Bài giảng Biology - Chapter 22: Descent with Modification: A Darwinian View of Life

Chapter 22Descent with Modification: A Darwinian View of LifeOverview: Darwin Introduces a Revolutionary TheoryA new era of biology began on November 24, 1859The day Charles Darwin published On the Origin of Species by Means of Natural SelectionThe Origin of SpeciesFocused biologists’ attention on the great diversity of organisms Figure 22.1Darwin made two major points in his bookHe presented evidence that the many species of organisms presently inhabiting the Earth are descendants of ancestral speciesHe proposed a mechanism for the evolutionary process, natural selectionConcept 22.1: The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging speciesIn order to understand why Darwin’s ideas were revolutionaryWe need to examine his views in the context of other Western ideas about Earth and its lifeThe historical context of Darwin’s life and ideasFigure 22.2Linnaeus (classification)Hutton (gradual geologic change)Lamarck (species can change)Malthus (population limits)Cuvier (fossils, extinction)Lyell (modern geology)Darwin (evolution, nutural selection)Mendel (inheritance)Wallace (evolution, natural selection)1750American RevolutionFrench RevolutionU.S. Civil War1800185019001795Hutton proposes his theory of gradualism.1798Malthus publishes “Essay on the Principle of Population.”1809Lamarck publishes his theory of evolution.1830Lyell publishes Principles of Geology.1831–1836Darwin travels around the world on HMS Beagle.Darwin begins his notebooks on the origin of species.1837Darwin writes his essay on the origin of species.1844Wallace sends his theory to Darwin.1858The Origin of Species is published.1859Mendel publishes inheritance papers.1865Resistance to the Idea of EvolutionThe Origin of SpeciesShook the deepest roots of Western cultureChallenged a worldview that had been prevalent for centuriesThe Scale of Nature and Classification of SpeciesThe Greek philosopher AristotleViewed species as fixed and unchanging The Old Testament of the BibleHolds that species were individually designed by God and therefore perfectCarolus LinnaeusInterpreted organismal adaptations as evidence that the Creator had designed each species for a specific purposeWas a founder of taxonomy, classifying life’s diversity “for the greater glory of God”Fossils, Cuvier, and CatastrophismThe study of fossilsHelped to lay the groundwork for Darwin’s ideasFossils are remains or traces of organisms from the pastUsually found in sedimentary rock, which appears in layers or strataFigure 22.3Paleontology, the study of fossilsWas largely developed by French scientist Georges CuvierCuvier opposed the idea of gradual evolutionary changeAnd instead advocated catastrophism, speculating that each boundary between strata represents a catastropheTheories of GradualismGradualismIs the idea that profound change can take place through the cumulative effect of slow but continuous processesGeologists Hutton and LyellPerceived that changes in Earth’s surface can result from slow continuous actions still operating todayExerted a strong influence on Darwin’s thinkingLamarck’s Theory of EvolutionLamarck hypothesized that species evolveThrough use and disuse and the inheritance of acquired traitsBut the mechanisms he proposed are unsupported by evidenceFigure 22.4Concept 22.2: In The Origin of Species, Darwin proposed that species change through natural selectionAs the 19th century dawnedIt was generally believed that species had remained unchanged since their creation, but a major change would challenge this thinkingDarwin’s ResearchAs a boy and into adulthood, Charles DarwinHad a consuming interest in natureSoon after Darwin received his B.A. degreeHe was accepted on board the HMS Beagle, which was about to embark on a voyage around the worldThe Voyage of the BeagleDuring his travels on the BeagleDarwin observed and collected many specimens of South American plants and animalsDarwin observed various adaptations of plants and animalsThat inhabited many diverse environmentsDarwin’s interest in the geographic distribution of speciesWas kindled by the Beagle’s stop at the Galápagos Islands near the equator west of South AmericaFigure 