Darwin and Natural SelectionDarwin and Natural Selection Was from England.Was from England. Beagle Expedition: found Beagle Expedition: found

unique species that looked unique species that looked similar to species from other similar to species from other parts of the world. parts of the world.

Found that many of the Found that many of the plants and animals on plants and animals on Galapagos resembled those Galapagos resembled those in nearby South Americain nearby South America

Voyage of the HMS BeagleVoyage of the HMS Beagle

The Origin of the SpeciesThe Origin of the Species

On The Origin of Species On The Origin of Species by Means of Natural by Means of Natural Selection Selection Nov. 1859 Nov. 1859 Charles DarwinCharles Darwin

Darwin suggested that Darwin suggested that humans are related to humans are related to apesapes

Other scientistOther scientist

Lamarck believed that over the lifetime of an Lamarck believed that over the lifetime of an individual, physical features increase in size individual, physical features increase in size because of use and decrease from nonusebecause of use and decrease from nonuse

Malthus suggested that human pops. do not Malthus suggested that human pops. do not grow unchecked because death caused by grow unchecked because death caused by disease, war, and famine slows growthdisease, war, and famine slows growth

Natural SelectionNatural Selection

Natural selection: organisms with Natural selection: organisms with favorable traits for a particular favorable traits for a particular environment survive, reproduce, and pass environment survive, reproduce, and pass these traits on to the next generation these traits on to the next generation (those with less favorable traits are less (those with less favorable traits are less likely to survive).likely to survive).

Adaptation- inherited trait that has become Adaptation- inherited trait that has become common in a population because the trait common in a population because the trait provides a selective advantageprovides a selective advantage

Evolution of HumansEvolution of Humans

The Descent of Man, The Descent of Man, and Selection in and Selection in Relation to Sex Relation to Sex Charles Darwin 1871Charles Darwin 1871

Darwin outlined Darwin outlined sexual selection to sexual selection to explain the evolution explain the evolution of humansof humans

4 Tenets of Natural 4 Tenets of Natural SelectionSelection

All populations have genetic variation. All populations have genetic variation. The environment presents challenges to The environment presents challenges to

successful reproduction. successful reproduction. Individuals tend to produce more offspring Individuals tend to produce more offspring

than the environment can support.than the environment can support. Individuals that are better fit their Individuals that are better fit their

environment tend to live longer, reproduce environment tend to live longer, reproduce more, and spread their genes throughout the more, and spread their genes throughout the population.population.

Darwin’s 4 FactsDarwin’s 4 Facts

Exponential Growth of PopulationsExponential Growth of Populations Factors will prevent Exponential Factors will prevent Exponential

Growth(Steady State)Growth(Steady State) Variability among speciesVariability among species Traits are inheritableTraits are inheritable

Darwin’s 2 InferencesDarwin’s 2 Inferences

Competition for resourcesCompetition for resources Individuals most fit for their environment Individuals most fit for their environment

will survive. will survive.

Sources of Genetic VariationSources of Genetic Variation Mutation/ Translocation- Mutation slowly Mutation/ Translocation- Mutation slowly

introduces new alleles which natural selection introduces new alleles which natural selection helps distribute (can be harmful, beneficial or helps distribute (can be harmful, beneficial or have no significance)have no significance)

Crossing Over- exchange of homologous Crossing Over- exchange of homologous chromosome segmentschromosome segments

Independent Assortment- assortment of Independent Assortment- assortment of chromosomeschromosomes

Sexual Reproduction- combination of allelles of Sexual Reproduction- combination of allelles of two individualstwo individuals

Immigration- incoming allelles to a gene poolImmigration- incoming allelles to a gene pool

Mechanisms for Evolutionary Mechanisms for Evolutionary ChangeChange

Natural SelectionNatural Selection

Population Genetics and Population Genetics and EvolutionEvolution

Populations evolve when natural selection causes changes Populations evolve when natural selection causes changes in their allele distribution.in their allele distribution.

Natural selection causes the greatest changes to Natural selection causes the greatest changes to populations’ gene pools, but is not the only cause populations’ gene pools, but is not the only cause of changeof change

Gene Pool- all the alleles of a population of a speciesGene Pool- all the alleles of a population of a species In a population’s gene pool, each allele has a certain In a population’s gene pool, each allele has a certain

frequency which governs the frequency of phenotypesfrequency which governs the frequency of phenotypes If a population’s allele frequencies do not change, it is not If a population’s allele frequencies do not change, it is not

evolving and is said to be in genetic equilibriumevolving and is said to be in genetic equilibrium Individuals don’t evolve, populations of species do!Individuals don’t evolve, populations of species do!

