Name: ______________________________________ Date: ________________________

Student Exploration: Natural Selection

Vocabulary: biological evolution, camouflage, Industrial Revolution, lichen, morph, natural

selection, peppered moth

Prior Knowledge Questions (Do these BEFORE using the Gizmo.)

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.

1. Which morph do you think would be easier to see on a

dark tree trunk? Light moths

2. Which morph do you think would be easier to see on a

light tree trunk? Dark moths

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.

1. Check that LIGHT TREES is selected. Click Play ( ),

and hunt moths for one year.

A. How many dark moths did you capture? 3

B. How many light moths did you capture? 3 How many moths can you find?

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? Light moths

2. If a forest contained mostly light-colored trees, which type of moth would you expect to be

most common? Light moths as they are more more fit to that environment.

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 Get the Gizmo ready:
Activity A:
 Click Reset ( ).
Light trees
 Check that the LIGHT TREES tab is selected.

Introduction: Before the 19th century in England, the air was very clean. The bark on trees was
usually light in color. Abundant lichens growing on tree trunks also lightened their appearance.

Question: How does the color of a peppered moth affect survival?

1. Predict: Over time, what will to happen to the populations of light and dark moths on light

trees? Light moths increase dark decrease.

2. 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.)

Year Dark moths Light moths

0 0.50 0.50
1 0.35 0.65
2 0.25 0.75
3 0.04 0.96
4 0.07 0.93
5 0 100

3. Analyze: What do your results show? As I predicted dark moths decrease while light
moths increase.

4. Apply: Which type of moth do you think was more common before the 19th century, when

most trees were light in color? Following logic I would say light moths.

5. Extend your thinking: What strategies did you use to hunt for moths? Pattern checking,
head shape, clicking randomly.

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 Get the Gizmo ready:
Activity B:
 Click Reset.
Dark trees
 Select the DARK TREES tab.

Introduction: The 19th century was the time of the Industrial Revolution in England. Most of
the new industries used coal for energy, and the air was polluted with black soot. In forests near
factories, the soot coated trees and killed lichens. As a result, tree trunks became darker.

Question: How did air pollution affect moth populations?

1. Predict: Over time, what will to happen to the populations of light and dark moths on dark

trees? Dark moths increase light moths decrease.

2. 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.

Year Dark moths Light moths

0 0.50 0.50
1 0.83 0.17
2 0.94 0.06
3 0.95 0.05
4 0.94 0.06
5 1 0

3. Analyze: What do your results show? It is as I expected the light moths decreased while
the dark moths increased.

4. Apply: Which type of moth do you think was more common during the 19th century? Why?

Following logic I would say dark moths as they would go better on those darkened
trees.

(Activity B continued on next page)

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Activity B (continued from previous page)

5. 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?

There were two states each one disadvantageous for one of the moth types, this
shows natural selection because if this were an environment the ones not fit for their
environment would die, while those who are fit would survive.

6. 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.

The second sample answer is correct. Each year the hidden moths would survive and
then their genes would be the ones that are most prevalent while reproduction
approaches carrying capacity.

7. 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.

Natural selection is a function in the class of evolution, given enough calls to it the
organism evolves. This is seen with the moths while this is an extreme example of
changing color entirely, this is still a step in the process of evolution. Most commonly
I presume evolution takes place with the little things like a slight increase to wing size
or a change in the shape of the head.

2019