Chapter 16: The Theory of Evolution

1. Chapter 16: The Theory of Evolution

2. 1. What is Evolution? • Evolution is the process by which species change over time. • 2. Charles Darwin is the English naturalist who studied the diversity of life and proposed a broad explanation for evolution • 3. A theory is a broad explanation that has been scientifically tested and supported

3. Charles Darwin (1809-1882) • An English scientist who formed ideas that are now the basis of modern evolutionary theory • When he was 21, Darwin took an apprenticeship on a 5-year scientific voyage on the HMS Beagle • He was the unofficial naturalist on the ship collecting many specimens along the way

4. Darwin’s voyage (Page 277) • The Galapagos Islands, off the coast of Ecuador, became the focal point in Darwin’s observations Darwin's journey

5. Darwin’s Observations • 6. While in South America, he collected fossils of giant, extinct armadillos. • He noticed that these fossils were similar, but not identical, to the living armadillos in the area

6. 7. He collected several different species of birds called finches. • Each of the finches are very similar, but differences can be seen in the size and shape of the beak for the different foods they eat

7. 8. Darwin proposed that the finches he collected descended from one ancestral finch species that migrated from South America. • The descendant finches were modified over time as different groups survived by eating different types of food. • Darwin called such change descent with modification

9. 9. In 1859, Darwin published his theories and ideas in the book On the Origin of Species by Natural Selection, 20 years after his voyage

10. 10. Artificial selection • Darwin also conducted many breeding experiments with pigeons and found that organisms with specific traits could be crossed to result in offspring that had those selected traits • Humans are the selecting agent in artificial selection

11. 11. The ideas of Lamarck, Malthus, Cuvier, and Lyell were important to Darwin’s work. • 12. Lamarck proposed that changes due to use or disuse of a characteristic would be passed on to offspring • Ex. The necks of giraffes

13. 13. Thomas Malthus observed that human populations were increasing faster than the food supply • Eventually, people would compete for resources as populations increased in size • Darwin concluded that populations are limited by their environment

14. 14. Cuvier did not see species as changing gradually over time. He thought that changes in the past must have occurred suddenly. • 15. From Lyell’s book, Darwin thought that Earth’s history was long enough for changes to happen gradually over time.

15. Section 16-2: Applying Darwin’s Ideas • 16. Darwin formed a key idea: Individuals that have traits that better suit their environment are more likely to survive. • The four steps of Darwin’s theory of Evolution are: • Overproduction • Variation • Selection • Adaptation

16. Four main principles to the theory of natural selection • Overproduction • Every population is capable of producing more offspring than can possibly survive. • Variation • Variation exists within every population. Much of this variation is in the form of inherited traits. • Selection • Some individuals leave more offspring than others do because they survive longer • Adaptation • Over time, those traits that improve survival and reproduction will become more common.

18. 18. An adaptation is an inherited trait that is present in a population because the trait helps individuals survive and reproduce in a given environment.  • 19. In order for groups of organisms to have adapted over time, populations must have evolved rather than individuals.

19. 20. Alfred Russel Wallace developed a theory similar to Charles Darwin’s, causing Charles to publish his book, On the Origin of Species by means of Natural Selection.

20. Evidence for Evolution • Fossil Record • Biogeography • Embryology • Body Structures (Anatomy) • Biochemistry

21. Fossil Record • Fossils of animals show a pattern of development from early ancestors to their modern descendants • “Intermediate” (missing links) species show how organisms evolved new adaptations

24. Problems with fossils • It is difficult to find fossils of soft-bodied organisms with no hard parts that can be left behind • Organisms decay at different rates and may not leave any traces

25. Biogeography • 24. Biogeography is the study of the locations of organisms around the world • Similar environments shape the evolution of organisms in similar ways

26. Embryology • The study of the development of embryos • Most embryos look very similar and have gill slits and tails. • This suggests a common ancestor.

27. Homologous Structures • Structural features with a common evolutionary origin

28. Analogous Structures • Structures that are similar in function but do not have a common evolutionary origin • There is no evolutionary tie between an insect and a bird and most likely adapted the ability to fly separately

29. Homologous structures versus Analogous structures

30. Biochemistry • A comparison of DNA or amino-acid sequences shows that some species are more genetically similar than others. • These comparisons, like those in anatomy, are evidence of hereditary relationships among the species.

