1. Natural Selection Problem
Goals: Students will be able to
1. Design a testable hypothesis
2. Analyze and interpret a simulation about an ecological problem
3. explain how evolution actually works.

2. Hummingbird Video www.pbs.org
What are the four
processes required
for natural selection?

3. Sex and the Single Guppy www.pbs.org

4. Introduction to the Question
In pools with many predators, male guppies are drab colored.
In pools with few predators, male guppies have bright coloration.
Why is there a difference?

5. Guppy Gallery

6. Design a Testable Hypothesis
In your groups, develop a hypothesis to explain the observed pattern of fish coloration in the pools.
Design an experiment to test your hypothesis.

7. Experimental Simulation
Before each simulation begins, predict what will happen, based on your hypothesis.
As the simulation is running, your group will record data for each generation.

8. Simulation 1

9. Results - Simulation 1

10. Data Table - Simulation 1

11. Simulation 2

12. Results - Simulation 2

13. Data Table - Simulation 2

14. Data Analysis
On your carbonless paper, plot a line graph of the changing proportions of color pattern over time.
What is the independent variable? Which axis should you plot it on?
Which is the dependent variable? Which axis should you plot it on?

15. Low Predation

16. High Predation

17. Analysis
Do these data match your prediction (support your hypothesis)?
Why or why not?

18. Questions for Discussion
What determines the color pattern of an individual guppy?
What role(s) does color play in guppy survival and reproduction?
Explain the results in terms of fitness and natural selection. Describe how sexual selection and natural selection push in opposite directions.

19. Questions for Assessment (from Anderson et al., 2002)
A typical natural population of guppies consists of hundreds
of guppies. Which statement best describes the guppies of
a single species in an isolated population?
a. The guppies share all of the same characteristics and
are identical to each other.
b. The guppies share all of the essential characteristics
of the species; the minor variations they display don’t
affect survival
c. The guppies are all identical on the inside, but have
many differences in appearance.
d. The guppies share many essential characteristics, but
also vary in many features.

20. Student Responses on Midterm (n=176)

21. Questions for Assessment (from Anderson et al., 2002)
Fitness is a term often used by biologists to explain the
evolutionary success of certain organisms. Which feature
would a biologist consider to be most important in
determining which guppies were the “most fit”?
a. large body size and ability to swim quickly away from predators
b. excellent ability to compete for food
c. high number of offspring that survived to reproductive age
d. high number of matings with many different females

22. Student Responses on Midterm (n=176)

23. Questions for Assessment (from Anderson et al., 2002)
In guppy populations, what are the primary changes that
occur gradually over time?
a. The traits of each individual guppy within a population
gradually change.
b. The proportions of guppies having different traits within a
population change.
c. Successful behaviors learned by certain guppies are
passed on to offspring.
d. Mutations occur to meet the needs of the guppies as the
environment changes.

24. Student Responses on Midterm (n=176)