1. Chapter 13Darwin and EvolutionLecture Outline See PowerPoint Image Slidesfor all figures and tables pre-inserted intoPowerPoint without notes.To run the animations you must be in Slideshow View. Use thebuttons on the animation to play, pause, and turn audio/text on oroff. Please note: once you have used any of the animationfunctions (such as Play or Pause), you must first click in the whitebackground before you advance the next slide.Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. Darwin Developed a Natural Selection Hypothesis 13-2 3. Darwin made a trip around the worldGeorges Cuvier knew that fossils showed asuccession of different life-forms through time Paleontology the study of fossilsJean-Baptiste de Lamarck concluded on thebasis of fossil evidence that more complexorganisms are descended from less complexorganisms13-3 4. Figure 13.1A One of the animals that Cuvier reconstructed fromfossils was the mastodon13-4 5. Figure 13.1B Lamarck thought the long neck of a giraffe was dueto continued stretching in each generation 13-5 6. December 1831 a 22-year-old naturalist namedCharles Darwin (18091882) set sail on theBritish naval vessel HMS Beagle Primary mission to expand navys knowledge ofnatural resources in foreign lands Darwin made many observations aboutsimilarities and differences among animals indifferent parts of the world13-6 7. Darwin also collected fossils Sediments deposited in strata Darwin was convinced that the Earths massivegeologic changes are the result of slowprocesses and that, therefore, in contrast tothought at that time, the Earth was old enough tohave allowed evolution to occur13-7 8. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Rhea Patagonian desert Earths strata contain fossilsGreatBritainEurope NorthAmerica ATLANTICOCEANPACIFICAfricaOCEANGalpagos SouthINDIANIslandsAmerica OCEAN AustraliaCharles Darwin, age 31 HMS Beagle Tropical rain forest Woodpecker finch Marine iguana 13-8(rhea): Nicole Duplaix/National Geographic/Getty Images; (desert): C. Luiz Claudio Marigo/Peter Arnold/Photolibrary; (rain forest): Chad Ehlers/Getty Images; (Darwin): CarolinaBiological/Visuals Unlimited; (iguana): Sami Sarkis/Getty RF; (finch): D. Parer & E. Parer-Cook/Ardea; (strata): Anthony L. Solis/Getty RF 9. Artificial selection mimics natural selection Darwin made a study of artificial selection Process by which humans choose, on the basis ofcertain traits, the animals and plants that willreproduce Example: Foxes are very shy and normally shunpeople, but Russian scientists have produced silverfoxes that are pets Example: Several varieties of vegetables can betraced to a single ancestor that exhibits variouscharacteristics13-9 10. Figure 13.2A Artificial selection has produced domesticatedfoxes 13-10 11. Figure 13.2B These three plants came from the wild mustard plantthrough artificial selection Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Chinese cabbage Brussels sprouts KohlrabiWild mustard 13-11(cabbage, brussel sprouts, kohlrabi): Courtesy W. Atlee Burpee Company; (wild mustard): Medioimages/Punchstock 12. Darwin formulated natural selection as a mechanism for evolution Thomas Malthus who had proposed that deathand famine are inevitable because the humanpopulation tends to increase faster than thesupply of food Darwin hypothesized there is a constant struggle forexistence, and only certain members of a populationsurvive and reproduce in each generation Those members that have some advantage are bestable to compete successfully for limited resources13-12 13. Darwin called the process by which organismswith an advantage reproduce more than othersof their kind natural selection Some aspect of the environment acts as aselective agent and chooses the members ofthe population with the advantageous phenotypeto reproduce more than the other members 13-13 14. Essential components of Natural Selection The members of a population have inheritablevariations A population is able to produce more offspring thanthe environment can support Only certain members of the population survive andreproduce Natural selection results in a population adapted tothe local environment Evolution Changes in a population over time due to theaccumulation of inherited differences 13-14 15. FIGURE 13.3 The brightly colored tree frog can hide among tropicalplants where the large red eyes confuse predators. The frog climbs trees and other plants assisted by toes with suction cups13-15 16. 