Click to return to the Evolution Home Page
darwin change extinction survival sex humans religion
Online Course for Teachers: Teaching Evolution

About this Course 


SESSION 4: What Are the Processes for Evolution?

Explain Part A: Sexual Selection

One thing that concerned Charles Darwin about his theory of natural selection was the fact that birds like peacocks had brightly colored long tails and yet seemed to survive quite well. He expected that the males' long tails would make them unwieldy for flight, be heavy to drag around, and would put them at a disadvantage when escaping from predators. Eventually, he recognized the value of color and ornamentation: it attracted females and improved the males' chances of reproducing. He called this kind of selection "sexual selection."

Close up of a peacock.

To understand more about sexual selection, the force behind nature's extravaganzas, watch the Evolution Show Five video segment, "Tale of the Peacock."

Tale of the Peacock
View in:
QuickTime | RealPlayer

When evolutionary biologist John Endler began studying Trinidad's wild guppies in the 1970s, he was struck by the wide color variation among guppies from different streams or even among guppies living in different parts of the same stream. Explore the pools of Trinidad in the "Sex and the Single Guppy" Web activity to learn how sexual selection interacts with natural selection. As you do the simulation, take notes on the population and environment you set up and record your results.

 Screen grab of the Sex and the Single Guppy web activity, showing a group of guppies in water.

Sex and the Single Guppy

When you have completed the simulation, use your notes to answer these questions:


What hypotheses did you test?


What conclusions did you reach based on your simulation results?


How do sexual selection and natural selection interact in this guppy simulation? In nature?


What other questions did the guppy simulation raise? How might you test for answers?



Facilitator Note 3


Next: Explain Part B: Speciation

Videos Web Activities Site Guide About the Project FAQ Glossary Site Map Feedback Help Shop