Evolution and Phylogeny in Morphologically Uniform Groups

Abstract

In homogeneous groups, strictly homologous features could not be separated from "pseudohomologous" ones on the basis of study of the features alone. Investigation of the phylogeny was essential to distinguish between homology and "pseudo-homology." When the necessary intermediate and ancestral groups were unknown, these conditions were indistinguishable. Members of homogeneous groups probably share a similar genetical-developmental potential from which the principle of evolutionary homodynamy is derived. This principle may be defined as: The number and ease with which an identical or very similar feature may arise independently within a group depends upon its degree of evolutionary homodynamy which in turn depends upon its common genetical-developmental potential. Homology is thus redefined as follows: Homologous features (or conditions of the features) in two or more organisms are ones that can be traced back to the same feature (or condition) in a group possessing a high degree of evolutionary homodynamy. Thus "pseudo-homologous" features which arise from a group possessing a high degree of evolutionary homodynamy are just as homologous as strictly homologous features. Homology is not an absolute quality, but is relative and varies just as much as does monophyly. The degree of homogeneity of groups therefore seems to influence the formulation of general principles of phylogeny; these principles must be examined to determine whether they are suitable before embarking upon a phylogenetic study of any group.