13.4 Wallace independently formulated anatural selection hypothesis Alfred Russel Wallace (18231913) was also aBritish naturalist Wallaces travels took him to the Amazon and MalayArchipeligo He too had read Malthuss essay, and in 1858 had theidea of survival of the fittest as well Darwin suggested that Wallaces paper bepublished immediately Lyell and others suggested that a joint paper be readto the Linnean Society 13-16 17. HOW SCIENCE PROGRESSES 13A Natural selection can be witnessed Darwin formed his idea of natural selection byobserving tortoises and finches on theGalpagos Islands Example: Finches Heavy beak of large, ground-dwelling finch suited to seeds Beak of warbler-finch suited to feeding on insects Longer, de-curved beak and split tongue of cactus-finch suited for probing cactus flowers for nectar Peter and Rosemary Grant are actually watchingnatural selection as it occurs in the finches 13-17 18. Figure 13A.1 Finches on the Galpagos Islands Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.A ground-dwelling finchA cactus-finch probes flowersfeeds on seeds.for nectar. A warbber-finch feeds on insects.13-18(ground finch, cactus finch): Laura L. Fellows; (warbler finch): Greg W. Lasley 19. Figure 13A.2 The beak depth of a ground finch varies fromgeneration to generation, according to the weather Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.wet year dry yeardry yeardry yearBeak Depth medium ground finch1977 19801982 1984 13-19 20. The Evidence for Evolution Is Strong13-20 21. 13.5 Fossils provide arecord of the past Best evidence for evolution comes from fossils Traces of past life, such as trails, footprints, burrows,worm casts, or preserved droppings Sedimentation Weathering and erosion of rocks produces anaccumulation of particles that vary in size and nature Sediment becomes a stratum, a recognizable layer inseveral layers Fossil record History of life recorded by fossils and the most directevidence we have that evolution has occurred13-21 22. Figure 13.5A a. Paleontologists carefully remove and study fossilsb. The deeper the stratum, the older are the fossils found there 13-22 23. Figure 13.5B Fossils are carefully cleaned, and organismsare reconstructed13-23 24. 13.6 Fossils are evidence for common descent Darwin used the phrase descent withmodification to explain evolution You and your cousins have a common ancestor in your grandparents, so one couple can give rise to many descendants Transitional fossil is either the commonancestor for the two different groups or is closelyrelated to the common ancestor Allow us to trace the descent of organisms Ex: Archaeopteryx lithographica 13-24 25. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. head tailwing Figure 13.6AFossil of Archaeopteryx and an artists representationfeet wing Archaeopteryx fossilreptile characteristicsbird characteristics feathersteeth tail with vertebrae claws13-25(fossil): Jason Edwards/Getty RF; (art): Joe Tucciarone 26. Figure 13.6B Ambulocetus natans, an ancestor of themodern toothed whale, and its fossil remains13-26 27. 13.7 Anatomic evidence supports common descent Anatomic similarities exist between fossils andbetween living organisms Homologous structures those that areanatomically similar because they are inherited from arecent common ancestor Analogous structures those that serve the samefunction, but they are not constructed similarly, nor dothey share a recent common ancestry 13-27 28. 13.7 Anatomic evidencesupports common descent Comparative anatomy Vertebrate forelimbs are used for flight, orientationduring swimming, running, climbing, or swinging fromtree branches Yet all vertebrate forelimbs contain the same sets ofbones organized in similar ways despite theirdissimilar functions Vestigial structures Fully developed in one group of organisms butreduced and possibly nonfunctional in similar groups Pelvic girdle in whales and snakes13-28 29. Figure 13.7ACopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Despite differences in bird humerus function, vertebrateulnaforelimbs have theradiusmetacarpalssame bonesphalangesbatwhale cathorsehuman 13-29 30. 13.7 Anatomic evidencesupports common descent Embryological evidence Homology shared by vertebrates extends to theirembryologic development At some time during development, all vertebrateshave a postanal tail and paired pharyngeal pouches Terrestrial vertebrates can trace their ancestry toamphibians and then to fishes13-30 31. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pig embryoFigure 13.7B Vertebrate embryos have features in common, despite different appearances as adultspharyngealpostanalpouches tail Chick embryo 13-31(both): Carolina Biological Supply/Phototake 32. 