The dynamics of a gene in a haploid population can be explained approximately by considering the average reproductive value of the gene. The dynamics of the average reproductive value are similar to those of a gene in a population with nonoverlapping generations with the following modifications: The effective population size, N(e), replaces N; the average mutation rates micro* and nu* replace micro and nu; the average overall selection r*+(T-1)s** replaces s; and time is measured in terms of generations, T. The implications of the average selection coefficient to adaptive life histories are discussed.