Each problem consisted of a matrix of coded and polarized phylogenetic data organized by taxa and characters. Four series of research problems were constructed that varied the numbers of solutions, taxa, and characters. In addition, some problems contained a revision component that required: additions to prior solutions, restructuring of prior solutions, or increased or decreased numbers of solutions. Nine expert phylogenetic systematists participated in the research project by thinking aloud while constructing phylogenetic trees to account for the problem data matrices.
A procedural model of expert performance for phylogenetic tree construction is described with associated strategies and heuristics. Three overall strategies were described: inclusion/exclusion, order of divergence, and duplicated taxa. Each overall strategy is represented as a pathway through the model. In addition, a new conceptual framework for understanding the nature of phylogenetic tree construction problems is described including factors that contribute to difficulty of phylogenetic problems.
The strategies related to the procedural model of expert performance are used to outline a model of desired performance. The model provides a basis for developing an approach to teaching evolution based on effects-to-causes problems. Examples are provided that illustrate how the results of this research can inform the development of a problem-based approach to teaching evolutionary biology. In addition, the implications for improved problem-solving environments for phylogenetic biology are described.