Darwin’s Theory of Evolution

1. Darwin’s Theory of Evolution By means of Natural Selection

2. Voyage of the HMS Beagle The individual who contributed more to our understanding of evolution than anyone was Charles Darwin.

3. Voyage of the HMS Beagle Shortly after completing his college studies, Darwin joined the crew of the H.M.S. Beagle. In 1831, he set sail from England for a voyage around the world.

4. Voyage of the HMS Beagle Darwin made numerous observations and collected evidence that led him to propose a revolutionary hypothesis about the way life changes over time. That hypothesis, now supported by a huge body of evidence, has become THE THEORY OF EVOLUTION. K:\High School\Campuses\CRHS\Science\Academic Biology 2009-10\Academic Biology Units\4th Six Weeks\Unit 10 Evolution & Classification\Video Clips\A_Brief_Biography_of_Charles_Darwin_.asf

5. Evolution, or change over time, is the process by which modern organisms have descended from ancient organisms. • A scientific theory is a well-supported testable explanation of phenomena that have occurred in the natural world.

7. The Galápagos Islands  • Of all the Beagle's ports of call, the one that influenced Darwin the most was a group of small islands located 1000 km west of South America. These are the Galápagos Islands.

8. Darwin noted that although they were close together, the islands had very different climates. • The smallest, lowest islands were hot, dry, and nearly barren.

9. Espanola Island, for example, had sparse vegetation.

10. The higher islands had greater rainfall and a different assortment of plants and animals. IsabelaIsland had rich vegetation.

11. Darwin was fascinated in particular by the land tortoises in the Galápagos. He learned that the giant tortoises varied in predictable ways from one island to another. The shape of a tortoise's shell could be used to identify which island a particular tortoise inhabited.

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15. K:\High School\Campuses\CRHS\Science\Academic Biology 2009-10\Academic Biology Units\4th Six Weeks\Unit 10 Evolution & Classification\Video Clips\speciation.asf

16. Ideas That Shaped Darwin's Thinking

17. Ideas That Shaped Darwin's Thinking

18. Ideas That Shaped Darwin's Thinking Hutton and Lyell helped scientists recognize that the earth is many millions of years old, and the processes that changed Earth in the past are the same processes that operate in the present.

19. This understanding of geology influenced Darwin in two ways.

21. Ideas That Shaped Darwin's Thinking The French naturalist Jean-Baptiste Lamarck was among the first scientists to recognize that living things have changed over time.

22. Lamarck proposed that by selective use ordisuse of organs, organisms acquired or lost certain traits during their lifetime.

23. For example, a giraffe could, over a lifetime of straining to reach high branches, develop an elongated neck (use).

24. Conversely, the wings of penguins would be smaller than those of other birds because penguins do not use them to fly (disuse).

31. Ideas That Shaped Darwin's Thinking Another important influence on Darwin came from the English economist ThomasMalthus.

33. Darwin applied this reasoning to plants and animals in the natural world. A mature maple tree can produce thousands of seeds in a single summer, and one oyster can produce millions of eggs each year.

34. The overwhelming majority of a species' offspring die. Further, only a few of those offspring that survive succeed in reproducing. What causes the death of so many individuals?

36. Ideas That Shaped Darwin's Thinking

37. Darwin Presents His Case Darwin returned to England in 1836, However, he did not publish his work, On the Origin of Species until 1859.

39. One of Darwin's most important insights was that members of each species vary from one another. Darwin argued that this variation mattered.

40. For example, some plants in a species bear larger fruit than others. Some cows give more milk than others. Plant and animal breeders have long used heritable variation to improve crops and livestock. Darwin termed this process artificial selection. In artificial selection, nature provided the variation, and humans selected those variations that they found useful.

42. The Struggle for Existence  The struggle for existence means that members of each species compete regularly to obtain food, living space, and other necessities of life. Darwin was convinced that a process like artificial selection worked in nature.

43. In this struggle, the predators that are faster or have a particular way of ensnaring other organisms can catch more prey. The prey that are faster, better camouflaged, or better protected can avoid being caught.

44. Survival of the Fittest  Darwin called the ability of an individual to survive and reproduce in its specific environment fitness. Darwin proposed that fitness is the result of adaptations.

45. An adaptation is any inherited characteristic that increases an organism's chance of survival. Successful adaptations enable organisms to become better suited to their environment and thus better able to survive and reproduce. Darwin called this process survival of the fittest

46. Because of its similarities to artificial selection, Darwin referred to the survival of the fittest as natural selection. Over time, natural selection results in changes in the inherited characteristics of a population. K:\High School\Campuses\CRHS\Science\Academic Biology 2009-10\Academic Biology Units\4th Six Weeks\Unit 10 Evolution & Classification\Video Clips\Nat Selection Mutation Adaptation.asf

48. Descent With Modification 

49. Summary of Darwin's Theory Darwin's theory of evolution can be summarized as follows: