Observing, Experimenting, Predicting and Validating
Introduction for Teachers
In this inquiry, two pieces of different colored felt will represent two different environments. Small creatures exposed on the surface of the felt will represent organisms living in that environment.
Students work in teams of two or three, and take turns being predatory “hawks” who swoop down and capture the “mice” that are easiest to see on each background. Students should also take turns recording their observations in an age appropriate way (younger students might count and draw the number of mice on each background; older students should record their data in table form and display it in a graph).
After a predator sweep, the individuals remaining will “reproduce.” The proportion of individuals will change from generation to generation to model natural selection.
Concepts & Content related to New Mexico Science Standards and Benchmarks:
Strand I Scientific Method & Scientific Thinking
observation
prediction
forming hypotheses
recording and interpreting data
proportion
Strand II Content/Life Sciences
variation among individual organisms in a population
adaptation
evolution through natural selection
population
heredity
reproduction
predator/prey relationships
food webs
Purpose:
In this inquiry you will investigate how natural selection works in two populations of mice living in different environments.
Materials:
Two pieces of different colored felt (24”x24”). To represent a natural environment, one might be gray; the other light brown.
100 pompon “mice” of each color to match the felt.
tweezers (representing hawk’s talons)
Quart-sized storage bags to hold pompon "mice."
Method:
Lay out the two pieces of felt. On each piece of felt, scatter 12 gray pompons and 12 brown pompons. You will go through two cycles of predator activity followed by reproduction, as described below.
Observe and Predict:
If hawks flying overhead catch the most visible mice, which mice will they capture more often on the gray felt? On the brown felt? Why?
After a hawk attack, the surviving mice will reproduce. Predict which color mouse will be the most common in the gray environment after several cycles of predation and reproduction? Predict which color mouse will be the most common in the brown environment after several cycles of predation and reproduction?
Write down your predictions in the form of a hypothesis (a guess about what will happen to the different colored mice).
Procedure
A. Mice in Gray Environment
1. First generation: Scatter 12 gray mice and 12 brown mice on the gray felt background.
2. Let one student act as a hawk, using the tweezers to capture as many easily visible mice as you can in ten seconds.
3. Put the captured mice in the storage bag.
4. Now the surviving mice will reproduce to make Generation 2. The offspring (children) will inherit their fur color from their parents. For every surviving gray mouse, add two gray pompon offspring. For every surviving brown mouse, add two brown pompon offspring.
5. Count your mouse population and record your observations in a drawing or table (see the example below).
6. Second Generation: Repeat
Let a hawk capture the most visible mice on each background. Let your surviving mice produce two offspring each. Count the new population and record your data.
7. Third Generation: Repeat
Let a hawk capture the most visible mice on each background. Count the remaining mice of each color and record your data. Let your surviving mice produce two offspring each. Count the new population and record your data.
Mice in brown Environment
Repeat steps 1-7, but this time the background will be brown and the hawk will capture more gray mice.
Observe and Record
Make sure to record your observations. Every time you change the number of mice through predation or reproduction, write down the number of mice present in the population. (Younger students should count the mice and draw what they see; older students should record their data in a table as shown below.)
Analyze and Discuss:
Older children should calculate and record the fraction of each type of mice on each background, and use their results to create a graph.
Calculation 1: gray mice/total mice on gray background
Calculation 2: brown mice/total mice on brown background
How does the proportion of gray mice and brown mice in the first generation compare with the second and third generations? How does the proportion or fraction of mice change in each generation? Do you see more gray mice or more brown mice in a gray environment in the third generation? Compare this with the fraction or gray and brown mice in the brown environment in the third generation.
Conclusion:
Did your observations match your predictions? Why or why not?
Real World Example: In New Mexico lava flows have colored some ground surfaces deep gray or black; in other places, limestone results in a pale brown background. Mice living in each environment tend to have fur that matches their environment.
Critical Thinking:
Read about Charles Darwin’s observations of sea slugs (pp. 32-35). Why do you think there were so few adult sea slugs compared to the number of eggs in the pool? What traits might help sea slugs to survive and reproduce?
Data Tables for Older Students
(Feel Free to download and copy for classroom use).
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Number of Mice Observed in Each Environment |
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Environment 1 (Gray Felt) |
Environment 2 (Brown Felt) |
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Gray Mice |
Brown Mice |
Gray Mice |
Brown Mice |
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Number of mice to start (first generation) |
12 |
12 |
12 |
12 |
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Number of mice in second generation |
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Number of mice in third generation |
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Fraction of Matching Mice Observed in Each Environment |
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Environment 1 (Gray Felt) |
Environment 2 (Brown Felt) |
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Fraction of mice matching their environment in the first generation |
˝ (= 0.5 or 50%) |
˝ (= 0.5 or 50%)
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Fraction of mice matching their environment in the second generation |
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Fraction of mice matching their environment in the third generation |
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