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MUSE | Natural Selection | Unit Overview and Materials | Section 2: Comparing Explanatory Models | 2A: Introduction... | Instructional Notes


Student Handouts


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Intended Learning Outcomes
  • Models are ideas that scientists use to explain patterns they see in the natural world
  • A model is an idea that has predictive and explanatory power and is consistent with other ideas about how the world works
  • Models can be compared based on data, the inferences made in the model, and the prior knowledge and beliefs upon which they are based

  • "Section 2-Three models explaining species diversity" handout
  • "What is a Scientific Model?" handout

Time Frame and Sequence

This discussion and reading can be completed in 15 to 20 minutes.

Begin by handing out the reading entitled "Section 2-Three models explaining species diversity". Have students either read it aloud or silently. At this point students should be told where the unit is going and how what they have done so far relates to the study of evolution. This is the first day of the second section of the unit. The goal of this discussion is to link the concepts developed earlier about data, inferences, and prior knowledge and beliefs to scientific argumentation and modeling. During this section, students will be examining three models that have been developed to account for species diversity. The three models are Paley's model of intelligent design, Lamarck's model of use inheritance, and Darwin's model of natural selection. The class will develop an understanding of these models in the coming days, but first it is important to discuss the nature and function of models in science.

After a brief overview of how this activity relates to the unit as a whole, have the students read the handout, "What is a Scientific Model?", aloud as a class. As they read, bring up some of the models they have studied in science classes as examples and link the reading back to the work on the cartoon activity. Students will already have some familiarity with the concept of a scientific argument as a series of inferences based on data and prior knowledge and beliefs. The goal in this discussion is to connect the structure of an argument to the idea of an explanatory model. Basically, a scientific model is a knowledge claim about how we think some part of the natural world works. Scientific models are often a complex set of ideas, but they can still be thought of as several inferences that are based on data and prior knowledge.

By the end of this discussion, students should have a clear idea of what a scientific model is and they should understand the connection between models and the concepts discussed during the cartoon activity-the role of data, inferences, and prior knowledge and beliefs.

Teaching Strategies

This discussion will be short, but it serves several important goals. First, it is always desirable for students to understand how the classroom activities relate to the larger goals of the unit. This is especially important at this point when students may be questioning how the activities they have been doing relate to evolution. Explaining to students that they are developing valuable skills that will help them during the rest of the unit will alleviate some of those concerns. Remind students of the class discussion on the first day when they heard that a major activity during this unit would be to solve realistic problems. In order to do that they must have the ability to examine and critique arguments. Second, it is imperative that the students have a vocabulary that allows them to discuss ideas with one another. The language of models and data, inferences, and prior knowledge and beliefs will become useful as students begin to examine the arguments of Paley, Lamarck, and Darwin in this section of the unit. Later in the unit they will be doing similar things with arguments generated by their classmates.


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