 If one retains the view that species are natural kinds one must confront the fact that a plethora of species concepts are available and as seen earlier, these species concepts do not always delineate the same species. For example, Mayr’s (1969) biological species concept (BSC) regards a species as a group of “interbreeding natural populations that are reproductively isolated from other such populations” (1969, 26). The phylogenetic species concept (PSC) holds that a species is “the smallest diagnosable cluster of individual organisms within which there is a parental pattern of ancestry and descent” (Cracraft 1983, 170). These definitions are not perfectly coextensive. (For a detailed discussion of species concepts see the entry on  species.)