13.8 Biogeographic evidencesupports common descent Biogeography is the study of the distribution ofplants and animals in different places throughoutthe world Such distributions are consistent with the hypothesisthat life-forms evolved in a particular locale Example: Both cactuses and euphorbia are succulent,spiny, flowering plants adapted to a hot, dryenvironment, but cactuses grow in North Americandeserts and euphorbia grow in African deserts It seems they just happened to evolve on their respective continents 13-32 33. 13.9 Molecular evidencesupports common descent Almost all organisms use the same basicbiochemical molecules, including DNA, ATP,and many enzymes All organisms use the same DNA triplet code and thesame 20 amino acids in their proteins Humans share a large number of genes with muchsimpler organisms Lifes vast diversity has come about by only a slightdifference in the regulation of genes13-33 34. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Species Figure 13.9 Biochemical 51differences indicate yeast degrees of relatedness among organisms30 moth20fish 18Cytochrome c is a small protein that plays an important role in turtlethe electron transport chain within mitochondria of all cells.11 duck 9 pig 2monkey05 10 1520 2530354045 50 55 60Number of amino acid differences 13-34compared to human cytochrome c. 35. Population Genetics Tells Us When Microevolution Occurs 13-35 36. 13.10 The human populationis diverse Population Members of a single species occupying a particulararea at the same time All humans are the same species Much of the genomic diversity of humans is due tomicrovariations such as single nucleotidepolymorphisms (differences) or SNPs Humans inherit patterns of base-pair differences nowcalled haplotypes13-36 37. FIGURE 13.10 The HapMap project compares DNA sequences among African, Asian, and European populations to discover unique base-pair differences 13-37 38. A Hardy-Weinberg equilibrium is not expected Gene pool of a population is composed of allthe alleles in all the individuals making up thepopulation When the allele frequencies for a populationchange, microevolution has occurred Peppered moth example Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. genotypes DD Dddd frequency of genotypes0.040.32 0.64 in the population0.04 + 0.160.16 + 0.64 frequency of alleles and gametes in the population 13-38 0.20 D 0.80 d 39. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. F1 generationGenotypes: DD Dd ddGenotype frequencies:0.040.32 0.64Allele and gamete frequencies: D = 0.20d = 0.80 eggs F2 generation 0.20 D 0.80 d0.20 Dsperm0.04 DD0.16 Dd0.80 d0.16 Dd 0.64 dd Offspring Genotype frequencies: 0.04 DD + 0.32 Dd + 0.64 dd = 1p2 + 2pq + q 2 = 1p2 = frequency of DD genotype (dark-colored) = (0.20)2= 0.042pq = frequency of Dd genotype (dark-colored) = 2(0.20)(0.80) = 0.32q2 = frequency of dd genotype (light-colored) = (0.80)2 = 0.641.00Figure 13.11 Calculating gene pool frequencies for F1 and F2 13-39 40. The Hardy-Weinberg Principle Potential constancy, or equilibrium state, of genepool frequencies was independently recognizedby G. H. Hardy and W. Weinberg Binomial equation (p2 + 2pq + q2 = 1) tocalculate the genotype and allele frequencies ofa population Formulated Hardy-Weinberg principle 13-40 41. 5 conditions for Hardy-Weinbergequilibrium1. No mutations2. No gene flow3. Random mating4. No genetic drift5. No natural selection13-41 42. Mutations & sexual recombination produce variations Mutations permanent genetic changes Without mutations, there could be no inheritablephenotypic variations 13-42 43. Mutations are the primary source ofgenetic differences among asexualprokaryotes In sexually reproducing organisms, sexualrecombination is as important as mutationin creating phenotypic differences Sexual recombination creates newcombinations of alleles 13-43 44. Nonrandom mating occurs when only certaingenotypes or phenotypes mate with one another Gene flow (gene migration) the movement ofalleles between populations Continued gene flow tends to make the gene poolssimilar and reduce the possibility of allele frequencydifferences between populations 13-44 45. Figure 13.13A The anatomy ofFigure 13.13B Occasional cross- the garden pea (Pisum sativum)pollination between a population of ensures self-pollination andPisum sativum and a population of nonrandom matingPisum arvense is an example of gene flowCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. gene flow self- pollination Pisum arvensestamen stigmaPisum sativam Pisum sativum 13-45 46. 