Chapters 16 - 17: Darwin’s Theory of Evolution & Population Genetics

1. Chapters 16 - 17: Darwin’s Theory of Evolution & Population Genetics

7. Human, Chimp, Gorilla, Orangutan

9. What is Evolution? • Evolution is the gradual change in a species over time. • Modern organisms have descended from ancient organisms

10. History of Charles Darwin • Born: 2/12/1809 – 1882 • Very wealthy (mom’s side were Wedgewoods) Married 1st cousin • Studied medicine & theology but ended up being a naturalist. • Took a 5 year voyage on the HMS Beagle in 1831 (England to SA), around SA’s Cape Horn to the Galapagos Islands, below Australia and the Cape of Good Horn, back to SA and then to England)

12. Darwin’s grave in Westminster Abbey, London

13. The Beagle's Voyage Galapagos Is

14. The Galapagos Islands • 1000km west of S. America – Volcanic chain of Islands • Low islands were hot, dry & basically void of life. Higher elevations islands had > rainfall & therefore more variety of life • Unique land tortoises & marine iguana. Species differed from island to island, especially the tortoise shells & the “little brown birds” later determined to be finches

15. Darwin was extremely seasick throughout the voyage! • Contracted Chagas disease (protozoan) • Published book: On the Origin of Species in 1858

16. What got Darwin questioning the modern day concepts? • Collected plant and animal specimens on his voyage. Made numerous notes & drawings • Noticed a pattern of diversity amongst organisms – observed 68 different beetle species/day in Brazilian forest • Found flightless rhea in grasslands of S. America and ostriches in Africa. In Australia, there were emus in the grasslands. See anything in common? • Collected fossils and noticed that they resembled organisms alive today & others totally different than of those today.

17. Darwin notices that different, related species occupying similar habitat tended to look more similar or have many physical traits in common. • Emu, ostrich and rhea • He also noticed that related species occupying different habitats took on physical traits that seemed to make them fit in better with the habitat. • Tortoises • He could even tell which island the species came from by their shells.

18. Galapagos Tortoises Isabela Tortoise Eats vegetation close to the ground Hood Island Tortoise Vegetation is all up higher and sparse.

19. Does this look like anything from today? Archaeopteryx

20. Do these resemble anything alive today?Darwin takes notice of this

21. Could these all have come from one common ancestor and changed to fit into the particular environment of the island?

22. Ideas that Shaped Darwin’s Thinking • Hutton and Lyell – Geologist who felt that the earth was millions of yrs old (actually 4.6 billion) & that the earth has changed over its history to its present form • Earth is in layers that formed very slowly & has been altered over time by forces of nature.

23. Using Lyell’s Principles of Geology: • Felt that if the earth could change, so could its living inhabitants • It would take a very long time for organisms to change & since the earth is “millions” of years old (according to the time), there was plenty of time for this change • The earth is actually ~ 4.6 billion years old

24. Pages from Darwin’s journals

25. Jean – Baptiste de Lamarck (1801) • Believe in decent from common ancestry • Proposed that through selective use and disuse of organs, organisms acquired or lost certain traits during their lifetime. • By passing on these acquiredtraits to their offspring, a species can change over time.

26. Lamarck’s theory • Tendency towards perfection – Always changing to help them live more successfully. Desire to change The giraffes had eaten all the food on the lower branches & needed to get to the food up higher. The giraffe got its long neck by stretching it to get to the higher up leaves.

27. Use and Disuse – Organisms can alter their shape or size by using their body in new ways. Stretch that neck and those legs giraffes! 3. Inheritance of Acquired traits – traits in an organism’s lifetime could be passed onto their offspring. Those giraffes that stretched their necks and lengthened their legs will have offspring with long necks and legs

28. Thomas Malthus (1798) • Reproduction rate is faster than death rate. • Population growth is an exponential growth. • Sooner or later, there will not be enough food or space • War, famine & disease are the only forces to keep the population size from outdistancing food supply • If organisms produce far more offspring than can survive, what factors determine which ones survive and reproduce?

