Perception and conception in understanding evolutionary trees

Relationships depicted in evolutionary trees depend solely on levels of most recent common ancestry. Integrating discipline-based education research in biology with perceptual/cognitive psychology, the authors predicted, however, that the Gestalt principles of perceptual grouping would affect how students interpret these relationships. Experiment 1 (N = 93) found that students segment 6-9 branch trees in accordance with the Gestalt principle of connectedness. Experiment 2 (N = 310) found that students in introductory through advanced biology classes predominantly believed, incorrectly, that the evolutionary relationships among a set of target taxa differed in two trees because the grouping of those taxa differed. Experiment 3 (N = 99) found that students from these same classes were more likely to make inferences consistent with the depicted evolutionary relationships when Gestalt grouping supported those inferences. The authors discuss implications for improving students' understanding of cladograms.