Original paper

Problematic issues of cladistics. 26. Hennig's threefold relationalism, the theory of measurement, and the description of an elephant

Reif, Wolf-Ernst


Hennig (1950, 1966) regarded the basic elements of his methodology of phylogenetic systematics: "character", "taxon" and "phylogenetic relationship" not as independent phenomena per se. Rather, character states exist and are understandable in relation to other character states; scope and rank of taxa exist and are understandable in relation to other taxa; degrees of relative phylogenetic relationship between two taxa exist and are understandable in relation to degrees of phylogenetic relationship to other taxa.Hennig based his methodology on the ontological concepts of the German philosophers and theoretical biologists E. Cassirer, H. Dingler, N. Hartmann, T. Ziehen, and L. V. Bertallanfy, but went much further than they did. Hennig's rather radical points of view have yet to be integrated into the modern theory of biology. Philosophers of biology have hardly recognized as yet that Hennig carried out an unprecedented paradigm-switch that violates the metaphysical world-views of many systematic biologists: Scope and rank of a taxon, specific features of a character and degrees of phylogenetic relationship are no longer regarded as definable and measurable entities, but they can only be characterized in relation to other such entities. In contrast to the expectations of many biologists and philosophers of science, relationalism does not lead to vague methods in systematic biology, but it leads - in full agreement with Hennig's proposals and criteria - to a much more precise systematics.


phylogenynatural systemtaxacategoriescharactersphylogenetic relationship