29. Point of Crisis Resources Increase in food supply is arithmetic while population increase in exponential. Crisis occurs when the population outdistances the available resources

30. Fossil Evidence • Fossil evidence shows that living things have been evolving on earth for millions of years. • Also showed that the geographic distribution of organisms lines up with the movement of the earth’s crusts & that newer (more modern) forms of fossilized organisms are found in the upper layers of rock

31. Homologous Structures • Structures that have similar form but different functions • Bones of our forearm, the front flipper of a whale, the wing of a bat & legs of a turtle. • Could all four limbed animals with backbones have descended with modification from a common ancestors? Analogous Structureshave same function but different structure. Occupies same niche (butterfly and bat wings)

32. What about structures that are no longer in use? • Vestigial organs • Structures which no longer have a function to the organism. • Our appendix, hair, coccyx, wisdom teeth These vestiges had a useful function at one time but since they are no longer of an adaptive use to the oganisms, they have become reduced with time.

33. Embryological & Biochemical Evidence • Not used by Darwin but in use today! 1. Early stages of development of many animals with backbones are very similar Children of Evolution video • Using modern biotechnology, examine the biochemicals, genes & DNA of organisms. Similar organisms will have more in common. The more closely related they are, the more recently they descended from a common ancestor Amino Acid Sequencing evidence

34. Darwin Puts it all Together!!

35. Darwin’s Theory of Evolution ***22 years after Beagle voyage, writes On the Origin of Species • Natural Variations Inherited variations/adaptations exists between organisms w/I a population 2. Malthusian Doctrine Organisms in nature produce more offspring than can survive • Competition for limited resources among members of a species • Struggle for existence Due to natural variations, there exists advantages & disadvantages among members of a species

36. Survival of the fittest & Natural Selection Those members of the population w/ the best natural variations (adaptations), will survive & pass these traits onto their offspring. Those without the variations will not survive “Fitness is measured in the # of grandchildren one has” Nature selects which variations are the best suited to the environment. • Species change over time Due to natural selection. New forms arise & other disappear Also known a Differential Reproduction

37. Natural Selection There is natural selection. Some are selected out, some aren’t There is variation in traits There is heredity. Survivors reproduce End result. Possible speciation

38. Natural Selection Peppered Moth Simulation

39. Common Descent Species alive today descended with modifications from past species No one ever said that we were monkeys though. We primates descended from a common ancestors • Adaptive radiation Darwin’s Finches – small brown birds Occurs when a species or group of species evolves into many new species to fit into a particular niche. Reduces competition and increases survival

40. Adaptive radiation • Some evolved a shorter, fat beak for cracking large seeds, some have a smaller, pointier beak for opening small seed, while others have a long pointed beak for getting into creases in bark for insects • Fill open niches depending on your particular adaptation. If everyone does the same thing, there will be too much competition and only the fittest will survive

41. Adaptive RadiationDarwin’s Finchesillustration

42. Natural Selection Lab Gene pool All the genes from a single population combined together 50:50 with our lab Relative gene frequency Number of times a particular allele occurs in the gene pool. 0.5: 0.5 at start of lab Changed through generations Small Lima bean gene frequency increased Large Lima bean gene frequency decreased

43. If you continued this lab through other generations, what do you think would have happened to the gene frequencies? • Small Lima bean’s gene frequency would continue to go up while the large bean’s would decrease over time. • Eventually, there wouldn’t be many large beans so the small limas would be easier to pick off (that’s all there is now). • The gene frequencies would then change again. • If all the larges though were picked out, they would become extinct

44. Natural Selection Lab

45. 1.0 Simulating Natural Selection Key: ___ = Small Lima ___ = Large Lima .5 Bean Frequency 0 2 4 5 3 6 1 1 Generation

46. Divergent Evolutionlecture • Two or more related populations become more and more dissimilar. (as seen in homologous structures) • Darwin’s finches, iguana & tortoises • Results inspeciation – formation of a new species • Adaptive radiation

47. What very important information was Darwin missing in his theory of evolution in 1836? • What was the source of variation? Mendel’s work not published until 1900 • How are these variations passed form generation to generation? 1910 – Scientists combined the two men’s concepts. Today, a combination of genetics, molecular biology & evolutionary theory work together to explain variations & natural selection

48. Sources of Genetic Variation • Mutation – may increase, decrease or no effect on the organism’s fitness • Gene shuffling – luck of the draw. During meiosis & fertilization, genes get shuffled, much like cards in a deck (Genetic recombination) • Crossing over – new combinations result during prophase I of meiosis

49. Sexual Reproduction • Provides new genes w/ each fertilization • This does not change the gene frequency though

50. Among the Amish population, polydactylism is very common. Why? Is it a favorable trait for working on farms & doing more “hand work”? Genetic Drift In a small population (isolated one), a particular allele may occur more frequently even though it doesn’t lead to the fitness of the population, it is just there Animation Sicilian family An Australian Aboriginal cave painting