Darwin’s Theory

1. Darwin’s Theory Chapter 6 Section 1

2. Darwin’s Observations • Background Info: Charles Darwin • Set sail on the HMS Beagle • 5 year trip around the world • Naturalist: a person who studies the natural world • He wanted to learn about the living things he saw on the voyage • He made many stops along the coast of South America then to the Galapagos islands His important observations included • Diversity of living things • The remains of ancient organisms • The characteristics of organisms on the Galapagos Islands

3. Diversity • Darwin was amazed by the tremendous diversity of living things • Scientists have observed 1.7 million species of organisms on Earth • Species • A groups of similar organisms that can mate with each other and produce fertile offspring

4. Fossils • Fossil • Preserved remains or traces of an organism that lived in the past

5. Galapagos Organisms • Darwin observed the greatest diversity of organisms on the Galapagos Islands Comparisons to South American Organisms • Many Galapagos organisms were similar to organisms on mainland South America • Darwin hypothesized that the ancestors of Galapagos animals and plants came from mainland South America • Blown out to sea during a storm? • Set adrift on a fallen log?

6. Comparisons Among the Galapagos Islands • Darwin traveled from island to island • He noticed many differences among the organisms • Dome-shaped tortoise shells • Saddle-shaped tortoise shells

7. Adaptations • The finches Darwin saw on the islands were noticeably different • Most obvious difference was the size and shape of their beaks • Finches that ate insects: narrow, needle-like beaks • Finches that ate seeds: strong, wide beaks • Adaptation • A trait that helps an organism survive and reproduce

8. Evolution • Darwin reasoned that plants or animals that arrived on the Galapagos Islands faced conditions different from mainland South America • He hypothesized the species gradually changed over time • Organisms became better adapted to the new conditions • Evolution • The gradual change in a species over time • Scientific Theory • A well-tested concept that explains a wide range of observations • Darwin’s Theory of Evolution

9. Selective Breeding • Breeding animals by only allowing certain animals to mate • Example • Race horses are selectively bred to obtain the trait of speed • Darwin bred pigeons with ONLY large, fan-shaped tail feathers

10. Natural Selection • Book by Charles Darwin, The Origin of Species • Explanation of how evolution COULD occur in nature • Natural Selection • The process by which individuals that are better adapted to their environment are more likely to survive and reproduce than other member of the same species • Factors that affect the process of natural selection • Overproduction • Competition • Variations

11. Overproduction • Effect cause by species producing more offspring than can survive • Example • Insects

12. Variations • Differences between individuals of the same species • Example • Different foods eaten by the same species of insects

14. Competition • Effect caused by limited food and other resources • Example • Direct (physical fights) • Indirect (not finding enough food to eat)

16. Environmental Change • Environment can affect an organism’s ability to survive • This can then lead to selection • Monkey Flowers • Can’t grow in soil with high concentration of copper

17. Genes and Natural Selection • Darwin could not explain what caused variations or how they were passed on • Scientists later learned, variations can result from mutation and the shuffling of alleles during meiosis • Genes are passed from parents to offspring • Only traits inherited, or controlled by genes can be acted upon by natural selection