darwinian evolution. charles darwin h.m.s. beagle naturalist???
TRANSCRIPT
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Darwinian EvolutionDarwinian Evolution
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Charles DarwinCharles Darwin
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H.M.S. BeagleH.M.S. Beagle
Naturalist???
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Patterns of DiversityPatterns of Diversity
Why do so many organisms seem so
well suited to surviving and
reproducing in a given environment?
Why do similar environments on
different continents have different
animals?
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Living Organisms and FossilsLiving Organisms and Fossils
Why do organisms become extinct?Why do organisms become extinct? How are extinct organisms related to How are extinct organisms related to
extant organisms?extant organisms?
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Galapagos IslandsGalapagos Islands
Why are there so many different forms of the same animals? Why do these forms
differ from others found around the world?
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The Journey HomeThe Journey Home
Why is there so much variation between organisms on the islands and organisms on South America?
Why is there so much variation between organisms on different islands?
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The Inspiration of GeologistsThe Inspiration of Geologists
James Hutton Charles Lyell
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Geology InspirationGeology Inspiration
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The Original EvolutionistThe Original Evolutionist
Jean-Baptiste Lamarck
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Lamarck ExampleLamarck Example
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The Economist ViewpointThe Economist Viewpoint
Thomas Malthus
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The Economist ContributionThe Economist Contribution
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The CompetitionThe Competition
Alfred Russel Wallace
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Natural VariationNatural Variation
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Selective BreedingSelective Breeding
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Natural SelectionNatural Selection
The process in which the most fit The process in which the most fit organism survives and reproduces organism survives and reproduces better than other less fit organismsbetter than other less fit organisms
Possess Possess adaptationsadaptations that provide that provide them with a reproductive advantage them with a reproductive advantage over other organismsover other organisms
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Are Adaptations Perfect?Are Adaptations Perfect?
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Geographic Distribution of SpeciesGeographic Distribution of Species
Kaibab Squirrel
North Rim of Grand
Canyon
Albert’s Squirrel
South Rim of Grand
Canyon
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Darwin’s TheoryDarwin’s Theory
Variation Exists in NatureVariation Exists in Nature
More Offspring are produced than can More Offspring are produced than can survive – Some will not reproducesurvive – Some will not reproduce
Resources are limited and competition Resources are limited and competition will ensue for these resourceswill ensue for these resources
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Darwin’s LogicDarwin’s Logic
Each organism possesses traits that Each organism possesses traits that either help or hinder it in this either help or hinder it in this competition for resourcescompetition for resources
Those best suited to survive and Those best suited to survive and reproduce in a given environment reproduce in a given environment will survive and reproduce and pass will survive and reproduce and pass on their geneson their genes
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Darwin’s LogicDarwin’s Logic
Species change over time and new Species change over time and new traits and new species will arisetraits and new species will arise
Today's species have descended Today's species have descended from ancestors but with modificationsfrom ancestors but with modifications
All organisms are united in a single All organisms are united in a single tree of life by common descenttree of life by common descent
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Homologous StructuresHomologous Structures
Indicates evolutionary relatedness
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Analogous StructuresAnalogous Structures
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Convergent EvolutionConvergent Evolution
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Embryonic SimilaritiesEmbryonic Similarities
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Evolution and GeneticsEvolution and Genetics
Darwin’s Disadvantage…Darwin’s Disadvantage…
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Populations and Gene PoolsPopulations and Gene Pools
What is a gene pool?What is a gene pool?
Relative Frequency of an allele?Relative Frequency of an allele? Example: Tasting PTC paperExample: Tasting PTC paper
In our survey – 85% could taste paper, 15% could In our survey – 85% could taste paper, 15% could notnot
Tasting paper is a dominant trait (25%TT or 60%Tt)Tasting paper is a dominant trait (25%TT or 60%Tt) Not Tasting is a recessive trait (15%tt)Not Tasting is a recessive trait (15%tt) This would mean that 55% of the alleles for this This would mean that 55% of the alleles for this
trait are dominant (T) and 45% are recessive (t)trait are dominant (T) and 45% are recessive (t)
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Sources of Genetic VariationSources of Genetic Variation
MutationsMutations – Can change allelic frequencies – Can change allelic frequencies Silent vs. Expressed mutationsSilent vs. Expressed mutations
Gene ShufflingGene Shuffling – Does not change allelic – Does not change allelic frequenciesfrequencies Independent Assortment of AllelesIndependent Assortment of Alleles Crossing OverCrossing Over
But why is variation important in terms of But why is variation important in terms of evolution?evolution?
