EvolutionEvolution

Pre-AP BiologyPre-AP Biology

Charles DarwinCharles Darwin

Known as the Father of EvolutionKnown as the Father of Evolution Wrote book Wrote book On the Origin of SpeciesOn the Origin of Species Sailed the world on a ship called the Sailed the world on a ship called the

BeagleBeagle

DarwinDarwin

Evidence for EvolutionEvidence for Evolution

The fossil recordThe fossil record – show biodiversity, mass – show biodiversity, mass extinctions and episodic speciationextinctions and episodic speciation

Geographic Distribution of Living SpeciesGeographic Distribution of Living Species – – shows similarities among species living on shows similarities among species living on different continentsdifferent continents

Homologous Body StructuresHomologous Body Structures – structures – structures that have different mature forms but come that have different mature forms but come from the same embryonic tissue.from the same embryonic tissue.

Similarities in Early DevelopmentSimilarities in Early Development – – embryos of many vertebrates are very embryos of many vertebrates are very similar.similar.

EmbryologyEmbryology

Fossils and EvolutionFossils and Evolution

Natural SelectionNatural Selection

Over time natural selection results in Over time natural selection results in changes in the inherited changes in the inherited characteristics of a population. These characteristics of a population. These changes increase a species’ fitness changes increase a species’ fitness (ability to survive and reproduce) in its (ability to survive and reproduce) in its environment.environment.

Natural Selection causes struggles for Natural Selection causes struggles for existence and survival of the fittest.existence and survival of the fittest.

Natural Selection act on the phenotype Natural Selection act on the phenotype rather than the genotype of a species.rather than the genotype of a species.

Gene PoolsGene Pools A A gene pool gene pool is the combined genetic information is the combined genetic information

of all the members of a particular population.of all the members of a particular population. A A gene pool gene pool typically has two or more alleles for typically has two or more alleles for

a given trait.a given trait. Homozygous lethal traits can be carried by Homozygous lethal traits can be carried by

heterozygous individuals and thus remain in a heterozygous individuals and thus remain in a gene pool.gene pool.

Relative Frequency Relative Frequency is the number of times an is the number of times an allele occurs in a gene pool compared with the allele occurs in a gene pool compared with the number of times other alleles occur.number of times other alleles occur.

MicroevolutionMicroevolution is evolution on its smallest scale; is evolution on its smallest scale; change in the relative frequencies of alleles in a change in the relative frequencies of alleles in a population over generations.population over generations.

What are gene pools?What are gene pools?

Sources of VariationSources of Variation

Two main sources are mutations and Two main sources are mutations and gene shuffling.gene shuffling.

MutationsMutations – changes in DNA – changes in DNA sequence. These may or may not sequence. These may or may not affect an organisms fitness.affect an organisms fitness.

Gene shufflingGene shuffling – is the random – is the random shuffling of genes caused by sexual shuffling of genes caused by sexual reproduction.reproduction.

Natural Selection on Single-Gene Natural Selection on Single-Gene TraitsTraits

Natural selection on single-gene Natural selection on single-gene traits can lead to changes in allele traits can lead to changes in allele frequencies and thus to evolution.frequencies and thus to evolution.

If the change is beneficial to the If the change is beneficial to the organism, the change may cause the organism, the change may cause the original form to fade out and the original form to fade out and the newer organisms to be more fit and newer organisms to be more fit and take over.take over.

Natural Selection on Polygenic Natural Selection on Polygenic TraitsTraits

Natural Selection can affect the Natural Selection can affect the distribution of phenotypes in a distribution of phenotypes in a population in any of three ways: population in any of three ways: directional, disruptive and stabilizing.directional, disruptive and stabilizing.

The 3 selectionsThe 3 selections DirectionalDirectional

One phenotype is favored (Larger Beak)One phenotype is favored (Larger Beak) StabilizingStabilizing

The average is best fit (Medium Beak)The average is best fit (Medium Beak) DisruptiveDisruptive

Both extremes are favored (Small and Both extremes are favored (Small and Large)Large)

Can lead to separate speciesCan lead to separate species

Directional SelectionDirectional Selection

Directional Directional SelectionSelection – – Evolution causes Evolution causes an increase in the an increase in the number of number of individuals with the individuals with the trait at one end of trait at one end of the curve.the curve.

