Evolution & Phylogenetic Analysis: Classroom Activities for Investigating Molecular & Morphological Concepts

Article excerpt

"Nothing in biology makes sense except in the light of evolution." The title of Theodore Dobzhansky's 1973 essay captures the importance of evolution in today's biology curriculum. Given evolution's central role in modern biology, the absence of abundant curricula is surprising. After years of being unsatisfied with using fictitious paper cut-out creatures to demonstrate phylogenetic processes, I set out to demonstrate large-scale evolutionary patterns and phylogenetic processes by developing hands-on activities based on real organisms. Several good experiments using Wisconsin FastPlants (http ://www. fastplants.org/activities. students.evolution.php), fruit flies (Kennington et al., 2003), or bacteria (McCarty & Marek, 1997; Weldon & Hossler, 2003) demonstrate natural selection through phenotypic changes in populations. Important evolutionary concepts are also covered by simulations and virtual activities (see "Understanding Evolution," http://evolution. berkeley.edu/evolibrary/home.php).

But as Bransford et al. (1999) demonstrated, learning retention and depth increase as active engagement increases. The importance of evolution as a unifying principle demands engaging activities based on real species and the exploration of real evolutionary questions. The activities described here begin to explore such questions. What is the evidence for or against current relationships between species? What kind of evidence do biologists use to develop phylogenetic trees? How does one discriminate between opposing theories in evolutionary biology and phylogenetic systematics? (For examples of three activities that tackle similar questions, see McMaster, 2004; Flory et al., 2005; Baum & Offner, 2008).

In designing my evolution lessons, I selected activities that utilize vertebrate skeletons and skulls of primates and hominids. Students begin with a materials-based problem set that introduces them to concepts of phylogenetic analysis, including homology, convergence, parsimony, and ancestral versus derived characters. The project concludes with students conducting a phylogenetic study on a set of vertebrate skeletons, primate skulls, or hominid skulls and then giving presentations comparing their findings with published results.

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I will discuss three separate activities that occur over the course of three consecutive 3-hour laboratory periods. Because of the modular nature of this lesson plan, the series of activities can be further broken down into any number of sessions to allow for various scheduling needs. These activities were originally designed for undergraduates in an introductory biology course, but several components have been used for 7th and 11th graders during an outreach program funded by Howard Hughes Medical Institute (HHMI) and sponsored by Bryn Mawr College (for suggested adaptations for various age groups, see Table 1). The outreach project is fully archived at http://www.brynmawr.edu/ scienceresearch/FridaysinLabHomepage.html. The bone material is readily available from various teaching-supply companies, and Mesquite is a free, Web-based phylogenetic software package (http://mesquiteproject.org/mesquite/mesquite. html ) that is easy to run from any computer with up-to-date Web browsers (for a materials list, see Figure 1).

** Background

Before students begin activities 1 and 2, we discuss Darwin's idea of descent with modification and what that implies for the diversity of organisms on earth. If descent with modification is the mechanism of phylogeny, or the patterns of relationship among organisms, then similarities exist between organisms because they share a common ancestor. Based on the same principles that make siblings more similar than cousins, similarity between species can be used to make inferences about the evolutionary relationships between them. Similar characteristics are called "homologous characters" if the similarity is due to common ancestry. …