Evolution Evolution

A Scientific Explanation for Similarities A Scientific Explanation for Similarities and Differences between Organismsand Differences between Organisms

DefinitionsDefinitions• Evolution is a change in the characteristics of a Evolution is a change in the characteristics of a

population over timepopulation over time• Two characteristics identified by Darwin’s workTwo characteristics identified by Darwin’s work

– Descent with modification: species diverge from Descent with modification: species diverge from a common ancestora common ancestor

– Natural selection: individuals with favorable traits Natural selection: individuals with favorable traits accumulate within a populationaccumulate within a population

• Evolution is a change in the genetic Evolution is a change in the genetic composition of a population from generation to composition of a population from generation to generation generation – Can include mechanisms other than natural Can include mechanisms other than natural

selection such as genetic drift and gene flowselection such as genetic drift and gene flow

Populations evolve as natural selection acts on its individuals.

Prior to DarwinPrior to Darwin• Prevailing view that species were unchangingPrevailing view that species were unchanging

– Aristotle proposed a “scale of nature”, that Aristotle proposed a “scale of nature”, that organized fixed species from least to most organized fixed species from least to most complexcomplex

– Special Creation as the origin of species was Special Creation as the origin of species was reinforced by religious thought and interpretation reinforced by religious thought and interpretation of scientific evidence, such as the classification of scientific evidence, such as the classification scheme of Linnaeusscheme of Linnaeus

• Differing views of the history of the earth as Differing views of the history of the earth as seen in the fossil recordseen in the fossil record– Catastrophism: events in past occurred suddenly Catastrophism: events in past occurred suddenly

and are unlike mechanisms of todayand are unlike mechanisms of today– Uniformitarianism: mechanisms of change are Uniformitarianism: mechanisms of change are

constant over timeconstant over time

Evolutionary Thought Before DarwinEvolutionary Thought Before Darwin

• Lamarck developed ideas for changes Lamarck developed ideas for changes among species among species

– Use and disuse – Individuals retain Use and disuse – Individuals retain characteristics that are required for their characteristics that are required for their survival, leads to adaptationsurvival, leads to adaptation

– Inheritance of acquired traits – Individuals Inheritance of acquired traits – Individuals inherit traits that were developed over the inherit traits that were developed over the lifetimes of their ancestorslifetimes of their ancestors

– Innate drive for species to become more Innate drive for species to become more complexcomplex

A Flowchart of Evolutionary ReasoningVariations exist

between members of a population

observations

inferences

Individuals whose inherited traits give a higher probability of

survival and reproduction leave a greater number of

offspring

Relatively constantresources and

population over time

At least some variation is hereditary

More offspring are born than survive and

reproduce

Favorable traits will accumulate in the population

over generations

Identify the inference that shows1. Evolution2. Natural Selection

1

2

Darwin’s Darwin’s ObservationsObservations

Islands with saddle Islands with saddle shell giant shell giant tortoise had tall tortoise had tall prickly pear cacti.prickly pear cacti.

Adaptation: Adaptation: characteristic that characteristic that favors survival favors survival and reproduction and reproduction

Darwin’s ObservationsDarwin’s Observations Galapagos finches had beak shapes suited to Galapagos finches had beak shapes suited to

food sources on specific islands.food sources on specific islands.

Cactus-eater Seed-eater

Insect-eater

Darwin’s ObservationsDarwin’s Observations

Galapagos finches resembled the Galapagos finches resembled the grassquit found on the coast of Ecuador.grassquit found on the coast of Ecuador.

Recent studies suggest that the finch Recent studies suggest that the finch ancestor may have originated from the ancestor may have originated from the Caribbean islands.Caribbean islands.

Explaining the long neck of a giraffeExplaining the long neck of a giraffe

Giraffes stretched their necks to reach food on tall trees andpassed the longer necks onto their offspring

Lamarck versus DarwinLamarck versus Darwin

Evolution as a Change in Genetic CompositionEvolution as a Change in Genetic Composition

Natural selection led to an increase in Natural selection led to an increase in dark colored peppered moths in dark colored peppered moths in industrial regions of Britain. industrial regions of Britain.

