An Evolutionary Systematist's View of Classification

Abstract

Ashlock, P. D. (Department of Entomology, University of Kansas, Lawrence, Kansas 66045) 1979. An evolutionary systematist's view of classification. Syst. Zool. 28:441-450.-The goal of evolutionary systematics, to provide classifications of maximum utility through maximnum use of evolutionary theory, has failed of accomplishment to the extent that practitioners of evolutionary systematics have relied upon descriptive rather than theoretical definitions of terms. Monophyly and related terms are discussed, a new definition of higher taxon is provided, and a new methodology for producing classifications of maximum utility, employing cladistic and anagenetic analysis, is partly outlined. Cladists, by ignoring a significant part of evolutionary theory, produce classifications that are less useful to systematist and nonsystematist alike. [Classification; evolutionary systematics; cladistics; monophyly; polyphyly; higher taxon.] Evolutionary systematics has always had as its goal the preparation of maximally useful classifications and as a means to that goal, maximal use of evolutionary theory. As a school, evolutionary systematics has itself evolved. The years since Darwin have seen much change in its methods of doing things as perceptions of evolutionary mechanisms have changed and new and more reliable ways of translating evolutionary principles into methodology have been found. The school has always had detractors, from the anti-evolutionists and typologists of the past to the numerical pheneticists and cladists of the present, but critics have provided much impetus for improvement. There are two kinds of problems to which evolutionary systematics can be applied. Those involving species and populations (microtaxonomy) are largely ignored in this paper. Among the other kind of problems, those of higher classification (macrotaxonomy) and historical biogeography, one of the most important is the evolutionary reason for the existence of groups of more or less similar species that can be arranged by these degrees of similarity into hierarchies. Such hierarchies have always been the basis of classification because similarities make identification easier, aid the memory, and make generalizations about large numbers of organisms possible. These classifications are most easily grasped by the nonsystematists who must use them. In the Origin of Species, Darwin explained the existence of groups of similar organisms-the taxa that were then generally recognized-through from a common ancestor. Fifteen years later, Haeckel (1874) wrote in support of a Cmonophyletic origin of the animal kingdom and its subordinate taxa and against independent stem-forms which required a polyphyletic descent of the animal kingdom. Though his phylogeny (p. 241) contains paraphyletic taxa, Haeckel clearly understood the value of homologous characters, and, using other terms, he employed the following modern principle: synapomorphous (i.e., shared derived) characters are necessary for analyzing relationships. Since Darwin and Haeckel, systematic analysis first has recognized higher taxa and then has asked whether these taxa are monophyletic. (Monophyletic here is used in its traditional sense, i.e., nonpolyphyletic, and includes the concepts of both holophyly and paraphyly.) The process is similar to that outlined by Mayr (1969) for problems at and below the species level, in which observed phena are analyzed to see if they are full