  A critical issue in this debate over the account of the species concept most appropriate for Darwinism is the extent to which the process of biological classification—taxonomy—should be informed by advances in biological theory. Besides those already discussed, the moderate pluralism associated with Robert Brandon and Brent Mischler or the more radical pluralism defended by Philip Kitcher, argues that different explanatory aims within the biological sciences will require different criteria for determining whether a group constitutes a species. Cladists, on the other hand, employ strictly defined phylogenetic tests to determine species rank (see Rheins 2011). 