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Prior Knowledge Questions
The peppered moth (Biston betularia) is a common moth found in Europe, Asia, and North America. It is commonly found in two forms, or morphs: a dark morph and a light, speckled morph. Birds are a frequent predator of the peppered moth.
- Which morph do you think would be easier to see on a dark tree trunk?
Answer: The light, speckled morph would be the easiest to see on a dark tree trunk.
- Which morph do you think would be easier to see on a light tree trunk?
Answer: The dark morph would be the easiest to see on a light tree trunk
Gizmo Warm-up
The Natural Selection Gizmo allows you to play the role of a bird feeding on peppered moths. The initial population of 40 moths is scattered over 20 tree trunks. Click on moths to capture them. Click the Next tree button (or the spacebar on your keyboard) to advance to the next tree.
- Check that LIGHT TREES is selected. Click Play, and hunt moths for one year.
A. How many dark moths did you capture?
Answer: 11 moths
B. How many light moths did you capture?
Answer: 5 moths
C. Camouflage is coloring or patterns that help an organism to blend in with the background. Which type of moth is better camouflaged on light bark?
Answer: The light, speckled moth.
- If a forest contained mostly light-colored trees, which type of moth would you expect to be most common?
Answer: The light, speckled moth rather than the black moth.
Question: How does the color of a peppered moth affect survival?
- Predict: Over time, what will to happen to the populations of light and dark moths on light trees?
Answer: I predict that overtime, the dark moths will begin to disappear and the light moths will remain and reproduce.
- Experiment: Click Play and hunt peppered moths on light tree trunks for five years. In each year, try to capture as many moths as you can. Note: You can use the spacebar on your keyboard to quickly advance to the next tree.
After 5 years, select the TABLE tab and record the percentages of each moth type. (Note: The table shows current populations of each moth, not the number of captured moths.)
Answer:
| Year | Dark moths | Light moths |
| 0 | 50% | 50% |
| 1 | 50% | 50% |
| 2 | 41% | 59% |
| 3 | 39% | 61% |
| 4 | 28% | 72% |
| 5 | 29% | 71% |
- Analyze: What do your results show?
Answer: My results show the light moth population gradually increasing and the dark moth population gradually decreasing.
- Apply: Which type of moth do you think was more common before the 19th century, when most trees were light in color?
Answer: The light colored moths were probably more common before the 19th century because they blended in with the trees compared to the black moths that stood out.
- Extent your thinking: What strategies did you use to hunt for moths?
Answer: the answer can vary.
Question: How did air pollution affect moth populations?
- Predict: Over time, what will to happen to the populations of light and dark moths on dark trees?
Answer: I think that the light moth population will decrease and the dark moth population will increase.
- Experiment: Click Play and hunt peppered moths on dark tree trunks for five years. In each year, try to capture as many moths as you can.
When you are done, select the TABLE tab and record the percentages of each moth type.
Answer:
| Year | Dark moths | Light moths |
| 0 | 50% | 50% |
| 1 | 57% | 43% |
| 2 | 88% | 13% |
| 3 | 77% | 23% |
| 4 | 100% | 0% |
| 5 | 100% | 0% |
- Analyze: What do your results show?
Answer: The results show the dark moth population drastically increasing until it reaches 100% and the light moth population drastically decreasing until it reaches 0%.
- Apply: Which type of moth do you think was more common during the 19th century? Why?
Answer: The dark moth was more common during the 19th century because during this time, the industrial revolution caused black soot from coal industries to pollute the air. This soot killed lichens causing the trees to go from a light color to a dark color. This exposed the white moths, causing them to be picked off one by one, leaving the back moths.
- Draw conclusions: Natural selection is the process by which favorable traits tend to increase in frequency over time. How does this experiment illustrate natural selection?
Answer: This experiment illustrates natural selection between the color of the peppered moth and the color of the tree. The trait of color determined which moth population increased versus which population decreased. If the tree color was dark, then the white moths would stick out, causing them to be seen by predators easier. This would leave the dark moths remaining to survive and reproduce. If the tree color was light, then the dark moths would be visible to predators and cause the moths to disappear in population while the light moths would blend in and thrive, causing their population to increase
- Think and Discuss: Did the changes you observed in the moth populations result from individual moths changing colors? Or did they occur because the best-hidden moths survived and reproduced, passing on their colors to their offspring? Explain your answer.
Answer: The changes I observed in the moth populations result from the best camouflaged moths who survived and reproduced, passing their colors along the way to their offspring. The moth themselves cannot change color but rather it is a trait that is passed on to them. The moths that blended in with the tree survived and were able to reproduce, passing the color they had to their offspring. The moths that did not match the tree did not survive, unable to reproduce and pass their color trait to their offspring
- Extend your thinking: Biological evolution is the process by which populations of organisms change over time. How could natural selection lead to evolution? If possible, discuss your answer with your classmates and teacher.
Answer: Natural selection can lead to evolution because in natural selection only the fittest survive. This means that the most suitable trait for an environment will survive and increase while another will decrease. In this experiment, the trait was about color and how peppered moths blended with their environment. If the trees that the moths were on was white, then the lighter colored moths on the tree will blend in while the darker moths will be eaten by the predators, decreasing their population over time. On the other hand, the lighter colored moths will survive, allowing them to reproduce, passing the genes of having a lighter color and increasing their population. Over time, the lighter colored moths will become more common while the darker colored moths will become less common. Eventually, the dark moths could become extinct or less dark colored traits will be passed on.
