Beacon Lesson Plan Library

Who Gets Eaten? A Study of Natural Selection

Carolyn Slygh


Students represent a new predator on a population of colored worms. They mathematically determine the effect of the new predator on the survival and reproductive rates of the worms, simulating natural selection at work.


The student understands the mechanisms of change (e.g., mutation and natural selection) that lead to adaptations in a species and their ability to survive naturally in changing conditions and to increase species diversity.

The student understands how genetic variation of offspring contributes to population control in an environment and that natural selection ensures that those who are best adapted to their surroundings survive to reproduce.


-Assorted colors of yarn cut into 1 cm. pieces
- 5 different colors, 60 pieces per color
-Student data chart and student questions (see Associated File)
-Overhead of Student data chart
-Plot of land marked off to represent the environment
-Graph paper and Percentage chart (see Associated File) for extension activity
-Clock or stop watch


Prior to class meeting:
1. Cut yarn into 1 cm. pieces. These represent the worms. The colors used can vary, but you should have one or two colors that will blend into the background of your -environment- and one or two colors that greatly contrast. All colors should be randomly spread out within the plot. Have extras available if needed.
2. Mark off a 20 meter X 20 meter plot of land using string or rope. The size of the plot can vary according to the number of students designated as predators.
3. Randomly spread the yarn throughout the plot.


1. Ask students why some organisms survive and some become extinct. List responses on the board or overhead. Ask how organisms adapt when something in their environment changes. The major misconception students have regarding natural selection is that they think an animal -changes- or mutates in response to the change. This activity will reinforce the concept that the variety found within a species will leave some better adapted to the change, thus increasing their reproductive rate.

2. Discuss the following original statements of Darwin regarding natural selection. These statements should be recorded on Student Question Sheet (see Associated File) Statements to be discussed are:
A. More organisms are born than the environment can support.
B. There is competition for limited natural resources (food, water, shelter, space).
C. Variety exists within a species (color, size, speed).
D. Those with the successful variation live to reproduce, thus passing those genes for that favorable variation on to their offspring.
In class:

3. After the class discussion, tell the students that they will represent a new predator that has moved into the territory of a population of colored worms. They are to capture as many worms as they can in a two minute time period. The time period can vary according to the size of the plot. A larger plot should allow a longer collection time.

4. Assign two students to be the -reproductive assistants-. They will go out between generations and assist the remaining worms with their reproductive success. Each surviving worm will pass their genes to the next generation and create two more worms of the same color.
5. Complete the student data chart with the beginning worm population as determined by the teacher. Complete this information under -generation one, initial population- on your overhead of the Student data sheet while students record it on their data sheets.

6.Take students to the plot and time them as they -feed- for two minutes. Feeding consists of gathering as many worms in the time allowed. Return to the lab and count how many worms were eaten. Record this on the Student data chart under -generation one.- Determine the number of worms remaining using the formula given. For each worm remaining, two new worms of the same color will be added to the plot by the -reproductive assistants.-
7. Repeat steps 3 and 4 two more times for generations two and three.

8. Answer questions on Student Question Sheet (see Associated File).

9. Extension: Determine the percentage of worms of each color for the three generations and graph the data. (see Associated File)


Each student should have completed the Student data table and answered the questions on the Student Question Sheet. Question responses should show an understanding that organisms do not change by will, but that some organisms in a population are genetically more successful due to influences of the particular environment they live in (camouflage, etc). Some of the genetic differences may be caused by mutation.
Essay - Explain how increased diversity leads to increased ability of survival in a changing environment.


If students must remain in the classroom, pieces of colored and clear acetate can be cut into small circles or squares and spread about on the classroom floor in a specific area. Extension can be made by determining the percentage of each color of worm over the three generations.
Return to the Beacon Lesson Plan Library.