Darwin's Theory of Evolution: Evidence and Concepts

1. Chapter 16: Darwin’s Theory of Evolution Section 16-3: Darwin Presents His Case

2. Darwin’s Ideas • Darwin wanted to gather evidence before making his ideas public • Waited 20 years after returning • Published On the Origin of Species in 1858

3. The Struggle for Existence • More individuals are produced than survive • Members of a population compete for food, living space, other limited necessities • Malthus

4. Variation and Adaptation • Individuals have natural variation in heritable traits, some better suited for the environment • Any heritable characteristic that increases an organism’s ability to survive and reproduce in its environment is an adaptation • Adaptations can be morphological, physiological, behavioral

5. Survival of the Fittest • An organism’s fitness as how well it can survive and reproduce in its environment • Adaptations increase fitness • Differences in fitness (survival rate and reproduction) called survival of the fittest • Survival = passing adaptations to next generation

6. Natural Selection • The process by which organisms with variations most suited to their local environment survive and leave more offspring • Mechanism of evolution • Environment influences fitness • Populations continue to change as they become better adapted and their environment changes • Acts only on inherited traits

7. Natural Selection

8. Natural Selection

9. Natural Selection

10. Natural Selection

11. Natural Selection • Does not make organisms “better” • Does not move in a fixed direction • Extinction can occur if conditions change faster than species can adapt

12. Common Descent • Over many generations adaptation caused successful species to evolve into new species • Descent with modification from common ancestors • Life has been on Earth a long time • Evidence in fossil record • Explains diversity of life