From conviction to anti-superfluity: old and new justifications of parsimony in phylogenetic inference

Traditional justifications of parsimony in phylogenetic inference assume a correspondence between character-state similarity and steps (character transformation events). In addition to similarity, justifying arguments appeal to conviction, descriptive efficiency, ad hoc hypotheses of homoplasy and frequentist probability. Each of these rationales fails in so far as the arguments are incoherent or logically inconsistent with the ontological status of what is assumed and being explained historically. An ideographic justification of parsimony, where character-states constitute transformation events, does, however, allow for a rational preference of most parsimonious phylogenetic hypotheses by invoking the anti-superfluity principle (ASP). According to ASP, explanatory power is maximized by minimizing the number of transformation events required to explain the character-states of the terminal taxa as hypotheses of homology, where the concept homology is restricted to just those inherited things shared by species. The empirical significance of this rationale is exemplified with the method of direct optimization, which can identify more parsimonious hypotheses than can be confirmed with an analysis of character-state similarities. (c) The Willi Hennig Society 2006.