Phylogenetic Systematics or Nelson ' S Version of Cladistics ?

In as much as our paper (de Queiroz and Donoghue, 1988) was intended to be a contribution to, rather than a criticism of, phylogenetic systematics, it seems odd that Nelson (1989: 277) views our efforts as being "potentially destructive to the independence of cladistics". On closer inspection, however, Nelson's reaction is understandable as a manifestation of fundamental differences between what he means by "cladistics" and what we mean by "phylogenetic systematics". Here we argue that (1) contrary to the impression given by Nelson, his version of cladistics is no more independent of a "model", as he terms it, than is phylogenetic systematics; (2) the tenet (model) underlying phylogenetic systematics has greater explanatory power than that underlying what Nelson calls "cladistics"; (3) while Nelson's version of cladistics may "not yet have found a comfortable home within one or another of the. .. metatheories of biology" (Nelson, 1989: 275), phylogenetic systematics is secure within the two general disciplines from which it derives its name; and (4) the perspective of phylogenetic systematics clarifies or provides deeper insight into several issues raised by Nelson, including the antagonism over paraphyletic taxa that developed between gradists and cladists, the primacy of common ancestry over characters, and the generality of the concept of monophyly and, consequently, of phylogenetic analysis. The relation between phylogenetic systematics and the principle of common descent not only separates this approach from Nelson's version of cladistics by a fundamental conceptual gap but also enables it to resolve what Nelson sees as incompatibihties between cladistics and theories about evolutionary processes.