Name: _________________________
Date: _________________________ Period: ____
BIOLOGY LAB
PEPPERED MOTH
SIMULATION
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
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.
In general, birds in the area hunted the moths for food. The camouflage of the moths
plays an important role in determining whether the birds could see and hunt their prey.
An Unpolluted Birch Forest
The light variety of the peppered moth
on a birch tree trunk.
The dark variety of the peppered moth
on a birch tree trunk.
A Polluted Birch Forest
The light variety of the peppered moth
on a soot-blackened tree trunk.
The dark variety of the peppered moth
on a soot-blackened tree trunk
Materials:
Dark box
Moth cutouts with various colors from white to black
Green box Squares cut of various sizes
Procedure
1. Place moths in dark background box and randomly stir and spread them out in the box.
2. While looking at the content quickly select out five moths one at a time. Compare your
moths to the normal distribution on board and record your data on the chart below.
3. Place the squares on the green colored box and randomly stir and spread them out in the
box.
4. While looking at the content quickly select out five squares one at a time. Compare your
squares to the normal distribution of squares and record your data in the second chart.
5. Collect class data for moths and squares.
6. Answer the analysis questions below.
The Selection of Varying Intensities of Moths
Color
White
Grey
Black
# of
each
moth
selected
Total
Class
Count
1
2
3
4
5
6
7
8
9
Results
The Selection of Different Sized Squares
Color
½”
¾”
1”
1 ¼”
1 ½”
1 ¾”
2”
1
2
3
4
5
6
7
# of each
moth
selected
Total
Class
Count
Conclusions
1. If the respective rows of colored moths or different sized square are arranged in a
single file from white to black or small to large, is there an equal number of objects
on either side of the middle stack?
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2. Look at the class data for which colored moths were selected. Add up all the
numbers on either side of the middle number. Do not include the middle number in
the count. Did the class select out more lighter- colored moths or more darkercolored moths? Use your results to support your answer.
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3. How would you explain the class results?
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4. Look at the data for which different sized squares were selected. Add up the
numbers on either side of the middle number. Do not include the middle number in
the count. Did the class select out more smaller-sized squares?
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5. How would you explain the class results?
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6. Kettlewell compared the color of the moths in the forest to the moths stored in a
museum that had been collected from the same forest over a hundred years ago.
What he discovered illustrates a basic concept in biology.
In a population of moths, there will be a normal distribution of colors. That
is, most of the moths will be the average color. A few will be lighter and few will be
darker. If this normal distribution curved were to be drawn on a graph, the
distribution of moth colors would look as follows.
Many
Number
of moths
few
Light
Medium
Dark
Image that most of the trees in this forest of over 100 years old had bark that was light
in color. In addition, some of the birds in this forest fed on moths.
7. What kind of moth would be eaten by the birds most frequently?
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8. If the uneaten moths mated, what color offspring would they tend to have a few more
of?__________
Further imagine that after a number of years, the nearby city became more and
more industrialized. Smoke poured out of the chimneys and settled on the tree
trunks.
9. What happened to the color of the tree trunks as time progressed?
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10. What kind of moth would be eaten now by the birds more frequently? Explain why?
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11. If the uneaten moths mated, what color offspring would they tend to have a few
more of?
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12. As the years continued, the trees became darker and darker. If the surviving moths of
each generation were to continue to mate, what do you think would happen in time to
the color of the entire population?
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13. You might say the moths have evolved from one color to another. What caused the
change to take place?
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To summarize, you have learned that individuals differ. Because of these differences,
some will have a better chance of surviving.
14. What difference will give some individuals a better chance of survival?
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15. According to Darwin, what was nature selecting?
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16. Using Darwin’s Theory, how would you explain how the giraffe got its longer neck?
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17. In summary, according to Darwin, what kind of individual survives?
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18. What is natural selection? How did your experiment show that natural selection
occurred in the moth populations? Use your results to support your answer.
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6. Examine the table and construct a graph.
a. Plot the years of the study on the X-axis and the number of moths captured on the
Y axis.
b. You should have 2 differently colored lines on your graph - one for light moths,
and one for dark moths.
c. Make a key that explains which colored line represents light moths and which
colored line represents dark moths.
Year
# of Light
Moths
Captured
# of Dark
Moths
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
Key for Graph:
7. Explain in your own words what BOTH LINES on the graph show.
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