The tree of life provides a fundamental roadmap to understanding biodiversity, yet requires integration across scales of the biological hierarchy and a unique set of tree thinking skills. This combination can be challenging for undergraduates at the introductory level because of their preconceptions regarding distinct fields of biology compounded by the unique structure of phylogenetic trees. To address these two challenges while providing an undergraduate research opportunity, we developed an activity for introductory biology students that integrates molecular, organismal, and evolutionary biology. This activity relies on woody plant identification, comparative morphology, and DNA sequence analysis to teach students how to reconstruct and interpret phylogenetic trees. After building separate phylogenetic hypotheses using morphological characters and molecular data, they compare their results with a master Tree of Trees to identify instances of homology and homoplasy. After delivering this activity, the majority of students scored the activity as “helpful to very helpful” in increasing their understanding of these concepts. Overall, we deliver a framework for developing comparable Tree of Trees–type activities that leverage students' interests in familiar organisms and requires them to span scales of the biological hierarchy while improving their tree thinking skills.

Dragons are a staple of fantasy literature, and various aspects of the creatures (most notably their anatomy) have been explored scientifically across different forms of media. Their distinct anatomical characteristics and the variations therein among the recognized “species” of dragons make the taxa appropriate models for basic phylogenetic analysis in an undergraduate general biology or systematics class. The wyvern, an obviously more primitive, distant cousin of the “true” dragons, is also an appropriate outgroup for these estimations of shared evolutionary history. Separating metallic from chromatic dragons, the generated tree shows relationships among the species that are consistent with their separation in the Dungeons & Dragons games according to alignment, scale color, and religion, three characters that are not used in the analysis. Manual construction of a character matrix and cladogram of dragons followed by repetition of this process via conventional computer software allows the students to track their progress not only in terms of understanding such concepts as choice of character states and parsimony but also in terms of the applicability of said software.

I offer comments on two recent articles in The American Biology Teacher by Davenport and colleagues addressing the interpretation and construction of phylogenetic trees. The “tree-thinking” literature suggests that students need to acquire a clear understanding of the meaning of phylogenetic tree diagrams. To this end, I provide clarifications of terminology and address the problematical status of “ancestors.” Cladograms are not genealogies viewed from a distance, but empirical hypotheses of relationship based on the distribution of shared derived character states. I describe an exercise employed in an introductory systematics course that emphasizes the empirical activities of character delimitation and formation of groups based on those characters.

In this classroom activity, students build a phylogeny for woody plant species based on the morphology of their twigs. Using any available twigs, students can practice the process of cladistics to test evolutionary hypotheses for real organisms. They identify homologous characters, determine polarity through outgroup comparison, and construct a parsimonious tree based on synapomorphies (shared derived characters). This activity efficiently demonstrates many systematics concepts, including homology, homoplasy (convergence and reversal), polarity, synapomorphy, symplesiomorphy, autapomorphy, polytomy, and parsimony. It also engages students in inquiry, promotes student collaboration, raises awareness of plant structure, and exposes students to the diversity of common local trees.

This exercise demonstrates the principle of parsimony in constructing cladograms. Although it is designed using mammalian cranial characters, the activity could be adapted for characters from any group of organisms. Students score categorical traits on skulls and record the data in a spreadsheet. Using the Mesquite software package, students generate arbitrary cladograms and measure tree length. They then move taxa around to reduce tree length. The exercise can become competitive when students report out on tree lengths and try to achieve shorter trees than their peers. The resulting cladograms can be compared with a published mammalian phylogeny. The exercise illustrates phylogenetics, the principle of parsimony, and hypothesis testing using morphological data.

In a flexible multisession laboratory, students investigate concepts of phylogenetic analysis at both the molecular and the morphological level. Students finish by conducting their own analysis on a collection of skeletons representing the major phyla of vertebrates, a collection of primate skulls, or a collection of hominid skulls.