How Undergraduate Students Misread Cladograms

Although phylogenetic systematics is used to reconstruct evolutionar 123y relationships, undergraduates have a difficult time mastering its fundamental concepts. Because it is a key part of the mainstream professional thinking, we explored in what ways students misread cladograms, which are the abstract and synthetic diagrams of phylogenetic systematics. We developed a questionnaire to examine the following four hypotheses as to how introductory college-level students (n=51) read cladograms: 1) students read cladograms correctly; 2) students infer that proximity of tips equals relatedness; 3) students read cladograms as they might an evolutionary tree, reading left to right as primitive to more advanced, and perceiving organisms as branching off; and 4) students infer ancestors at the nodes. Most responses fell into one of the four hypotheses, with 55% following the scientific (‘correct’) hypothesis. Most students answered between six and eight of the ten questions correctly. Slightly more than half of the students generally followed the scientific hypothesis, while others applied both the scientific and proximity (hypothesis 2, above) hypotheses together. A few students followed the primitive hypothesis (hypothesis 3, above). Our recommendation is that instructors address discrepancies between the scientific and proximity hypotheses in particular. For undergraduates, generally, cladograms require focused teaching, explanation, and active-learning approaches to be successfully used to teach phylogenetic systematics.