EVOLUTIONEvolution: genetic change in a

population of organisms over time

Macroevolution (large-scale)Macroevolution (large-scale) Origins of new species and life forms as well as extinctionsOrigins of new species and life forms as well as extinctions

Microevolution (small scale)Microevolution (small scale) Changes in gene frequencies within a speciesChanges in gene frequencies within a species

Jean-Baptiste LamarckJean-Baptiste LamarckProposed that variation is created within a species based on life experiences (acquired characteristics) which can

then be inherited by offspringEXAMPLE:

Key: Change is driven by an inner “need” or desire! If you work hard enough, you will have the trait and pass it on!

Charles DarwinCharles Darwin In 1831, Charles Darwin In 1831, Charles Darwin

took on the role of took on the role of naturalist of the ship naturalist of the ship HMS HMS BeagleBeagle

The The BeagleBeagle set sail on a set sail on a five-year navigational trip five-year navigational trip around the worldaround the world

Charles Darwin (1809-1882)

Darwin’s TripDarwin’s Trip

Darwin studied a wide variety of plants and Darwin studied a wide variety of plants and animals across the globe, particularly on the animals across the globe, particularly on the Galapagos IslandsGalapagos Islands

In 1859, he published his book In 1859, he published his book On the Origin On the Origin of Speciesof Species In it he proposed that evolution occurs through In it he proposed that evolution occurs through

natural selectionnatural selection

Darwin’s Evidences for Natural Darwin’s Evidences for Natural SelectionSelection

Fossils of extinct species resembled living species Fossils of extinct species resembled living species in the same areain the same area

Galapagos finches differed slightly in appearance Galapagos finches differed slightly in appearance but resembled those on the S. American mainlandbut resembled those on the S. American mainland

He believed it was “descent with modification” from He believed it was “descent with modification” from a common ancestor (AKA evolution!)a common ancestor (AKA evolution!)

Darwin’s Book & WallaceDarwin’s Book & Wallace

Darwin drafted a preliminary transcript of his book in Darwin drafted a preliminary transcript of his book in 18421842 However, he shelved it for 16 years, probably because of its However, he shelved it for 16 years, probably because of its

controversial naturecontroversial nature

Alfred Russel Wallace (1823-1913) independently Alfred Russel Wallace (1823-1913) independently developed a similar theory to Darwin’sdeveloped a similar theory to Darwin’s Correspondence between the two spurred Darwin to publish Correspondence between the two spurred Darwin to publish

his theory in 1859his theory in 1859

Natural SelectionNatural Selection

Natural SelectionNatural Selection refers to the differential refers to the differential reproduction of genotypes caused by reproduction of genotypes caused by factors in the environmentfactors in the environment

More simply put… factors in the environment, such as climate, competition for food, or predators, affect which organisms will survive and therefore reproduce to pass on their genes

Steps of Natural SelectionSteps of Natural Selection

1. Gene variation exists among individuals in a population 1. Gene variation exists among individuals in a population (some are “fitter” than others)(some are “fitter” than others)

2. This variation can be passed to offspring (variation is 2. This variation can be passed to offspring (variation is due to differences in DNA)due to differences in DNA)

3. All populations overproduce offspring (not all will live)3. All populations overproduce offspring (not all will live) 4. Individuals with traits that aid survival and reproduction 4. Individuals with traits that aid survival and reproduction

have a better chance of contributing to the next generation have a better chance of contributing to the next generation (those that will live will have babies!)(those that will live will have babies!)

5. Over time, the population changes such that the traits of 5. Over time, the population changes such that the traits of the more successful reproducers are more prevalent (those the more successful reproducers are more prevalent (those that live pass on their traits that made them more successful that live pass on their traits that made them more successful in the first place!)in the first place!)

Natural SelectionNatural Selection

Adaptation: changes that increase the likelihood of survival and reproduction of particular genetic traits in a population

The Rate of EvolutionThe Rate of Evolution

Different kinds of organisms evolve at different Different kinds of organisms evolve at different ratesratesEx: Bacteria evolve much faster than eukaryotesEx: Bacteria evolve much faster than eukaryotes

The rate of evolution also differs within the same The rate of evolution also differs within the same group of speciesgroup of species In In punctuated equilibriumpunctuated equilibrium, evolution occurs in , evolution occurs in

spurtsspurts In In gradualismgradualism, evolution occurs in a gradual, uniform , evolution occurs in a gradual, uniform

wayway

a) Punctuated equilibrium b) Gradualism

Scientists still debate

as to which

happens…there

seems to be

evidence for both!

Evidence for EvolutionEvidence for Evolution

Evidence for evolution comes from the Evidence for evolution comes from the followingfollowing

Fossil recordFossil record

Molecular recordMolecular record

Anatomical recordAnatomical record

Fossil RecordFossil Record

FossilsFossils are the preserved remains, tracks, or traces of are the preserved remains, tracks, or traces of once-living organismsonce-living organisms They form when organisms become buried in sediment and They form when organisms become buried in sediment and

calcium in hard surfaces mineralizescalcium in hard surfaces mineralizes

Arraying fossils according to age often provides Arraying fossils according to age often provides evidence of successive evolutionary changeevidence of successive evolutionary change

Fossils…how to put in order?Fossils…how to put in order?

