Students' Use of Alternative Strategies When Reading Evolutionary Trees.

Evolutionary trees present hypotheses of the relationships among taxa. Some undergraduate biology students have trouble properly interpreting relationships on these trees; instead of using the most recent common ancestor (MRCA), many students use alternative strategies such as tip proximity, node counting, or morphological similarity to determine relationships. I designed questions to examine these alternative strategies and the use of the MRCA strategy to measure the most commonly, and the most consistently, used strategies by students in college introductory biology. I developed three highly reliable multiple-choice questionnaires, with each of the four possible answers for a question indicating the use of a different strategy (Cronbach’s α = 0.83; α = 0.89; α = 0.89). I administered the questionnaires to undergraduate students in their first core biology class after they received instruction on reading evolutionary trees (n = 197; n = 115; n = 97). Some students’ alternative strategy use was consistent. Students were much more likely to choose answers consistent with the tip proximity and node counting strategies than the morphological similarity strategy. The students looked at the expected areas for their chosen strategy when taking the questionnaire using eye-tracking equipment. Over 53% of the students missed at least one question on the questionnaires. The taxa and tree structure may have influenced the students’ use of the alternative strategies on the questionnaires. These questionnaires allow us to understand how students determine evolutionary relatedness among species and can help instructors of biology courses improve students’ understanding of evolutionary trees.