The questions developed using the process described here address understanding of a conceptual model of the evolutionary history of taxa, a phylogeny (phyl: kind or tribe; geny: origin), more specifically, the key tree-thinking skill of determining evolutionary relatedness among taxa on a phylogeny. Given the well-documented problems acquiring this skill, we discuss how tree-thinking questions constructed following our method can be used to improve understanding of evolutionary relatedness among taxa and other evolution concepts.
The method for question construction provides the means for instructors to customize questions in three ways: (1) taxa included, (2) tree structure, and (3) question design. First, instructors may select the taxa of their choice to be included in a question allowing them to design questions with course specificity (e.g., marine organisms for a marine biology course) and select taxa that live in a local ecosystem to increase relevance and student engagement. Freedom in taxa selection also enables instructors to control question difficulty because they are able to design questions ranging from less difficult (questions containing familiar taxa) to more difficult (questions containing unfamiliar taxa). Next, instructors are able to customize the structure of the evolutionary tree in a question by changing the number of lineages and changing the branching appearance of the lineages. Varying tree structure facilitates question novelty and minimizes false-positive results that arise when students become familiar with a tree structure and are able to answer a question correctly because they recognize a pattern instead of answering correctly because they have acquired the skill of determining evolutionary relatedness. Lastly, instructors can select between two forced-choice question designs: binary-choice or four-choice enabling instructors to design a question that includes one incorrect strategy and therefore one distracter or includes three incorrect strategies and therefore three distracters.
The method presented here provides a valuable tool for instruction because the question resources are concrete examples that can be used to facilitate discussions about abstract concepts (e.g., homology, homoplasy, synapomorphy, and symplesiomorphy) and commonly held alternative strategies used to interpret evolutionary trees. To exemplify, an instructor can address the incorrect similarity strategy by presenting an assessment tree containing taxa with independent evolution toward a similar body form (homoplasy) as evidence to counter the similarity strategy because parallel selective pressures experienced by the species resulted in similar body form, not common ancestry. Another example of using this method for instruction addresses the proximity incorrect strategy. Constructing assessment trees depicting the same evolutionary relationships among taxa while having different sequences of taxa along the branch tips can be used to demonstrate the fault with the proximity strategy. By presenting phylogenies depicting the same taxa with the same evolutionary relationships but different sequences of taxa along the branch tips, students will be exposed to the inconsequential nature of the sequence of taxa along the branch tips when determining evolutionary relationships among taxa.
Instructors can also use the assessment trees and questions to explore how a phylogeny can show evolutionary relationships among organisms at any taxonomic level. Using phylogenies with a variety of taxonomic levels, instructors can demonstrate to students how clades can be collapsed (lineages extending toward the present from an internal node can be retracted) to represent taxonomic groups that are more inclusive or they can be expanded (lineages can be radiated from terminal taxa) to represent more specific taxonomic groups. When instructors use phylogenies with a diversity of taxonomic groups from less inclusive to more inclusive, greater clarity is given to the properties of internal nodes. Internal nodes represent the hypothetical common ancestors of the lineages; they depict the point at which the taxa in the lineages extending from the internal node exchanged genetic material before reproductive isolation and genetic divergence led to taxa that are recognized as separate from one another. Presenting phylogenies in this way will help dispel the false assumption that evolutionary change only occurs at internals nodes that leads to the alternative strategy node counting.
Questions constructed using the methods presented here can be incorporated within a course as formative and summative assessments. Formative assessments are used within the learning process to provide feedback to the instructor and students about the level of understanding so that deficiencies in understanding can be addressed with further instruction and study (Oosterhof 1999). Therefore, they provide information for metacognition allowing students to monitor and regulate their tree-thinking process. Summative assessments solely focus on how much someone has learned at the completion of a learning cycle (Oosterhof 1999). An example of using questions developed using the method presented here for a summative assessment is an instructor including them on an exam.
The assessment trees and questions developed using the method presented here are a valuable tool in formative assessments because they are intentionally constructed to include common incorrect strategies as distracters to the correct strategy facilitating metacognitive analysis by the students. To obtain an accurate measure of understanding about phylogenies, assessment questions should include the pitfalls that are encountered when interpreting a phylogeny. Including incorrect strategies as distracters can lead to students experiencing cognitive dissonance, the discord of held beliefs with new evidence, if the strategy they employ cannot be used or leads to an incorrect response. Students are motivated to resolve the dissonance (Festinger 1957) therefore eliminating the incorrect strategy and adopting the correct strategy. To further enhance student metacognition and learning, instructors can design learning activities, which include the questions developed using our methods. For example, an instructor could initiate student metacognitive analysis by having students answer questions and also prompt students to explain why the responses they selected as the correct responses are correct and the responses they did not select as the correct responses are incorrect. In addition to students using feedback from the assessment trees and questions to further knowledge acquisition, instructors can use the assessment trees and questions to identify learning deficits and address them with specificity using further instruction or learning activities.
These questions may also be used in a summative assessment to evaluate student understanding at the completion of the learning cycle. If instructors would prefer to not have to create their own evolutionary trees, these assessment trees and example questions are ready-to-use. Assessment trees and questions are a valuable resource for summative assessments because they were found to have validity, reliability, and discrimination; in addition, the assessment trees and questions deliberately employ common incorrect strategies as distracters and include taxa commonly seen in college textbooks.