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Innovative Approaches to Teaching Sedimentary Geology, Geomorphology, and Paleontology
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Cutting Edge > Sedimentary Geology > Sedimentology, Geomorphology, and Paleontology 2014 > Teaching Activities > Candy Phylogeny

Candy Phylogeny

Lisa Whitenack, Allegheny College
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This activity was selected for the On the Cutting Edge Reviewed Teaching Collection

This activity has received positive reviews in a peer review process involving five review categories. The five categories included in the process are

  • Scientific Accuracy
  • Alignment of Learning Goals, Activities, and Assessments
  • Pedagogic Effectiveness
  • Robustness (usability and dependability of all components)
  • Completeness of the ActivitySheet web page

For more information about the peer review process itself, please see http://serc.carleton.edu/NAGTWorkshops/review.html.


This page first made public: May 28, 2014

Summary

Students learn how make phylogenetic trees from morphological data using a variety of candy. Techniques and concepts learned include outgroup analysis, making a character matrix, coding characters, parsimony, building phylogenetic trees, monophyly, polytomy, synapomorphy, and why scientists can get wildly different trees with the same taxa.

Context

Audience

This will be part of the laboratory portion of an upper-level undergraduate paleobiology course elective. I have used this activity previously in an upper-level evolution course in a biology department.

Skills and concepts that students must have mastered

This activity typically follows a lecture on how to read phylogenetic trees and using morphological data to make trees. Therefore students have been introduced to the concepts of outgroup analysis, character coding and polarity, etc., though they have not mastered these concepts yet.

How the activity is situated in the course

The evolution course that I currently use this in does not have a lab, so it is an in class activity that takes approximately 50 minutes. However, it can be used as a laboratory activity as well.

Goals

Content/concepts goals for this activity

Outgroup analysis, coding morphological data, choosing characters, parsimony, making phylogenetic trees, monophyly, polytomy, reading phylogenetic trees

Higher order thinking skills goals for this activity

Choosing appropriate characters, interpreting phylogenetic trees, critical evaluation of competing phylogenetic trees

Other skills goals for this activity

Working in groups

Description and Teaching Materials

This activity teaches students how to make phylogenetic trees from morphological data, how to read and interpret those trees, and why we can have very different trees for the same exact organisms. In this case, we remove preconceived notions of who is related to whom by using candy. I have also used Pokémon for this activity, but candy seems to work better. Students are introduced to the basics of character coding, tree reading, and outgroup analysis before starting this activity.

Students work in small groups (2 or 3 students), and each group receives a bag of assorted candy. I provide a mix of fruity candy and chocolate candy, some sort of powdered or liquid candy that could be considered more ancestral (e.g. Pixie Stix or wax bottles), and candy that doesn't fall into any neat category that might also complicate things (e.g. Tootsie rolls, which may or may not be chocolate, as well as the fruity Tootsie Rolls and Tootsie Pops). Depending on what is available at the grocery store, students receive anywhere between 15 and 20 different pieces of candy.

Students are asked to make phylogenetic trees of their candy using outgroup analysis and parsimony. Students are required to choose an outgroup that is not in their bag (often, they choose syrup or sugar) and must use the outgroup to determine character polarity, though they are allowed to have multistate characters as well. Students then decide on their characters and compose a character matrix, followed by using the character matrix to compose their tree. Students are also asked to mark a few monophyletic groups, along with their synapomorphies, on their trees.

When the students have finished composing their trees, I ask for volunteers to draw their trees on the board and explain their outgroup choice, their character choice, and their tree topology. This allows the entire class to chime in with what they did similarly or differently. We also examine the monophyletic groups and synapomorphies together, which allows us to clear up any misconceptions about these topics. Often times, this is a good opportunity to reinforce how to read trees (common ancestor identification, who is more closely related to whom, etc.). Finally, we discuss why the trees are so different and what this means for scientific papers on organism phylogeny.

For my paleobiology course, I also hold back one or two pieces of candy to represent "new fossil finds" (or fossils that their grad student forgot in the truck). Students are asked to try to work them into the existing phylogeny, and we follow this with a discussion of how this works in the "real world" of paleobiology.

Teaching Notes and Tips

Most years, this activity has taken about 50 minutes, however it is very much dependent on the comfort level of the students with this type of material. The students really do enjoy this activity, and the candy has worked better than other iterations I have tried (Caminicules, playing cards, etc.). This activity also lends itself to a lot of customization, depending on what aspects of tree building and analysis you want to emphasize, and can be used to talk about species concepts as well (are different flavors of the same kind of candy considered different species? Some students will say yes, some will say no).

Assessment

Most of my assessment comes during the course of discussing the trees. Are they reading the trees correctly? Are they interpreting the trees correctly? Are taxa placed on the tips of the tree branches? However, students are asked to analyze and make trees from a given character matrix on the subsequent exam.

References and Resources

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