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MUSE | Natural Selection | Unit Overview and Materials | Section 1: The Nature of Scientific Arguments | 1B: Sequencing Events (Cartoon Activity) | Instructional Notes



Student handouts

Section 2: Comparing Explanatory Models (coming soon!)


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Intended Learning Outcomes

Related to scientific arguments

  • Several inferences make up most scientific arguments
  • Inferences are based on data (observations) and prior knowledge and beliefs
  • It is possible to critique arguments based on disagreements with observations or the prior knowledge and beliefs used

Related to historical reconstruction

  • Not all scientific practice is based on experimental manipulation
  • Evolutionary biology has as a central goal reconstructing past events
  • Historical reconstruction involves making inferences about past events based on data available today


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

  • Cartoon cards*
  • Boards/Sheets of butcher paper
  • Cartoon activity handout which includes the in-class assignment
  • Homework handout: Data, Inferences, and Prior Knowledge and Beliefs

Time Frame and Sequence

This activity will take 2-3 class periods. The first day begins with an introduction to the activity, followed by time for the students to begin arranging the cards. On the second day students are given more time to complete their arrangement of cards and then share that arrangement, along with the rationale, to other student groups.

Day One

Start by reading the quotation from Michael Crichton's The Lost World that is at the beginning of the Student Handout. Next, paraphrase the three paragraphs that follow the quote, as they include information about the task. This introduction should include a description of the task scientists face when reconstructing historical events when the evidence (data) at hand, "snapshots" in time, leaves gaps in the record. The students should also be introduced to the idea that each of us brings to the data a set of prior knowledge and beliefs which affect the types of inferences we make about that data.

The introductory paragraphs also provide a rationale for using a scientifically "neutral" context, a context that depends less on prior scientific knowledge, therefore allowing students to begin on a more level playing field. A main purpose of this activity is to allow students to think about their reasoning and not to test any specific scientific knowledge.

The last item to emphasize before the students begin the task is that while they attempt to reconstruct a story from these snapshots in time, they should pay close attention to the decisions they make about the placement of each card. This includes not only the placement of each card, but the reasoning behind the placement. The writing task, however, asks them to describe only one of those decisions in terms of the data (observations) they gleaned from the card, along with any prior knowledge and beliefs that influenced that decision.

A set of cards can now be handed out to each of the student groups, and they can begin making observations on the cards and placing them in a sequence that makes sense to them. With several minutes remaining in the period ask the students to stack their cards in the same order as they have tentatively placed them and then return them to a central location. They should have a way to identify which stack of cards they were arranging. The backs of each particular stack can be labeled with a different letter or number, so that they can easily be identified by the groups on Day Two of the activity. Alternatively, if multiple classes will be using the same cards, number or letter the backs of the cards and have students use these numbers to record their particular sequence (be sure you number randomly and tell the students that the only reason for the numbers on the back is for them to keep track. They do not correspond to the "real" sequence!)

Day Two

Begin the second day by passing back the cards to their respective groups and allowing approximately 10 minutes for them to continue to reason about the order of those cards. At this time they should be able to complete the in-class writing assignment. Before moving on to discuss the issues raised by this activity, the students should attach their cards, in sequence, to a board, a large sheet of paper, or any large surface that will be visible to the rest of the class.

Depending on the size of the class you might take one of two courses of action. For a smaller class you may be able to ask each group to briefly describe the story they have constructed from the cards. It quickly becomes obvious that all stories are different. In the discussion that ensues, ask the students to explain why the stories were different. As students talk, try to highlight a few things. First, it should come up that each group might have made one or more observations that differed from those of other groups. It also should become clear that even though they may have noticed the same things they did not all attend to them in the same way. Differences in interpretation were probably influenced by the prior knowledge and beliefs held by various members of the group. Introduce the term inference if it does not come up and help the students come to an understanding that their sequences were really based on a number of inferences which were themselves based on the data (observations of the cards themselves) and their own ideas coming into the activity (their prior knowledge and beliefs).

Next it is helpful to focus on a particular card and ask each group where they placed it in their story and why. This helps to emphasize even further the effect that making different observations, and coming to those observations with differing prior knowledge and beliefs, has on the inferences that are made.

If the class is larger and therefore composed of more student groups, groups could pair up and share their stories between two groups. Then the class could meet as a whole to listen to the stories of several, but not all groups. That could then be followed by several other groups speaking to their placement of a particular card.

Woven into the discussion can be the idea that reconstruction of past events is often based on snapshots between which gaps are common. Explain that this is a common type of reasoning in evolutionary biology.

Before the class ends, pass out the Homework Assignment about Data, Inferences, and Prior Knowledge and Beliefs. For this assignment students will read a paragraph and pick out examples of observations, prior knowledge and beliefs, and inferences. Included in the assignment are definitions/descriptions for each of those terms. The definitions/descriptions should be read as a class, to ensure the students have an accurate idea about each.

Day Three

Begin the class period by going over the homework assignment. Although the concepts of data, inferences, and prior knowledge and beliefs may be relatively clear to students in the abstract, it is often difficult for them to distinguish between them in a piece of writing. The discussion around the paragraph from Attenborough's book should be lively, as it is unlikely that all students will have categorized statements in the same way. For example, some students might say that the statement, "There were 14 dinosaur species found at the site" was an observation. Other students will call this an inference because of the need to determine which bone goes with which species. Encourage students to cite several examples from each category so that the distinction can become clearer.

