Fitness and Evolutionary Explanation: a Response (original) (raw)

1991, Biology and Philosophy

Our approach to explicating the concept of fitness is to examine the parameters and variables that appear in models used in population biology, how they are interpreted, and what general relationships exist among them. When these models are examined, three general kinds of variables or parameters can be distinguished: rates of increase of genotypes, parameters representing the environment and heritable properties of genotypes. Beginning with R.A. Fisher, the concept of fitness refers to a genotype's rate of increase (F-fitness), which is the bottom line in evolution. As mentioned in our paper, there are other fitness concepts, for example, expected reproductive success, that appear in the models. However, since these concepts are intervening functions used in the calculation of F-fitness we do not belabor them. Maynard Smith notes that F-fitness is not the measure of Darwinian fitness w as expected number of progeny per individual. The terminology can be confusing here, but the bottom line fitness of a genotype which determines expected gene frequency change is F-fitness, which includes the rate of increase due to the genetic system. Why is there a need for general explication of the concept "fitness"? One such need arises from the tortuous discussions of the purported tautology problem by critics of Darwinian evolution. Evolutionists have sometimes been goaded into giving responses which deepen rather than alleviate the confusion. Many evolutionists, however, feel that there is nothing wrong with their actual use of the concept "fitness" (Darwinian fitness, selection coefficients) in their models. Why then should they bother with philosophical analyses of the "real meaning" of 'fitness'? Aside from the notorious tautology challenge there are complexities in interpreting fitness, adaptedness and related concepts due both to ambiguities among different uses of the terms and to subtleties concerning evolutionary explanation. We want some understanding of what various models of evolution