Chapter 15-16 Darwin and Chapter 15-16 Darwin and the Theory of Evolutionthe Theory of Evolution

15-1 Charles Darwin15-1 Charles Darwin

Born 2/12/1809Born 2/12/1809

•Sailed on the Beagle in 1831Sailed on the Beagle in 1831

•Travels- particularly to the Galapagos Travels- particularly to the Galapagos IslandsIslands

Sailed around the worldSailed around the world

Darwin’s ObservationsDarwin’s Observations

• On Galapagos Islands – On Galapagos Islands – – Finches had different-Finches had different-

shaped beaks from shaped beaks from finches on the mainlandfinches on the mainland

– Tortoises had different-Tortoises had different-shaped shells from shaped shells from mainland tortoisesmainland tortoises

• The plants and animals were well-suited to The plants and animals were well-suited to their environmenttheir environment

• Certain species live in one environment, and Certain species live in one environment, and not anothernot another

15.215.2Ideas that shaped Darwin’s thinkingIdeas that shaped Darwin’s thinking

• James Hutton and Charles LyellJames Hutton and Charles Lyell– Recognized that the Earth is millions of Recognized that the Earth is millions of

years old and still changingyears old and still changing

• Thomas MalthusThomas Malthus– If the human population continues to If the human population continues to

grow unchecked, then eventually there grow unchecked, then eventually there would not be enough resourceswould not be enough resources

• There was already a rich fossil record There was already a rich fossil record that was challenging the traditional that was challenging the traditional thinking that all organisms exist as thinking that all organisms exist as created.created.

Charles Lyell’s Charles Lyell’s Principles of GeologyPrinciples of Geology showed evidence of Earth’s extreme showed evidence of Earth’s extreme age.age.

This book led Darwin to wonder if life This book led Darwin to wonder if life could have changed very slowly over could have changed very slowly over a long period of time.a long period of time.

Jean-Baptiste Jean-Baptiste LamarckLamarck• One of the first scientists to One of the first scientists to

notice living things have notice living things have changed over timechanged over time

• Proposed that by selective Proposed that by selective use or disuseuse or disuse of organs, of organs, organisms acquired or lost organisms acquired or lost certain traits during their certain traits during their lifetimeslifetimes

• These traits could then be These traits could then be passed on to their offspringpassed on to their offspring

• Do you agree with this Do you agree with this theory?theory?

Checkpoint!Checkpoint!• Where is Darwin most known for his Where is Darwin most known for his

research?research?– A. Caribbean IslandsA. Caribbean IslandsC. Galapagos IslandsC. Galapagos Islands– B. Hawaiian Islands B. Hawaiian Islands D. English IslandsD. English Islands

• What did Darwin consider as a reason for What did Darwin consider as a reason for the different beaks on the island and the different beaks on the island and mainland finches?mainland finches?– A. they had a common ancestorA. they had a common ancestor– B. they were the same species with mutationsB. they were the same species with mutations– C. they were not the same speciesC. they were not the same species– D. they had no common relativesD. they had no common relatives

15-3 Darwin Presents His 15-3 Darwin Presents His CaseCase

• observations on species led to his observations on species led to his concept of evolutionconcept of evolution

• In 1858 another scientist named In 1858 another scientist named Alfred Wallace sent an essay Alfred Wallace sent an essay summarizing his thought on summarizing his thought on evolutionary change. This spurred evolutionary change. This spurred Darwin to go ahead and publish his Darwin to go ahead and publish his ideas.ideas.

• In 1859, Darwin published In 1859, Darwin published On the On the Origin of SpeciesOrigin of Species– In it, he proposed a mechanism for In it, he proposed a mechanism for

evolution he called evolution he called natural selectionnatural selection – – (process of change in species over time)(process of change in species over time)

Natural SelectionNatural Selection

• ““Survival of the Fittest”Survival of the Fittest”

• Members of the same population compete for Members of the same population compete for food, living space, and other necessities of lifefood, living space, and other necessities of life

• The predators that are successful in getting The predators that are successful in getting food and the prey that are successfully food and the prey that are successfully camouflaged or better protected will survive camouflaged or better protected will survive and pass on their DNAand pass on their DNA

• FitnessFitness – the ability of an individual to survive – the ability of an individual to survive and reproduce in its specific environmentand reproduce in its specific environment

Checkpoint!Checkpoint!• Whose idea stated that organisms Whose idea stated that organisms

changed through generations by passing changed through generations by passing on acquired characteristics?on acquired characteristics?– A. MalthusA. Malthus B. LyellB. Lyell– C. LamarckC. Lamarck D. HuttonD. Hutton

• What was the reason Darwin decided to What was the reason Darwin decided to publish?publish?– A. he diedA. he died– B. Wallace’s essayB. Wallace’s essay– C. Malthus theory was rightC. Malthus theory was right– D. Hutton encouraged himD. Hutton encouraged him

AdaptationAdaptation

• Over time, natural selection results in Over time, natural selection results in changes in the inherited changes in the inherited characteristics of a populationcharacteristics of a population

• These changes increase a species’ These changes increase a species’ fitness in its environmentfitness in its environment

• AdaptationAdaptation – inherited – inherited characteristic that can be physical or characteristic that can be physical or behavioralbehavioral

• Artificial SelectionArtificial Selection– Nature provides the variation, and Nature provides the variation, and

humans selected those variations that humans selected those variations that they found usefulthey found useful•This process has been used in choosing the This process has been used in choosing the

best domesticated animals and plants to best domesticated animals and plants to increase food productionincrease food production

Checkpoint!Checkpoint!• What is the term for the ability to survive What is the term for the ability to survive

and reproduce?and reproduce?– A. exerciseA. exercise B. fitnessB. fitness– C. cardioC. cardio D. fertilityD. fertility

• If a white moth and a black moth live in a If a white moth and a black moth live in a forest of black-barked trees, and the forest of black-barked trees, and the white moths get hunted more regularly white moths get hunted more regularly by birds, what is that called?by birds, what is that called?– A. competitionA. competition B. artificial selectionB. artificial selection– C. adaptationC. adaptation D. survival of the fittestD. survival of the fittest

Evidence of EvolutionEvidence of Evolution• FossilsFossils

– People in Darwin’s time understood that fossils People in Darwin’s time understood that fossils were preserved remains of ancient organisms.were preserved remains of ancient organisms.

• Geographic Distribution of Living Things Geographic Distribution of Living Things called called biogeographybiogeography– Species varied by locationSpecies varied by location

• Homologous Body StructuresHomologous Body Structures– Structures that have different mature forms but Structures that have different mature forms but

develop from the same embryonic tissuesdevelop from the same embryonic tissues– Vestigial Organs – traces of homologous organs Vestigial Organs – traces of homologous organs

that serve no obvious purposethat serve no obvious purpose– Examples: limbs of reptiles, birds, and Examples: limbs of reptiles, birds, and

mammalsmammals• Similarities in EmbryologySimilarities in Embryology

– Early stages of embryos, many animals with Early stages of embryos, many animals with backbones are similarbackbones are similar

WARM UPWARM UP

• How might vestigial organs provide How might vestigial organs provide clues to an animal’s evolutionary clues to an animal’s evolutionary history?history?

Chapter 16 – Evolution of Chapter 16 – Evolution of PopulationsPopulations

• 16-1 Genes and Variations16-1 Genes and Variations• Genetic variation is studied in populations Genetic variation is studied in populations

(group of same species that interbreed)(group of same species that interbreed)

• Gene pool – all genes that are present in a Gene pool – all genes that are present in a populationpopulation

• Relative frequency – number of times an Relative frequency – number of times an allele occurs in a gene pool, compared allele occurs in a gene pool, compared with the number of times other alleles for with the number of times other alleles for the same gene occurthe same gene occur

• Evolution is change in the relative Evolution is change in the relative frequency of alleles in a populationfrequency of alleles in a population

Genetic VariationGenetic Variation

• Two main sources of genetic Two main sources of genetic variationvariation– MutationsMutations

•Change in a sequence of DNAChange in a sequence of DNA

– Gene shufflingGene shuffling• Independent movement of chromosomes Independent movement of chromosomes

during meiosis and Crossing-Overduring meiosis and Crossing-Over

Checkpoint!Checkpoint!

• Write down 2 different things that Darwin Write down 2 different things that Darwin thought of as evidence for evolution.thought of as evidence for evolution.

• What is the term for all the genes present What is the term for all the genes present in a population?in a population?– A. gene poolA. gene pool B. relative frequencyB. relative frequency– C. possible inheritanceC. possible inheritance D. gene shufflingD. gene shuffling

• Write down two sources of genetic Write down two sources of genetic variations?variations?

Single-Gene and Polygenic Single-Gene and Polygenic TraitsTraits• The number of phenotypes produced The number of phenotypes produced

for a trait depends on how many for a trait depends on how many genes control the traitgenes control the trait– Single-gene traitSingle-gene trait

•Single gene with two allelesSingle gene with two alleles•Fewer phenotypes than polygenic traitsFewer phenotypes than polygenic traits•Ex: widow’s peakEx: widow’s peak

– Polygenic traitPolygenic trait•Controlled by two or more genes (each with Controlled by two or more genes (each with

more than 2 alleles)more than 2 alleles)•Many different genotypes and phenotypesMany different genotypes and phenotypes•Ex: heightEx: height

Distribution of Phenotypes Distribution of Phenotypes Polygenic TraitsPolygenic Traits

• Directional SelectionDirectional Selection– Individuals at one end of the curve have Individuals at one end of the curve have

higher fitness than those in the middle or higher fitness than those in the middle or the other endthe other end

Directional Selection

Food becomes scarce.

Low mortality, high fitnessHigh mortality, low fitness

• Stabilizing SelectionStabilizing Selection– Individuals near the center have higher Individuals near the center have higher

fitness than those at either end of the fitness than those at either end of the curve.curve.

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Birth Weight

Selection against both

extremes keep curve

narrow and in same place.

Low mortality, high fitnessHigh mortality, low fitness

Stabilizing Selection

• Stabilizing selection favors the norm, the common, Stabilizing selection favors the norm, the common, average traits in a population. Look at the Siberian average traits in a population. Look at the Siberian Husky, a dog bred for working in the snow. The Husky, a dog bred for working in the snow. The Siberian Husky is a medium dog, males weighing 16-Siberian Husky is a medium dog, males weighing 16-27kg (35-60lbs). These dogs have strong pectoral 27kg (35-60lbs). These dogs have strong pectoral and leg muscles, allowing it to move through dense and leg muscles, allowing it to move through dense snow. The Siberian Husky is well designed for snow. The Siberian Husky is well designed for working in the snow. If the Siberian Husky had working in the snow. If the Siberian Husky had heavier muscles, it would sink deeper into the snow, heavier muscles, it would sink deeper into the snow, so they would move slower or would sink and get so they would move slower or would sink and get stuck in the snow. Yet if the Siberian Husky had stuck in the snow. Yet if the Siberian Husky had lighter muscles, it would not be strong enough to pull lighter muscles, it would not be strong enough to pull sleds and equipment, so the dog would have little sleds and equipment, so the dog would have little value as a working dog. So stabilizing selection has value as a working dog. So stabilizing selection has chosen a norm for the the size of the Siberian Husky.chosen a norm for the the size of the Siberian Husky.

• Disruptive SelectionDisruptive Selection– Individuals at the upper and lower ends Individuals at the upper and lower ends

of the curve have higher fitness than of the curve have higher fitness than those in the middle.those in the middle.

Disruptive Selection

Largest and smallest seeds become more common.

Num

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Beak Size

Population splits into two subgroups specializing in different seeds.

Beak SizeN

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Low mortality, high fitness

High mortality, low fitness

• Suppose there is a population of rabbits. The color of the Suppose there is a population of rabbits. The color of the rabbits is governed by two incompletely dominant traits: black rabbits is governed by two incompletely dominant traits: black fur represented by “B” and white fur represented by “b”. A fur represented by “B” and white fur represented by “b”. A rabbit with the rabbit with the genotype of “BB” would have a of “BB” would have a phenotype of of black fur, a genotype of “Bb” would have gray fur (a display of black fur, a genotype of “Bb” would have gray fur (a display of both black and white) and a genotype of “bb” would have a both black and white) and a genotype of “bb” would have a phenotype of white fur.phenotype of white fur.

• If this population of rabbits were put into an area that had very If this population of rabbits were put into an area that had very dark black rocks as well as very white colored stone, the rabbits dark black rocks as well as very white colored stone, the rabbits with black fur would be able to hide from predators amongst with black fur would be able to hide from predators amongst the black rocks and the white furred rabbits would be able to the black rocks and the white furred rabbits would be able to hide in the white rocks, but the gray furred rabbits would stand hide in the white rocks, but the gray furred rabbits would stand out in both of the habitats and would suffer greater predation.out in both of the habitats and would suffer greater predation.

