Argues for the primacy of the phylogenetic system as the general reference system in biology. This book, first published in 1966, generated significant controversy and opened possibilities for evolutionary biology.

The correct explanation of why species, in evolutionary theory, are individuals and not classes is the cladistic species concept. The cladistic species concept defines species as the group of organisms between two speciation events, or between one speciation event and one extinction event, or (for living species) that are descended from a speciation event. It is a theoretical concept, and therefore has the virtue of distinguishing clearly the theoretical nature of species from the practical criteria by which species may be (...) recognized at any one time. Ecological or biological (reproductive) criteria may help in the practical recognition of species. Ecological and biological species concepts are also needed to explain why cladistic species exist as distinct lineages, and to explain what exactly takes place during a speciation event. The ecological and biological species concepts work only as sub-theories of the cladistic species concept and if taken by themselves independently of cladism they are liable to blunder. The biological species concept neither provides a better explanation of species indivudualism than the ecological species concept, nor, taken by itself, can the biological species concept even be reconciled with species individualism. Taking the individuality of species seriously requires subordinating the biological, to the cladistic, species concept. (shrink)

Historically, naturalists who propose theories of evolution, including Darwin and Wallace, have done so in order to explain the apparent relationship of natural classification. This book begins by exploring the intimate historical relationship between patterns of classification and patterns of phylogeny. It is a circular argument, however, to use the data for classification and the concept of homology as evidence for evolution, when evolution is the theory explaining the phenomenon of natural classification. Alec Panchen presents other evidence for evolution in (...) the form of a historically-based but rigorously logical argument. This is then followed by a history of methods of classification and phylogeny reconstruction including current mathematical and molecular techniques. The author makes the important claim that if the hierarchical pattern of classification is a real phenomenon, then biology is unique as a science in making taxonomic statements. This conclusion is reached by way of historical reviews of theories of evolutionary mechanism and the philosophy of science as applied to biology. (shrink)

In Phylogenetic Systematics (1966), Willi Hennig conflates the Linnaean hierarchy with what Hennig refers to as the divisional hierarchy. In doing so, he lays the foundations of that school of biological taxonomy known as cladism on a philosophically ambiguous basis. This paper compares and contrasts the two hierarchies and demonstrates that Hennig conflates them. It shows that Hennig's followers also conflate them. Finally, it illuminates five persistent problems in cladism by suggesting that they arise from Hennig's original confusion.