Kefyn M. Catley

Seeing the Wood for the Trees: An Analysis of Evolutionary Diagrams in Biology Textbooks

ABSTRACT This study presents the findings of an analysis of evolutionary diagrams found in 31 biology textbooks for students ranging from middle school to the undergraduate level. Since the early 1990s, cladograms have found their way into high school biology textbooks, yet we know little about their effectiveness as interpretive and instructional tools in biology education. In this article we document the frequency and types of cladograms found in 31 textbooks, and classify and survey the other types of evolutionary diagrams used in the texts. Although cladograms comprised approximately 72 percent of the diagrams overall, we found virtually no attempt to explain their structure and theoretical underpinnings. Various other noncladogenic evolutionary diagrams, comprising 28 percent of the total, were distributed throughout all textbooks studied. On the basis of our analysis, we conclude that many of these evolutionary diagrams are confusing and may reinforce alternative conceptions of macroevolution. Biology educators should therefore recognize these problems and take measures to ameliorate their effects.

Reasoning About Evolution’s Grand Patterns College Students’ Understanding of the Tree of Life

Tree thinking involves using cladograms, hierarchical diagrams depicting the evolutionary history of a set of taxa, to reason about evolutionary relationships and support inferences. Tree thinking is indispensable in modern science. College students’ tree-thinking skills were investigated using tree (much more common in professional biology) and ladder (somewhat more common in textbooks) cladogram formats. Students’ responses to questions assessing five tree-thinking skills provided evidence for several perceptual and conceptual factors that impact reasoning (e.g., the Gestalt principles of good continuation and spatial proximity, prior knowledge). Instructional implications of the results include using the tree format for initial instruction and clarifying that most recent common ancestry determines evolutionary relatedness. Broader implications for designing scientific diagrams and promoting diagrammatic literacy are considered.

Characters Are Key: The Effect of Synapomorphies on Cladogram Comprehension

Cladograms, phylogenetic trees that depict evolutionary relationships among a set of taxa, are one of the most powerful predictive tools in modern biology. They are usually depicted in one of two formats—tree or ladder. Previous research (Novick and Catley 2007) has found that college students have much greater difficulty understanding a cladogram’s hierarchical structure when it is depicted in the ladder format. Such understanding would seem to be a prerequisite for successful tree thinking. The present research examined the effect of a theoretically guided manipulation—adding a synapomorphy on each branch that supports two or more taxa—on students’ understanding of the hierarchical structure of ladder cladograms. Synapomorphies are characters shared by a group of taxa due to inheritance from a common ancestor. Thus, their depiction on a cladogram may facilitate the understanding of evolutionary relationships. Students’ comprehension was assessed in terms of success at translating relationships depicted in the ladder format to the tree format. The results indicated that adding synapomorphies provided powerful conceptual scaffolding that improved comprehension for students with both weaker and stronger backgrounds in biology. For stronger background students, the benefit of adding synapomorphies to the ladders was comparable to that of approximately two hours of instruction in phylogenetics that emphasized the ladder format.

Linear Versus Branching Depictions of Evolutionary History: Implications for Diagram Design

This article reports the results of an experiment involving 108 college students with varying backgrounds in biology. Subjects answered questions about the evolutionary history of sets of hominid and equine taxa. Each set of taxa was presented in one of three diagrammatic formats: a noncladogenic diagram found in a contemporary biology textbook or a cladogram in either the ladder or tree format. As predicted, the textbook diagrams, which contained linear components, were more likely than the cladogram formats to yield explanations of speciation as an anagenic process, a common misconception among students. In contrast, the branching cladogram formats yielded more appropriate explanations concerning levels of ancestry than did the textbook diagrams. Although students with stronger backgrounds in biology did better than those with weaker biology backgrounds, they generally showed the same effects of diagrammatic format. Implications of these results for evolution education and for diagram design more generally are discussed.

Reasoning about Evolutionary History: Post-Secondary Students' Knowledge of Most Recent Common Ancestry and Homoplasy.

