Numerical Classification And Complexity Developing A Classification Of Classifications

The difference between monothetic and polythetic classification is well established in the literature (Sneath, 1962; Sokal & Sneath, 1963; Needham, 1975). Monothetic classification defines a group such that all members share specific common features, and that, at least in regard to their defining characteristics, any member of the group is substitutable for another. Polythetic groups, on the other hand, are "composed of organisms with the highest overall similarity, and this means that no single feature is either essential to group membership or is sufficient to make an organism a member of the group" (Sneath, 1962, p. 291). Numerical classifications, per Sokal and Sneath, are defined as a type of polytheticism. We argue that polythetic and numerical classification are not coterminous, and that all three classifications vary along an axis of complexity. Distinguishing characteristics of complexity include the number and nature of membership criteria, the internal structure of a classification, and the nature of consensus used in determination of a classification.