Materials Included In Kit

Additional Materials Required

Safety Precautions

This laboratory activity is considered nonhazardous. Exercise caution when using scissors. Please follow all classroom safety guidelines.

Disposal

All materials may be saved and stored for future use.

Lab Hints

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. All materials are reusable. The laboratory activity can reasonably be completed in one 50-minute class period. The prelaboratory assignment may be completed before coming to lab, and the data compilation and calculations may be completed the day after the lab.
• Make a data table on the board so the class can average the classroom data to increase statistical relevance.
• Photocopy more peppered moth sheets. After the procedure has been completed once, have students calculate how many moths of each variety were left on each background. For every pair of moths of one variety, add another pair of the same variety. Do not add any for single moths. Repeat the procedure with the new starting number. Repeat the above procedure several times and observe how the population changes over time for each backgound.

Answers to Prelab Questions

1. What are the two main premises made by Charles Darwin in his book Origin of Species?

   The first premise is that all species inhabiting Earth descended from ancestral species. The second premise is natural selection is the means by which evolution occurred.

2. Explain natural selection in your own words.

   Natural selection is the process by which a certain beneficial trait enhances survival. Thus those that survive pass on their beneficial heritable trait to their offspring increasing their population.

Sample Data

Answers to Questions

1. 1. Average the class data for the quantity of each moth captured on each type of tree bark background.

      Add up the number of moths in each category and divide by the number of students in the class.

   2. Which form of the peppered moth appeared to be more easily spotted by prey against the light tree bark background? Dark tree bark?

      The carbonaria moth was most easily spotted on light tree bark and the typica form was spotted most easily on the dark tree bark.

   3. Using the average class data, what was the ratio of survival for typica vs. carbonaria moths for each background?

      Light background 0.5:2.5, dark background 3.0.

2. What would you predict would happen to the ratio of the peppered moth population as a result of cleaner burning fuels?

   Most likely the typica moth would become more prevalent. Without soot covering trees the color of tree bark will camouflage the typica moth from predators.

3. Explain how this activity simulates the process of natural selection and how this process leads to evolutionary adaptation.

   After the Industrial Revolution the beneficial heritable trait was dark coloration of the carbonaria moths. They survived in greater numbers leaving more offspring increasing their concentration in the population leading to evolutionary adaptation.

4. In Western Africa there are birds called black-bellied seedcrackers. Some have small bills and feed on soft seeds while others have large bills which are able to crack the shells of hard seeds. Would you predict natural selection for or against survival of birds with an intermediate sized beak? What are the variables or environmental conditions that would affect their survival?

   One might initially think that a bird with an intermediate sized beak would be selected for as it seems it could select both soft or hard seeds. However, their beaks are not strong enough to crack large seeds therefore it is more likely they would be selected against.

Teacher Handouts

11012_Student1.pdf

Introduction

Natural selection is the process by which certain heritable traits increase the likelihood of an organism’s survival resulting in successful reproduction. Over successive generations the organism will increase in population. Use this activity to simulate the classic study of natural selection involving peppered moths.

Concepts

• Natural selection
• Predator vs. prey relationship

Background

On November 24, 1859, Charles Darwin (1809–1882) published On the Origin of Species by Means of Natural Selection. The Origin of Species focuses on two main points. First, Darwin presented Natural Selection to account for supporting evidence that species inhabiting Earth today descended from ancestral species. Secondly, Darwin proposed a mechanism for evolution. The basic premise of natural selection is that populations of organisms will change over time if individuals with certain heritable traits that are beneficial for survival survive in greater numbers than those without the trait. They are able to leave more offspring resulting in a larger concentration of that trait in the population. Over time natural selection results in evolutionary adaptation. Evolutionary adaptation is a prevalence of inherited characteristics that benefit organisms’ survival and reproduction in specific environments.

The story of the peppered moth, Biston betularia, is one of the most chronicled examples of natural selection. The peppered moth has several phenotypes. They range from a very light-colored moth commonly referred to as typica to a darker colored carbonaria form, with several variations in between. In Manchester, England the typica form was predominant before the industrial revolution. The typica moth is light colored with speckled wings. Many trees in England have light colored bark that camouflages the typica moth quite well (see Figure 1).

The carbonaria variety were present but not in large numbers—this observation was attributed to the darker moths being much easier for birds (predators) to spot (see Figure 2). Natural selection maintained a small population of dark moths. The Industrial Revolution produced soot and smoke that deposited on the light-barked trees. This change resulted in a drastic increase in carbonaria moths in urban areas. Over time scientists discovered that although the typica form remained prevalent in rural areas, the carbonaria form became more prevalent in the urban areas with more pollution. The hypothesis was that with the tree bark becoming darker in color the typica form was much easier for predators to spot. The majority of the typica moths were eaten. Hence, they were not available to produce offspring. The increase in urban carbonaria concentration was attributed to them now being more camouflaged on the darker tree bark. They were not as easily spotted by predators, therefore, they were available to perpetuate offspring, increasing their overall population.

Experiment Overview

The purpose of this experiment is to simulate the classic study of natural selection by exploring the survival of two different phenotypes of paper “peppered moths.” Students will act as predators when both phenotypes are placed against light and then dark backgrounds.

Materials

Prelab Questions

1. What are the two main premises made by Charles Darwin in his book Origin of Species?
2. Explain natural selection in your own words.

Safety Precautions

The materials used in this laboratory activity are considered nonhazardous.

Procedure

1. Obtain a peppered moth sheet. Using scissors cut out the five squares representing typica moths and the 5 squares representing carbonaria moths.
2. Obtain the background sheet corresponding to light tree bark.
3. Have one lab partner turn around so he or she cannot see the background.
4. The second lab partner should randomly spread the 10 moth squares around the background.
5. The partner who wasn’t looking turns around and rapidly selects three moths as quickly as he or she can.
6. Record the quantity of each type of moth that was captured on the Natural Selection Worksheet.
7. Repeat steps 2–7 switching roles with your partner.
8. Obtain the background sheet corresponding to dark tree bark.
9. Repeat steps 3–6 using the dark background.
10. Switch roles with your partner and repeat.
11. Record both partners’ data in a large classroom data table.

Student Worksheet PDF

11012_Student1.pdf