Darwinian Darwinian EvolutionEvolution

Ch. 16Ch. 16

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Darwin’s AchievementDarwin’s Achievement

Darwin’s Theory of Evolution is Darwin’s Theory of Evolution is one of the greatest intellectual one of the greatest intellectual achievements in history of achievements in history of science.science.

Why? And how did he do it? That Why? And how did he do it? That is the topic of this presentation.is the topic of this presentation.

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Brief Darwin (1809 – Brief Darwin (1809 – 1882)1882)

Darwin’s ideas formed the basis for modern Darwin’s ideas formed the basis for modern evolutionary theory.evolutionary theory.

Poor student, he was a challenge for his Poor student, he was a challenge for his father.father.

In l831, when Darwin was only 22 he signed In l831, when Darwin was only 22 he signed on as the ship’s naturalist aboard the on as the ship’s naturalist aboard the Beagle on a 5-year expedition around the Beagle on a 5-year expedition around the world.world.

Darwin studied and collected many different Darwin studied and collected many different and usual specimens which contributed to and usual specimens which contributed to his theory.his theory.

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Darwin’s Voyage to the Darwin’s Voyage to the Galapagos IslandsGalapagos Islands

Some of Darwin’s most important Some of Darwin’s most important observations were made on the observations were made on the Galapagos Islands.Galapagos Islands.

The islands are near the equator, 1000km The islands are near the equator, 1000km off the west coast of South America.off the west coast of South America.

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More Animals of the More Animals of the Galapagos Islands:Galapagos Islands:

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Blue Footed Boobies in the Galapagos

Assumptions at that Assumptions at that time:time:

Species are fixed (do not change)Species are fixed (do not change)

Aristotle’s Aristotle’s Scala Scala naturae-He believed that naturae-He believed that species were fixed creations that never species were fixed creations that never changed and they were arranged from least changed and they were arranged from least complex to most complex-worms on the complex to most complex-worms on the bottom and man on the top.bottom and man on the top.

Earth is only a few thousand years old.Earth is only a few thousand years old.

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Darwin’s Revolutionary Darwin’s Revolutionary Ideas:Ideas:

On the Origin of SpeciesOn the Origin of Species published 1859 published 18591)1)Species change (they are not fixed)Species change (they are not fixed)

2)2)Species changed or evolved from common Species changed or evolved from common ancestry over time (implying a much older ancestry over time (implying a much older Earth)Earth)

3)3)Natural SelectionNatural Selection is the mechanism for is the mechanism for changechange

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Why species change?Why species change?

Darwin observes organisms with Darwin observes organisms with slight differences slight differences

or variationsor variations

Ex: GalápagosEx: Galápagosfinches withfinches withdifferent beaksdifferent beaks

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Why Common Ancestry?Why Common Ancestry?

Darwin also finds fossils of organisms Darwin also finds fossils of organisms unlike any that live today.unlike any that live today.

Ex: giant sloth in ArgentinaEx: giant sloth in Argentina(modern armadillos and(modern armadillos andsloths related, but MUCHsloths related, but MUCHsmaller)smaller)

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There are many Common There are many Common Ancestry Implications Ancestry Implications noted by Darwin:noted by Darwin:

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Why Earth had to be Why Earth had to be older than 6,000 years?older than 6,000 years?

He read geology papers (Lyell’s He read geology papers (Lyell’s work showed growing evidence work showed growing evidence for gradual change of landforms)for gradual change of landforms)

Found evidence of long extinct Found evidence of long extinct habitats (fossil sea shells in habitats (fossil sea shells in Andes Mountains)Andes Mountains)

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How does change How does change happen?happen?

Ideas for selection started with Ideas for selection started with interviewing pigeon breedersinterviewing pigeon breeders

artificialartificialselection in selection in

animals and animals and

plantsplants

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What about in nature?What about in nature?

What force “selects” which organisms What force “selects” which organisms reproduce? The Environmentreproduce? The Environment

What does the environment include?What does the environment include?

Influenced by Malthus (economist) Influenced by Malthus (economist) writing about competition for scarce writing about competition for scarce resources.resources.

If organisms must compete for survival, If organisms must compete for survival, the survivors would reproduce more.the survivors would reproduce more.

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Darwin’s Natural Darwin’s Natural SelectionSelection

1)1) OverproductionOverproduction-Organisms produce more -Organisms produce more offspring than can survive because of offspring than can survive because of competition for resources.competition for resources.

2)2) VarietyVariety within a population or species within a population or species

3)3) SelectionSelection-having a particular trait can make -having a particular trait can make individuals more or less likely to survive individuals more or less likely to survive and produce offspringand produce offspring

4) 4) AdaptationAdaptation–over time, the traits that aid –over time, the traits that aid survival and reproduction become commonsurvival and reproduction become common

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Darwin’s Natural Darwin’s Natural SelectionSelectionSummary:Summary:

Given: Too many organisms + Given: Too many organisms + scarce resources = fierce scarce resources = fierce competitioncompetition

Given: Individuals have Given: Individuals have heritableheritable variationsvariations

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Darwin’s Natural Darwin’s Natural SelectionSelection

ConclusionConclusion: Individuals with : Individuals with beneficial variations out-beneficial variations out-reproduce othersreproduce others

ConclusionConclusion: Over many : Over many generations, many in the generations, many in the population have beneficial traitpopulation have beneficial trait

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Does natural selection Does natural selection occur now?occur now?