13.14 The effects of genetic drift are unpredictable Genetic drift changes in the allelefrequencies of a gene pool due to chancerather than selection by the environment 2 mechanisms1. Bottleneck effect2. Founder effect 13-46 47. Small Versus Large Populations Although genetic drift occurs in populations of allsizes, a smaller population is more likely to show theeffects of drift Bottleneck and Founder Effects Bottleneck effect prevents the majority of genotypesfrom participating in the next generation Founder effect is an example of genetic drift in whichrare alleles, or combinations of alleles, occur at ahigher frequency in a population isolated from thegeneral population13-47 48. Figure 13.14A Chance events can cause allele frequencychanges and genetic driftCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 10% ofnatural disaster kills populationfive green frogs 20% of population 13-48 49. Figure 13.14B A rare form of dwarfism that is linked to polydactylism isseen among the Amish in Pennsylvania (1/1,000 in general population,1/14 in Amish community)13-49 50. 13.15 Natural selection can bestabilizing, directional, or disruptive Stabilizing selection Occurs when an intermediate phenotype is favored Improves adaptation of the population to those aspects of the environment that remain constant Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20 100 Percent of Births in Population70 Percent Infant Mortality 15 5030Figure 13.15B Stabilizing20selection as exemplified by 10 10human birth weight7 55322 34 5 6 7 8 9 10 13-50Birth Weight (in pounds) 51. Directional selection Occurs when an extreme phenotype is favored, andthe distribution curve shifts in that direction Such a shift can occur when a population is adaptingto a changing environment Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. NoAll guppiespredationare draband smallAmount of Color Lowabove waterfallpredation High predation below waterfall0 4812Monthsa. Experimental siteb. Result (a): Helen RoddFigure 13.15C Directional selection in guppies 13-51 52. Disruptive selection Two or more extreme phenotypes are favored overany intermediate phenotypeCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ForestedLow-lying areas vegetation Bob Evans/Peter Arnold/Photolibrary 13-52Figure 13.15D Disruptive selection in snails 53. Figure 13.15A Phenotype ranges before and after three types of selectionBlue represents favored phenotype(s)Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Number of IndividualsPhenotype Range Phenotype RangePhenotype Rangea. stabilizing selectionb. directional selection c. disruptive selectionNumber of Individuals Peak narrows. Peak shifts. Two peaks result. Phenotype Range Phenotype Range Phenotype Range13-53 54. 13.16 Stabilizing selection can help maintain the heterozygote Variations are maintained in a population for anynumber of reasons Mutations, gene flow, genetic drift and disruptiveselection can maintain or increase variations in apopulation Cystic Fibrosis Recessive allele codes for defective membraneprotein Northwestern European descent Typhoid fever agent can use normal version of thisprotein, but not the defective one to enter cells 13-54 Heterozygote superiority 55. Sickle-Cell Disease Condition due to abnormal form of hemoglobin (Hb) People who are heterozygous (HbA HbS) have anadvantage because they dont die from sickle-celldisease and they dont die from malaria Frequency of the HbS allele is declining among AfricanAmericans because the heterozygote has noparticular advantage in US with low to no malaria13-55 56. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Genotype Phenotype ResultDies due toHbA HbANormalmalarial infectionLives due toHbA HbsSickle-cell traitprotection from bothHbs HbsSickle-cellDies due to diseasesickle-cell disease13-56 57. Figure 13.16 Sickle-cell disease is more prevalent in areas of Africawhere malaria is more common Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.malaria sickle-cell overlap of both 13-57 58. Connecting the Concepts: Chapter 13 Darwin developed theory of natural selectionbased on his own observations and the work ofothers Evolution explains the unity and diversity of life Life is unified because of common descent, and it is diverse because of adaptations to particular environments Application of principles of genetics to evolution Hardy-Weinberg equilibrium Natural selection is the only agent of evolution that results in adaptation to the environment 13-58