Evolution in Sexual and Asexual Populations

In a simple model case, the rates of evolution in an asexual and a sexual haploid population are compared. It is shown that, if the genetic variance of the population is generated by mutation in a uniform environment, sexual reproduction confers no advantage. But if the genetic variance has arisen because selection has favored different genotypes in different environments, then sexual reproduction will accelerate adaptation to a new environment. These conclusions differ sharply from those reached by Crow and Kimura (1965). The difference arises because those authors treated mutations as unique events, whereas they are here treated as recurrent events.