Evolution curricula are replete with information about Darwins theory of evolution as well as microevolutionary mechanisms underlying this process of change. However, other fundamental facets of evolutionary theory, particularly those related to macroevolution are often missing. One crucial idea typically overlooked is that of most recent common ancestry and its relevance for investigating evolutionary relationships among taxa. Deep understanding of most recent common ancestry is particularly important for comprehending the reciprocal concept of homoplasy (convergent evolution). This study examines knowledge of these two concepts among 127 postsecondary students as a function of their biology background. Analyses of responses to two questions indicate that students fail to acquire and/or retain knowledge of the significance of most recent common ancestry and of homoplasy, despite potential for prior exposure to them throughout K-12 and post-secondary education. These results indicate a need for improvement in evolution education to ensure that students acquire an appropriate understanding of evolutionary relationships and processes as a whole.

Teaching Tree Thinking to College Students: It’s Not as Easy as You Think

The ability to understand and reason with tree-of-life diagrams (i.e., cladograms), referred to as tree thinking, is an essential skill for biology students. Yet, recent findings indicate that cladograms are cognitively opaque to many college students, leading them to misinterpret the information depicted. The current studies address the impact of prior biological background and instruction in phylogenetics on students’ competence at two foundational tree-thinking skills. In Study 1, college students with stronger (N = 52) and weaker (N = 60) backgrounds in biology were asked to (a) identify all the nested clades in two cladograms and (b) evaluate evolutionary relatedness among taxa positioned at different hierarchical levels (two questions) and included in a polytomy (two questions). Stronger-background students were more successful than weaker-background students. In Study 2, a subset of the stronger-background students (N = 41) who were enrolled in an evolution class subsequently received two days of instruction on phylogenetics. As expected, these students’ tree-thinking skills generally improved with instruction. However, although these students did very well at marking the nested clades, fundamental misinterpretations of relative evolutionary relatedness remained. The latter was especially, although not exclusively, the case for taxa included in a polytomy. These results highlight the importance of teaching cladistics, as well as the need to tailor such instruction to the difficulties students have learning key macroevolutionary concepts.

Fostering 21st-Century Evolutionary Reasoning: Teaching Tree Thinking to Introductory Biology Students.

The ability to interpret and reason from Tree of Life diagrams is a vital aspect of 21st-century science literacy. This article reports the development, implementation, and evaluation of a research-based curriculum (an instructional booklet, lectures, and laboratory) to teach such tree thinking in an undergraduate biology class for science majors.

Depicting the tree of life in museums: guiding principles from psychological research

The Tree of Life is revolutionizing our understanding of life on Earth, and, accordingly, evolutionary trees are increasingly important parts of exhibits on biodiversity and evolution. The authors argue that in using these trees to effectively communicate evolutionary principles, museums need to take into account research results from cognitive, developmental, and educational psychology while maintaining a focus on visitor engagement and enjoyment. Six guiding principles for depicting evolutionary trees in museum exhibits distilled from this research literature were used to evaluate five current or recent museum trees. One of the trees was then redesigned in light of the research while preserving the exhibits original learning goals. By attending both to traditional factors that influence museum exhibit design and to psychological research on how people understand diagrams in general and Tree of Life graphics in particular, museums can play a key role in fostering 21st century scientific literacy.

Teaching Tree Thinking in an Upper Level Organismal Biology Course: Testing the Effectiveness of a Multifaceted Curriculum.

Abstract The ability to interpret and reason from Tree of Life diagrams is a key component of twenty-first century science literacy. This article reports on the authors’ continued development of a multifaceted research-based curriculum – including an instructional booklet, lectures, laboratories and a field activity – to teach such tree thinking to biology students. Results are presented from a study involving biology students enrolled in an upper level organismal biology class. All students received the multi-week tree-thinking curriculum, and learning was assessed by comparing pretest and posttest scores on the novel tree-thinking assessment instrument developed by the authors. Quantitatively, the authors found large gains in tree-thinking abilities due to their instruction. The results also provided qualitative evidence that the authors succeeded in their more general goal of helping students to appreciate the interconnectedness of Earth’s biodiversity through the utility of phylogenetic trees.