Ontogeny and Character Phylogeny

Abstract— The doctrine of recapitulation was long ago exchanged for a view that ontogeny is orderly and recapitulates ancestral ontogenies. Only recently has the pattern of ontogeny, as a means for determining individual character phylogenies (polarities), been explicitly explored by Gareth Nelson and other cladists. Constraints on outgroup comparisons are suggested to apply to Nelson's rule equally, and the supposed distinction between “direct” and “indirect” methods is suggested to be nonexistent. Nelson's rule is concluded to measure character adjacency directly, but polarity indirectly. Nelson's (ontogenetic) rule is compared to the Outgroup Rule of Watrous and Wheeler, based on 60 postembryonic larval characters of three species of slime‐mold beetles of the genus Agathidium ( onisemdes Palisot de Beauvois, pulchrum LeConte, aristerium Wheeler), and reference to larvae of Amsotoma basalts (Le Conte) as an outgroup. Polarities were hypothesized based on each rule and cladograms constructed with the microcomputer programs Henning86 (J. S. Farris) and CLADOS (K. C. Nixon). With levels of analytical error, or homoplasy, measured as the consistency index, the results were compared and the least homoplastic solutions preferred. It is concluded that the outgroup rule and Nelson's rule arc of about the same efficacy as criteria for polarity, and that each is ultimately justified on the basis of parsimony. The following hypothesis of relationships is accepted for the species studied: ( Anisotoma basalts + ( Agathidium oniscoides + ( Agathidium pulchrum + Agathidium arislerium ))).