Character mapping and cladogram comparison versus the requirement of total evidence: does it matter for polychaete systematics?

Abstract

The practice of partitioning data for the inferences of phylogenetic hypotheses has become a routine practice in biological systematics. Two popular approaches: (i) mapping ‘morphological’ characters onto ‘molecular’ phylogenies, and (ii) comparing ‘morphological’ and ‘molecular’ phylogenies, are examined in light of what is known as the requirement of total evidence. Inferences of phylogenetic hypotheses, indeed all taxa, occur by a type of non-deductive reasoning known as abduction. The intent of abduction is to offer at least tentative causal accounts that explain character data. The rational acceptance of abductively derived hypotheses is subject to conditions of the requirement of total evidence as a matter of the evidential support for those hypotheses. It is shown that both character mapping and comparisons of cladograms using partitioned datasets are procedures that severely reduce the credibility of phylogenetic hypotheses. This problem is alleviated by acknowledging the formal structure of the why-questions we ask in relation to character data, for which phylogenetic hypotheses serve as answers.