Natural Selection with the Bear-Eating Monster
For this activity, you are a Bear-Eating Monster!!! In your habitat,
there are two kinds of bears: Happy Bears and Sad Bears. Happy
Bears hold their hands up high. Sad Bears hold their hands down
low. Which bear is which in the picture below?
Happy Bears taste sweet and are easy to catch.
Sad Bears taste bitter, are sneaky, and difficult to catch.
Because you eat bears to survive, you only eat Happy Bears if at all
possible. How would this affect the bear population?
Answer some questions about what might happen to the bear
population.
1) Over time, what do you think will happen to the population of
Happy Bears?
2) Over time, what do you think will happen to the population of
Sad Bears?
Now let’s do an experiment to see what really happens:
Purpose
The purpose of this experiment is to see what happens to the bear
population when the Bear-Eating Monster only eats one kind of bear.
Materials
Happy Bears
Sad Bears
Paper Towel
Pencil
Graph Paper
Lab Sheet
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Natural Selection with the Bear-Eating Monster
Procedure—Part One—“Generation 1”
1. Get a “population” of bears from the lab station. Pour them out
on your paper towel.
2. Count the total number of bears and record this number on the
table.
3. Separate the bears into two groups: Happy Bears and Sad
Bears. Count the number of each. Record these numbers on
the table.
4. Check your numbers. The total number of bears should be
equal to the number of Happy Bears plus the number of Sad
Bears.
5. Eat three Happy Bears. If you have fewer than three, it’s okay.
Eat all the Happy Bears you have—but NO MORE THAN
THREE.
In every habitat, organisms reproduce. In this habitat, baby bears are
born one time every year. The number of baby bears born is equal to
the number of bears left after the Bear-Eating Monster has eaten its 3
bears for the year. The baby bears are called the “new generation.”
Procedure—Part Two—“Generation 2”
1. Get the “new generation” from your teacher. Add them to the
bear population.
2. Count the total number of bears and record this number on the
table for “Generation 2.”
3. Separate the bears into two groups: Happy Bears and Sad
Bears. Count the number of each. Record these numbers on
the table for “Generation 2.”
4. Check your numbers. The total number of bears should be
equal to the number of Happy Bears plus the number of Sad
Bears.
5. Eat three Happy Bears. If you have fewer than three, it’s okay.
Eat all the Happy Bears you have—but NO MORE THAN
THREE.
Repeat this two more times—for “Generation 3” and “Generation 4.”
Make sure your numbers are all recorded in the chart.
Good work! You are a great Bear-Eating Monster!
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Natural Selection with the Bear-Eating Monster
Fill in the Percentage Table by calculating the percent of each type of
bear. This is an alternate way of showing your results for the
experiment.
If you can’t remember how to calculate percents, just take the number
of one type of bear (Happy or Sad) and then divide it by the total
number of bears--then multiply by 100. For example,
Number of Happy Bears
Total Number of Bears
x 100 = Percent of Happy Bears
How would you calculate the percent of Sad Bears? Write how you
would do that below. Have your teacher check this. 
Now do your calculations for each of the four generations and fill in
the Percentage Table. You can do it! One way to check your work is
to see if your percentages add up to 100 for each generation.
Graphing
To see what happens to the bears over time, a graph can be very
helpful. The best type of graph to see this is a bar graph. You have
made these in your math classes before.
 The vertical side should be labeled “Number of Bears.”
 The horizontal side should be labeled “Generations.”
 At each generation, graph the number of Happy Bears and the
number of Sad Bears. It might be cool to do Happy Bears one
color and Sad Bears another color.
 The title of the graph should be “Bear Population Over Time.”
Please use a ruler to draw straight lines. Ask your teacher for help in
deciding how to put the numbers on the vertical side or how big to
make each bar. 
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Natural Selection with the Bear-Eating Monster
Conclusion
Look at your charts and your graph. Examine them to see what
happened to the bear population.
Now answer these questions:
1) What happened to the total bear population over time?
2) What happened to the population of Happy Bears over time?
3) Why do you think this happened?
4) What happened to the population of Sad Bears over time?
5) Why do you think this happened?
6) How do the results compare to what you said at the beginning
of this activity (questions on the first page)?
Using What You Just Learned…
Natural Selection is a process that occurs over time in a population
of organisms. In this process, organisms that have traits that
increase their chances of survival are more successful. This means,
they are more likely to live and carry on to future generations.
Using the Happy and Sad Bears activity you just finished, write a
paragraph that tells me how the bears’ situation is an example of the
process of natural selection. You can do it! You’re a good scientist!
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Natural Selection with the Bear-Eating Monster
Bear Population Table
Generation
Total Number
of Bears
Number of
HAPPY bears
Number of
SAD bears
1
How many baby bears were born?
2
How many baby bears were born?
3
How many baby bears were born?
4
Check your numbers! Make sure they are all filled in.
Bear Percentage Table
Generation
1
% Happy Bears
% Sad Bears
2
3
4
Check your numbers! Each generation’s percentages should add up to 100.
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