Download of Dark Moths

Name
N A T U R A L
S E L E C T I O N
BACKGROUND/INTRODUCTION
In all our talks of NATURAL SELECTION, we have always said that it take millions of years for a
species to show any kind of change. While this is true for the most part, there are circumstances that
allow us to see evolution happening on a much quicker scale.
In the 19th century, England was going through an industrial revolution. During this time period the
country saw a great increase in coal burning due to the many factories that were in business. When
coal is burned, soot is produced. This soot began to coat the trees and buildings that were near the
city. The bark on the birch trees, in those areas, were blackened by the soot.
Before this time period the peppered moths in this area were mostly lightly colored. This allowed
them to be camouflaged against the white birch trees from their natural predators, birds. During this
industrial revolution, a dark form of the moth became more and more common. Since this shift in
pigmentation was caused by industry, the rise of these dark colored moths came to be known as
INDUSTRIAL MELANISM (the pigment in moths that gives them this coloration is called melanin).
In this lab, you will be the moths’ natural predator, a bird, and we will see why these conditions
caused such a rapid change in this species of moth.
*****READ THE WHOLE PROCEDURE FIRST, THEN BEGIN*****
PROCEDURE:
1. You will obtain a background (either light, medium, or dark), and an envelope of light moths
and envelope of dark moths.
2. One person is the predator and this person should turn their back so they cannot see the
background. Meanwhile, the other person, the recorder, will lay 5 light and 5 dark moths
randomly on that background.
3. When ready, the recorder will tell the predator to turn around and the predator will have 5
seconds to remove/pick up as many moths as possible. YOU CAN ONLY REMOVE ONE
MOTH AT A TIME AND YOU MUST USE YOUR THUMB AND FOREFINGER TO REMOVE
THEM.
4. After the 5 seconds, count the “survivors” left on the background and record in Generation 1 in
Table 1.
5. All survivors now have the ability to reproduce. Therefore, for every surviving moth, add one
more to the background. Basically, double the survivors.
6. Again, the predator should turn their back and recorder scatters moths randomly then allows 5
seconds for predation. Record results as generation 2.
7. Once doubling the survivors, just like before, obtain data for generation 3.
8. Then complete Table 2 by using your information, then find groups that had different
backgrounds than your own to complete Table 2.
GRAPHING:
Make a LINE graph comparing the percentage of dark moths over the 3 trials/generations. You
should have 3 lines (one for each background). Use different color pens/markers and make a key.
You are graphing the generation/trial against the percentage change. YOUR GRAPH MUST USE AT
LEAST HALF OF THE GRAPH PAPER AND YOU MUST FOLLOW ALL GRAPHING RULES.
ANALYSIS QUESTIONS:
1. Using your data in Table 2, compare the 3 backgrounds. What trends did you observe from
Generation 1 to Generation 3 for the :
Light Background:
Medium Background:
Dark Background:
2. Let’s say that we went out to 4 generations in this activity. Make a prediction (using actual
numbers) as to what you expect to see if we actually completed Generation 4 for the light
moths and the dark moths.
Predicted # of light moths for Generation 4 = _____
Predicted # of dark moths for Generation 4 = _____
3. Explain, in terms of evolution, why you received the results that you did. Use appropriate
terminology.
4. Given that today, there are more air pollution laws, what do you think is occurring with the
number of light moths and number of dark moths in England?
5. As a preview of what is coming up in our studies, what type of natural selection does the
peppered moth example demonstrate….directional, stabilizing, or disruptive? Read (in Chapter
16) and research if necessary.
Table 1: Color of the Background ___________________________
# of Light Moths
# of Dark Moths
Original Population
Generation 1 Survivors
Generation 2 Survivors
Generation 3 Survivors
Table 2: Group Data
Background Color
Light
Medium
Dark
% of Dark in
Generation 1
% of Dark in
Generation 2
% of Dark in
Generation 3