Abstract

It has been argued by Hull and others that a remnant of essentialism impeded taxonomic progress until systematists abandoned attempting to define taxa on the basis of characters necessary and sufficient for group membership. The advent of cladistics suggests instead that it is an essentialistic view of characters, not of taxa, that should be abandoned, and that only a transformational view of characters allows evolutionary novelties to be identified, much less explained. Conventional Darwinian explanations are not tautologous but are difficult to test and scarcely explain evolutionary novelties, probably because of their emphasis on genetic rather than epigenetic (developmental) processes.