Biological EvolutionDarwinian EvolutionandNatural SelectionMajor Concepts1. Linnaean Classification2. Fossils3. Radioactive Dating4. Fossil Record and Genetic Analysis5. Theory of EvolutionRandom, Inheritable VariationsNatural Selection6. Examples of Evolution7. Gradualism and Punctuated Equilibrium8. Mass Extinctions9. Sex and Evolution10. Timescales11. Estimate of fi (includes next lecture)Major Concepts, cont.Diversity of LifeMore than 1.8 × 106 species knownMostly Insects!More species on land than in sea (~10 times)Bacteria & other prokaryotes? (hard to count)Samples of DNA in nature: > 99% unidentifiedSimilarity at biochemical level (genetic code)⇒ Common ancestorOrigin of Diversity?1.8 × 106 known107 - 108 ?E. O. Wilson: The Diversity of LifeHierarchical Classification• Originally by Linnaeus• Based on outward form• Now can be checked with genetic analysis• Lower levels imply closer relationship• Higher levels are more inclusive• Until recently, kingdom was highest level• Traditionally 5 kingdomsFive KingdomsProkaryotesProtoctists:FungiPlantsAnimalsArchaebacteriaEubacteriaEukaryote Micro-organisms+ immediate descendentsEukaryotesReminder: Eukaryote and ProkaryotesFirst appeared ~ 1.5 - 2 × 109 years agocomplex structure, ~ 104 - 105 genesFirst appeared~ 3 - 4 ×109 years agoFew thousand genesGenetic AnalysisSequencing nucleic acidsNew information on genetic distance of speciese.g., chimpanzees and humans share 99% of DNAShows that “archaebacteria” are very differentfrom other (true) bacteria3 domains (new highest level)Archaea Eubacteria Eukaryotes(Eukarya)Examples of ClassificationGarlicEucaryaPlantaeAngiospermophytaMonocotyledonheaeLilialesLiliaceaeAlliumSativumHuman BeingsEucaryaAnimaliaChordataMammaliaPrimatesHominidaeHomoSapiensDomainKingdomPhylumClassOrderFamilyGenusSpeciesThe Oldest Life (based on genetic analysis)More phyla in sea (35) than on land (10)Root of tree of life lies between Archaea& Eubacteria - closer to ArchaeaAdapted to heatEvidence for life back to 3.8 × 109 yr ago Earthwas still being bombardedSome challenges to oldest fossils; secure toAbout 2.8 x 109 yr agoMandala of Lifewww.npaci.edu/envision/ v16.3/hillis.htmlTree of LifeCiccarelli et al. 2006Science, 311, 1283Web may be better metaphor than treeLateral transfer ofgenes:Very common amongprokaryotesAlso in eukaryotic cell(organelles)FossilsHard parts: bones, teeth, …petrification mineralsMolds petrification (preserves soft parts)Bacteria - stromatolites, microfossilsIsotopic ratios - characteristic of lifeDating FossilsRelative DatingRadioactive decay absolute datese.g. 14C produced by cosmic raysC.R. + 14N 14C 14NWorks to < 60,000 yr 1/2 in 5,730 yrFor older fossils, get date of layers above & below from volcanos -e.g. 40K 40Ar, …~Decay of Radioactive AtomsEraPeriodMyrAgoLife FormsEventsCenozoicQuaternary2H. sapiensIce AgesTertiary65PrimatesExtinction of DinosaursMesozoicCretaceous136BirdsSouth Atlantic open to 1900miles.Jurassic190North Atlantic open to 600 milesTriassic225MammalsContinental DriftPaleozoicPermian280ReptilesPangaea breaks upCarboniferous345AmphibiansFormation of coalDevonian395InsectsSilurian430Land PlantsOrdovician500Fish (Chordata)Burgess Shale formsCambrian543TrilobitesPrecambrian545Small Shellyfossils580Ediacarans600–800Snowball Earth episodesMulticellular lifeMyr AgoEraFossil GroupEventNowCenozoicMesozoicBurgess ShalePaleozoicMacroscopic LifeEdiacaraSnowball EarthPrecambrian1000Bitter SpringsWorm tracks (?)Multicellular AlgaeBeck Spring DolomiteEukaryotes certainMcArthur GroupSexual Reproduction (?)2000Gunflint ChertEukaryotes possibleProterozoicOxygen-Rich AtmosphereSnowball EarthFormation of continents3000BulawayanFig TreeOnverwachtWarrawoonaAutotrophs–StromatolitesArcheanLife Begins (?)(Prokaryote Heterotrophs)4000Formation of oceansBombardment decreasesFrequent impactsHadeanFormation of Earth5000Fossils from Burgess Shale ~ 530 Myr Ago(S.J. Gould)Many basic body plans (phyla)tried out in Cambrian; somedid not survive; neverattempted again.Correct Version of HallucigeniaDiversity RisingNumber of FamiliesMajorextinctions600 500 400 300 200 100 0E. O. Wilson: The Diversity of LifeNumber of Species/Flora400 200 E. O. Wilson: The Diversity of LifeSummary of Fossil RecordSimple organisms first, more complex laterProkaryotes, eukaryotes, multi-cellularNot deterministic “progress”Recent (last 150 Myr) rise in diversity caused byflowering plants and insect hostsSome organisms become more complexMany stay about the sameIncrease in diversity and a “left wall of minimalcomplexity”S. J. GouldTheory of EvolutionDeveloped independently by Darwin and WallaceBased on earlier ideas, but key feature was the roleof selectionTwo Key ingredients:1. Random, inheritable variations2. Natural Selection (competition for scarceresources produces “survival of the fittest”)1. Mutation is ultimate source of variation(but sexual reproduction produces greatvariation without many mutations)2. SelectionOrganism level species gradually evolvesSpecies level (speciation + extinction)“Life” evolvesTopics:Sexual ReproductionGradualism vs. Punctuated EquilibriumSpeciation: the role of geographical isolationEcological nichesWhy Sex?(Or why do males exist?)• Sexual reproduction (meiosis) allows more variation– Allows favorable mutations from two lines tocombine– Protects against harmful mutations• But, if only females, more gene copies, more efficientreproduction– Short term fitness might favor asexual• Recent studies in water fleas indicate that protectionagainst harmful mutations is key feature• “Males are allowed to exist after all, because theyhelp females get rid of deleterious mutations.”– Science, 311, 960 (Feb. 17, 2006)Elephants and relativesGradualistPunctuatedEquilibriumSpeciation• Darwin’s “Origin of Species” did not explain• Modern synthesis – Ernst Mayr– Geographic isolation• Islands• Mountaintops– Genetic drift– Varieties no longer interfertile: new species• Adapting to different, but close environments– Hybrids are not well adaptedEcological Niches• “Niche” (a way of making a living)– Different food source– Different microclimate– Species diversity high when environment iscomplex• Convergence– With long geographic isolation– Find similar
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