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Forms of SelectionForms of Selection Variation typically exists in a population and Variation typically exists in a population and
when graphed, this variation typically takes on when graphed, this variation typically takes on the shape of a bell curvethe shape of a bell curve
Selection can change the position of this curve Selection can change the position of this curve in three different waysin three different ways
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Directional SelectionDirectional Selection
Definition: Definition:
Examples:Examples: Darwin’s FinchsDarwin’s Finchs Guppies and Coloration Guppies and Coloration
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Stabilizing SelectionStabilizing Selection Definition:Definition:
Example:Example: Weight of human infants at birthWeight of human infants at birth Dalmatians and spotsDalmatians and spots
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Disruptive SelectionDisruptive Selection
Definition:Definition:
***Can lead to speciation******Can lead to speciation***
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Changes in Allelic FrequenciesChanges in Allelic Frequencies
Genetic Drift – Change in the allelic Genetic Drift – Change in the allelic frequencies of a population by frequencies of a population by chancechance Typically affects smaller populations. Why?Typically affects smaller populations. Why?
Bean ExampleBean Example
Examples of DriftExamples of Drift Founder effectFounder effect Bottleneck effect Bottleneck effect
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Founder EffectFounder Effect
Definition:Definition:
Example: Amish + PolydactylyExample: Amish + Polydactyly
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Bottleneck EffectBottleneck Effect
Definition:Definition:
Examples: Humans, CheetahsExamples: Humans, Cheetahs
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Evolution Vs. Genetic EquilibriumEvolution Vs. Genetic Equilibrium
Genetic EquilibriumGenetic Equilibrium – No changes in – No changes in allelic frequencies within a allelic frequencies within a populationpopulation
But under what conditions does But under what conditions does genetic equilibrium take place???genetic equilibrium take place???
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Hardy-Weinberg PrincipleHardy-Weinberg Principle
Genetic equilibrium will occur as long Genetic equilibrium will occur as long as the following criteria are met.as the following criteria are met.
1.1. Random matingRandom mating among members of among members of populationpopulation
2.2. Large population sizeLarge population size
3.3. No gene flowNo gene flow (immigration or (immigration or emigration)emigration)
4.4. No mutationsNo mutations
5.5. No natural selectionNo natural selection
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SpeciationSpeciation
Species Definitions:Species Definitions: Anatomical – Anatomical – Biological – Biological – Evolutionary – Evolutionary –
All species definitions have their All species definitions have their benefits and limitationsbenefits and limitations
Take home messageTake home message – We do not have – We do not have a definition that is valid for all a definition that is valid for all situationssituations
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Speciation – The ProcessSpeciation – The Process
In order for speciation to occur, there In order for speciation to occur, there must be a disruption in the gene poolmust be a disruption in the gene pool 2 sub-sets of the population must 2 sub-sets of the population must
become isolated and begin to evolve become isolated and begin to evolve separately from one anotherseparately from one another
Large PopulationSub-pop A
Sub-pop B
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Types of IsolationTypes of Isolation
Behavioral Isolation – Behavioral Isolation – Example: Eastern and Western Example: Eastern and Western
MeadowlarksMeadowlarks
Other example: FirefliesOther example: Fireflies
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Types of IsolationTypes of Isolation
Geographic Isolation – Geographic Isolation – Example: Abert Squirrel and Kaibab SquirrelExample: Abert Squirrel and Kaibab Squirrel
Other example: Mammal + Monotreme Other example: Mammal + Monotreme evolutionevolution
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Types of IsolationTypes of Isolation
Temporal Isolation – Temporal Isolation – Example: Orchids reproduce at different Example: Orchids reproduce at different
timestimes
Other Example: Palm treesOther Example: Palm trees
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How Rapid is SpeciationHow Rapid is Speciation
Early Beliefs: Early Beliefs:
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How Rapid is SpeciationHow Rapid is Speciation
Stephen Jay Gould – Punctuated Stephen Jay Gould – Punctuated EquilibriumEquilibrium
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But how does rapid change occur?But how does rapid change occur?
Cumulative SelectionCumulative Selection
Silent genes are expressedSilent genes are expressed
Master Control Genes – Hox genesMaster Control Genes – Hox genes
Mutations at different times during Mutations at different times during developmentdevelopment
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Hox GenesHox Genes
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Hox genes and evolutionHox genes and evolution