Understanding Evolutionary Trees

Abstract

Charles Darwin sketched his first evolutionary tree in 1837, and trees have remained a central metaphor in evolutionary biology up to the present. Today, phylogenetics-the science of constructing and evaluating hypotheses about historical patterns of descent in the form of evolutionary trees-has become pervasive within and increasingly outside evolutionary biology. Fostering skills in "tree thinking" is therefore a critical component of biological education. Conversely, misconceptions about evolutionary trees can be very detrimental to one's understanding of the patterns and processes that have occurred in the history of life. This paper provides a basic introduction to evolutionary trees, including some guidelines for how and how not to read them. Ten of the most common misconceptions about evolutionary trees and their implications for understanding evolution are addressed.

From Tree to Map: Using Cognitive Learning Theory to Suggest Alternative Ways to Visualize Macroevolution

“…Presenting diagrams oriented horizontally or radically may help viewers avoid the misconception that taxa at the top of the tree are superior to those below them (e.g., Catley and Novick 2008;Torrens and Barahona 2012). Finally, careful consideration of branching topology can help avoid misconceptions about evolutionary advancement and primitiveness among taxa (e.g., Gregory 2008;Catley et al 2010).…”

“…However, contemporary projects that focus on applying digital tools to visualize macroevolution primarily concentrate on using interactivity to improve the "tree-thinking" skills of users. While this is a key goal of evolution education (e.g., Maddison et al 2007;Gregory 2008), by focusing on only creating interactive tree-based imagery we do not take advantage of the full capabilities that digital tools give us to create alternative visual metaphors to depict evolution. Additionally, because most tools retain tree-based imagery, they may retain design elements that foster existing student misconceptions about the evolutionary process (e.g., Matuk 2008).…”

“…For example, one affordance that tree diagrams can depict well, depending upon the specific tree, is the significance of shared descent and a macroevolutionary pattern that shows a unitary origin of life (Torrens and Barahona 2012). Another positive feature of tree diagrams is their emphasis on cladogenesis as a key feature in macroevolution (Catley and Novick 2008;Gregory 2008). These features of tree diagrams provide affordances that are crucial for the accurate understanding of evolutionary theory.…”

“…Time in tree diagrams should be read from the root of the tree to the tips of the branches, as the metaphor of a growing tree suggests to readers. However, research shows that students may assume an incorrect temporal orientation (Gregory 2008) or not orient themselves temporally at all unless a time scale is explicitly included (Catley and Novick 2009). The problem of continuity between ancestral and descendent phyla is a bit more complex because the units of evolution are clades rather than groups with fixed characteristics (O'Hara 1988).…”

A Name by Any Other Tree

“…The widespread availability of evolutionary trees is reshaping how biologists ask and answer biological questions. For a review of how to read and understand evolutionary trees, see Gregory (2009)…”