A valid assessment of students’ skill in determining relationships on evolutionary trees

Abstract

Background: Evolutionary trees illustrate relationships among taxa. Interpreting these relationships requires developing a set of "tree-thinking" skills that are typically included in introductory college biology courses. One of these skills is determining relationships among taxa using the most recent common ancestor, yet many students instead use one or more alternate strategies to determine relationships. Several alternate strategies have been well documented and these include using superficial similarity, proximity at the tips of a tree, or the fewest intervening nodes in the tree to group taxa. Results: We administered interviews (n = 16) and pencil-and-paper questionnaires (n = 205), and constructed a valid and reliable assessment that measured how well students determined relationships among taxa on an evolutionary tree. Our questions asked students to consider a focal taxon and identify which of two additional taxa is most closely related to it. We paired the use of most recent common ancestor with one of three alternative strategies (i.e., similarity, proximity, or node-counting) to explicitly test students' understanding of the relationships among the taxa on each tree. Conclusions: Our assessment enables us to identify students who are effectively distracted by an alternative strategy, those who use the most recent common ancestor inconsistently, or who are guessing in order to determine relationships among taxa. Our 18-question tool (see Additional file 1) can be used for formative assessment of student understanding of how to interpret relationships on evolutionary trees. Because our assessment tests for the same skill throughout, students who answer incorrectly, even once, likely have an incomplete understanding of how to determine relationships on evolutionary trees and should receive follow-up instruction.

Understanding the tree of life: an overview of tree-reading skill frameworks

“…Teaching the evaluation of relative evolutionary relationships presented in a tree can be seen as the heart of tree-reading. Here, educators should stress the importance of examining the most recent common ancestor as the central way to begin evaluating evolutionary relatedness (Blacquiere and Hoese 2016). Numerous known misconceptions may play a crucial role here and should be taken into account by educators (Gregory 2008;Meir et al 2007).…”

“…Some authors describe tree-thinking as a mere set of skills needed to extract relationship information from an evolutionary tree (O'Hara 1997), while others describe it as a "habit of mind that uses the history of life on earth as its first line of evidence while providing students with a hierarchical view of the natural world" (Catley and Novick 2008) or as "the ability to visualize evolution in tree form and to use tree diagrams to communicate and analyze evolutionary phenomena" (Baum and Smith 2013). There is no unifying definition of the term tree-thinking, but the various definitions and descriptions tend to resemble each other closely (Blacquiere and Hoese 2016;Catley et al 2012;Gibson and Hoefnagels 2015;Halverson et al 2011). The common idea across the different definitions is that tree-thinking is needed in order to be able to extract information about relationships from an evolutionary tree, to make conclusions and inferences about the displayed course of evolution, and to construct evolutionary trees from the given data.…”

“…Focusing on one particular skill in their study assessing college students' skills in reading evolutionary relatedness from phylogenetic trees, Blacquiere and Hoese (2016) claim that one of the most fundamental skills in tree-thinking is knowing about the concept of the MRCA. Deciding which two species share a more recent common ancestor than the others is a key aspect in evaluating evolutionary relationships (Blacquiere and Hoese 2016). The study focused on establishing a valid assessment tool with an emphasis on the stated skill.…”

“…Skill (C) "reconstructing trees" is omitted in this work, as it deals with building evolutionary trees. Blacquiere and Hoese's (2016) statement that knowledge of MRCA is the most important for treethinking is represented in this comparison by Halverson and Friedrichsen's level (6) ("scientific use of representation"), and is the basis for two of Novick and Catley's skills (E and F) for assessing the relative evolutionary relatedness of three taxa.…”

Further Effects of Phylogenetic Tree Style on Student Comprehension in an Introductory Biology Course

“…Despite the significance of phylogenetic trees, students at all levels routinely struggle to interpret these diagrams ( Meir et al , 2007 ; Halverson et al , 2011 ; Catley et al , 2013 ; Novick and Catley, 2013 ; Blacquiere and Hoese, 2016 ), even after explicit instruction ( Phillips et al , 2012 ; Smith et al , 2013 ; Dees et al , 2014 ). Student difficulties with phylogenetic trees have been attributed to a number of factors, starting with abstractness.…”