SESSION 4

Engage

Explore

Part A: 

Natural Selection

Part B: 

Adaptations

Part C: 

Genetic Variation By Mutation

Part D: 

Genetic Variation By Recombination

Part E: 

Nonselective Mechanisms

Explain

Elaborate

Evaluate

Resources

Facilitator Notes

SESSION 4: What Are the Processes for Evolution?

Explore Part B: Adaptations

The process of natural selection favors individuals within a population that have genetic variations that adapt them to their environment. Since these individuals are more likely to survive and reproduce, the future population will include more of these offspring with the selected-for traits, or adaptations. Adaptations may result from cumulative small changes. They may be simple changes such as beak depth or complex adaptations such as the eye. Adaptations may be structural or behavioral, but each must have a genetic basis. Acquired structures, such as muscles built up by strength training, or behaviors, such as the use of tools, are not heritable.

		Look at these examples of adaptations of animals and plants: •  Evolution Show One video segment "Evolution of Camouflage" •    Mimicry: The Orchid and the Bee •  How the Woodpecker Avoids a Headache For information about the adaptations of blue whales see the Discovery School Web site.
Evolution of Camouflage View in: QuickTime | RealPlayer

Choose one species you just learned about. What environmental factors might exert the selective pressures that favor its particular adaptations? How might the concept of "fit enough" relate to these adaptations?

Natural selection does not lead to perfection, only adaptation. One of the best indicators that evolution does not result in "perfect adaptations" is the existence of relatively imperfect contrivances, structures modified and used for functions quite different from the ancestral functions of those same structures. To learn more about adaptations and contrivances, do the activity Contrivances: Orchids and the Panda's Thumb at the ENSI Web site.

		For an interesting article on adaptive compromises in humans, see Olshansky, Carnes, and Butler, "If Humans Were Built to Last," Scientific American. (March, 2001 pp. 50-55)

Next: Explore Part C: Genetic Variation By Mutation