• As a consequence of the selective pressures of their As a consequence of the selective pressures of their environment, our hypothetical rabbit population would be environment, our hypothetical rabbit population would be disruptively selected for extreme values of the fur color trait: disruptively selected for extreme values of the fur color trait: white or black, but not gray.white or black, but not gray.

Genetic EquilibriumGenetic EquilibriumHardy-Weinberg principleHardy-Weinberg principle

• If a population did not evolve, or change, If a population did not evolve, or change, the population would reach equilibrium – the population would reach equilibrium – when allele frequencies stay the samewhen allele frequencies stay the same

• Conditions required to reach equilibrium:Conditions required to reach equilibrium:– Random matingRandom mating– Large populationLarge population– No movement in or out of populationNo movement in or out of population– No mutationsNo mutations– No natural selectionNo natural selection

SpeciationSpeciation• Isolation prevents interbreeding Isolation prevents interbreeding

between populationsbetween populations– Behavioral isolationBehavioral isolation

•Different courtship rituals or reproductive Different courtship rituals or reproductive strategiesstrategies

•Example: remember the Example: remember the Drosophila Drosophila fly songs?fly songs?

– Geographic isolationGeographic isolation•Two populations are separated by geographic Two populations are separated by geographic

barriers (rivers, mountains, oceans, etc..)barriers (rivers, mountains, oceans, etc..)

– Temporal isolationTemporal isolation•Species reproduce at different times (winter –Species reproduce at different times (winter –

vs- spring)vs- spring)

• Genetic DriftGenetic Drift– Random changes in allele frequencies that Random changes in allele frequencies that

occur in a small population because of occur in a small population because of possible reproductive abilities of some possible reproductive abilities of some and not othersand not others

– Could result from a bottleneck or founder Could result from a bottleneck or founder effecteffect

– Example:Example:Northern elephant seals have reduced genetic variation probably Northern elephant seals have reduced genetic variation probably because of a population bottleneck humans inflicted on them in because of a population bottleneck humans inflicted on them in the 1890s. Hunting reduced their population size to as few as 20 the 1890s. Hunting reduced their population size to as few as 20 individuals at the end of the 19th century. Their population has individuals at the end of the 19th century. Their population has since rebounded to over 30,000 — but their genes still carry the since rebounded to over 30,000 — but their genes still carry the marks of this bottleneck: they have much less genetic variation marks of this bottleneck: they have much less genetic variation than a population of southern elephant seals that was not so than a population of southern elephant seals that was not so intensely hunted.intensely hunted.

Bottleneck: Bottleneck: an intense pressure or calamity an intense pressure or calamity reduces the numbers in a populationreduces the numbers in a population

Founder Effect:Founder Effect:–Changes in allele frequencies as a result of Changes in allele frequencies as a result of migration of a small subgroupmigration of a small subgroup–Example: the Afrikaner population of Dutch settlers in South Example: the Afrikaner population of Dutch settlers in South Africa is descended mainly from a few colonists. Today, the Africa is descended mainly from a few colonists. Today, the Afrikaner population has an unusually high frequency of the Afrikaner population has an unusually high frequency of the gene that causes Huntington's disease, because those gene that causes Huntington's disease, because those original Dutch colonists just happened to carry that gene original Dutch colonists just happened to carry that gene with unusually high frequency. This effect is easy to with unusually high frequency. This effect is easy to recognize in genetic diseases, but of course, the frequencies recognize in genetic diseases, but of course, the frequencies of all sorts of genes are affected by founder eventsof all sorts of genes are affected by founder events

Checkpoint!Checkpoint!• Which of these is Which of these is notnot a characteristic of a a characteristic of a

population in equilibrium?population in equilibrium?– A. no mutationsA. no mutations B. no movementB. no movement– C. no natural selectionC. no natural selection D. non random matingD. non random mating

• When a daffodil blooms in the spring and a When a daffodil blooms in the spring and a sunflower blooms in the summer, what kind sunflower blooms in the summer, what kind of isolation keeps them from interbreeding?of isolation keeps them from interbreeding?– A. behavioralA. behavioral B. temporalB. temporal– C. geographicC. geographic D. physicalD. physical