Philosophy and the Transformation of Cladistics

Platnick, N. I. (Department of Entomology, The American Museum of Natural History, New York, New York 10024) 1979. Philosophy and the transformation of cladistics. Syst. Zool. 28:537–546 .—Although Hennig presented cladistic methods by referring to a model of the evolutionary process, neither the value nor the success of the methods is limited by the value or success of that evolutionary model. Dichotomous cladograms can be preferred simply on the basis of their maximal information content, without reference to speciation mechanisms. Because only the interrelationships of diagnosable taxa (those with unique sets of apomorphic characters) can be investigated, questions about whether speciation can occur without branching, or whether species become extinct at branching points, are irrelevant to cladistic practice. The distinction between plesiomorphic and apomorphic character states depends not on the reconstruction of actual evolutionary history, but on the discrimination of more general from less general characters; groups based on plesiomorphy are defined by the absence of characters and are therefore artificial. Hence cladistic methods are not the methods of phylogenetics per se , but the methods of natural classification in general; phylogenetic conclusions are an extrapolation from hypotheses about natural order.