Relative Age:Relative Age: Looked at the fossils pulled Looked at the fossils pulled from the ground…Law of Superposition from the ground…Law of Superposition states that the farther down it is, the older states that the farther down it is, the older it isit is

Absolute Age:Absolute Age: Use radioactive isotopes to Use radioactive isotopes to find the precise age (fossil dating)find the precise age (fossil dating)

Fossils have been Fossils have been found linking all the found linking all the major groupsmajor groups

The forms linking The forms linking mammals to reptiles mammals to reptiles are particularly well are particularly well knownknown

EmbryologyEmbryologyAll organisms in their early developmental patterns look similar…links to a common ancestor?

Anatomical RecordAnatomical Record

Looking at the anatomy of organisms Looking at the anatomy of organisms shows similarities…shows similarities…

Homologous Homologous structuresstructures Built of the Built of the

same same basic basic components, components, but serve but serve different different functionsfunctions

Anatomical RecordAnatomical Record

Analogous structuresAnalogous structures Different anatomical structures and ancestors, Different anatomical structures and ancestors,

but the structures serve the same purposebut the structures serve the same purpose

Anatomical RecordAnatomical Record

Vestigial organsVestigial organs Structures that are no longer in use, but still Structures that are no longer in use, but still

presentpresent

DNA EvidenceDNA Evidence

Evolutionary changes involve a continual accumulation Evolutionary changes involve a continual accumulation of genetic changesof genetic changes Distantly-related organisms accumulate a greater Distantly-related organisms accumulate a greater

number of evolutionary differences than closely-number of evolutionary differences than closely-related onesrelated ones

Compare the DNA sequences among organisms! The Compare the DNA sequences among organisms! The most closely related organisms have more similar DNA most closely related organisms have more similar DNA sequences!sequences!

**BEST EVIDENCE!!**

DNA EvidenceDNA EvidenceThe greater the

evolutionary distance

The greater the number of amino acid differences

Patterns of EvolutionPatterns of Evolution

1.1. Coevolution: long term, evolutionary adjustment of Coevolution: long term, evolutionary adjustment of organisms to each otherorganisms to each other

Example: flowers and their pollinatorsExample: flowers and their pollinators

Patterns of EvolutionPatterns of Evolution

2.2. Convergent Evolution: organisms that have Convergent Evolution: organisms that have NO common ancestry look similar due to the NO common ancestry look similar due to the environment in which they liveenvironment in which they live

Example: sharks and dolphins (analogous Example: sharks and dolphins (analogous structures)structures)

3.3. Divergent Evolution: organisms that HAVE Divergent Evolution: organisms that HAVE a common ancestry, but look different due to a common ancestry, but look different due to the environment in which they livesthe environment in which they lives

Example: finches!Example: finches!

Back to Natural Selection…Back to Natural Selection…

FitnessFitness: an organism’s : an organism’s fitness describes how fitness describes how well that organism will well that organism will survive and reproducesurvive and reproduce

Artificial SelectionArtificial Selection: the : the intentional reproduction intentional reproduction of specific individuals of specific individuals in a population in a population Example: purebred dogs, Example: purebred dogs,

horses, crops, etc.horses, crops, etc.

Patterns of Natural SelectionPatterns of Natural Selection

Directional SelectionDirectional Selection: One phenotype is more : One phenotype is more favorable; allele frequency shifts in one directionfavorable; allele frequency shifts in one direction

Example: Peppered Moth! Light colored was favored before Industrial Revolution. After, there was a lot of soot in the air, darker moths became favored. The gene frequency shifted in favor of dark moths!

Patterns of Natural SelectionPatterns of Natural Selection Stabilizing SelectionStabilizing Selection: population becomes less : population becomes less

varied and more normalizedvaried and more normalized

Example: Human birth weights! Babies weighing between 7.5-8.5 pounds at birth have the highest survival rate (98.5%). Anything below or above this drops the survival rate. Birth weight is now stabilized around 8 lbs.

Patterns of Natural SelectionPatterns of Natural Selection Disruptive SelectionDisruptive Selection: extreme values for a trait : extreme values for a trait

are favored over intermediatesare favored over intermediates

Example: Think of fish! If you are small, you can hide. If you are large, you can scare away predators or threats. If you are the intermediate size…you’ll be eaten.