How is this trait inherited? How is this trait inherited? • Wing color is the result of a single gene with two Wing color is the result of a single gene with two

alternative forms called allelesalternative forms called alleles• One allele codes for dark color, the other codes for One allele codes for dark color, the other codes for

light colorlight color• Each moth inherits two alleles for wing colorEach moth inherits two alleles for wing color• Only one dark allele is needed for the moth to have Only one dark allele is needed for the moth to have

dark wings since the dark color allele is dominant dark wings since the dark color allele is dominant over the recessive light color alleleover the recessive light color allele

• Two light color alleles are required for a moth to have Two light color alleles are required for a moth to have light wings light wings

• If birds remove light winged moths from the If birds remove light winged moths from the population, dark winged moths survive and pass the population, dark winged moths survive and pass the dominant allele for dark wings to their offspringdominant allele for dark wings to their offspring

• The increase in frequency of the dark wing allele is The increase in frequency of the dark wing allele is evidence of evolutionary changeevidence of evolutionary change

How is this trait inherited?How is this trait inherited?

PhenotypePhenotype(trait)(trait)

GenotypeGenotype(inherited alleles)(inherited alleles)

Dark mothDark moth DD DD HomozygousHomozygous(identical alleles)(identical alleles)

Dark mothDark moth DdDd HeterozygousHeterozygous(different alleles)(different alleles)

Light mothLight moth dddd homozygoushomozygous

The homologous chromosomes carrying alleles of The homologous chromosomes carrying alleles of the same gene separate during Meiosis I so that the same gene separate during Meiosis I so that each gamete receives only one of the two alleles. each gamete receives only one of the two alleles.

How is this trait inherited?How is this trait inherited?

Genotype for Dark mothGenotype for Dark moth Genotype for Light mothGenotype for Light moth

DdDd dddd

DD

dd

d d d d

DdDd

dddd

DdDd

dddd50% dark moths50% dark moths50% light moths50% light moths

Genotype for Dark mothGenotype for Dark moth Genotype for Dark mothGenotype for Dark moth

DdDd DdDd

DD

dd

D d D d

DDDD

DdDd

DdDd

dddd75% dark moths75% dark moths25% light moths25% light moths

Simulating Simulating Natural SelectionNatural Selection

Dd

dd

dd

dd

Dd dd

dd

dd

dd

20% dark wing moths

dd

Birds remove half of light wing moths

Dd

dd

dd

Dd

dd

dd

33.3% dark wing moths

Reproduction occurs

Dd x dd 50% Dd + 50% dd

Dd x dd 50% Dd + 50% dd

dd x dd 0% D_ + 100% dd

Total Dd = 100/300 = 33.3%dark wing moths

Natural selection acts on the phenotype. Evolution is the resulting change in genotypes within the population.

Evidence for Evolution: Artificial SelectionEvidence for Evolution: Artificial Selection

Evidence for Evolution: AdaptationEvidence for Evolution: AdaptationObject Mimicry provides camouflageObject Mimicry provides camouflage

for evading predators for evading predators

Walking stickWalking stick

TreehoppersTreehoppers

Evidence for Evolution: Direct ObservationEvidence for Evolution: Direct ObservationIncrease in guppy coloration with predator changeIncrease in guppy coloration with predator change

Evidence for Evolution: Direct ObservationEvidence for Evolution: Direct ObservationResistance of HIV virus to drug therapyResistance of HIV virus to drug therapy

Evidence for Evolution: Fossil RecordEvidence for Evolution: Fossil RecordLiving organisms resemble extinct fossil formsLiving organisms resemble extinct fossil forms

