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Online Course for Teachers: Teaching Evolution

About this Course 

SESSION 4

SESSION 4: What Are the Processes for Evolution?

Facilitator Notes for SESSION 4

Engage Part A
Note 1: Conduct a discussion after participants have read the Life's Grand Design Web essay.

Explore Part C
Note 2: An important concept is that natural selection acts on the phenotype of traits, but at the same time may reduce the frequency of certain genes in future populations. Hidden variations that are not expressed in the phenotype cannot be selected against. Deleterious genes for traits such as Tay-Sachs and Huntington's disease may remain in the gene pool if they do not express themselves until after individuals have reached reproductive maturity and begun having offspring. "Fitness" means reproductive fitness; as long as an individual is able to reproduce, its genes will remain in the gene pool of the population.

Explain Part A
Note 3: After participants have completed the simulation, ask them to work in teams to discuss: the hypotheses they tested; how they tested them (what population they set up for guppies and predators, and the environment they used); their results; and the conclusion they reached based on their results. Have participants compare hypotheses and make a group list of conclusions and their supporting evidence. Have each team present their conclusions and evidence to the class.

Explain Part B
Note 4: The biological definition of species is a population that interbreeds and produces fertile offspring. When organisms live in different geographical areas in the wild, it may be difficult to determine whether they are the same species since you cannot determine whether they would interbreed if they were in the same area. Reproductive isolation that leads to speciation may be geographical, ecological, temporal, behavioral, mechanical, gametic, or due to hybrid inviability or hybrid sterility. For more information on reproductive isolation, have participants look at the suggested links.

Evaluate Part A
Note 5: Examples that can be used to explain the key statements about natural selection include:
1. Finches in Grant's study
2. and 3. Sickle cell anemia genes in West Africa
4. Pekinese dogs evolved from wolves
5. Human eye
6. Bacteria that are antibiotic resistant are not as advanced as humans but are very successful organisms.

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