Phylogenies of organisms are inferred on the basis of characters, the observational data gathered by systematists. Unlike many other systematic concepts, however, the concept of 'character" has received almost no attention from systematic theorists. With this postdoctoral fellowship, Dr. O'Hara, a systematist, is working with Dr. Elliott Sober, a philosopher of science, to develop a conceptual analysis of the character concept of systematics. Starting from his own definition, developed in his doctoral dissertation research in 1989, of a character as an observed difference from which we infer an evolutionary event, Dr. O'Hara is developing arguments to show that: (1) although "character" is an inherently comparative concept, the entities being compared in character descriptions have not always been clearly specified; (2) the "character problem" in systematics (how are characters recognized in practice, and how should they be scored for cladistic analysis) maps directly onto what may be called the "event problem" in philosophy; and that (3) it is possible to identify the specific points in this mapping process at which all the uncertainty in our estimates of phylogeny is introduced. As a result of this study, the language of character descriptions in systematics should become more precise, and the epistemological foundations of our knowledge of evolutionary history should be better understood.
