Schramm et al. Evo Edu Outreach (2019) 12:11 https://doi.org/10.1186/s12052-019-0104-3 Evolution: Education and Outreach REVIEW Open Access Understanding the tree of life: an overview of tree-reading skill frameworks Thilo Schramm* , Yvonne Schachtschneider and Philipp Schmiemann Abstract Diagrammatic depictions of evolutionary relationships play an increasingly important role in scientifc and educa- tional literature. Reading evolutionary trees is seen as a major challenge for biologists in learning about evolution and its applications in research. The skills needed to read, interpret, and construct evolutionary trees are subsumed under the term “tree-thinking,” which can be divided into “tree-reading” and “tree-building.” The purpose of this paper is two-fold. First, we review relevant literature on tree-reading skills to examine regularly reported skills for an up-to- date overview of the topic and to determine where further investigation might be needed. Second, we compare and contrast published skills and skill systems to highlight commonalities and diferences using a published hierarchical system as a framework and integrating the skills identifed by other authors by arranging them with their correspond- ing skills within the framework. The resulting insights suggest a possible synthetic tree-reading model. By bringing together the relevant literature about tree-reading skills, we show that research on tree-thinking skills has until now been conducted mainly following theoretical or observational approaches, often lacking cross-references linking diferent works; this has resulted in multiple approaches. Furthermore, as most published systems have not been empirically tested, it seems useful to collect existing fndings for empirical testing to create a synthetic tree-reading skill model that can be used by educators to structure and organize their learning environments. Teaching the sub- domains of tree-reading in order of difculty can facilitate the entire learning process. Furthermore, the skill model can be used to design testing instruments for education and research that incorporate the full range of tree-reading subdomains and thus, may be better suited to distinguish more advanced learners from less advanced ones. Keywords: Tree-thinking, Tree-reading, Evolutionary tree, Phylogenetic tree Introduction: why are evolutionary trees that may not be observed by students. Furthermore, the important? concept of evolution is not intuitive (Gregory 2009). Graphical representations play a major role in modern Evolution is the conjunctive core principle of biol- learning environments. Various types of graphs, dia- ogy (Dobzhansky 1973; Futuyma 2013) and in order to grams, charts, and schemata can be found in all areas of develop a deeper understanding of any biological dis- scientifc research and various forms of learning mate- cipline, one needs to grasp the concepts of evolution rials (Lee 2010; Purchase 2014; Shah et al. 2005). Tis (Meisel 2010). Its understanding requires knowledge applies in particular to biology, where students are reg- of various diferent and seemingly unrelated topics like ularly confronted with a large variety of diferent rep- genetics, ecology, and morphology (Horwitz 2013), and resentational styles in its many subdomains (Roth and opportunities for practical work are rare (Besterman and Pozzer-Ardenghi 2013; Wiley et al. 2017). La Baggott 2007). Tis leads to evolution being seen as Teaching biological felds like microbiology, genet- one of the most challenging topics to teach in introduc- ics, and evolution involves teaching abstract processes tory science courses (Beardsley et al. 2012; Besterman and La Baggott 2007). Te difculty in teaching evolution *Correspondence: [email protected] is compounded by numerous and very persistent miscon- Biology Education, University of Duisburg-Essen, Universitätsstraße 5, ceptions prevalent among learners of all ages and educa- 45141 Essen, Germany tion levels (Gregory 2009; Chinsamy and Plagányi 2008; © The Author(s) 2019. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creat iveco mmons .org/licen ses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creat iveco mmons .org/ publi cdoma in/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Schramm et al. Evo Edu Outreach (2019) 12:11 Page 2 of 13 Hokayem and BouJaoude 2008; Mead and Scott 2010a, b; Evolutionary trees can be used to visualize how cer- Yates and Marek 2014, 2015). tain traits of a living organism evolved in relation to other traits and organisms (see Fig. 1). In the absence of Evolutionary trees as a representation of evolution other data (like a rich fossil-record), the most parsimo- Evolutionary diagrams are diagrammatic depictions of nious explanation is typically used to make claims about diferent species or groups and their relatedness. Tey the course of the development of certain traits. Follow- can exist in diferent forms (e.g., the ladder of life or the ing this approach, the most plausible pattern of rela- Great Chain of Being), although treelike depictions are tionships is the one that requires the lowest number of the most common (Catley and Novick 2008). Crucial for evolutionary changes (Baum and Ofner 2008). Many evolutionary diagrams is that they present the evolution- evolutionary trees show the changes in the characteris- ary development of species and groups rather than the tics along with the development of groups by labeling the development or relatedness of individual organisms. In tree with newly developed traits (Baum and Smith 2013). this paper, we will treat terms like “evolutionary tree,” Tese labeled traits are often subsumed under the term “phylogenetic tree,” and “phylogeny” as interchangeable, apomorphies, although phylogeneticists further distin- although some experts in the feld might use them with guish them with expressions like plesiomorphic, autapo- diferent connotations. morphic, or homoplasic. By analyzing the occurrence of Evolutionary trees are a very common way to visual- diferent traits across diferent groups, one can infer the ize patterns of macroevolutionary processes and there- pattern of the relationship of these groups. fore play a central role in teaching evolution (Baum et al. Besides visualizing and confrming the course of evolu- 2005; Nehm and Kampourakis 2014). Tey serve as a tion, evolutionary trees can be used in a variety of con- tool to depict multiple relationships in one diagram, thus texts, such as conservation biology (illegal whale hunting) presenting processes and developments that are hard (Baker and Palumbi 1994), forensics (the ways in which to describe in a simple way (Halverson and Friedrich- HIV is transmitted) (Ou et al. 1992), agriculture (the sen 2013). In order to understand how evolution works, efects of pesticides) (Engelen et al. 1998), medicine (the one has to understand how cladogenesis works, which is development of the hantavirus) (Yates et al. 2002), drug facilitated by knowing how speciation processes are rep- development (predictive evolution) (Bush et al. 1999), or resented in diagrams (Catley et al. 2012; Meisel 2010). drug design (Searls 2003). As phylogenies and biological A Clade1 (B, C, andD) B CharacteriscA Clade2 (C andD) C D Line E Terminal CharacteriscB Nodes Apomorphy F Internal Nodes Fig. 1 Properties of an evolutionary tree. An evolutionary tree consists of three basic components: internal nodes, lines, and terminal nodes. Lines are representations of lineages. Points where a lineage bifurcates are marked by internal nodes, representing the most recent common ancestor of all descending groups. Terminal nodes appear at the end of lineages and most regularly represent extant species or groups. Along the lines, apomorphies (evolutionary newly developed traits) can be displayed to emphasize and explain the bifurcation event. A nested hierarchy of clades (a common ancestor and all its descendants) is created by the bifurcations at internal nodes Schramm et al. Evo Edu Outreach (2019) 12:11 Page 3 of 13 classifcation are an important part of biology, they are novices in biology, as they often base their interpretation part of the school curricula of such countries as the USA, of evolutionary relationship only on single characters the UK, Australia, and New Zealand (Catley et al. 2013). (e.g., a specifc morphological trait, or a certain behavior) instead of considering all given information, especially Tree‑thinking the branching pattern (Gregory 2008; Halverson et al. When working with evolutionary trees, one has to ana- 2011). Relying on a single trait or a small number of char- lyze, interpret, and reason with the information given in acteristics is not seen as suitable to get a reliable estimate the representation. Tis practice is called tree-thinking on the relative relationship of species (Gendron 2000). (O’Hara 1997). Some authors describe tree-thinking as Diferent studies have shown that students struggle with a mere set of skills needed to extract relationship infor- understanding evolutionary trees and display a great mation from an evolutionary tree (O’Hara 1997), while variety of widespread learners’ misconceptions (Baum others