Assumptions Underlying the Use of Ontogenetic Sequences for Determining Character State Order

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Abstract
The study of ontogeny yields two types of information of potential use for phylogenetic reconstruction: information about characters and about transformation among the states within characters. Transformational information is used to construct hypotheses of character state homology, polarity, and order. Character state order refers to the evolutionary connections among character states, whereas polarity refers to the direction of evolution along hypothesized connections (i.e., which character conditions are primitive and which are derived). Hypotheses of either character state order or polarity require assumptions about evolutionary processes and constrain phylogenetic construction. The use of ontogeny to infer phylogenetic order among character states requires the assumption that evolution modifies states one at a time, through addition or deletion, terminally or nonterminally, in the sequence. When phylogenetic change involves the simultaneous addition or deletion of two or more states from a c...