Natural Selection

1. Natural Selection Darwin’s Theory – read aloud

2. Introduction • Follow Darwin’s voyage, using the map in figure 1

3. Darwin’s Observations • In Darwin’s day, most people believed that all living things were created at the same time and that they never changed. Give two reasons why Darwin questioned this belief. After reading about Darwin’s observations, discuss this question.

4. Species • a group of similar organisms that can mate with each other and produce fertile offspring.

5. Galapagos Organisms • Look at figure 2. In what other ways are the iguanas different? • What did Darwin hypothesize after making his observations? • Darwin believed that a small number of plants and animals came to the Galapagos Islands from the mainland.

6. Darwin’s finches • Using figure 3, identify specific differences in the finches’ beaks.

7. Evolution • The gradual change in a species over time.

8. Natural selection • the process by which individuals that are betteradapted to their environments are more likely to survive.

9. Factors that affect natural selection • overproduction – most species produce more offspring then will survive. • Example:

10. Factors that affect natural selection(continued) • variation – any differencebetweenindividuals of the same species. • Example:

11. Factors that affect natural selection(continued) • competition – members of a species must compete for food and other resources in order to survive.

12. Figure 6 • What are some variations that sea turtles might show? • How might sea turtles compete? • What is an example of overproduction by sea turtles? • How does Fig 6 illustrate the process of natural selection?

13. Conclusion • Darwin proposed that, over a long time, natural selection can lead to change. Helpful variations may gradually accumulate in a species, while unfavorable ones may disappear. • Only traits that are inherited, or controlled by genes, can be acted upon by natural selection.