Goal – study a model organism Goal – study a model organism with fast life cyclewith fast life cycle

How about bacteria? How about bacteria?

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Bacterial EvolutionBacterial Evolution

Resistance to antibiotic medicines Resistance to antibiotic medicines

First wide use of antibiotic First wide use of antibiotic penicillin in 1940spenicillin in 1940s

Open books to p. 484 to figure 12Open books to p. 484 to figure 12

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Darwin vs. LamarckDarwin vs. Lamarck

Darwinian evolutionDarwinian evolution Genetic variation Genetic variation

Individuals with Individuals with beneficial variations beneficial variations reproduce morereproduce more

Population evolves, Population evolves, NOT individualsNOT individuals

Lamarckian evolutionLamarckian evolution Individuals change traits Individuals change traits

by use and disuseby use and disuse

Individuals pass acquired Individuals pass acquired changes throughout life changes throughout life to offspring to offspring

Individuals evolve Individuals evolve because they “want” because they “want” changechange

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Lamark’s TheoryLamark’s Theory

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“Use and Disuse”

1.Use of structure results in Evolution

2.Does not take into account DNA or sex cell Mutations

Did Evolution occur in Did Evolution occur in history?history?

Yes … transitional fossil evidenceYes … transitional fossil evidence ArchaeopteryxArchaeopteryx – reptile / bird – reptile / bird

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Transitional FossilsTransitional Fossils

TiktaalikTiktaalik – fish / amphibian – fish / amphibian

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Homologous StructuresHomologous Structures

Homo = ?Homo = ?

Same Same evolutionary evolutionary historyhistory

Different Different functions in functions in different different environmentsenvironments 2323

Homologous DNAHomologous DNA

Most powerful evidence for a common Most powerful evidence for a common ancestor ancestor

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Homologous Homologous DevelopmentDevelopment

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Homologous Cell ProcessesHomologous Cell Processes

Respiration / photosynthesis Respiration / photosynthesis pathways are similar processes in pathways are similar processes in most speciesmost species

Mitosis process is the same in all Mitosis process is the same in all eukaryoteseukaryotes

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Vestigial structures-lost Vestigial structures-lost over timeover time

“use it or lose it”

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Vestigial StructuresVestigial Structures

“use it or lose it”2828

                                                                           

Ambulocetus natansAmbulocetus natans in action. A reconstruction of an early close cousin of in action. A reconstruction of an early close cousin of whales.whales.

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See Page 382 for Whale Evolution

Adaptations: CamouflageAdaptations: Camouflage

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Adaptations: MimicryAdaptations: Mimicry

3131Owl butterfly

We think this mimicry has evolved so that potential predators, such as fish, learn more quickly that red spots are a sign that the animal has large glands of distasteful chemicals in their mantle.

Vestiges and SelectionVestiges and Selection

Natural selection not only Natural selection not only changes populations over time…changes populations over time…

Selection also Selection also preservespreserves crucial crucial traits needed for survivaltraits needed for survival

Example: The Wolf’s sense of Example: The Wolf’s sense of smell.smell.

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MisconceptionsMisconceptions

Evolution does not just add Evolution does not just add complexity, it can take it away as wellcomplexity, it can take it away as well

Great example: tapeworm-lacks many Great example: tapeworm-lacks many organ systemsorgan systems

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Imperfections in HumansImperfections in Humans Evolution does not “finish” with a “perfect Evolution does not “finish” with a “perfect

trait”trait”

Eye photoreceptor setup and blind spotsEye photoreceptor setup and blind spotsincoming light

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Complex Changes-How?Complex Changes-How? How does random mutation lead to How does random mutation lead to

complex changes? complex changes? The icefish below is able to withstand The icefish below is able to withstand

the Anarctic freeze. How?the Anarctic freeze. How?

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Evolution of ComplexityEvolution of Complexity

Organisms often “borrow” from pre Organisms often “borrow” from pre existing, successful genes, which existing, successful genes, which are adapted for new purposes.are adapted for new purposes.

Example: Icefish antifreeze protein is closely Example: Icefish antifreeze protein is closely related to fish trypsinogen protein already related to fish trypsinogen protein already produced by the fish. The antifreeze protein is produced by the fish. The antifreeze protein is simply modified from typsinogen.simply modified from typsinogen.

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Patterns of EvolutionPatterns of Evolution

Populations are not isolated, and Populations are not isolated, and often evolve in often evolve in response to each response to each otherother

Coevolution – two species are Coevolution – two species are competing to “one up” each other competing to “one up” each other with adaptationswith adaptations

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CoevolutionCoevolution

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DivergentDivergent Convergent Convergentevolutionevolution evolutionevolutionAlso called Adaptive Also called Adaptive Radiation Radiation

common ancestor

new organisms

different ancestries

some similar organisms develop in similar environments in different parts of the world

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See Page 383, Figure 8See Page 383, Figure 8

Adaptive RadiationAdaptive Radiation

Special case of divergent evolution - when many niches are available

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Patterns of EvolutionPatterns of Evolution Gradualism vs. punctuated Gradualism vs. punctuated

equilibriumequilibrium

Slow, even change Long periods of no change with bursts of rapid change4141

The EndThe End

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