Natural Selection: Weigh the Evidence

Students revisit the three models presented at the beginning of the module. They consider how several lines of evidence relate to each model and explain why they think one model is correct.

1. Distribute the Natural Selection: Weigh the Evidence handout.
2. Discuss the statement at the top of the handout:
   • Scientific ideas can never be proven true. They can only be disproved, or proven false. To disprove an idea, it takes evidence that contradicts it. That’s why contradicting evidence is the most important kind for helping scientists refine and update their ideas.
3. Share Evidence 7: Woolly Mammoth Extinction. Discuss how it contradicts model A (if individual animals had been able to change their traits to fit the environment, the species would not have died out) and model C (the individuals that survived the longest were not the healthiest and strongest). Can students think of other extinction examples that contradict these models?
4. Distribute one or more lines of evidence to each pair or group of students.
   • You can use all the evidence provided or choose a subset that will work best for your students.
   • Evidence is numbered from easiest (1) to hardest (6). The Woolly Mammoth evidence (7) is only for the example (Step 1).
   • Each group should look at their evidence with all 3 models in mind.
     • You may want to have the students underline or circle important points in the evidence and add labels A, B, and C, according to the model it applies to.
5. When everyone is finished, have students share their results with other groups or with the class. Fill out the Whole Class Evidence table as a group so that students can weigh all the evidence together. Make the point that when scientists evaluate models, they need to consider all the evidence—not just the evidence that fits their favorite model.
6. Discuss how supporting evidence helps scientists build and refine their models. Have students read their evidence again, looking for ways it supports Model B.
7. Hand back the Natural Selection: Three Models copies that students completed at the beginning of the module. Have them fill out questions 3-5.

• As traits that favor survival and reproduction are passed down through generations, those traits become more common.

Copies

Natural Selection Evidence (pdf)
Natural Selection: Weigh the Evidence (pdf)
Whole Class Evidence Table (pdf)

Corliss, B. A., Delalio, L. J., Stevenson Keller IV, T. C., Keller, A. S., Keller, D. A., Corliss, B. H., & Isakson, B. E. (2019). Vascular expression of hemoglobin alpha in Antarctic icefish supports iron limitation as novel evolutionary driver. Frontiers in physiology, 10, 1389.
Deshmukh, R., Baral, S., Gandhimathi, A., Kuwalekar, M., & Kunte, K. (2018). Mimicry in butterflies: co‐option and a bag of magnificent developmental genetic tricks. Wiley interdisciplinary reviews: developmental biology, 7(1), e291.
Endler, J. A. (1980). Natural selection on color patterns in Poecilia reticulata. Evolution, 34(1), 76-91.
Fry, E., Kim, S. K., Chigurapti, S., Mika, K. M., Ratan, A., Dammermann, A., ... & Lynch, V. J. (2020). Functional architecture of deleterious genetic variants in the genome of a Wrangel Island mammoth. Genome biology and evolution, 12(3), 48-58.
Kuhn, D. E., O'Brien, K. M., & Crockett, E. L. (2016). Expansion of capacities for iron transport and sequestration reflects plasma volumes and heart mass among white-blooded notothenioid fishes. American journal of physiology-regulatory, integrative and comparative physiology, 311(4), R649-R657.
Niu, Y., Stevens, M., & Sun, H. (2021). Commercial harvesting has driven the evolution of camouflage in an alpine plant. Current biology, 31(2), 446-449.
Yeh, P. J. (2004). Rapid evolution of a sexually selected trait following population establishment in a novel habitat. Evolution, 58(1), 166-174.

The materials on this page are derivatives of the MEL Teaching Resources (accessed June 17, 2021), developed as part of The MEL Project by the Science Education Resource Center (SERC) at Carlton College, and licensed under Creative Commons Non-Commercial Share Alike 3.0.

Materials on this page are offered under a Creative Commons license Non-Commercial Share Alike 3.0.