Graph of Directional SelectionGraph of Directional Selection

Stabilizing SelectionStabilizing Selection

Individuals in the Individuals in the center of the curve center of the curve and more fit and and more fit and thus the curve thus the curve narrowsnarrows

Graph of Stabilizing SelectionGraph of Stabilizing Selection

Disruptive SelectionDisruptive Selection

Individuals at the Individuals at the ends of the curve ends of the curve are more fit than are more fit than the ones in the the ones in the middle causing two middle causing two curves to form and curves to form and possible new possible new species to form.species to form.

Genetic DriftGenetic Drift

In small populations, individuals that In small populations, individuals that carry a particular allele may leave carry a particular allele may leave more descendants than other more descendants than other individuals, just by chance. Over individuals, just by chance. Over time, a series of chance occurrences time, a series of chance occurrences of this type can cause an allele to of this type can cause an allele to become common in a population.become common in a population.

Hardy-WeinbergHardy-Weinberg

Genetic equilibrium takes place when allele Genetic equilibrium takes place when allele frequencies remain constant.frequencies remain constant.

In order for genetic equilibrium to take In order for genetic equilibrium to take place, five factors must remain true.place, five factors must remain true.

1. random mating1. random mating 2. Large Population2. Large Population 3. No movement in or out of the population3. No movement in or out of the population 4. No Mutations4. No Mutations 5. No Natural Selection5. No Natural Selection

Hardy-WeinbergHardy-Weinberg

H-W ConditionsH-W Conditions

SpeciationSpeciation

Reproductive IsolationReproductive Isolation occurs occurs when members of two populations when members of two populations cannot interbreed. At that point, cannot interbreed. At that point, they have different gene pools.they have different gene pools.

Types of IsolationTypes of Isolation

Behavioral IsolationBehavioral Isolation – Two populations – Two populations capable of interbreeding but have capable of interbreeding but have differences in courtship rituals or other differences in courtship rituals or other types of behavior.types of behavior.

Geographic IsolationGeographic Isolation – Populations are – Populations are separated by geographic barriers such separated by geographic barriers such as rivers, mountains, or bodies of as rivers, mountains, or bodies of water.water.

Temporal IsolationTemporal Isolation – Species reproduce – Species reproduce at different times of the year.at different times of the year.

SpeciationSpeciation

Galapagos FinchesGalapagos Finches

Speciation in the Galapagos Finches Speciation in the Galapagos Finches occurred by founding of new occurred by founding of new populations, geographic isolation, populations, geographic isolation, gene pool changes, reproductive gene pool changes, reproductive isolation, and ecological competition.isolation, and ecological competition.

Survival Survival

Variation within a species help insure Variation within a species help insure that some will survive major changes that some will survive major changes in the environment.in the environment.

Major diversity of species also insure Major diversity of species also insure that some of the species will survive that some of the species will survive major environmental changes.major environmental changes.

MACROEVOLUTIONMACROEVOLUTION

Evolutionary change on a grand Evolutionary change on a grand scale, including the origin of scale, including the origin of new species and large scale new species and large scale evolutionary trends.evolutionary trends.

Mass ExtinctionMass Extinction

Mass Extinction means that MOST, Mass Extinction means that MOST, but NOT ALL species went extinct but NOT ALL species went extinct during a short time period.during a short time period.

Because of Because of GREAT BIOLOGICAL GREAT BIOLOGICAL DIVERSITYDIVERSITY before a catastrophic before a catastrophic event, some individuals of some event, some individuals of some species survive the event.species survive the event.

