With perhaps a thousand species present in the endemic fauna, the Hawaiian Drosophilidae represents one of the most striking examples of explosive adaptive radiation known in the animal kingdom. However, there is mounting evidence that it is shifts within the sexual environment that are more important in the speciation process. Classical concepts of sexual selection theory are reviewed and some new ideas regarding the role of sexual selection in the origin of secondary sexual characters are presented. It is suggested that there is a range of mating types in both sexes and that differential selection between the two sexes, i.e. selection for males with superior mating ability and for less discriminant females, results in the maintenance of an optimum behavioural phenotype in the population. It is further suggested that the dynamics of the sexual selection process and the effects of pleiotropy play a significant role in levels of genetic variability in a single interbreeding population.
