ABSTRACT
Introduction
Since the publication of Nelson and Platnick (1991) there has been debate, primarily in the journal Cladistics (see Chapter 9), about a new method for analysing systematic data called three-taxon statement (TTS) analysis. The debate surrounding the method has, in part, roots in the distinction made by Hull (1979) between so-called 'pattern cladistics' and the standard approach to cladistic analysis sensu Hennig (1966) as interpreted by, for example, Farris et al. (1970) and Farris (1983). An issue of discussion concerns the relationship between evolutionary theory, phylogeny and systematics. A second issue concerns the concept of homology and what constitutes systematic data. Until the publication of Nelson and Platnick (1991) issues in relation to pattern cladistics were largely philosophical in nature (Platnick, 1979; Brady, 1985), restricted to differences in terminology (Patterson, 1982), the distinction between trees and cladograms (Platnick, 1977), the role of ontogeny (Nelson, 1978), the justification provided for using cladistic methods (Nelson and Platnick, 1981) and whether evolution is axiomatic for systematics (Nelson, 1989a). Platnick (1985) stated that 'Hennig, Patterson, and myself would all arrive at the same cladogram for any data set we examined'. However, Nelson and Platnick (1991) provide a method for analysing systematic data, based on a taxic view of homology and the information content therein. As such it represents a systematic method that does not rely or seek justification on any aspect of evolutionary theory or presumed knowledge of phylogeny for its implementation. Furthermore, the method often yields different results relative to standard cladistic analysis (Nelson and Platnick, 1991; Siebert and Williams, 1998; Carine and Scotland, 1999). This chapter seeks to explain and explore TTS analysis and the concept of taxic homology sensu Patterson (1982, 1988a).
