Constructing Explanations with Finches for 9th Graders
Evolution caps off our year for introductory biology (9th grade). This is when I want students to look out the window at the diversity of life and wonder, “Where did all of these different organisms come from?” — when they are looking out the window wondering, “When will I get out of here?”
I use BioInteractive resources to get my students interested in evolution and help them learn about adaptations and diversity. The stories and images of different animals spark their interest. They begin our evolution unit by watching the short film The Making of a Theory for homework, which gives them a basic understanding of the importance of adaptations, as well as an appreciation of Darwin and Wallace. We also use the Phenomenal Image “The Lone Anole” to discuss traits that are advantageous for anole lizards and how a species is adapted to its environment.
I then turn to the story of the Galápagos finches, a well-known model for adaptation and diversity. Using the activity “Natural Selection and the Evolution of Darwin’s Finches,” students can reveal what they understand about species and how organisms are grouped into species. I think the key to the success of the activity is keeping an active pace and allowing the students to discuss more than they write. This allows students to have rich discussions rather than focus on a written assignment.
Students begin the activity by sorting finch cards into groupings before any formal introduction to the material. I follow the implementation steps as outlined in the “Educator Materials” but modify the steps for my classes. Students work in teams of three, and I circulate around the teams. Each team gets a set of 13 finch cards that have already been laminated and cut out. They begin by sorting the finches into groups that make sense to them and then arranging the cards on their tables. Using sticky notes or neon markers, they explain the reasoning for the groupings. Often, students use finch color as a basis for groupings, but a few might use differences in beaks or other structures. I keep track of misconceptions and make sure that we address them later. This process takes up to 10 minutes.
I do not use the “Student Handout” on the activity’s webpage but rather PowerPoint slides I’ve created based on the handout to keep students on task. In addition to eliminating paper, the projected slides provide a focal point for the task, and follow the guidelines and pose the questions in the “Student Handout.” By using slides, there are no misplaced pages or questions about what students should be doing. Students read the directions to one another and keep their teams on task.
Once students have completed their own groupings, they have a chance to view other teams’. I explain a rotation pattern where each team visits three other teams to compare their work. For each team they visit, they leave a sticky note with an observation or question. For example, they might note similarities in groupings or ask others why they placed a particular bird in a particular group. After reading the sticky notes they received from the other teams, students revisit and modify their own groups or keep them as is. This gallery walk and revision may take about 10–15 minutes.
We then transition into a class discussion about why scientists group things. I begin by asking why we group animals and let students come up with some ideas. They might mention that it would help to understand relationships or to see how similar animals are to one another. We also recall what it means to be a species and what evidence to look for to support the claim that two birds belong to different species. So there are differences but also similarities that could indicate evolutionary relationships. This discussion provides insight into students’ observations and also serves as a formative assessment of their working knowledge of what it means to be a species.
Now we start revealing the story of the finches and the work of Rosemary and Peter Grant with the finches on Daphne Major. As specified in the “Educator Materials,” we watch the first part of the film The Beak of the Finch (up to 5:36), which is followed by a brief discussion centered on the following questions:
- What do the different beaks tell us about the different finch species?
- What evidence did scientists use to determine that the 13 species of finches on the Galápagos arose from a single common ancestor?
Following that discussion, students go back to their cards, revise their groupings, and write down the reasons for revisions. Most groups make revisions. I walk around and provide quick feedback. I may note such things as “I see you regrouped the birds based on beak size or shape” or “I see you are not using finch color to group the birds.” We do not do another gallery walk.
Now we watch the next section of the film (5:36 to 9:00) and, as a whole class, we discuss the prompts/questions in the “Educator Materials”:
- Describe the beak sizes of the medium ground finch population.
- How did the population of medium ground finches on the island of Daphne Major change as a result of environmental changes?
Students show their understanding of the changes in the population of medium ground finches as a result of the drought by drawing a bar graph of the number of birds with each beak size before and immediately after the drought (x-axis: beak sizes; y-axis: number of birds). I have to model this in order for students to make sense of the task. I draw the axes on the board, and we talk about the variations that exist in the beaks. Based on this discussion, we come up with groupings of small, medium, large, and X-large for finch beaks.
On paper, each student draws a graph comparing the beak sizes in the population before and immediately after the drought. After discussion, each team gets a whiteboard to draw a graph its members agree on. Informally, the different groups compare their graphs, followed by a whole-class discussion. The biggest misconception is that they do not show that 80% of the population died during the drought. I do not point that out, but they will see it when they watch the next part of the film.
We quickly discuss the trends we see in the graphs (a higher number of birds with bigger beaks immediately after the drought) and then show the next segment of the film (9:00–11:12). I have a slide of the graph in the film that I put up after the segment, and we compare the actual graph to the ones students predicted. We look at the reduction in the population size and the change in the average beak size after the drought.
On the board, we analyze the graph using the I2 (Identify and Interpret) strategy and discuss. Examples of I2 statements might be:
- “I see there are fewer birds with small beaks after the drought. This is because the birds with small beaks couldn’t eat the bigger, harder cactus seeds, and many of them died.”
- “I see that a lot more birds with large beaks were able to survive the drought. This is because they were able to eat the bigger cactus seeds and had enough food to survive.”
We transition into discussing more about the data by answering questions such as:
- How did the Grants react to these data?
- Is there evidence of natural selection acting on the population of finches?
- Will there be a new species after the drought? What happens to the medium ground finches if the drought continues?
Now, we watch the final segment of the film. To wrap up the activity, we do two things. First, in groups and using the task from the “Educator Materials” (p. 7, step 14), students show how one species of finch can give rise to two distinct species. I provide a comic strip template so they can draw a process. (I provide feedback on these and return them later.)
Finally, students answer the following question in their notebooks: “How did my understanding of natural selection change as a result of the finch activity?” As a metacognitive moment, this provides students an opportunity to reflect on their learning and recognize how this experience has changed their perceptions. In the past, students have noted that natural selection can happen without producing a new species, but instead can happen within a species. They have also remarked on the time it took to see the changes; in other words, that change could be seen in a year or two, not thousands of years. One student said that natural selection must be happening all the time.
The reflection is not graded, and students may share what they wrote in a quick wrap-up discussion or as an exit ticket. I often use Google Forms for the latter. Altogether, the total time spent on this suite of activities is 80–90 minutes. During this experience, I don’t grade anything, but do provide feedback and have students examine what they learned. The idea of the change in numbers in the graphs is critical and an “aha!” moment for students after they visualize the number of birds in the population immediately after the drought and see that it is so much lower. It is important that they can see that individual birds either live or die and that the change is in the numbers and proportions of birds with different beak sizes. During this learning activity, students moved, talked, looked for patterns, revised their work, and reflected on their learning.