The concepts of fitness and selection in evolutionary biology

This paper examines the concepts of selection and fitness as they have been defined and used by various workers in evolutionary biology. In doing so, it presents several closely related versions of the theory of organic evolution. The paper argues that the several concepts of selection are related in a fairly simple way. Some of the concepts are equivalent to each other and lead to equivalent formulations of the theory of organic evolution. Other concepts of selection are not equivalent to those in the fn'st group. These non-equivalent concepts, however, lead to versions of the theory of evolution that are logically very close to the equivalent formulations of the theory. The paper discusses four major definitions of fitness ( ' tautological ' fitness, Darwinian fitness, Thodayan fitness and inclusive fitness), and presents the main properties of each. It is argued here that under each definit ion of fitness, fitness can be understood as a measure of the intensity of selection. This explains why the basic theory of organic evolution can be stated without mentioning fitness. Finally, the question of whether the theory of organic evolution is ' tautological ' is addressed. Many authors have thought that it is. If the accounts of selection, of fitness, and of the several versions of the theory of evolution here presented are even approximately correct, the theory of evolution is not the kind of thing that can be tautological. This is because it makes fairly straightforward existential claims and existential claims of the sort envisioned here cannot be tautological or analytic.