Hardy-Weinberg EquilibriumHardy-Weinberg Equilibrium

Genetic variation in populations puzzled Genetic variation in populations puzzled scientistsscientists Dominant alleles were believed to drive recessive Dominant alleles were believed to drive recessive

alleles out of populationsalleles out of populations In 1908, G. Hardy and W. Weinberg pointed In 1908, G. Hardy and W. Weinberg pointed

out that in large populations with random out that in large populations with random mating, mating, alleleallele frequenciesfrequencies remain constant remain constant Dominant alleles do not, in fact, replace recessive Dominant alleles do not, in fact, replace recessive

onesones

Hardy-Weinberg EquilibriumHardy-Weinberg Equilibrium Hardy-Weinberg EquilibriumHardy-Weinberg Equilibrium: : A state in which genotype A state in which genotype

frequencies and ratios remain constant from generation to frequencies and ratios remain constant from generation to generation and in which genotype frequencies are a product of generation and in which genotype frequencies are a product of allele frequencies allele frequencies

A population that is in A population that is in Hardy-Weinberg equilibriumHardy-Weinberg equilibrium is NOT evolving, meaning:is NOT evolving, meaning:

1. Large population size1. Large population size2. Random mating2. Random mating3. No mutation3. No mutation4. No migration 4. No migration 5. No natural selection5. No natural selection

Hardy-Weinberg EquilibriumHardy-Weinberg Equilibrium

Let’s look at a gene for cat’s coat color. The cats can Let’s look at a gene for cat’s coat color. The cats can either be black or white. There are 2 possible alleles: either be black or white. There are 2 possible alleles: B or b.B or b. The more common allele (B) is designated The more common allele (B) is designated pp The less common allele (b) is designated The less common allele (b) is designated qq p p ++ q q = 1 = 1 (Only 2 alleles, must add up to 100%!)(Only 2 alleles, must add up to 100%!)

Hardy-Weinberg EquilibriumHardy-Weinberg Equilibrium

The Hardy-Weinberg equilibrium can be written as The Hardy-Weinberg equilibrium can be written as an equationan equation 1 = 1 = pp22 + 2 + 2pqpq + + qq22

Individuals homozygous for allele B

Individuals heterozygous for alleles B and b

Individuals homozygous for allele b

The equation allows calculation of allele frequencies

Hardy-Weinberg EquilibriumHardy-Weinberg Equilibrium

Back to our example, let’s say that out of 100 Back to our example, let’s say that out of 100 cats, 16 are white and 84 are black. This cats, 16 are white and 84 are black. This gives us some information…gives us some information…

Frequency of white cats (bb) = 0.16Frequency of white cats (bb) = 0.16 qq22 = 0.16 = 0.16 qq = = √0.16 = 0.4√0.16 = 0.4 pp++qq=1 Therefore… =1 Therefore… pp=0.6=0.6 Frequency of homozygous dominant? Frequency of homozygous dominant? pp22

Frequency of heterozygous? 2Frequency of heterozygous? 2pqpq

Hardy-Weinberg ExampleHardy-Weinberg Example

If 9% of an African population is born with a If 9% of an African population is born with a severe form of sickle-cell anemia (ss), what severe form of sickle-cell anemia (ss), what percentage of the population will be percentage of the population will be heterozygous(Ss) for the sickle-cell gene? heterozygous(Ss) for the sickle-cell gene?

Why do allele frequencies change?Why do allele frequencies change?

Five evolutionary forces can significantly alter the Five evolutionary forces can significantly alter the allele frequencies of a populationallele frequencies of a population

1. Mutation1. Mutation 2. Migration2. Migration 3. Genetic drift3. Genetic drift 4. Nonrandom mating4. Nonrandom mating 5. Selection5. Selection

MutationMutation

Errors in DNA Errors in DNA replicationreplication

The ultimate source of The ultimate source of new variationnew variation

However, mutations are However, mutations are rare…they are only one rare…they are only one small factorsmall factor

MigrationMigration

Movement of individuals from Movement of individuals from one population to anotherone population to another ImmigrationImmigration: movement into : movement into

a populationa population EmigrationEmigration: movement out : movement out

of a populationof a population

A very potent agent of changeA very potent agent of change

Genetic DriftGenetic Drift Random loss of allelesRandom loss of alleles

More likely to occur in smaller More likely to occur in smaller populationpopulation

Founder effectFounder effect Small group of individuals Small group of individuals

establishes a population in a new establishes a population in a new location, those genes take overlocation, those genes take over

Bottleneck effectBottleneck effect A sudden decrease in population size A sudden decrease in population size

to natural forces; whoever lives to natural forces; whoever lives passes their genes onpasses their genes on

Nonrandom MatingNonrandom Mating

Mating that occurs more or less Mating that occurs more or less frequently than expected by frequently than expected by chancechance

Inbreeding Inbreeding Mating with relativesMating with relatives Increases homozygosityIncreases homozygosity

OutbreedingOutbreeding Mating with non-relativesMating with non-relatives Increases heterozygosityIncreases heterozygosity

SelectionSelection Some individuals leave Some individuals leave

behind more offspring than behind more offspring than othersothers

Artificial selection Artificial selection Breeder selects for Breeder selects for

desired characteristicsdesired characteristics Natural selectionNatural selection

Environment selects for Environment selects for adapted characteristicsadapted characteristics