Misunderstanding the unambiguous: Student misconceptions in phylogenetic systematics

Cladograms depict hypothetical relationships unambiguously among select taxa. I investigated introductory college biology students' understanding of cladograms both before and after instruction. My study was composed of two parts, a written survey as well as a focused interview. Using semi-structured pilot interviews I developed a written survey and a directed interview. The written survey was administered to over 300 students enrolled in an introductory biology course for majors at a large state university over three semesters. I conducted interviews with 23 students prior to instruction and 22 students following instruction. I found that the style and orientation of a tree diagram affected student interpretation of the direction of time, and interpretation of the relationships among the organisms presented. I also found that prior to instruction most students did not use nested hierarchies to organize relationships. After instruction most students drew trees to show relationships among taxa but they still did not use nested hierarchies to organize their taxa, and subsequently most of the student constructed tree diagrams did not show the correct relationships among taxa. In both interpreting tree diagrams and in constructing their own, many students used a ladder-like progression to explain relationships among taxa. Using this ladder-like progression students often explained that extant animals evolve into other extant animals as they "progress" up the "main branch."...