Cladistics, populations and species in geographical space: the case of Heliconius butterflies

The paradox of the species in evolutionary thought has promoted much debate and numerous incompatible definitions and concepts. This chapter argues that although the phylogenetic species concept (the author's version of it, at least) is no more accurate a description of "speciesness" than any other species concept (indeed, the notion of accuracy is irrelevant, as will be seen), it links species definition to species diagnosis via explicit criteria, which renders phylogenetic species more amenable to empirical testing than species defined by other concepts. The practical implications of cladistic species concepts for determining the boundaries between geographically differentiated sister taxa are explored using the example of Heliconius, based on my work and the recent studies of Mallet and others. The problem of circumscription is also addressed, with particular reference to the concepts of subspecies and geographical races.