Abstract
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.
Highlights
Phylogenetic trees are graphical representations of evolutionary relationships and are fundamentally important in modern biology, taxonomy and evolutionary biology [1,2,3]
The main difference between this category in our study and the corresponding one in Catley and Novick’s 2008 study is that we focused on a broader spectrum of evolutionary trees, while they addressed cladograms
Following Fisher’s exact test (FET), we found a significant difference in tree orientation between German and US diagrams (p < 0.001, FET = 23.498) with a small effect size (V = 0.141)
Summary
Phylogenetic trees are graphical representations of evolutionary relationships and are fundamentally important in modern biology, taxonomy and evolutionary biology [1,2,3] Are they indispensable tools in teaching about evolution [2,4,5], but they are used in a wide variety of practical applications [6,7]. In the earliest depictions of the organization of nature, we find linear arrangements, called the ‘chain of being’ or ‘ladder of life’ [16] These depictions typically depicted biological species or groups, but showed other aspects like elements, angels, or God. Similar hierarchical organizations of the world are known to go back to the ancient Greeks [17]. The idea of more or less developed species is still present today and is seen as one of the most widespread learners’ misconceptions in the field of evolutionary trees [18,19,20]
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