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MUSE | Natural Selection | Unit Overview and Materials | Section 4: Extending the Natural Selection Model... | 4B: The Pheasant Case | Instructional Notes

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INSTRUCTIONAL NOTES


Intended Learning Outcomes

Natural Selection:

  • Populations are made up of individual organisms whose traits (structural, behavioral, biochemical) exhibit variation from one individual to the next

  • Many trait variations are inherited

  • Some trait variations may be advantageous and others not advantageous

  • Whether or not a variation is advantageous depends on the environment within which a population lives

  • The frequency of particular trait variations in a population may change over time due to differential survival and reproduction

  • Evolutionary changes occur in populations or species, not individuals

  • Offspring are not exactly like their parents-they also vary, but the variations of their traits are likely to be similar to those of their parents

  • Variability in a population can be represented graphically

  • Organisms produce more offspring than can survive

  • There is competition between organisms for resources

Modeling:

  • Models are ideas that scientists use to explain patterns they see in the world
  • A model is an idea that has predictive and explanatory power and is consistent with other ideas about how the world works
  • Knowledge claims are based on data, inferences and prior knowledge and beliefs

General:

  • Use of classroom norms (basic interpersonal skills)
  • Make observations
  • Organize data

Supplies
  • Pheasant case materials
  • File folders to hold student work
  • Pheasant case critique forms

Time Frame and Sequence

This case requires approximately 5 class periods. Like the monarch/viceroy case, the time can be divided into 3 work days and 2 presentation days.

Day One

Begin by explaining to the students that this is the last case study they will be looking at during this unit. Like the monarch/viceroy case, this one is based on real organisms. Next, pass out the Case Materials.

Go through the first page of the case (the problem statement) with the students. This page describes the striking difference in color between the male and female ring-necked pheasant. The task for this case is much like what the students have previously done with the seed case and the monarch/viceroy cases in that they will be writing a Darwinian explanation. Within that explanation, they need to include the prior knowledge or data they used to develop their explanations. The second part of the task is for them to identify one area of their explanation that could use strengthening and imagine how they might collect data to support that component. This part of the task will take the form of a research proposal that will be submitted as part of a grant funding competition. At the conclusion of the work on this case, students will present their explanations and their proposals to the class.

After the brief introduction to the task at hand, have students get together with their group members to look over the materials. Students should have a significant portion of the class period remaining to become familiar with the case materials and to begin to develop a work plan for the next several days.

Day Two

The second day of work on the case should be a work day for students. By this point in the unit they will probably be fairly proficient at writing Darwinian explanations, so a reasonable expectation is for them to have a draft of their explanation by the end of class today. While students are working, walk around and ask them to discuss their thinking and to cite evidence from the case that supports their claims. Encourage students to write their Darwinian explanation before they attempt to identify a research proposal. Typically, students will develop explanations consistent with sexual selection, but there may be some variation on this theme. As long as the explanations are consistent with the Darwinian model and are supported by the evidence presented in the case, they should be considered acceptable.

Day Three

Begin today with a whole class discussion about the research proposals. Have students suggest a set of criteria for judging their classmates' proposals that can then guide them as they write their own proposals. In the past some of our students have suggested judging proposals based on:

  • Quality of Darwinian explanation
  • Clarity of the experimental design
  • Clear links between research and Darwinian explanation
  • Significance of the research to the argument (is it key or trivial)
  • Whether or not the research results would be conclusive

There are many other areas that could be important to students when judging the proposals. Whatever the criteria end up being, it is important that students have a voice in developing them and that they have discussed them ahead of time. A sample of the criteria developed by our students and the form used during the presentations is included under the link, Pheasant Case Critique. This discussion should help focus the students' work for the remainder of the period as they finalize both parts of the case. Remind students that presentations will begin tomorrow, so whatever is left unfinished at the end of class will have to be completed at home.

Days Four and Five

These two days should be used for presentations. The time allowed for each group will vary depending on the number of groups and the length of the class period. We allow each group 10 minutes for their presentation and discussion. The presentation consists of both the Darwinian explanation and the research proposal because they should be directly related to one another.

Before beginning the presentations have students take out materials to use to take notes on the presentations of others or use the Pheasant Case Critique forms. Remind them that they will be deciding which proposal will be funded and in order to make that decision they should have detailed notes on each presentation.

After all of the groups have presented, have the students discuss the merits or deficiencies of the proposals overall. We then have the students individually rank the proposals to fund. Each student turns in a page that indicates their recommendation as to which proposal to fund and the justification for their decisions. In our class this is usually a homework assignment that is given after the second day of presentations. Alternatively, you could have the students decide on a 'winner' after each day and then have the class decide between the two daily winners. The important feature of this activity is to have students justify which proposal they thought was best using the criteria that were established on Day Three.


Teaching Strategies and Student Ideas

Like the monarch/viceroy case, the pheasant case will require students to extend the natural selection model to account for bright coloration. We consider this an extension of the model because the selective advantage of brightly colored males may not be immediately apparent to students. The key in this case is the importance of reproductive success from an evolutionary perspective. This case is helpful in making the point that in order for a trait to persist over time, organisms with that trait must successfully reproduce.

This case may also address a common idea that students develop during instruction on natural selection. Many students believe that the result of natural selection will be organisms that are perfectly adapted to their environment. However, as this case shows, there are often trade-offs that may result in adaptations that do not appear to be advantageous or that confer an advantage in reproductive terms, but a disadvantage in terms of that particular individual's survival. Here again is an opportunity to make a clear point of the importance of reproduction and heritability to the Darwinian model.

The research proposal will most likely be the most challenging portion of this case for students. It is often difficult for students to imagine an experiment or research program that is appropriate. If this occurs, remind students that they are trying to bolster some aspect of their Darwinian explanations, so a fruitful place to look for ideas is the explanation itself. In our experience, the most common proposals seek to establish the female preference for brightly colored males. The actual proposals around this theme differ widely with some proposing lab research and others using a more field-based approach. Another common type of proposal that students present is intended to determine why bright coloration is more attractive to females by looking to see if it is linked to any other advantageous traits such as increased immunity or intelligence. Don't be concerned if the research questions between groups are similar because it is likely that the actual proposals will differ markedly. We have found the grant funding competition to be one of the most rewarding portions of our unit as it requires students to synthesize much of the information they have learned regarding natural selection and it also allows them to be creative.

 

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