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Evolution Chapter 15 1

Evolution Chapter 15 1. 2 “Nothing in biology makes sense EXCEPT in the light of evolution.” Theodosius Dobzhansky Evolution Charles Darwin in later years.

Jan 17, 2016



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  • EvolutionChapter 15*

  • *Nothing in biology makes sense EXCEPT in the light of evolution. Theodosius DobzhanskyEvolutionCharles Darwin in later years

  • 15-1Darwins Theory of Natural Selection*

  • Early Ideas On Earths OrganismsAristotle believed species were fixed creations arranged by their complexityIdea lasted 2000 years


  • Contributors to Darwins thinking included:Charles Lyell geologic processes still changing Earth (Principles of Geology book)Georges Cuvier species extinction (Catastrophism)Thomas Malthus struggle for existence (resources)*:

  • Contributors to Darwins thinking included:James Hutton - GradualismJohn Baptiste Lamarck developed idea of change over time. Inheritance of Acquired Characteristics and Law of Use and DisuseAlfred Russel Wallace organisms evolved from common ancestors*:

  • Lamarcks Theory of EvolutionLaw of Use and DisuseIf a body part were used, it got strongerIf body part was NOT used, it dissappeared*

  • *

  • Lamarcks Theory of EvolutionInheritance Of Acquired TraitsTraits Acquired During Ones Lifetime Would Be Passed To Offspring*Clipped ears of dogs could be passed to offspring!

  • Lamarcks MistakesLamarck Did NOT Know how traits were inherited (Traits are passed through genes)Genes Are NOT Changed By Activities In LifeChange Through Mutation Occurs Before An Organism Is Born*

  • Charles Darwin the Naturalist*

  • Voyage of the BeagleCharles DarwinBorn Feb. 12, 1809Joined Crew of HMS Beagle, 1831Naturalist5 Year Voyage around worldAvid Collector of Flora & FaunaAstounded By Variety of Life*

  • Darwins Voyage of Discovery*A reconstruction of the HMS Beagle sailing off Patagonia.

  • Darwin Left England in 1831*Darwin returned 5 years later in 1836

  • The Galapagos IslandsSmall Group of Islands 1000 km West of South AmericaSimilar ClimatesAnimals On Islands UniqueTortoisesIguanasFinchesMockingbirds


  • The Galapagos IslandsVolcanic islands off the coast of South AmericaIsland species varied from mainland species & from island-to-island species*

  • *

  • The Galapagos IslandsFinches on the islands resembled a mainland finchMore types of finches appeared on the islands where the available food was different (seeds, nuts, berries, insects)Finches had different types of beaks adapted to their type of food gatheringMockingbirds had different traits suited for their niche!*

  • *

  • Darwins ObservationsPatterns of Diversity were shownUnique Adaptations in organismsSpecies Not Evenly DistributedAustralia, Kangaroos, but No RabbitsS. America, Llamas*

  • Darwins ObservationsBoth Living Organisms & Fossils collectedFossils included:TrilobitesGiant Ground Sloth of South America

    *This species NO longer existed. What had happened to them?

  • DefinitionEvolution is the slow, gradual change in a population of organisms over time


  • Darwins ObservationsLeft unchecked, the number of organisms of each species will increase exponentially, generation to generationIn nature, populations tend to remain stable in sizeEnvironmental resources are limited*

  • Darwins ConclusionProduction of more individuals than can be supported by the environment leads to a struggle for existence among individualsOnly a fraction of offspring survive each generationSurvival of the Fittest


  • Darwins ObservationsIndividuals of a population vary extensively in their characteristics with no two individuals being exactly alike.Much of this variation between individuals is inheritable.*

  • Darwins ConclusionIndividuals who inherit characteristics most fit for their environment are likely to leave more offspring than less fit individualsCalled Natural Selection*

  • *The unequal ability of individuals to survive and reproduce leads to a gradual change in a population, with favorable characteristics accumulating over generations (natural selection)New species evolveDarwins Theory of Evolution

  • Natural Variation and Artificial SelectionAbandoned The Idea That Species Were Perfect & UnchangingObserved Significant Variation in All Species ObservedObserved Farmers Use Variation To Improve Crops & Livestock Called Selective Breeding*

  • Natural Variation and Artificial SelectionNatural VariationDifferences Among Individuals Of A SpeciesArtificial SelectionSelective Breeding To Enhance Desired Traits Among Stock or Crops*

  • *

  • Natural Selection4 Principles of Natural Selection:1. Variation2. Heritability3. Overproduction4. Reproductive Advantage*.

  • Natural Selection ConceptsThe Struggle for Existence (compete for food, mates, space, water, etc.)Survival of the Fittest (able to survive and reproduce)Descent with Modification (new species arise from common ancestor replacing less fit species)*

  • Survival of the FittestFitnessAbility of an Individual To Survive & ReproduceAdaptations Can Be:PhysicalSpeed, Camouflage, Claws, Quills, etc.BehavioralSolitary, Herds, Packs, Activity, etc.*

  • Natural SelectionCannot Be Seen DirectlyIt Can Only Be Observed As Changes In A Population Over Many Successive GenerationsRadiationFossil Record*

  • *Evidence for Evolution Evolution ObservedSelection against small guppies results in an increase in average size

  • Descent With ModificationTakes Place Over Long Periods of TimeNatural Selection Can Be Observed As Changes InBody StructuresEcological NichesHabitats*

