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 B: Speciation

Variation in populations and natural selection alone cannot explain the great diversity of species on the earth. Though it was the title of his book, Darwin didn't really explain the origin of species. His theory of natural selection explained how populations became better adapted to their environments, but not how new species developed.

Screen grab from the An Origin of Species Web activity, showing a bird perched on a branch.

To explore how a single species can diversify into many species, spend some time with the Web activity, An Origin of Species.

An Origin of Species

Jot down the answers to these questions:


What is a biological species?


How can one species, such as the hypothetical pollenpeeper, adaptively radiate into different species?


What conditions contribute to speciation in a localized area?


In what different ways might species become reproductively isolated (unable to reproduce fertile offspring)?



Now compare your answers to this description of speciation.


For more information on reproductive isolation, see "Isolating Mechanisms" and look at the University College London Department of Biology Web site.

 Image of a cicada.

Isolating Mechanisms


Facilitator Note 4


Next: Elaborate Part A: Speciation without Geographic Isolation

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