural selection focus on two questions: first, is natural selection a causal process or is it a statistical consequence of lower-level events? And second, is natural selection at the population level or at the level of individuals? Bouchard and Rosenberg (Br J Philos Sci, 55:693–712, 2004) argue that natural selection is causal and at the level of individuals, as opposed to Matthen and Ariew (J Philos, 99:55–83, 2002) and Walsh et al. (Philos Sci, 69:452–473, 2002), who argue that natural selection is at the population level and purely statistical. In addition to these two polar extreme positions, Millstein (Br J Philos Sci, 57:627–653, 2006) tries to steer a middle course by arguing that natural selection is a population-level causal process. I will make three points in this chapter: first, Millstein’s account of natural selection is incomplete, in the sense that nowhere in her account can one find a place for cases of natural selection-of. Second, we should prefer Brandon’s account of natural selection and drift over Millstein’s, on the grounds that her account fails to meet a plausible requirement that Brandon’s account succeeds in meeting: namely, whenever natural selection and drift operate together, a change in the strength of natural selection implies an inverse change in the strength of drift, and vice versa. Third, the prospects of the view that natural selection is a population-level causal process depend on a satisfactory solution to both the epiphenomenon and the overdetermination problems. With the help of an analogy, I will show how the two problems can be dealt with.