31. Section 16-3: Beyond Darwinian Theory • 27. Speciation is the formation of new species, can be seen as a process of genetic change or as a pattern of change in the form of organisms. • 28. Species is a group of organisms that are closely related and that can mate to produce fertile offspring

32. 29. Migration is the movement of individuals into, out of, or between populations • 30. Convergent Evolution • If evolution is strongly directed by the environment, then species living in similar environments should evolve similar adaptations. • 31. Coevolution • Organisms are part of one other’s environment, so they can affect one another’s evolution. Species that live in close contact often have clear adaptations to one another’s existence • 32. Extinction is when all members of a lineage die off or simply fail to reproduce

33. Chapter 17

34. How do population’s genes change over time? • Changes occur when the collection of all the alleles in a population (gene pool) is not in genetic equilibrium. (frequency of alleles stays the same) • Allelic frequency—the percentage of any specific allele in the gene pool • Ex. Tall phenotype (T), short phenotype (t) • Genetic equilibrium would be 0.75 or 75% T and 0.25 (25%) t for all its generations • Evolution of a population will occur when those percentages are disrupted

35. Conditions necessary for stable allele frequency • Large population size • Random mating • No mutation in the gene of interest • No large-scale migration into or out of the population • No selective pressure

36. Sources of change • Mutation, genetic drift, and gene flow may significantly affect the evolution of small and isolated gene pools. • Natural selection causes changes in both large and small gene pools

37. Sources of change cont. • Mutations arise by chance and can be bad or good • Generally bad mutations will be eliminated before they are spread throughout the population • Sometimes good mutations will be of some use to an organism and become part of the population’s gene pool

38. Sources of change cont. • Genetic drift—the alteration of allelic frequencies by chance events • Ex. Natural disaster, earthquake, drought, flood, mutation, etc… • Real example: Polydactyly in Amish population (page 414) • One of 30 founding families carried the recessive allele for polydactyly resulting in a higher frequency of that mutated allele • 1 in 14 Amish people have the allele • In US, 1 in 1,000 have the allele Polydactyly

39. Sources of change cont. • Gene flow—migrating individuals move from 1 population to another • Genes are reduced in a gene pool when someone leaves and genes are increased when someone comes into a gene pool • Ex. Pollen seeds blowing into neighboring plants

40. Types of Natural Selection • Stabilizing selection • Directional selection • Disruptive selection

41. Stabilizing selection • Average individuals are favored • Result: variation is reduced in a population • Ex. Small spiders have a harder time of finding food; large spiders are easily targeted by predators http://www.kmitl.ac.th/agritech/nutthakorn/04090035_2202/multiweb/environ/images/be_13.gif

42. Directional Selection • One of the extreme variations is favored • Result: rapid evolution • Ex. After drought, hard seeds are left to birds that have tougher beaks that can crack open the seeds http://www.detectingdesign.com/images/NaturalSelection/natura2.jpg

43. Disruptive Selection • Individuals with either extreme are favored • Results: evolution of two species • Ex. Dark and light colored limpets

44. http://abyss.uoregon.edu/~js/images/selection_change.gif

45. Evolution of a Species • Species—group of organisms that look alike and can breed together to form fertile offspring • Speciation—members of similar populations no longer interbreed to produce fertile offspring

46. Mechanisms that prevent interbreeding • Geographic isolation—physical barriers divide a population • Ex. Sea-level changes that form islands, lava flows and divides an area, river cuts through an area • Reproductive isolation—when interbreeding organisms can no longer mate and produce fertile offspring • Ex. Female Choice, different times for reproduction

47. Mechanisms that prevent interbreeding • Polyploidy—any species with more than one set of chromosomes • Is a result of mistakes made during mitosis and meiosis • Species cannot mate with each other if they have different numbers of chromosomes • Ex. Wheat, corn, bananas, strawberries, and apples are originated by polyploidy

48. Rates of Evolution • Gradualism—the idea that species originate through a gradual change of adaptations • Occurs over a long period of time and includes intermediate species • There is fossil evidence that supports this (example on page 408)

49. Rates of Evolution • Punctuated Equilibrium—hypothesis that says speciation occurs in rapid bursts along with periods of genetic equilibrium in between • Change occurs in a short period of time with no intermediate species • Also supported with fossil evidence (page 419) • Both result in speciation

50. Rates of Evolution cont.