Macroevolution PatternsMacroevolution Patterns

Adaptive RadiationAdaptive Radiation: When many species : When many species disappear, habitats and ecological disappear, habitats and ecological opportunities are left open for survivors opportunities are left open for survivors take overtake over

The result seems to be a burst of The result seems to be a burst of evolution that produces many new evolution that produces many new speciesspecies

For example, when the dinosaurs went For example, when the dinosaurs went extinct, that cleared the way for extinct, that cleared the way for evolution of modern mammals and birdsevolution of modern mammals and birds

Let’s pretend that this is a small Let’s pretend that this is a small population of rhinospopulation of rhinos

Macroevolution PatternsMacroevolution Patterns

Macroevolution = Macroevolution = large scale large scale evolutionary changesevolutionary changes Mass ExtinctionMass Extinction Adaptive RadiationAdaptive Radiation Convergent EvolutionConvergent Evolution CoevolutionCoevolution Punctuated EquilibriumPunctuated Equilibrium Changes in developmental genesChanges in developmental genes

Mass ExtinctionMass Extinction Extinction occurs all the time: more than Extinction occurs all the time: more than

99% of all species that ever lived on Earth 99% of all species that ever lived on Earth are now extinct!are now extinct!

Mass extinction = Mass extinction = huge numbers of huge numbers of species disappearspecies disappear

Mass extinctions extinguish species and Mass extinctions extinguish species and also wipe out whole ecological systemsalso wipe out whole ecological systems

It is difficult to determine the causes of It is difficult to determine the causes of mass extinctions, possibly volcanoes, mass extinctions, possibly volcanoes, continental shifts, changing sea level, continental shifts, changing sea level, asteroids?asteroids?

Mass extinctions often Mass extinctions often result in bursts of result in bursts of evolution producing many new speciesevolution producing many new species

Adaptive RadiationAdaptive Radiation A single species or a small group of A single species or a small group of

species species evolved into several differentevolved into several different forms that live in different waysforms that live in different ways For example, Darwin’s finchesFor example, Darwin’s finches When dinosaurs became extinct, it When dinosaurs became extinct, it

made way for adaptive radiation of made way for adaptive radiation of mammalsmammals

Convergent EvolutionConvergent Evolution

Groups of Groups of different (unrelated) organismsdifferent (unrelated) organisms can undergo adaptive radiation in different can undergo adaptive radiation in different places or at different times but in places or at different times but in similar similar environmentsenvironments and and natural selectionnatural selection may may mold different body structures to mold different body structures to look very look very similarsimilar

So, unrelated organisms come to resemble So, unrelated organisms come to resemble one anotherone another Analogous structuresAnalogous structures = structures which = structures which

look and function similarly, but do not look and function similarly, but do not share a common evolutionary historyshare a common evolutionary history

CoevolutionCoevolution

Organisms that are closely Organisms that are closely connected to one another by connected to one another by ecological interactions can ecological interactions can evolve evolve together in response to each other’s together in response to each other’s changeschanges over time over time For example, flowers and pollinatorsFor example, flowers and pollinators

Punctuated EquilibriumPunctuated Equilibrium

Evolution can occur at different rates for different Evolution can occur at different rates for different organisms at different times during Earth’s organisms at different times during Earth’s history:history: GradualismGradualism = biological changes occur slow and steady or = biological changes occur slow and steady or

gradually over timegradually over time EquilibriumEquilibrium = little or no change over time = little or no change over time Punctuated equilibriumPunctuated equilibrium = new species produced by period of = new species produced by period of

rapid change after long periods of equilibriumrapid change after long periods of equilibrium Can be due to isolation, genetic variation, mass extinctions, Can be due to isolation, genetic variation, mass extinctions,

etcetc

Phylogenic TreePhylogenic Tree

A diagram that indicated probable A diagram that indicated probable pathway of evolutionpathway of evolution. .

Branches were species separate and Branches were species separate and form new species. form new species.

The more branches shared, the The more branches shared, the closer the relationship.closer the relationship.

ReviewReview

1.1. Explain what happened to the Explain what happened to the gene pool of the moths color gene pool of the moths color during the Industrial Revolution. during the Industrial Revolution.

2.2. What would you expect to What would you expect to happen to the color of the moths happen to the color of the moths if natural selection did not act on if natural selection did not act on color?color?

3.3. Natural selection acts on the Natural selection acts on the (phenotype/genotype). Genes (phenotype/genotype). Genes only help pass on the traits.only help pass on the traits.