EvolutionEvolutionandand

DarwinDarwin

EvolutionEvolution• The processesprocesses that have transformed life on

earth from it’s earliest formsearliest forms to the vast diversitydiversity that characterizes it today.

• A changechange in the genes!!!!!!!!genes!!!!!!!!

Old Theories of EvolutionOld Theories of Evolution• Jean Baptiste LamarckJean Baptiste Lamarck (early 1800’s) proposed:

““The inheritance of acquired characteristics”The inheritance of acquired characteristics”

• He proposed that by using or not using its body parts, an individual tends to developdevelop certain characteristicscharacteristics, which it passespasses on to its offspringoffspring.

““The Inheritance of Acquired The Inheritance of Acquired Characteristics”Characteristics”

• Example:Example:A giraffe acquired its long neck because its ancestor stretched higher and higher into the trees to reach leaves, and that the animal’s increasingly lengthened neck was passed on to its offspring.

Charles DarwinCharles Darwin• Influenced by Charles LyellInfluenced by Charles Lyell who published

“Principles of Geology”.“Principles of Geology”.

• This publication led DarwinDarwin to realize that natural forces gradually change Earth’s surface and that the forces of the past are still operating in modern times.

Charles DarwinCharles Darwin• Darwin set sail on the H.M.S. BeagleH.M.S. Beagle (1831-1836)

to survey the south seas (mainly South America (mainly South America and the Galapagos Islands)and the Galapagos Islands) to collect plants and animals.

• On the Galapagos Islands, Galapagos Islands, Darwin observed species that lived no where else in the world.

• These observations led Darwin to write a book.

Charles DarwinCharles Darwin• Wrote in 1859Wrote in 1859: “On the Origin of Species by “On the Origin of Species by

Means of Natural Selection”Means of Natural Selection”

• Two main points:Two main points:1.1. Species were not created in their present Species were not created in their present form, but evolved from ancestral species.form, but evolved from ancestral species.

2.2. Proposed a mechanism for evolution:Proposed a mechanism for evolution: NATURAL SELECTIONNATURAL SELECTION

Natural SelectionNatural Selection• IndividualsIndividuals with favourablefavourable traitstraits are more

likely to leave more offspring better suited for their environmentenvironment.

• Also known as “Differential Reproduction”“Differential Reproduction”

• Example:Example:English peppered moth (English peppered moth (Biston betularia))

- light and dark phases- light and dark phases

Artificial SelectionArtificial Selection• The selective breedingselective breeding of domesticated

plants and animals by man.

• Question:Question:What’s the ancestor of the domesticated dog?

• Answer:Answer: WOLFWOLF

Evidence of EvolutionEvidence of Evolution

1.1. Biogeography: Biogeography:Geographical distribution of species.Geographical distribution of species.

2. Fossil Record:2. Fossil Record:Fossils and the order in which they Fossils and the order in which they

appear appear in layers of sedimentary rock in layers of sedimentary rock (strongest (strongest evidence).evidence).

Eastern Long Necked Turtle

Evidence of EvolutionEvidence of Evolution

3. Taxonomy:3. Taxonomy:Classification of life forms.Classification of life forms.

4. Homologous structures:4. Homologous structures:Structures that are similar because Structures that are similar because

of of common ancestry common ancestry (comparative (comparative anatomy)anatomy)

Evidence of EvolutionEvidence of Evolution

5. Comparative embryology:5. Comparative embryology:Study of structures that appear Study of structures that appear

during during embryonic development.embryonic development.

6. Molecular biology:6. Molecular biology:DNA and proteins (amino acids)DNA and proteins (amino acids)

Population GeneticsPopulation Genetics

• The sciencescience of genetic changegenetic change in population.

• Remember:Remember: Hardy-Weinberg equation.(A level only)

PopulationPopulation

• A localized group of individualsindividuals belonging to the same speciessame species.

SpeciesSpecies• A group of populationspopulations whose individualsindividuals

have the potential to interbreedinterbreed and produce viableviable offspring.

GCSE stop

Gene PoolGene Pool

• The total collection of genescollection of genes in a population at any one time.

Hardy-Weinberg PrincipleHardy-Weinberg Principle• The conceptconcept that the shuffling of genesshuffling of genes that

occur during sexual reproduction, by itself, cannot changecannot change the overall genetic makeup of a population.

Hardy-Weinberg PrincipleHardy-Weinberg Principle• This principleprinciple will be maintained in nature only

if all fivefive of the following conditions are met:

1.1. Very large populationVery large population2.2. Isolation from other populationsIsolation from other populations3.3. No net mutationsNo net mutations4.4. Random matingRandom mating5.5. No natural selectionNo natural selection

Hardy-Weinberg PrincipleHardy-Weinberg Principle

• Remember:Remember:If these conditions are met, the

population is at equilibriumequilibrium.

• This means “No Change” or “No “No Change” or “No Evolution”.Evolution”.

MacroevolutionMacroevolution

• The origin of taxonomic groups higher higher than the species levelthan the species level.

MicroevolutionMicroevolution• A change in a population’s gene poolpopulation’s gene pool

over a secession of generations.

• Evolutionary changesEvolutionary changes in species over relatively brief periods of geological timegeological time.

Five Mechanisms of MicroevolutionFive Mechanisms of Microevolution

1. Genetic drift:1. Genetic drift:Change in the gene pool of a Change in the gene pool of a

small small population due to chance.population due to chance.

