Using Cladograms

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Objective

SWBAT use a cladogram to determine evolutionary relationships.

Big Idea

Cladograms are much more than pretty pictures. They can be used to answer questions such as, "What did a T-Rex taste like?"

Hook

5 minutes

I display the following image, and ask students, "What could you do to answer the question?"

I tell the students to think about their answer, making it a point to mention that we are not answering the question being displayed, but rather what could you do to answer it. This is an important difference, since I am looking to activate their knowledge of cladograms and how they are used to determine evolutionary relationships.

After a minute of thinking time, I have the students share their response with their elbow partner, stating "Partner on the left will answer using the frame "I would ____", partner on the right will listen, and then respond using the frame "I agree/disagree, because ____." Using these frames, which the students have been taught to do, elicits the answer to the correct question, as opposed to the answer to the question being displayed.

After students have shared with their partners I use popsicle sticks to select a couple of students to share out their own thoughts or what their partners said. Giving the students the choice of what to share out relieves them from the threat of looking inexperienced when called upon, since they can use what they heard in the conversation to formulate a response. Watch a couple of volunteers share their response:

Using Cladograms

40 minutes

I explain to the students that they will be working with a partner on a module called "What did the T. rex taste like?" developed by the University of Berkeley. They will begin on Folder 3 (of the Berkeley module) to review some of what we learned the day before and find definitions to words they will need to know. Then they will proceed to Folder 4, where they will be gathering evidence to respond to the question, "Who is the closest relative to the T. rex?" 

I tell the students that they will use only one computer per partnership, but each student is responsible for his/her own answers. I then ask one student in each partnership to get their computers, while the second partner gets two copies of the note-catcher. I also tell the students that they should proceed through Folder 3 quickly so they will have time to finish Folder 4 AND complete their ACE answers.

Note to teachers: Students could work individually through each of the modules. However I prefer that students work with a partner since this creates an opportunity to have a conversation. Conversing about the content helps students dig into their own thinking because it requires that they put their thinking into words (SP8). 

Students working through the modules create a cladogram which acts as a model that helps them understand evolutionary relationships (SP2) and use it to analyze the physical relationships between organisms (SP4), recognizing patterns in the data between living and extinct organisms (CCC Patterns - Patterns can be used to identify cause and effect relationships). Once students have gathered their evidence, they must use it to defend their explanation (SP7), and present their findings in writing (WHST.6-8.10). Here are some samples of student work where you can see how they cited the evidence gathered from the model to defend their explanation (SW1SW2SW3SW4SW5).

As students are working through the modules, I am circulating the room making sure that students remain on-task, and having conversations with them about what they are learning about the evolutionary relationships between the T-rex and the other organisms. Here is some of what we talked about - Did you see the smile of my vegetarian student as he describes how surprised he was by what he found?

Closure

5 minutes

To close this lesson, I re-display the image from the beginning of the lesson, and invite students to answer the question using the evidence they gathered.

As you saw in the student work (SW1SW2SW3SW4SW5), all students concluded that the parrot is the closest relative to the T. rex, mentioning evidence like bipedalism and having three fingers as the determining factor that leads to this conclusion.