Distance as a Measure of Taxonomic Similarity

T HE, LAST FEW YEARS have seen the development of a number of methods for quantifying the classificatory process in systematics (Michener and Sokal, 1957; Sokal and Michener, 1958; Sokal, 1958; Sneath, 1957a; Sneath, 1957b, Cain and Harrison, 1958; Rogers and Tanimoto, 1960). These sudden developments, largely independently arrived at, appear to stem from, a growing dissatisfaction with the arbitrariness and subjectivity of the customary taxonomic procedure and would also appear to. be connected with the increasing availability of rapidmethods of data processing and computation. In spite of certain differences among them, these methods show substantial philosophical and procedural agreements. They call first of all for the computation of a measure of resemblance or similarity between taxa. Resemblances are computed between every pair of taxa in a given study and these resemblances are arranged in the form of a so-called Q-type matrix, which is a matrix of similarities among taxa. These matrices are subsequently analyzed by various types of clus-