An idealized concept of the true cladistic character

Abstract

Estimating evolutionary relationships is basic to the objectives of systematics. Comparative data, structured as taxonomic characters, are usually the essential considerations on which such estimates are founded. Some taxonomic characters are more useful than others for structuring plausible estimates of evolutionary relationship. Thus, one of the primary challenges to the systematist is the construction of taxonomic characters most useful for this purpose. Since taxonomic characters are the result of action on the part of the systematist, they must be defined operationally. It is our hope, however, that these operationally defined characters will conform to an ideal that, itself, cannot be operationally defined insofar as the concept depends on history that is, usually, inherently unknowable. It is, nonetheless, essential to our conceptual methods that this ideal concept be well defined. Here we present a series of definitions leading to a clear ideal concept of true cladistic character. This series includes definitions of the concepts: evolutionary unit, qualitative taxonomic character, monophyletic group, divergent character, true cladistic character, operational cladistic character, and the post-factum ideal relation between an operational cladistic character and an estimate of cladistic history. A concise characterization of true cladistic character is presented and proved.