Interactions of Natural Selection with Other Evolutionary Forces and the Detection of Natural Selection

Mutation is the source of new allelic variation and directly changes allele frequencies by converting a copy of one allele (thereby decreasing its frequency) into another type of allele (thereby increasing its frequency). The system of mating can also interact with natural selection to influence evolutionary dynamics and equilibria. The interaction of selection with system of mating is more direct than with many other evolutionary forces because system of mating directly influences the average excess. Gene flow can influence the adaptive course of natural selection both by determining what genetic variation is available within a deme's gene pool and by directly altering allele frequencies. The chapter examines the fate of newly arisen, selected mutations—an area in which both Fisher and Wright agreed that drift plays an important evolutionary role. Genetic drift is powerful in such a population, but the primary manifestation of the power of drift is the rapid loss of genetic variation.