The Evolution of Life Histories

Abstract

The fitness of organisms is the primary focus of evolutionary biology. Since the fittest are those which provide more descendants to future generations than their competitors, and fitness is largely determined by the age-dependent schedule of behavior, birth, death, and development rates, life histories are adaptations of unique importance to the analysis of Darwinian evolution (Stearns 1976; Bell 1980). Life history characters covary and function together, and so constitute complex adaptations because they are interdependent (Frazetta 1975). Such sets of covarying traits are often referred to as ``strategies'' or ``tactics'' in the literature of ecology and evolution, meaning that they are ``coadapted traits designed, by natural selection, to solve particular ecological problems'' (Stearns 1976). Because of their relation to fitness, a great deal of theory, experiment, and field study has been directed at determining which associations of life history traits will evolve under particular ecological conditions.