The limits of understanding in biological systematics

Ernst Mayr’s (1961, Science 131: 1501–1506) distinction between proximate and ultimate causation in biology is examined with regard to the acquisition of understanding in biological systematics. Rather than a two-part distinction, understanding in systematics is characterized by relations between three explanatory components: descriptive (observation statements)—proximate (ontogenetic hypotheses)—ultimate (e.g. specific and phylogenetic hypotheses). Initial inferential actions in each component involve reasoning to explanatory hypotheses via abductive inference, providing preliminary understanding. Testing hypotheses, to critically assess understanding, is varied. Descriptiveand proximate-level hypotheses are routinely tested, but ultimate hypotheses present inherent difficulties that impose severe limits, contrary to what is usually claimed in the systematics literature. The problem is compounded by imprecise considerations of ‘evidence’ and ‘support.’ For instance, in most cases, the ‘evidence’ offering ‘support’ for phylogenetic hypotheses, as cladograms, is nothing more than the abductive evidence (premises) used to infer those hypotheses, i.e. character data and associated phylogenetic-based theories. By definition, such evidence only offers initial, trivial understanding, whereas the pertinent evidence sought in the sciences is test evidence, which cannot be supplanted by character data. The pursuit of ultimate understanding by way of spurious procedures such as contrived testing, Bremer support, and resampling methods are discussed with regard to phylogenetic hypotheses.