Information Content and Most Parsimonious Trees

Abstract

Recent work by Farris (1977, 1979a, 1979b, 1980) has provided an explicit, logical definition of information content and contrasts different classification approaches based upon this concept. However, his conclusion that the use of parsimonious trees that are nested monophyletic groups (phylogenetic analysis) is a necessary consequence of the goal of maximal information content can be questioned. As an alternative, the possible use of paraphyletic groups is considered. Evolutionary taxonomists have proposed the use of alternatives to monophyletic (sensu Hennig 1966) groups with the justification that such groups should lead to classifications with greater predictivity or information content (e.g. Ashlock 1979; Mayr 1981). In this study the definitions of paraphyly of Faith (1982) are related to Farris’ (1977) criterion of information content, in order to evaluate the potential of paraphyletic groups as separate taxa. Paraphyly can be defined in terms of two types of distinguishing characters. In both cases, the group in question (call it ‘G’) is distinguished in the data set by having one state for a set of binary characters. This distinction is understood in the context of the overall monophyletic group that minimally includes the members of G.