Launching Units with Primary Sources: From Grass to Corn

Have you considered using primary sources as launching phenomena in your classroom? Primary sources often present a puzzle that needs to be solved; content related to your discipline can help put the pieces together. For example, in a biology classroom students can utilize the Crossville Chronicle newspaper article entitled “From Grass to Corn in Eighteen Years” (August 17,1921) when launching a unit on evolution.

Present your students with the image that shows “Nine Years’ Development of Teosinte” (the image from a German-language newspaper, inserted here, is clearer than the image in the Crossville Chronicle) and support them as they observe, reflect, and question using the Primary Source Analysis Tool. Students might observe that the plant on the left of the image has fewer kernels than the plant on the right. They may also infer that these plants are related to corn. After students share their observations, reflections, and questions, ask: “How is teosinte related to corn?” This will serve as the driving question for the unit.

Provide students time to respond to the driving question based on their own prior knowledge. Students might suggest that teosinte is an ancestor of corn and the process of evolution can help explain the relationship if they have taken a biology class before. Prompt students to share as many possible responses as they can and record them.

After the class generates several possible hypotheses to explain the relationship between teosinte and corn, ask what they will need to do to arrive at an answer to the driving question. Based on the steps the students outline, the class can embark on a series of activities that will build their knowledge of evolution and selective breeding. Students may run an experiment with fast growing seeds to observe how traits can be selected over time. Many of the activities you typically use in an evolution unit will likely be useful for students on this journey.

Once students have constructed their understanding of evolution and selective breeding, revisit the driving question and possible hypotheses. Are there any that can be negated? Supported? At this point, provide students with the full text of the Crossville Chronicle article. Ask students to outline how Luther Burbank explained the relationship between teosinte and corn. Students may benefit from working independently at first, and then collaborating with a group to identify as many of the processes details as possible. Do students see any connections between Burbank’s explanation and their own? How did their processes to find an answer compare to Burbank’s?

Consider having a conversation with students about the language used to describe the role of indigenous populations in the evolution of modern-day corn. What does some of the language imply about how the processes of indigenous populations were viewed in the scientific community? Does this view still exist among today’s scientists? The population at large? As an assessment for the unit, challenge students to re-write the article to address any inaccuracies about evolution, insert new information that has been learned after the time of publication, and rephrase information to inform a 21^st century audience.

Primary sources can provide launching phenomena that challenge students to learn new content, reflect on scientific practices, and be reminded of the constructive nature of science.

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