22.5EnglandEUROPENORTHAMERICAGalápagosIslandsDarwin in 1840,after his returnSOUTHAMERICACape ofGood HopeCape HornTierra del FuegoAFRICAHMS Beagle in portAUSTRALIATasmaniaNewZealandPACIFICOCEANAndesATLANTICOCEANDarwin’s Focus on AdaptationAs Darwin reassessed all that he had observed during the voyage of the BeagleHe began to perceive adaptation to the environment and the origin of new species as closely related processesFrom studies made years after Darwin’s voyageBiologists have concluded that this is indeed what happened to the Galápagos finchesFigure 22.6a–c(a) Cactus eater. The long,sharp beak of the cactusground finch (Geospizascandens) helps it tearand eat cactus flowersand pulp.(c) Seed eater. The large groundfinch (Geospiza magnirostris)has a large beak adapted forcracking seeds that fall fromplants to the ground.(b) Insect eater. The green warbler finch (Certhidea olivacea) uses itsnarrow, pointed beak to grasp insects.In 1844, Darwin wrote a long essay on the origin of species and natural selectionBut he was reluctant to introduce his theory publicly, anticipating the uproar it would causeIn June 1858 Darwin received a manuscript from Alfred Russell WallaceWho had developed a theory of natural selection similar to Darwin’sDarwin quickly finished The Origin of SpeciesAnd published it the next yearThe Origin of SpeciesDarwin developed two main ideasEvolution explains life’s unity and diversityNatural selection is a cause of adaptive evolutionDescent with ModificationThe phrase descent with modificationSummarized Darwin’s perception of the unity of lifeStates that all organisms are related through descent from an ancestor that lived in the remote pastIn the Darwinian view, the history of life is like a treeWith multiple branchings from a common trunk to the tips of the youngest twigs that represent the diversity of living organismsFigure 22.7Hyracoidea(Hyraxes)Sirenia(Manateesand relatives)Years agoMillions of years agoDeinotheriumMammutStegodonMammuthusPlatybelodonBarytheriumMoeritheriumElephasmaximus(Asia)Loxodontaafricana(Africa)Loxodontacyclotis(Africa)Natural Selection and AdaptationEvolutionary biologist Ernst MayrHas dissected the logic of Darwin’s theory into three inferences based on five observationsObservation #1: For any species, population sizes would increase exponentiallyIf all individuals that are born reproduced successfullyFigure 22.8Observation #2: Nonetheless, populations tend to be stable in sizeExcept for seasonal fluctuationsObservation #3: Resources are limitedInference #1: Production of more individuals than the environment can supportLeads to a struggle for existence among individuals of a population, with only a fraction of their offspring survivingObservation #4: Members of a population vary extensively in their characteristicsNo two individuals are exactly alikeFigure 22.9Observation #5: Much of this variation is heritableInference #2: Survival depends in part on inherited traitsIndividuals whose inherited traits give them a high probability of surviving and reproducing are likely to leave more offspring than other individualsInference #3: This unequal ability of individuals to survive and reproduceWill lead to a gradual change in a population, with favorable characteristics accumulating over generationsArtificial SelectionIn the process of artificial selectionHumans have modified other species over many generations by selecting and breeding individuals that possess desired traitsFigure 22.10TerminalbudLateralbudsBrussels sproutsCabbageFlowerclusterLeavesCauliflowerFlowerandstemsBroccoliWild mustardKohlrabiStemKaleSummary of Natural SelectionNatural selection is differential success in reproductionThat results from the interaction between individuals that vary in heritable traits and their environmentNatural selection can produce an increase over timeIn the adaptation of organisms to their environmentFigure 22.11(a) A flower mantidin Malaysia(b) A stick mantidin AfricaIf an environment changes over timeNatural selection may result in adaptation to these new conditionsConcept 22.3: Darwin’s theory explains a wide range of observationsDarwin’s theory of evolutionContinues to be tested by how effectively it can account for additional observations and experimental