Chapter 5: Changes over Time Section 1: Darwin’s Theory Who was Charles Darwin?

1. Chapter 5: Changes over TimeSection 1: Darwin’s TheoryWho was Charles Darwin? • A naturalist (a person who studies the natural world) • His observations of plants and animals led him to develop the theory of evolution by naturalselection

2. Darwin observed many species during his voyage on the HMS Beagle, what is a species? • A group of similar organisms that can mate with each other and produce fertile offspring

3. What did Darwin notice on the Galapagos Islands? • Many of the plants and animals on the Galapagos were similar to organisms on mainland South America • However, there were also important differences between the organisms on the islands and those on the mainland

4. What did Darwin conclude led to the differences between species? • After studying the different finches on the Galapagos Islands Darwin concluded that their different beak shape was due to an adaptation • Adaptation – A trait that helps an organism survive and reproduce

5. What did Darwin start to believe was occurring amongst the different species? • Darwin thought the species gradually changed over many generations and became better adapted to the new conditions • Evolution – the gradual change in a species over time

6. Why was Darwin’s idea considered a scientific theory? • It was a well-tested concept that explains a wide range of observations

7. Darwin and Alfred Russell eventually proposed an explanation for how evolution occurs in a book called what? • The Origin of Species • This book explained that evolution occurs by means of naturalselection

8. What is Natural Selection? • The process by which individuals that are better adapted to their environment are more likely to survive and reproduce than other members of the same species

9. What are the factors that affect the process of natural selection? • Overproduction • Competition • Variations • Selection

10. How does overproduction affect natural selection? • So many species are produced that there are not enough resources (food, water, and living space)

11. How does competition affect natural selection? • Since food and other resources are limited, the offspring must compete in order to survive

12. How do Variations affect natural selection? • Any difference between individuals of the same species is called a variation • Some variations of a species may provide an advantage over the other members of the species without the variation

13. How does the environment select which organisms survive? • Individuals that are better adapted to their environment are more likely to survive and reproduce passing on the helpful trait to the next generation • In effect, The environment “selects” those organisms with helpful traits to be the parents of the next generation

14. How is natural selection related to evolution? • Over a long period of time, natural selection can lead to evolution • Helpful variations gradually accumulate in a species, while unfavorable ones disappear

15. What role do genes “play” in evolution? • Darwin did not know anything about genes or mutations so he could not explain what caused the variations or how they were passed on • Only traits that are inherited, or controlled by genes, can be acted upon by natural selection

16. Evolution Controversy Video Clips • http://www.cbsnews.com/video/watch/?id=657122n

17. Section 2: Evidence of EvolutionWhat evidence supports the theory of evolution? • Fossils • Patterns of Early Development • Similar Body Structures

18. What are homologous structures? • Body parts that are structurally similar in related species; provide evidence that the structures were inherited from a common ancestor

19. Do whales and humans share an ancestor? • Scientists have recently found fossils of ancient whale-like creatures that show that they had legs and walked on land

20. How do scientists infer evolutionary relationships among organisms? • Similarities in DNA • Protein Structure • Fossils • Early Development • Body Structure

21. What is one thing scientists use to show how organisms are related? • A branching tree – a diagram that shows how scientists think different groups of organisms are related

22. How do new species form? • Geographic isolation – when some members of a species become cut off from the rest of the species • Once members are isolated they can no longer mate with members of the rest of the species

23. Section 3: The Fossil RecordWhat is a fossil? • The preserved remains or traces of an organism that lived in the past • Can be formed from a bone, tooth, shell, or other part of an organism

24. Prehistoric Snake • http://www.guardian.co.uk/science/2009/feb/04/snake-giant-fossil-titanoboa

25. How do fossils form? • Most fossils form when organisms that die become buried in sediments (particles of soil and rock)

26. What are petrified fossils? • A fossil formed when minerals replace all or part of an organism

27. How are mold and casts related to fossils? • Mold – A type of fossil formed when shell or other hard part of an organism dissolves, leaving an empty space in the shape of the part • Cast – A type of fossil that forms when a mold becomes filled in with minerals that then harden

28. Wooly Mammoth • http://www.cbsnews.com/video/watch/?id=4622301n

29. How else are remains preserved? • Entire organisms, such as the huge elephant-like mammoths have been preserved in ice • Bones and teeth have been preserved in tarpits • Insects and other organisms can become stuck in sticky sap. The sap then hardens forming amber

30. How do you determine a fossil’s age? • Relative dating • Radioactive dating

31. What is relative dating? • A technique used to determine which of two fossils is older • Can only be used when the rock layers have been preserved in their original sequence

32. What is radioactive dating? • A technique used to determine the actual age of a fossil • The rocks that fossils are found near contain radioactive elements, scientists use these elements to determine decay (half-life)

33. What are radioactive elements? • Unstable elements that decay, or break down, into different elements

34. What is half-life? • The time it takes for half of the atoms in a sample to decay • Scientists can compare the amount of a radioactive element in a sample to the amount of the element into which it breaks down

35. What do fossils reveal? • Fossils help scientists piece together information about Earth’s past • The millions of fossils that scientists have collected are called the fossil record

36. When is a species extinct? • A species is extinct if no members of that species are still alive

37. What else does the fossil record provide? • Clues about how and when new groups of organisms evolved • The first animals (invertebrates) appeared in the sea about 540 million years ago • About 500 million years ago, fishes evolved (the first vertebrates) • 410 million years ago the first plants evolved

38. What is the Geological Time Scale? • Scientist have used the ages of rocks and fossils to create a “calendar” of Earth’s history that spans 4.6 billion years • Scientists have divided this large time period into smaller units called eras and periods sometimes called the Geologic Time Scale

39. How is the Geological Time Scale Divided? • Pre-cambrian • Paleozoic Era • Mesozoic Era • Cenozoic Era

40. What is the largest span of time in the Geologic Time Scale? • Precambrian Time • Covers the first 4 billion years of Earth’s history – very few fossils exist from this time period

41. What are the theories on how fast does Evolution Occur? • Gradualism – Evolution occurs slowly but steadily (Darwin) • Punctuated Equilibria – Species evolve during short periods of rapid change