Charles Darwin Charles Darwin and the and the Theory of EvolutionTheory of Evolution

Charles Darwin’s Voyage of Charles Darwin’s Voyage of the Beaglethe Beagle

Galapagos IslandsGalapagos IslandsEven though these islands are close together they varied greatly in their climates Amount of rainfall, vegetation differences, different species!

Darwin’s ObservationsDarwin’s Observations•The plants and animals were well-suited to their environmentThe plants and animals were well-suited to their environment Example: A Cactus is adapted to live in dry areasExample: A Cactus is adapted to live in dry areas

•Species vary in traits and some traits are better suited Species vary in traits and some traits are better suited for different areasfor different areas

Darwin’s FinchesDarwin’s Finches• The The beaksbeaks were were

different from different from island to islandisland to island

• Beaks were better Beaks were better suited for feeding suited for feeding depending upon depending upon location (islands)location (islands)

Darwin’s TortoisesDarwin’s Tortoises

• Due to Due to differences in differences in plant life; Darwin plant life; Darwin noticed that noticed that tortoises had tortoises had differences in differences in SHELLSHELL shapeshape and and NECK lengthsNECK lengths

15-2 15-2 Jean-Baptiste LamarckJean-Baptiste Lamarck• 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?

Darwin Presents His Case-Darwin Presents His Case-18591859

In this book, Darwin In this book, Darwin proposed the concept of proposed the concept of EVOLUTIONEVOLUTION by the method by the method of of NATURAL SELECTIONNATURAL SELECTION..

Evolution is?Evolution is?

Natural Selection is?Natural Selection is?

Speciation is?Speciation is?

Explain how these relate?Explain how these relate?

Evolution by Natural Evolution by Natural SelectionSelection

• Struggle for ExistenceStruggle for ExistenceEach species will compete for food, space, Each species will compete for food, space,

basic needsbasic needs

• Survival of the Fittest/Natural SelectionSurvival of the Fittest/Natural Selection

Fitness=able to survive and reproduce!Fitness=able to survive and reproduce!

• Descent with ModificationDescent with Modification

The “fittest” reproduce thus passing on The “fittest” reproduce thus passing on their GREAT traits!their GREAT traits!

AdaptationsAdaptationsA inherited characteristic that A inherited characteristic that increasesincreases an an organisms chance of survival.organisms chance of survival.

Examples:Examples:

1.1.Anatomical/stucturalAnatomical/stuctural- porcupines sharp - porcupines sharp quills, camouflage, mimicryquills, camouflage, mimicry

2.2.BehavioralBehavioral- mating rituals - mating rituals

3.3.PhysiologicalPhysiological-plant performing -plant performing photosynthesisphotosynthesis

Evolution occurs in Evolution occurs in PopulationsPopulations

But what is a population? *A group of inter-breeding species

*not individuals*

Evolution of PopulationsEvolution of Populations• 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 Gene pool – all genes that are present in – all genes that are present in a populationa population

• Relative frequency Relative frequency – number of times an – 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

How do we know when How do we know when Evolution has occurred?Evolution has occurred?

A change in the A change in the relative frequencyrelative frequency of of alleles in a populationalleles in a population

allele for brown fur

allele for black fur48%

heterozygous black

16% homozygous

black36%

homozygous brown

60% or 30/50=brown allele

Genetic Variation in Genetic Variation in PopulationsPopulations

• 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

3 Causes of 3 Causes of EvolutionEvolution

1. Genetic Drift1. Genetic Drift: : change in the gene pool due to change in the gene pool due to chance (small populations will be greatly affected)chance (small populations will be greatly affected)

A. A. Bottleneck EffectBottleneck Effect- - over hunting, over hunting, earthquake, fire etc…earthquake, fire etc…

*this can lead to endangered species!*this can lead to endangered species!

B. B. Founder Effect- Founder Effect- small group leaves the small group leaves the source population to establish their ownsource population to establish their ownExampleExample:Polydactyly in Amish that came :Polydactyly in Amish that came

to the United Statesto the United States ( (they carried the allelethey carried the allele))

3 Causes of Evolution 3 Causes of Evolution con’tcon’t

2. Gene Flow: 2. Gene Flow: FertileFertile immigrants or emigrants immigrants or emigrants bringing or taking alleles from the bringing or taking alleles from the populationpopulation

Example:Example: If your 2If your 2ndnd period class has all period class has all blue eyed people (bb) and someone comes blue eyed people (bb) and someone comes in that has brown eyes (BB)in that has brown eyes (BB)

3 Causes of Evolution 3 Causes of Evolution con’tcon’t

• Natural Selection: Natural Selection:

Well suited organisms increase their Well suited organisms increase their chance of surviving thus reproducing chance of surviving thus reproducing to pass on their genes (alleles) to the to pass on their genes (alleles) to the next generationnext generation

Example:

Peppered Moth example

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

trait depends on how many genes control the trait depends on how many genes control the traittrait– Single-gene traitSingle-gene trait

•Single gene with Single gene with two allelestwo alleles

•Fewer Fewer phenotypes than phenotypes than polygenic traitspolygenic traits

•Ex: widow’s peakEx: widow’s peak

– Polygenic traitPolygenic trait•Controlled by two Controlled by two

or more genes or more genes (each with more (each with more than 2 alleles)than 2 alleles)

•Many different Many different genotypes and genotypes and phenotypesphenotypes

•Ex: heightEx: height

Natural Selection acts on Natural Selection acts on Polygenic Traits 3 waysPolygenic Traits 3 ways

Disruptive SelectionDirectional Selection Stabilizing Selection

Genetic EquilibriumGenetic Equilibrium

• If a population was to not evolve, or If a population was to not evolve, or change, the population would reach change, the population would reach equilibrium – when allele frequencies equilibrium – when allele frequencies stay the samestay the same

• Conditions required to reach Conditions required to reach equilibrium: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

– 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)