Education Graphical representations of evolutionary relationships among taxa have a long history in biology. The pervasive effect of two particularly influential representations, the "Chain of Being," rooted in the ideas of Plato and Aristotle, and the "Tree of Life," epitomized by Haeckel's trees of the late 1800s, can still be seen in contemporary representations. The Chain of Being encompasses the physical and metaphysical world in an unbroken chain that stretches from nonliving matter all the way to "supernatural" beings. It is possible to trace a connection from the Great Chain of Being depicted in Didacus Valades's 1579 Rhetorica Christiana (Lovejoy 1936), through Bonnet's (1745) scala naturae (scale of being) and Lamarck's (1809) extension of the "chain" in Philosophie Zoologique, to Haeckel's trees of the late 1800s. The Chain of Being and Tree of Life are founded on the concept of a linear evolutionary progression from simple to complex, with a distinctively teleological perspective. Although many other forms-both hierarchical and otherwise-have also appeared in the scientific press over the past 300 or so years, many current representations of evolution mirror the great chain as a process of orderly progression (Nee 2005).This study documents the type, frequency, and distribution of evolutionary diagrams in 31 contemporary textbooks aimed at a wide array of readers from middle school to the undergraduate level. Today, practicing biologists use phylogenetic trees in the form of cladograms and phylograms to hypothesize and study phylogenies. Some would argue that phylograms are a subset of cladograms, but they are based on quite different methodologies and underlying philosophies. The topologies, however, can be identical, except for nonequal branch lengths. These attempt to convey the inferred degree of relatedness based on, for example, the number of nucleotide substitutions between taxa.We found that cladograms (sensu stricto) were well represented (n = 505) in textbooks. Phylograms, in contrast, were very rare (n = 6). We also found a large number of other types of diagrams (n = 192) that at best are open to multiple interpretations and, at worst, are ambiguous or based on long discredited evolutionary mechanisms. Because there were so few phylograms (four examples in two introductory biology textbooks for majors and two examples in two botany textbooks), we excluded those diagrams from our analyses.Although cladograms began to appear in high-school textbooks in the early 1990s, there has been virtually no research examining the functionality of these or other types of evolutionary diagrams in life science pedagogy. How well do evolutionary diagrams in textbooks reflect current thinking in evolutionary biology? More important, do they reinforce or reduce common misconceptions of evolutionary processes? Such information is vital to understanding how best to Kefyn M. Catley (e-mail: kcatley@wcu.edu

Cladograms, hierarchical diagrams depicting evolutionary histories among (groups of) species, are commonly drawn in 2 informationally equivalent formats--tree and ladder. The authors hypothesize that these formats are not computationally equivalent because the Gestalt principle of good continuation obscures the hierarchical structure of ladders. Experimental results confirmed that university students (N = 44) prefer to subdivide ladders in accordance with good continuation rather than with the underlying hierarchical structure. Two subsequent experiments (N = 164) investigated cladogram understanding by examining students' ability to translate between formats (e.g., from tree to ladder). As predicted, students had greater difficulty understanding ladders than trees. This effect was larger for students with weaker backgrounds in biology. These results have important implications for evolution education reform.

Some ability to comprehend deep time is a prerequisite for understanding macroevolution. This study examines students' knowledge of deep time in the context of seven major historical and evolutionary events (e.g., the age of the Earth, the emergence of life, the appearance of a pre‐modern human, Homo habilis). The subjects were 126 students recruited from psychology, education, and biology classes at two universities. They were assigned to stronger and weaker background groups based on their college‐level biology coursework. Subjects provided startlingly large time ranges for all questions, ranging over several orders of magnitude (e.g., from 1,000 to 600 billion years ago for when most dinosaurs became extinct), coupled with the strong tendency to underestimate how long ago the events occurred. Converting absolute time estimates to relative time estimates allowed subjects' knowledge of the spacing of the events to be examined and also provided a clearer picture of their patterns of over and underestimation. The results of this study suggest that many students are without an effective conceptual framework to make sense of very large time frames. Although there were no consistent differences in the accuracy of students' responses as a function of their biology background, the weaker background students showed greater variability, providing more time estimates at both the low and high extremes. We describe a pedagogical strategy that uses a relative approach presenting major evolutionary events as they unfolded in time and advocate a tool from professional practice to depict events in time and space. © 2009 Wiley Periodicals, Inc. J Res Sci Teach 46: 311–332, 2009

Microevolutionary mechanisms are taught almost exclusively in our schools, to the detriment of those mechanisms that allow us to understand the larger picturemacroevolution. The results are demonstrable; as a result of the strong emphasis on micro processes in evolution education, students and teachers still have poor understanding of the processes which operate at the macro level, and virtually no understanding at all of the history of life on our planet. Natural selection has become synonymous with the suite of processes we call evolution. This paper makes the case for a paradigm shift in evolution education, so that both perspectives-micro and macro-are given equal weight. Increasingly, issues of bioethics, human origins, cloning, etc., are being cast in a light that requires an understanding of macroevolution. To deny our students access to this debate is to deny the call for universal science literacy. A methodology from professional practice is proposed that could achieve this goal, and discussed in light of its utility, theoretical underpinnings, and historical legacy. A mandate for research is proposed that focuses on learners' understanding of several challenging macroevolutionary concepts, including species, the formation of higher groups, deep time, and hierarchical thinking.

The authors argue that some diagrams in biology textbooks and the popular press presented as depicting evolutionary relationships suggest an inappropriate (anagenic) conception of evolutionary history. The goal of this research was to provide baseline data that begin to document how college students conceptualize the evolutionary relationships depicted in such noncladogenic diagrams and how they think about the underlying evolutionary processes. Study 1 investigated how students (n = 50) interpreted the evolutionary relationships depicted in four such evolutionary diagrams. In Study 2, new students (n = 62) were asked to interpret what the students in Study 1 meant when they used the terms evolved into/from and ancestor/descendant of. The results show the interpretations fell broadly into two categories: (a) evolution as an anagenic rather than cladogenic process, and (b) evolution as a teleological (purpose‐driven) process. These results imply that noncladogenic diagrams are inappropriate for use in evolution education because they lead to the misinterpretation of many evolutionary processes. © 2009 Wiley Periodicals, Inc. J Res Sci Teach 47:861–882, 2010