Phylogenetic trees are important tools for teaching and understanding evolution, yet students struggle to read and interpret them correctly. In this study, we extend a study conducted by Catley and Novick (2008) by investigating depictions of evolutionary trees in US textbooks. We investigated 1197 diagrams from 11 German and 11 United States university textbooks, conducting a cross-country comparison and comparing the results with data from the 2008 study. A coding manual was developed based on the 2008 study, with extensions focused on additional important aspects of evolutionary trees. The US and German books showed only a low number of significant differences, typically with very small impacts. In both samples, some characteristics that can render reading trees more difficult or foster misconceptions were found to be prevalent in various portions of the diagrams. Furthermore, US textbooks showed fewer problematic properties in our sample than in the 2008 sample. We conclude that evolutionary trees in US and German textbooks are represented comparably and that depictions in US textbooks have improved over the past 12 years. As students are confronted with comparable depictions of evolutionary relatedness, we argue that findings and materials from one country should easily be transferable to the other.
Reading evolutionary trees is a challenging task for students. Item response theory was used to investigate a tree-reading skill system, and the different skills were found to be empirically distinguishable, although there was no evidence for the assumed hierarchy. The results are compared with a different approach by other authors.
We present material and instructions to teach the construction of phylogenetic trees using specifically designed images of dragons. Using fictional creatures, we can control the number and properties of characteristics, as well as present students with a context they might consider interesting. Besides creating evolutionary trees from data, students can learn that trees based on morphological characteristics might contradict and trees based on genetic analysis are a more reliable tool in classification. The material used in this learning environment is freely available, so educators can use and customize it freely. Students working with this material declared a high motivation to work with the fictional animals and engaged in very active discussions about different classifications of the dragons.
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