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As we saw in Chapter 7, phenetic clustering is based on the use of distance methods, however the original data are coded. Thus, as I pointed out at the beginning of Chapter 8, pheneticists have to use separate techniques for the construction of classifications and the reconstruction of phylogeny. The methods of “numerical cladistics” arose from within the school of phenetics as a result of attempts to reconstruct phylogeny, but its practitioners diverged from their pheneticist colleagues and converged on mainstream cladistics as a result of their conviction that classification should be hylogenetic. In this chapter, I describe the development of numerical cladistics and its eventual repudiation of the use of undifferentiated distance data in favour of reliance on apomorphy and parsimony. While this was happening, from the 1960s onwards, various techniques of phylogenetic reconstruction involving the use of biochemical and molecular data were developing. These interacted with other schools of phylogeny reconstruction, and posed problems, notably those concerned with the use of distance data, in an acute form. In this chapter, I review some of these techniques, particularly as they concern the relationship between phylogeny and classification. Then in Chapter 10, I shall attempt some general summary of that relationship. But a complete statement of my position will be possible only after we have considered theories of evolutionary mechanism and something of philosophy. [ABSTRACT FROM AUTHOR]

It is taken for granted today, at least by zoologists, that systematic classifications of organisms can be represented by branching diagrams (dendrograms: Mayr, Linsley, and Usinger 1953) that represent hierarchical arrangements - Darwin's (1859) “groups within groups”. The nested groups are taxa, each of which belongs to a category that represents its level in the hierarchy (Simpson 1961a). In the tenth edition of Linnaeus 's Systema Naturae (1758), he proposed the following categories: Regnum (Kingdom), Classis, Ordo, Genus, Species, to which the categories Phylum and Family were added later. All the taxa at the same level in the hierarchy occupy the same rank and are given the same category. Thus “the rank of a taxon is that of the category of which it is a member” (Simpson 1961a). Modern biological classification is therefore a process of “ordinally stratified hierarchical clustering” (Jardine and Sibson 1971, p. 127), and the result is an aggregational hierarchy (Mayr 1982, pp. 64-6) in which the units, usually species, which constitute its lowest rank, are aggregated in successively higher ranks. The hierarchy is also an inclusive one (Mayr 1982, pp. 205-8) as opposed to an exclusive one: Military ranks from private, corporal, sergeant, lieutenant, captain up to general are a typical example of an exclusive hierarchy. A lower rank is not a subdivision of a higher rank; thus lieutenants are not a subdivision of captains. […] [ABSTRACT FROM AUTHOR]