Emphasize to the students that examining scientific arguments based on the observations, prior knowledge, and inferences that went into them provides a powerful tool for critique. Sometimes it is possible to see that the observations made were not very thorough or were flawed in some other way. Other times it may be possible to take issue with the prior knowledge or beliefs of the person making the argument. Either one of these situations could result in questionable or unwarranted inferences. Being able to deconstruct arguments in this way will help students during the rest of the unit when examination and critique of arguments made by their classmates becomes central to class discussions.

This discussion will take approximately 20 minutes. After the discussion, there is a Quiz included under the assessments link that could be used to test for understanding of these distinctions. It is similar in form to the homework assignment.

Teaching Strategies and Student Ideas

Day One

Many students will be focused on developing the "correct" sequence. It will be important to emphasize that the only way of judging between sequences will be to look at the evidence used to make decisions about the order of the cards. Just like the case of the fossil record, there is no one to ask about the order, no one to check their answers other than their peers. It may be helpful to make sure that students know that you do not know the "real" answer either. However, this is not to suggest that there is not a sequence that guided the conception of these cartoon frames. They are not simply a set of random images. Again, just like the case of the fossil record, there is an actual sequence that occurred, we just don't have access to it. The same is true with the cards.

As students are working, walk around and listen to them as they reason about the order of the cards. In the subsequent discussions you may be able to use some of the things you heard to facilitate the conversation and to make specific points about observations.

Students generally enjoy this activity quite a bit. They will come up with a wide range of stories and have fun sharing their ideas with one another. One of the reasons we have chosen to use cartoons is so that the students all feel that they can contribute and are not reliant on prior scientific ideas. Also, we have found that the fun atmosphere that develops encourages student interaction about their reasoning. Because everyone is beginning with the same set of information, few students become so attached to their ideas as to get defensive about them. In other words, they are able to attend to the ideas of their peers without feeling the need to overzealously defend their own ideas.

Day Two

Data, Prior Knowledge and Beliefs, and Inferences

The cartoon activity, followed by the assignment and quiz on data, prior knowledge and beliefs, and inference, focuses on the important idea that the observations we make, colored by our prior knowledge and beliefs are basic determinants of the inferences we make. This may help students understand why the original readings that they will study (Section 2 of this website), including those of Paley, Lamarck and Darwin, present different arguments to explain life on earth.

The discussion that develops from different groups' arrangements of the cartoon cards points out these ideas without depending on the scientific knowledge base that students bring to the class. Using, as in this case, a story that combines two common children's stories allows most, if not all students to contribute to the work of their group. Be sure to ask students how their knowledge of the stories of the Three Little Pigs and Little Red Riding Hood either helped or hindered their own story development. We included these familiar tales in order to make a strong point about the role of prior knowledge in inference making.

A number of students will be surprised when students from other groups make different observations. They are also surprised when another group brings to their observations differing prior knowledge and beliefs. It becomes very obvious from the diversity of the stories that are told that both the variation in observations and in prior knowledge and beliefs can significantly affect the inferences we make.

This makes the diversity of ideas that scientists propose more understandable. It allows students to get a more realistic picture of the development of ideas in a scientific community. Also, students often have the erroneous notion that scientists who proposed earlier ideas (models), that may no longer be accepted, must have made poor arguments. Thinking about how available data changes, how our collective pool of knowledge is altered all the time, and how prevailing beliefs also change can help students see the context dependency of scientific ideas. Rather than thinking that people in the past were just not as intelligent as modern scientists, they may be able to better appreciate how ideas change over time.

Historical Reconstruction

Another point to be made in this activity is that all scientific thinking does not revolve around laboratories and experimental results. An important part of reasoning in evolutionary biology involves considering how things may have been in the past using evidence available now. These past events are not available for experimental manipulation and therefore require a different kind of reasoning. Although different, historical reconstruction is no less scientific than carefully controlled lab work. There are standards of evidence and inferences are evaluated by the scientific community. Many students will not have ever considered this type of scientific endeavor. You may want to point out that in addition to evolutionary biology, fields like cosmology and geology are also largely concerned with historical reconstruction.

Day Three

Use this time to clarify and wrap up the ideas presented on day two. As mentioned above, students may have some difficulty, especially with the distinction between inferences and observations. It may be helpful to talk about observations as things that would be standard from one person to another. For example, the paragraph on the assignment talks about the section being 4 meters thick. That is fairly clearly an observation. Another example is the statement that the bones were all facing the same direction. That is an observation used along with prior knowledge about the effects of currents on long objects that led to an inference about the direction of water flow in the ancient river.

In the case of trying to determine prior knowledge, it is relatively rare that those statements are actually found in the reading. Rather, more commonly we have to imagine what knowledge might have been necessary in order to make particular inferences. One example is given above. Another example would be the prior knowledge about sedimentation that would be necessary to make a statement about the deposit being laid down over a 100-year span.

*If access to the cartoon cards is problematic, there are several alternatives. The first would be to use duplicate sets of snapshots from a family photo album. Another would be to buy multiple copies of an inexpensive children's story book, that has interesting pictures, which can then be laminated.


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