Why the Causal View of Fitness Survives

Abstract

We critically examine Denis Walsh's latest attack on the causalist view of fitness. Relying on Judea Pearl's Sure-Thing Principle and geneticist John Gillespie's model for fitness, Walsh has argued that the causal interpretation of fitness results in a reductio. We show that his conclusion only follows from misuse of the models, that is, (1) the disregard of the real biological bearing of the population-size parameter in Gillespie's model and (2) the confusion of the distinction between ordinary probability and Pearl's causal probability. Properly understood, the models used by Walsh do not threaten the causalist view of fitness.

The early history of chance in evolution

“…Precisely the same worry about the relationship between statistical theories and biological processes has been hotly debated, under the guise of the "causalist/statisticalist debate." On the one side, we have "causalists," who argue that natural selection and genetic drift describe causally efficacious processes (e.g., Brandon, 1978;Mills and Beatty, 1979;Hodge, 1987;Stephens, 2004;Ramsey, 2006;Abrams, 2009;Otsuka et al, 2011). They are opposed by the "statisticalists," who claim on the contrary that these theories are merely statistical summaries of genuinely causal events at the level of the individual organism (e.g., Matthen and Ariew, 2002;Walsh et al, 2002;Ariew and Lewontin, 2004;Krimbas, 2004;Walsh, 2007;Ariew and Ernst, 2009;Walsh, 2010).…”

Populations and pigeons: Prosaic pluralism about evolutionary causes

“…Asking questions about such populations should not be ruled out a priori. 15 However, Otsuka et al (2011) make a number of remarks that might suggest that populations are fixed only by conditions in nature. This paper focuses primarily on Walsh's (2010) use of Gillespie's work (1974; 1975; 1977), but also makes reference to (Walsh, 2007).…”

“…Abrams, 2009cAbrams, , 2012b. Remarks in (Otsuka et al, 2011) seem to suggest that what counts as a population depends on correct methods for calculating effective population size. Rather, it seems, given a choice of population to study, effective population size can then be defined.…”

Causal Foundations of Evolutionary Genetics

“…Millstein (2006), for example, argues that selection is a population-level cause of evolution, while Matthen and Ariew (2009) and Lewens (2010) deny any causal power to selection. Walsh (2007Walsh ( , 2010 claims that fitness is causally inert since it fails to satisfy certain criteria of causality, while his argument was criticized by Otsuka et al (2011). Sober (2013, finally, argues that fitness itself does not cause population change, but its variance does.…”

“…Another contention in the statisticalist debate is whether fitness and/or selection can be regarded as a cause of evolutionary change (Millstein, 2006;Stephens, 2004;Otsuka et al, 2011;Sober, 2013) or not (Matthen andAriew, 2002, 2009;Walsh et al, 2002;Walsh, 2007Walsh, , 2010). The causal model defined above provides a clear cut solution to this entangled debate.…”