  • Descent With ModificationSpecies Today Look Different From Their AncestorsEach Living Species HasDescendedWith ChangesFrom Other SpeciesOver Time*

  • Descent With Modification*

  • Descent With ModificationImpliesAll Living Organisms Are RelatedSingle Tree of LifeDNA, Body Structures, Energy SourcesCommon DescentAll Species, Living & Extinct, Were Derived From Common Ancestors*

  • Theory of Evolution TodaySupporting Evidence15-2*

  • Evidence of EvolutionKey ConceptEvidence For This Process Could Be Found In:The Fossil RecordThe Geographical Distribution of Living SpeciesHomologous Structures of Living OrganismsSimilarities In Early Development*

  • Fossil RecordEarth is Billions of Years OldFossils In Different Layers of Rock (sedimentary Rock Strata) Showed Evidence Of Gradual Change Over TimeDerived Traits newly evolved featuresAncestral Traits old features*

  • *Evidence for Evolution The Fossil Record

  • Geographic Distribution of Living SpeciesDifferent Animals On Different Continents But Similar Adaptations To Shared Environments*

  • Homologous Body StructuresScientists Noticed Animals With Backbones (Vertebrates) Had Similar Bone StructureMay Differ In Form or FunctionLimb Bones Develop In Similar PatternsArms, Wings, Legs, Flippers*

  • Homologous Body Structures*

  • *Homologous Structures

  • Vestigial Body StructuresNot All Serve Important FunctionsVestigial OrgansAppendix In ManLegs On Skinks or Leg Bones on Snakes*

  • Analogous StructuresUsed the same but was not made the same way.Bird wings versus insect wings*

  • Similarities In Early DevelopmentEmbryonic Structures Of Different Species Show Significant SimilaritiesEmbryo early stages of vertebrate development*

  • *Evidence for Evolution - Comparative EmbryologySimilarities In Embryonic Development

  • *ChickenTurtleRat

  • Human Fetus 5 weeks*

  • *Similarities in DNA Sequence

  • AdaptationsCamouflageMimicryAntimicrobial Resistance*

  • *Evolutionary Time ScalesMacroevolution: Long time scale events that create and destroy species.

  • *Microevolution: Short time scale events (generation-to-generation) that change the genotypes and phenotypes of populationsEvolutionary Time Scales

  • Shaping Evolutionary Theory15-3Population GeneticsHardy-Weinberg Principle genetic equilibrium (constant frequencies over time)p + q = 1 allele frequencyp2 + 2pq + q2 = 1 genotypic frequencyTable 15.3 (page 432)*

  • Mechanisms of EvolutionGenetic DriftFounder EffectBottleneckGene FlowNonrandom MatingMutationNatural Selection*

  • Genetic DriftIn each generation, some individuals may, just by chance, leave behind a few more descendents (and genes, of course!) than other individuals. The genes of the next generation will be the genes of the lucky individuals, not necessarily the healthier or better individuals. That, in a nutshell, is genetic drift. It happens to ALL populationstheres no avoiding the vagaries of chance.*

  • Founder EffectA founder effect occurs when a new colony is started by a few members of the original population. This small population size means that the colony may have:reduced genetic variation from the original population.a non-random sample of the genes in the original population.Example, the Afrikaner population of Dutch settlers in South Africa is descended mainly from a few colonists. Today, the Afrikaner population has an unusually high frequency of the gene that causes Huntingtons disease, because those original Dutch colonists just happened to carry that gene with unusually high frequency. This effect is easy to recognize in genetic diseases, but of course, the frequencies of all sorts of genes are affected by founder events.


  • BottleneckPopulation bottlenecks occur when a populations size is reduced for at least one generation. Because genetic drift acts more quickly to reduce genetic variation in small populations, undergoing a bottleneck can reduce a populations genetic variation by a lot, even if the bottleneck doesnt last for very many generations. This is illustrated by the bags of marbles shown above, where, in generation 2, an unusually small draw creates a bottleneck.

    *The elephant seal population was bottlenecked due to hunting in the 1890s.

  • Gene FlowSome individuals from a population of brown beetles might have joined a population of green beetles. That would make the genes for brown beetles more frequent in the green beetle population.*

  • Nonrandom MatingSexual Selection individuals choose mates based on certain traits.*

  • MutationA mutation could cause parents with genes for bright green coloration to have offspring with a gene for brown coloration. That would make the genes for brown beetles more frequent in the population.*

  • Natural SelectionThere is variation in traits. There is differential reproduction.

    There is heredity.

    One trait tends to become more common. *

  • Types of Selection3 types of Natural Selection:Stabilizing - averageDirectional one extremeDisruptive both extremes


  • Reproductive IsolationPrezygoticHabitat isolationTemporal isolationBehavioral isolationMechanical isolationGametes diePostzygoticZygote diesHybrids sterileHybrids inviabilityLow hybrid fitness*

  • SpeciationAllopatric due to geographic isolation. Isolation might occur because of great distance or a physical barrier, such as a desert or riverSympatric - Merely exploiting a new niche may automatically reduce gene flow with individuals exploiting the other niche. This may occasionally happen when, for example, herbivorous insects try out a new host plant.*

  • Patterns of EvolutionDivergent EvolutionAdaptive radiationCoevolutionPredator/prey and parasite/host Competitive species Mutualistic species Convergent EvolutionAnalogous featuresBird and bat wings*