LECTURE 9:

Evidence for Evolution

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• Abandoned The IdeaAbandoned The Idea That Species That Species Were Perfect & UnchangingWere Perfect & Unchanging

• Observed Observed Significant Variation in All Significant Variation in All SpeciesSpecies Observed Observed

• Observed Observed Farmers Use VariationFarmers Use Variation To To Improve Crops & Livestock Improve Crops & Livestock

• Called Called Selective BreedingSelective Breeding

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What is the difference between What is the difference between natural variation and Artificial natural variation and Artificial

Selection?Selection?

• Natural VariationNatural Variation– Differences Among Individuals Of A Differences Among Individuals Of A

SpeciesSpecies

• Artificial SelectionArtificial Selection– Selective Breeding To Enhance Selective Breeding To Enhance

Desired Traits Among Stock or CropsDesired Traits Among Stock or Crops

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Natural Variation and Artificial Natural Variation and Artificial SelectionSelection

Key Concept:Key Concept:

In In Artificial SelectionArtificial Selection,, Nature Nature Provided The Variation Among Provided The Variation Among Different Organisms, And Different Organisms, And Humans Selected Those Humans Selected Those Variations That They Found Variations That They Found UsefulUseful

5

.

Major Problem in Darwin’s Theory

• No mechanism to explain natural selection

• How could favorable variations be transmitted to later generations?

• With the rediscovery of Mendel’s work in the first half of the 20th century, the missing link in evolutionary theory was found

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What is the Evidence of What is the Evidence of Evolution?Evolution?

Darwin Argued That Living Things Have Darwin Argued That Living Things Have Been Evolving On Earth For Millions of Been Evolving On Earth For Millions of Years. Evidence For This Process Years. Evidence For This Process Could Be Found In:Could Be Found In:

– The The Fossil RecordFossil Record– The The Geographical DistributionGeographical Distribution of Living of Living

Species (BIOGEOGRAPHY)Species (BIOGEOGRAPHY)– Homologous StructuresHomologous Structures of Living of Living

OrganismsOrganisms– Similarities In Similarities In Early DevelopmentEarly Development

• The Darwinian view of life predicts that evolutionary transitions should leave signs in the fossil record

• Paleontologists have discovered fossils of many such transitional forms

The Fossil Records

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Fossil RecordFossil Record

• Earth is Earth is Billions of Years OldBillions of Years Old

• Fossils In Different Layers of Rock Fossils In Different Layers of Rock (sedimentary Rock Strata) Showed (sedimentary Rock Strata) Showed Evidence Of Gradual Change Over TimeEvidence Of Gradual Change Over Time

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Geographic Distribution of Geographic Distribution of Living SpeciesLiving Species

• Different Animals On Different Animals On Different Continents Different Continents But Similar But Similar Adaptations To Adaptations To Shared Shared EnvironmentsEnvironments

LE 22-17

Sugarglider

Flyingsquirrel

NORTHAMERICA

AUSTRALIA

•Some similar mammals that have adapted to similar

environments have evolved independently from different

ancestors

• Another example: while the sugar glider and Another example: while the sugar glider and flying squirrel have adapted to the same mode of flying squirrel have adapted to the same mode of life, they are not closely related, genetically.life, they are not closely related, genetically.

• Instead, the sugar glider from Australia is more closely Instead, the sugar glider from Australia is more closely related to other marsupial mammals from Australia than related to other marsupial mammals from Australia than to to the flying squirrel, a the flying squirrel, a placental mammal placental mammal from North America.from North America.

• The resemblanceThe resemblancebetween them is an between them is an example ofexample ofconvergentconvergentevolution.evolution.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 22.15

Evidence for Evolution

• Evolutionary relationships are determined from shared characteristics between groups of organisms

• What are these characteristics called?– Homologous structures

• are those that have the same evolutionary origin but may or may not have similar functions—

• has been modified to best suit its particular function in each species.

• DIVERGENT EVOLUTION

• Analogous Structures: perform same function, evolved separately

– CONVERGENT EVOLUTION

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Homologous StructuresHomologous Structures

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Homologous Body StructuresHomologous Body Structures

• Not All Serve Important FunctionsNot All Serve Important Functions– Vestigial OrgansVestigial Organs

• Appendix In ManAppendix In Man• Legs On SkinksLegs On Skinks

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What is Divergent Evolution?What is Divergent Evolution?

• Structures That Have Different Mature Structures That Have Different Mature Forms But Develop From The Same Forms But Develop From The Same Embryonic TissuesEmbryonic Tissues

• Strong Evidence That Strong Evidence That All Four-Limbed All Four-Limbed Animals With Backbones Descended, Animals With Backbones Descended, With Modification, From A With Modification, From A Common Common AncestorAncestor

• Help Scientist Group AnimalsHelp Scientist Group Animals

Convergent Evolution

• Convergent Evolution:– The evolution of

species from different ancestors toward a similar form

“New” Evidence for Evolution?

• Molecular Biology– Similarities in DNA sequences

– Developmental Biology

What are Molecular Homologies?

• Examples of homologies at the molecular level are genes shared among organisms inherited from a common ancestor–Ex: Homeobox

LE 22-16

Percent of Amino Acids That AreIdentical to the Amino Acids in aHuman Hemoglobin Polypeptide

100%

95%

87%

69%

54%

14%

Rhesus monkey

Species

Human

Mouse

Chicken

Frog

Lamprey

21Similarities in DNA Similarities in DNA

SequenceSequence

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Similarities In Early Similarities In Early DevelopmentDevelopment

• Embryonic Structures Of Different Embryonic Structures Of Different Species Show Significant SimilaritiesSpecies Show Significant Similarities

• EmbryoEmbryo – early stages of vertebrate – early stages of vertebrate developmentdevelopment

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Evidence for Evolution - Comparative Embryology

Similarities In Embryonic Development

Even when homologies are not obvious in adults, they may be quite apparent in embryonic stages

Which one is the human?

Evidence for the Theory of Evolution by Natural Selection

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Human Fetus – 5 weeksHuman Fetus – 5 weeks

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Chicken Turtle

Rat

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Evolution Evolution of of

pesticide pesticide resistancresistanc

e in e in response response

to to selectionselection

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Evidence for Evolution – Evolution Observed

Evolution of drug-resistance in HIV