The Canalized Evolutionary Potential: Inconsistencies in Phylogenetic Reasoning

Abstract

Holomorphological similarities can be based on synapomorphies, symplesiomorphies, convergences, diffuse parallelisms through parallel selection and underlying synapomorphies (i.e., close parallelism as a result of inherited factors within a monophyletic group causing incomplete synapomorphy). Two sets of minimum criteria for asserting synapomorphies are given; one does not allow for outside parallelism and secondary reductions, reversals or change; the other allows for reductions in apomorphic part taxa (subgroups) and outside parallelism in groups which cannot be sister groups. A theoretical scheme of argumentation (cladogram) secured through synapomorphies satisfying the strictest criteria is drawn. Three modifications of synapomorphies satisfying the 2nd set of criteria are discussed and exemplified. The remaining 6 hypothetical trends can be explained as underlying synapomorphies, as diffuse parallel selections (including convergence) or as secondary reductions (and reversals). Hypothetical phylogenetic trees with the distribution of character alternatives for each taxon including hypothetical ancestors are given for each alternate explanation, discussed and exemplified from chironomid morphology. When the monophyly of every taxon is established, underlying synapomorphy may assert monophyly for the collective taxon. As the underlying synapomorphy consists in the capacity to develop synapomorphy, loss of this capacity can be regarded, under certain circumstances, as a new synapomorphy. There appears to be analogy between species genetics (pleiotropy, polygenes, suppressive genes) and supraspecific phylogenetics. The canalized evolutionary potential exemplified through underlying synapomorphies corresponds to the potential information classes of Wiley and Brooks (1982).