Evidence for Evolution: Fossil RecordEvidence for Evolution: Fossil Record Progressive changes can be seen fromProgressive changes can be seen from

simpler to more complex organismssimpler to more complex organisms

Evidence for Evolution: Evidence for Evolution: Comparative AnatomyComparative Anatomy

• Structures that do not show a common Structures that do not show a common originorigin– Analogous structures: superficially similarAnalogous structures: superficially similar

• Structures that show a common originStructures that show a common origin– Homologous Structures: same Homologous Structures: same

evolutionary origin despite differences in evolutionary origin despite differences in functionfunction

– Vestigial Structures: serve no purpose but Vestigial Structures: serve no purpose but are homologous to structures in related are homologous to structures in related organismsorganisms

Analogous and Homologous StructuresAnalogous and Homologous Structures

NotNot homologous; homologous;notnot analogous analogous

Homologous;Homologous;notnot analogous analogous

NotNot homologous; homologous;analogousanalogous

Homologous;Homologous;analogousanalogous

Homologous Structures

FlyingFlying SwimmingSwimming RunningRunning GraspingGrasping

Vestigial Vestigial StructuresStructures

Functional hindlimb Functional hindlimb in salamanderin salamander

Remnants of Remnants of hindlimb seen in hindlimb seen in boa and whaleboa and whale

Vestigial StructuresVestigial Structures

Evidence for Evolution: Developmental BiologyEvidence for Evolution: Developmental Biology

Evidence for Evolution: BiochemistryEvidence for Evolution: BiochemistryMolecular similarities between different organismsMolecular similarities between different organisms

Evidence for Evolution: Molecular BiologyEvidence for Evolution: Molecular BiologySimilarities in sequence measured by ease of Similarities in sequence measured by ease of

separating hybrid DNA strands by heatseparating hybrid DNA strands by heat

Evidence for Evolution: GeneticsEvidence for Evolution: Genetics

• Mutation generates diversityMutation generates diversity• Meiosis and Fertilization generate new Meiosis and Fertilization generate new

combinations due to combinations due to – Crossing Over Crossing Over – Alternate patterns of chromosome Alternate patterns of chromosome

segregationsegregation– Unique chromosomes of fertilizing Unique chromosomes of fertilizing

sperm combined with unique sperm combined with unique chromosomes of egg chromosomes of egg

Evidence for Evolution: BiogeographyEvidence for Evolution: Biogeography Plants and animals of each continent are distinctivePlants and animals of each continent are distinctive

Evidence for Evolution: Convergent EvolutionEvidence for Evolution: Convergent Evolution Unrelated organisms in similar environmentsUnrelated organisms in similar environments

show some of the same adaptations show some of the same adaptations

Evidence for Evolution: Evidence for Evolution: Convergent EvolutionConvergent Evolution

Meadowlark of Meadowlark of North AmericaNorth America

Yellow-ThroatedYellow-ThroatedLongclaw of AfricaLongclaw of Africa

Cactus of North America

Euphorb of Africa

Other Patterns: Divergent EvolutionOther Patterns: Divergent EvolutionDifferent phenotypes arise as related species Different phenotypes arise as related species

encounter environmental differencesencounter environmental differences

Other Patterns: Coevolution Other Patterns: Coevolution Interacting species adjust together Interacting species adjust together

to maintain a relationshipto maintain a relationship

Flowering plants Flowering plants and their Pollinatorsand their Pollinators

Predators Predators and their Preyand their Prey

Applying Your KnowledgeApplying Your Knowledge

A.A. Leads to similar traits in unrelated Leads to similar traits in unrelated speciesspecies

B.B. Traits that have a common origin Traits that have a common origin C.C. A trait that makes a species A trait that makes a species

survival more likely is called a(n)survival more likely is called a(n)

1.1. AdaptationAdaptation2.2. Homologous StructuresHomologous Structures3.3. Analogous StructuresAnalogous Structures4.4. Divergent EvolutionDivergent Evolution5.5. Convergent EvolutionConvergent Evolution