Darwinian EvolutionDarwinian Evolution

Charles DarwinCharles Darwin

H.M.S. BeagleH.M.S. Beagle

Naturalist???

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?

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?

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?

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?

The Inspiration of GeologistsThe Inspiration of Geologists

James Hutton Charles Lyell

Geology InspirationGeology Inspiration

The Original EvolutionistThe Original Evolutionist

Jean-Baptiste Lamarck

Lamarck ExampleLamarck Example

The Economist ViewpointThe Economist Viewpoint

Thomas Malthus

The Economist ContributionThe Economist Contribution

The CompetitionThe Competition

Alfred Russel Wallace

Natural VariationNatural Variation

Selective BreedingSelective Breeding

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

Are Adaptations Perfect?Are Adaptations Perfect?

Geographic Distribution of SpeciesGeographic Distribution of Species

Kaibab Squirrel

North Rim of Grand

Canyon

Albert’s Squirrel

South Rim of Grand

Canyon

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

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

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

Homologous StructuresHomologous Structures

Indicates evolutionary relatedness

Analogous StructuresAnalogous Structures

Convergent EvolutionConvergent Evolution

Embryonic SimilaritiesEmbryonic Similarities

Evolution and GeneticsEvolution and Genetics

Darwin’s Disadvantage…Darwin’s Disadvantage…

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)

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?

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

Directional SelectionDirectional Selection

Definition: Definition:

Examples:Examples: Darwin’s FinchsDarwin’s Finchs Guppies and Coloration Guppies and Coloration

Stabilizing SelectionStabilizing Selection Definition:Definition:

Example:Example: Weight of human infants at birthWeight of human infants at birth Dalmatians and spotsDalmatians and spots

Disruptive SelectionDisruptive Selection

Definition:Definition:

***Can lead to speciation******Can lead to speciation***

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

Founder EffectFounder Effect

Definition:Definition:

Example: Amish + PolydactylyExample: Amish + Polydactyly

Bottleneck EffectBottleneck Effect

Definition:Definition:

Examples: Humans, CheetahsExamples: Humans, Cheetahs

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???

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

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

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

Types of IsolationTypes of Isolation

Behavioral Isolation – Behavioral Isolation – Example: Eastern and Western Example: Eastern and Western

MeadowlarksMeadowlarks

Other example: FirefliesOther example: Fireflies

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

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

How Rapid is SpeciationHow Rapid is Speciation

Early Beliefs: Early Beliefs:

How Rapid is SpeciationHow Rapid is Speciation

Stephen Jay Gould – Punctuated Stephen Jay Gould – Punctuated EquilibriumEquilibrium

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

Hox GenesHox Genes

Hox genes and evolutionHox genes and evolution