Peppered Moth Case Study
IB Biology Lab Report
Name ______________________________
Lab Partner _________________________
Date/s lab was done ____________________
Title:
ADAPTATION AND THE PEPPERED MOTH CASE STUDY
Purpose: To examine how changes in the peppered moth are an example of a workable
adaptation.
Design
Data
Collection
&
Processing
Conclusion
&
Evaluation
Manipulative
Skills
Personal
Skills
C
P
N
Mark
Teacher’s Initials _______________
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Peppered Moth Case Study
Background Information
Although uncertain about the mechanisms involved, Darwin felt that natural selection was the basis of
evolutionary change. Today, scientists know that while the effect of natural selection may be subtle and
complex, the basic concept is simple. Every population has a broad range of inheritable variations. Some
characteristics make an organism better adapted to survive and reproduce, while others impede
adaptation. Organisms that are best adapted will be most successful at reproducing, and relatively more
of their offspring will enter the population. Over time, an increasing proportion of the population will
have the adaptive trait.
The Case Study
In 19th-century England, collecting butterflies and moths was a popular hobby. Records indicate that
one species, the peppered moth (Biston betularia), was especially common during the first half of the
century. It had a whitish appearance with minute dots and speckles, from which it got its common name.
The pigmentation gave it a remarkable resemblance to the light-colored lichens on the tree barks on
which it rested. Because it was difficult to see, it was protected from predatory birds.
The first melanic, or black, specimen was recorded near Manchester, England, around 1848. The
difference between the black and white forms is due to a single mutation. The factor that produces black
forms is dominant to the factor that produces the normal, whitish appearance. Although melanic forms
were quite rare at the time, the mutation is known to occur quite frequently. There is little doubt that
melanic individuals appeared before 1848, but they would have been at a distinct disadvantage. Their
dark color would have made them easy prey for insect-eating birds.
The industrial revolution, which reached its peak in Manchester in the mid-1800s, introduced an
unpredictable change to the environment of the peppered moth. Industrial fumes, containing excessive
amounts of sulfur dioxide, destroyed almost all the lichens in the region. The tree bark became coated
with coal dust, soot, and other dirt, and the adaptive advantage of the peppered moth was quickly
diminished. In fact, the melanic individuals now had a selective advantage as they were more difficult
for predators to see against the background of soot-stained tree bark. Eventually, this selection pressure
caused the population to change from one dominated by light-colored individuals to one dominated by
melanic individuals.
Whitish and melanic forms of white and black peppered moths
on light- colored bark
on polluted background
.
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Peppered Moth Case Study
From what has been presented so far, answer the following questions:
a) What might have caused the appearance of the first melanic form? Explain.
b) If the environment caused the selection pressure for change, what was the actual selecting agent in
this case?
Repeated studies and experiments have been undertaken during this century to determine the extent of
the selection pressure on the peppered moth in both polluted and nonpolluted locations In one
experiment recordings have been made from direct observations of large numbers of both melanic and
normal forms of Biston betularia, The procedure involved the release of both types of moths, followed
by tabulations based on recapture rate The results (shown in the table below) have enabled scientists to
calculate the selection pressure against melanic forms as well as that against normal whitish forms
Location
Non-Polluted
Polluted
Number Released
M
N
473
496
447
137
Number recaptured
M
N
30
62
137
18
% recaptured
M
N
6.3
12.5
27.5
13.0
c) What might have happened to the moths that were not recaptured?
d) How can you account for the differences in the recapture numbers for polluted and nonpolluted sites?
.
e) What generalization do the results suggest about environmental selection for the two forms of moth?
f) Explain why the melanic form is more abundant today than in the early part of the 19th century
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Peppered Moth Case Study
Case-Study Application Questions
1 Even a population that is 98% melanic retains the factor for light color in some of its members. What
would happen if the environmental conditions were again reversed?
2 Explain the following statements as they apply to this case study
• Evolution and adaptation need not always involve long periods of time
• While the change was quick it was actually quite small
• Evolution and adaptation usually occur by means of small changes.
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Peppered Moth Case Study
Peppered Moth Simulation Lab
I. Purpose:
In this lab, you will simulate how predators locate prey in different environments. You
will analyze how color affects an organism's ability to survive in certain environments.
II. Background:
Describe the importance of coloration in avoiding predation. Relate
environmental change to changes in organisms. Explain how natural selection causes populations to
change.
Industrial Melanism is a term used to describe the adaptation of a population in response to pollution.
One example of rapid industrial melanism occurred in populations of peppered moths in the area of
Manchester, England from 1845 to 1890. Before the industrial revolution, the trunks of the trees in the
forest around Manchester were light grayish-green due to the presence of lichens. Most of the peppered
moths in the area were light colored with dark spots. As the industrial revolution progressed, the tree
trunks became covered with soot and turned dark. Over a period of 45 years, the dark variety of the
peppered moth became more common.
III. Hypothesis: Make your hypothesis based on this question: How does color affect an organism’s
ability to survive in certain environments?
IV. Materials







Sheet of white paper
Newspaper
Forceps
Colored Pencils
Clock with Second Hand
30 newspaper circles (made with hole punch)
30 white circles (made with hole punch)
V. Procedure
1. Place a sheet of white paper on the table and have one person spread 30 white circles and 30
newspaper circles over the surface while the other person (“predator”) isn't looking.
2. The "predator" will then use forceps to pick up as many of the circles as she/he can in 30 seconds.
Record the data in chart below.
3. Repeat this procedure having you and your partner switch jobs for trial 2. Record the data in chart
below.
4. Repeat this procedure using the newspaper background for trials 3 & 4. Record the data in chart
below.
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Peppered Moth Case Study
VI. Data Collection:
Starting Population
Trial
Background
Newspaper
White
1
white
30
30
2
white
30
30
3
newspaper
30
30
4
newspaper
30
30
Number Picked up
White
Newspaper
VII. Data Analysis:
1. What did the experiment show about how prey is selected by predators?
2. What moth coloration is the best adaptation for a dark (newspaper) background? How do you know?
3. Calculate how many white and peppered moths remain after trial 1. What would you expect the next
generation of moths to look like after trial 1? What about the next generation after trial 3?
4. How does this simulation model natural selection?
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Peppered Moth Case Study
5. Examine the table and construct a graph. Plot the years of the study on the X-axis, and the number of
moths captured on the Y axis. You should have 2 lines on your graph - one for light moths, and one for
dark moths.
# of
# of
Light
Dark
Year
Moths
Moths
Captured Captured
2
537
112
3
484
198
4
392
210
5
246
281
6
225
337
7
193
412
8
147
503
9
84
550
10
56
599
6. Explain in your own words what the graph shows.
7. Describe a situation where this type of selection might occur.
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Peppered Moth Case Study
VIII. Evaluation: Did your data support your hypothesis? Why or why not? What does the graphed
information above reveal about inherited characteristics in a population changing over time?
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