Kaneshiro (1976) and Ohta (1978) observed asymmetrical behavioral isolation between species pairs of Hawaiian Drosophila whose phylogenetic relationships had previously been inferred from cytology, morphology, and biogeography. The mating patterns were onesided in that males from putative ancestral populations confined with ancestral and derived females exhibited either random mating or heterogamic mating, while derived males in the same situation mated homogamically. These observations were seminal to the development of Kaneshiro's hypothesis that such ancestral/ descendent asymmetries are the norm and thus may provide a basis for determining the direction of evolution among a group of closely related species or populations of the same species. The original hypothesis suggested that some elements of male courtship behavior are lost during founder events leading to the establishment of a new population. Derived females recognize and accept the courtship repertoire of ancestral males, which is complete, but ancestral females discriminate against derived males due to their deficient courtship sequence. Ohta (1978) proposed that founder events might also involve selection for decreased female discrimination, and this idea was subsequently incorporated into the hypothesis (Kaneshiro 1980, 1983; Kaneshiro and Giddings, 1987). A basic assumption was that mating propensities were equal in ancestral and derived populations. Thus, the hypothesis explained the results of male choice experiments in terms of female mate choice decisions, and relied heavily on the role of female discrimination. If this model describes a typical sequence of events, then asymmetrical mating patterns should demonstrate unambiguous directions of evolution, and would be of significant value in phylogenetic analysis. Summary discussions concerning this possibility appeared recently (Kaneshiro and Giddings, 1987; Ehrman and Wasserman, 1987; DeSalle and Templeton, 1987). Giddings and Templeton (1983) presented evidence supporting the model, but included two new constraints which they deemed essential for its applica-