Two Ways of Thinking About Fitness and Natural Selection

Abstract

he concept of fitness is, Philip Kitcher' says, "important both to informal presentations of evolutionary theory and to the mathematical formulations of [population genetics]" (ibid., p. 50).He is absolutely right.The difficulty is to harmonize these very different ways of understanding its role.We examine here how fitness and natural selection relate to the other explanatory factors invoked by evolutionary theory.We argue that the "informal presentations" to which Kitcher alludes give an incoherent account of the relation.A more appropriate model is drawn from the statistical framework of population genetics.We argue that this model demands a far-reaching revision of some widely accepted notions of causal relations in evolution. I. VERNACULAR FITNESS AND PREDICTIVE FITNESSThe two formulations of fitness are well illustrated by expositions given by Kitcher himself.Consider:The principle of variation in fitness: Organisms differ in ways that affect their competitive abilities.Some organisms have characteristics that better enable them to survive and reproduce than others (ibid., p. 38).

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