• Two examples:Two examples:a. Bottleneck effecta. Bottleneck effectb. Founder effectb. Founder effect

a. Bottleneck Effecta. Bottleneck Effect• Genetic driftGenetic drift (reduction of alleles in a population)

resulting from a disasterdisaster that drastically reduces reduces population sizepopulation size.

• Examples:Examples:1.1. EarthquakesEarthquakes2.2. VolcanoesVolcanoes

b. Founder Effectb. Founder Effect• Genetic driftGenetic drift resulting from the colonizationcolonization

of a new location by a small number of individuals.

• Results in random changerandom change of the gene pool.

• Example:Example:1.1. Islands (first Darwin finch)Islands (first Darwin finch)

Five Mechanisms of MicroevolutionFive Mechanisms of Microevolution

2. Gene Flow:2. Gene Flow:TThe gain or loss of allelesgain or loss of alleles from a population by the movementmovement of individuals or gametes.

• Immigration or emigrationImmigration or emigration.

Five Mechanisms of MicroevolutionFive Mechanisms of Microevolution

3. Mutation:3. Mutation:Change in an organism’s DNA thatChange in an organism’s DNA that creates creates a new allele.a new allele.

4. Non-random mating:4. Non-random mating:The selection of mates other thanThe selection of mates other than by by chance.chance.

5. Natural selection:5. Natural selection:Differential reproduction.Differential reproduction.

Modes of ActionModes of Action• Natural selectionNatural selection has three modesthree modes of action:

1.1. Stabilizing selectionStabilizing selection2.2. Directional selectionDirectional selection3.3. Diversifying selectionDiversifying selection

Number ofIndividuals

Size of individualsSmall Large

1.1. Stabilizing SelectionStabilizing Selection• ActsActs upon extremesextremes and favorsfavors the

intermediateintermediate.

Number ofIndividuals

Size of individualsSmall Large

2.2. Directional SelectionDirectional Selection• FavorsFavors variants of one extremeone extreme.

Number ofIndividuals

Size of individualsSmall Large

3.3. Diversifying SelectionDiversifying Selection• FavorsFavors variants of opposite extremesopposite extremes.

Number ofIndividuals

Size of individualsSmall Large

SpeciationSpeciation• The evolutionevolution of new species.

Reproductive BarriersReproductive Barriers• Any mechanismmechanism that impedesimpedes two species

from producing fertile and/or viable hybrid fertile and/or viable hybrid offspringoffspring.

• Two barriers:Two barriers:1.1. Pre-zygotic barriersPre-zygotic barriers2.2. Post-zygotic barriersPost-zygotic barriers

1.1. Pre-zygotic BarriersPre-zygotic Barriersa. Temporal isolation:a. Temporal isolation:

Breeding occurs at different times for different species.

b. Habitat isolation:b. Habitat isolation:Species breed in different habitats.

c. Behavioral isolation:c. Behavioral isolation:Little or no sexual attraction between species.

1.1. Pre-zygotic BarriersPre-zygotic Barriers

d. Mechanical isolation:d. Mechanical isolation:Structural differences prevent gamete

exchange.

e. Gametic isolation:e. Gametic isolation:Gametes die before uniting with

gametes of other species, or gametes fail to unite.

2.2. Post-zygotic BarriersPost-zygotic Barriersa. Hybrid inviability:a. Hybrid inviability:

Hybrid zygotes fail to develop or fail to reach sexual maturity.

b. Hybrid sterility:b. Hybrid sterility:Hybrid fails to produce functional gametes.

c. Hybrid breakdown:c. Hybrid breakdown:Offspring of hybrids are weak or infertile.

Allopatric SpeciationAllopatric Speciation• Induced when the ancestralancestral population

becomes separatedseparated by a geographical geographical barrier.barrier.

• Example:Example:Grand Canyon and ground squirrels

Adaptive RadiationAdaptive Radiation• Emergence of numerous speciesEmergence of numerous species from a

common ancestorcommon ancestor introduced to new and diverse environments.

• Example:Example:Darwin’s FinchesDarwin’s Finches

Sympatric SpeciationSympatric Speciation• Result of a radical change in the genome that

produces a reproductively isolated sub-reproductively isolated sub-populationpopulation within the parent population (rare).

• Example: Plant evolution - polyploidExample: Plant evolution - polyploidA species doubles it’s chromosome #chromosome #

to become tetraploid.

reproductive sub-population

Parent population

Interpretations of SpeciationInterpretations of Speciation• Two theories:Two theories:

1.1. Gradualist Model (Neo-Darwinian):Gradualist Model (Neo-Darwinian):Slow changes in species overtime.

2.2. Punctuated Equilibrium:Punctuated Equilibrium:Evolution occurs in spurts of relatively

rapid change.

Convergent EvolutionConvergent Evolution• SpeciesSpecies from different evolutionary branchesevolutionary branches

may come to resemble one another if they live in very similar environments.very similar environments.

• Example:Example:1.1. Ostrich (Africa) and Emu (Australia).Ostrich (Africa) and Emu (Australia).2.2. Sidewinder (Mojave Desert) andSidewinder (Mojave Desert) and

Horned Viper (Middle East Desert)Horned Viper (Middle East Desert)

CoevolutionCoevolution• Evolutionary changeEvolutionary change, in which one species

act as a selective forceselective force on a secondsecond species, inducing adaptations that in turn act as selective force on the firstfirst species.

• Example:Example:1.1. Acacia ants and acacia treesAcacia ants and acacia trees2.2. Humming birds and plants with Humming birds and plants with flowers flowers with long tubeswith long tubes