outcomesNatural Selection in ActionTwo examplesProvide evidence for natural selectionDifferential Predation in Guppy PopulationsResearchers have observed natural selectionLeading to adaptive evolution in guppy populations Reznick and Endler transplanted guppies from pike-cichlid pools to killifish pools and measured the average age and size of guppies at maturity over an 11-year period (30 to 60 generations).EXPERIMENTPools with killifish,but not guppies priorto transplantExperimentaltransplant ofguppiesPredator: Killifish; preysmainly on small guppiesGuppies:Larger atsexual maturitythan those in“pike-cichlid pools”Predator: Pike-cichlid; preys mainly on large guppiesGuppies: Smaller at sexual maturity thanthose in “killifish pools”Figure 22.12RESULTS After 11 years, the average size and age at maturity of guppies in the transplanted populations increased compared to those of guppies in control populations.161.5185.667.5Weight of guppiesat maturity (mg)Age of guppiesat maturity (days)92.348.5Control Population: Guppiesfrom pools with pike-cichlids as predatorsExperimental Population:Guppies transplanted topools with killifish aspredators76.1MalesFemales85.758.2MalesFemalesCONCLUSION Reznick and Endler concluded that the change in predator resulted in different variations in the population (larger size and faster maturation) being favored. Over a relatively short time, this altered selection pressure resulted in an observable evolutionary change in the experimental population.The Evolution of Drug-Resistant HIVIn humans, the use of drugsSelects for pathogens that through chance mutations are resistant to the drugs’ effectsNatural selection is a cause of adaptive evolutionResearchers have developed numerous drugs to combat HIVBut using these medications selects for viruses resistant to the drugsFigure 22.13PatientNo. 1Patient No. 2Patient No. 3Percent of HIV resistant to 3TCWeeksThe ability of bacteria and viruses to evolve rapidlyPoses a challenge to our societyHomology, Biogeography, and the Fossil RecordEvolutionary theoryProvides a cohesive explanation for many kinds of observationsHomologyHomologyIs similarity resulting from common ancestryAnatomical HomologiesHomologous structures between organismsAre anatomical resemblances that represent variations on a structural theme that was present in a common ancestorFigure 22.14HumanCatWhaleBatComparative embryologyReveals additional anatomical homologies not visible in adult organismsFigure 22.15PharyngealpouchesPost-analtailChick embryoHuman embryoVestigial organsAre some of the most intriguing homologous structuresAre remnants of structures that served important functions in the organism’s ancestorsMolecular HomologiesBiologists also observe homologies among organisms at the molecular levelSuch as genes that are shared among organisms inherited from a common ancestorHomologies and the Tree of LifeThe Darwinian concept of an evolutionary tree of lifeCan explain the homologies that researchers have observedAnatomical resemblances among speciesAre generally reflected in their molecules, their genes, and their gene productsFigure 22.16SpeciesHumanRhesus monkeyMouseChickenFrogLamprey14%54%69%87%95%100%Percent of Amino Acids That AreIdentical to the Amino Acids in aHuman Hemoglobin PolypeptideBiogeographyDarwin’s observations of the geographic distribution of species, biogeographyFormed an important part of his theory of evolutionSugargliderAUSTRALIANORTHAMERICAFlyingsquirrelFigure 22.17Some similar mammals that have adapted to similar environmentsHave evolved independently from different ancestorsThe Fossil RecordThe succession of forms observed in the fossil recordIs consistent with other inferences about the major branches of descent in the tree of lifeThe Darwinian view of lifePredicts that evolutionary transitions should leave signs in the fossil recordPaleontologistsHave discovered fossils of many such transitional formsFigure 22.18What Is Theoretical about the Darwinian View of Life?In science, a theoryAccounts for many observations and data and attempts to explain and integrate a great variety of phenomenaDarwin’s theory of evolution by natural selectionIntegrates diverse areas of biological study and stimulates many new research questions