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Character coding

Jeffrey Wilson
,
University of Michigan
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This activity has benefited from input from faculty educators beyond the author through a review and suggestion process.

This review took place as a part of a faculty professional development workshop where groups of faculty reviewed each others' activities and offered feedback and ideas for improvements. To learn more about the process On the Cutting Edge uses for activity review, see http://serc.carleton.edu/NAGTWorkshops/review.html.

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: Jul 24, 2009

Summary

Learning about the different ways the morphological variation can be coded into phylogenetic character data, with emphasis on the limitations and assumptions of each.

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Context

Audience

Upper level undergraduate/graduate student course Methods in Paleontology.

Skills and concepts that students must have mastered

Students should understand basic underpinnings of phylogenetic analysis, and they should have some background on how characters are constructed.

How the activity is situated in the course

The activity was designed as a take-home assignment but could easily be done in class. It follows a series of lectures on the philosophy underlying systematics, characters, and operational taxonomic units. This is one of a series of exercises.

Goals

Content/concepts goals for this activity

I would like students to develop a definition of what a character is.

I would like them to appreciate that there are different ways of coding characters, and that these ways have effects on phylogenetic analysis.

I would like students to be able to visualize coding strategies – i.e., schools of thought on how morphology should be coded.


Higher order thinking skills goals for this activity

How do assumptions influence outcomes (in this case of a phylogenetic analysis)?

I would like students to develop the identify the assumptions implicit in phylogenetic analysis.

Other skills goals for this activity

Description of the activity/assignment

Character coding has been called the bete noire of phylogenetic analysis. As you may have seen from class, the definition of "character" is squishy and varies between authors. Although there isn't agreement on exactly what a character is, it is possible to predict how certain character definitions and coding strategies affect phylogenetic analysis.

This activity focuses on character coding, specifically about how different coding strategies can affect analysis. In this exercise we will try to look at different coding strategies by considering the simple shapes below.

Student handout for Character Coding

(1) What is a character, and what qualities do characters have?

(2) Given the 'morphology' depicted above, what features vary?

(3) Given the variation you identified, come up with as many character codings as you can; i.e., different ways that this variation can be coded into characters.

(4) For each of the coding strategies you come up with in question 3, identify its assumptions, limitations, and strengths.

(5) Identify your preferred coding strategy and defend your choice.



Students asked to define what a character is and to discuss what they 'require', and then to come up with an exhaustive list of coding strategies for the sample morphology. They are then asked to list assumptions/limitations of each strategy.


Determining whether students have met the goals

Students turn in answers to this assignment, and I check it against my own response to the same questions.

More information about assessment tools and techniques.

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