Other Influences on the Gene Other Influences on the Gene PoolPool

In In small small populations, change events populations, change events (crossing over, translation errors) can (crossing over, translation errors) can cause shifts in a gene pool = genetic drift cause shifts in a gene pool = genetic drift

Individuals may move into or out of a Individuals may move into or out of a population, bringing or taking alleles with population, bringing or taking alleles with them = migrationthem = migration

Population EvolutionPopulation Evolution Gene flow-the movement of genes into or Gene flow-the movement of genes into or

out of a population due to interbreeding.out of a population due to interbreeding. Immigration- the flow of alleles into a Immigration- the flow of alleles into a

population.population. Emigration-the flow of alleles out of a Emigration-the flow of alleles out of a

population.population. Genetic drift- the random change of allele Genetic drift- the random change of allele

frequency in a population, not due to natural frequency in a population, not due to natural selection.selection.

Population EvolutionPopulation Evolution

Artificial selection- a process in which humans Artificial selection- a process in which humans consciously select for or against particular features consciously select for or against particular features in organisms. in organisms.

Genetic bottleneck-an event in which the Genetic bottleneck-an event in which the populations’ size is greatly reduced; reduces populations’ size is greatly reduced; reduces genetic variabilitygenetic variability

Founder effect-changes in gene frequency from Founder effect-changes in gene frequency from starting a new population from a small number of starting a new population from a small number of individuals; reduces genetic variability. individuals; reduces genetic variability.

AdaptationsAdaptations Structural:Structural:

Can change the size and/or shape of a body partCan change the size and/or shape of a body part For example: thorns, wings, mimicry (copy the appearance For example: thorns, wings, mimicry (copy the appearance

of another species), camouflage (blend in with environment) of another species), camouflage (blend in with environment) Change within a population over time (anywhere from 100 Change within a population over time (anywhere from 100

years to millions of years) depending on type of adaptation, years to millions of years) depending on type of adaptation, rate of reproduction and environmental factorsrate of reproduction and environmental factors

PhysiologicalPhysiological Help populations overcome chemicals they encounter Help populations overcome chemicals they encounter

(antibiotics, pesticides, herbicides, etc)(antibiotics, pesticides, herbicides, etc) Develop rapidly (example: bacterial resistance to penicillin) Develop rapidly (example: bacterial resistance to penicillin)

Evidence for EvolutionEvidence for Evolution

FossilsFossils Anatomical relationshipsAnatomical relationships Embryological developmentEmbryological development Genetic comparisonsGenetic comparisons

FossilsFossils

Fossils can help provide a record for lifeFossils can help provide a record for life However, the fossil record is incomplete - However, the fossil record is incomplete -

there are large gaps - therefore each and there are large gaps - therefore each and every step of evolution can not be followedevery step of evolution can not be followed

Scientists need to find intermediate Scientists need to find intermediate species - and once they do, they can species - and once they do, they can provide us with a step by step sequence of provide us with a step by step sequence of evolutionevolution

Anatomical ComparisonsAnatomical Comparisons

Homologous structuresHomologous structures Same form, different useSame form, different use Indication of common evolutionary ancestorIndication of common evolutionary ancestor

Vestigial structuresVestigial structures Evolutionary remnants of structures that were Evolutionary remnants of structures that were

important in a past ancestorimportant in a past ancestor

Embryological DevelopmentEmbryological Development

There are noted similarities between the There are noted similarities between the embryological development of all embryological development of all vertebrates (fish, chicken, rabbit, human, vertebrates (fish, chicken, rabbit, human, etc)etc) Presence of gills and tails in all supports Presence of gills and tails in all supports

evidence that gill-breathing vertebrates evidence that gill-breathing vertebrates preceded air-breathing, terrestrial speciespreceded air-breathing, terrestrial species

Genetic ComparisonsGenetic Comparisons

All living things use DNA. All living things use DNA. All living things use the same genetic code.All living things use the same genetic code. Can show relationships between species Can show relationships between species

(human and chimpanzee DNA are 99% (human and chimpanzee DNA are 99% identical and are closer than chimpanzees identical and are closer than chimpanzees are to apes)are to apes)

Can help reveal when species diverged Can help reveal when species diverged from their ancestral typesfrom their ancestral types

Types of Natural SelectionTypes of Natural Selection Stabilizing Selection - favors average traits Stabilizing Selection - favors average traits

(average sized spiders fair better than (average sized spiders fair better than both large and small)both large and small)

Directional Selection - favors one extreme Directional Selection - favors one extreme of a trait (the longer the beak the better)of a trait (the longer the beak the better)

Disruptive Selection - favors both Disruptive Selection - favors both extremes of a trait (intermediate at extremes of a trait (intermediate at disadvantage - often eliminated)disadvantage - often eliminated)

Evolution of a Species = Evolution of a Species = SpeciationSpeciation

Species = group of organisms that look Species = group of organisms that look alike and have the ability to interbreed and alike and have the ability to interbreed and produce fertile offspring in natureproduce fertile offspring in nature

Speciation occurs whenSpeciation occurs when Interbreeding is preventedInterbreeding is prevented Production of fertile offspring is preventedProduction of fertile offspring is prevented

Causes of SpeciationCauses of Speciation Isolation of populations Isolation of populations - Two populations of the - Two populations of the

same species do not mate because of some same species do not mate because of some form of separationform of separation If populations can’t interbreed due to isolation, their If populations can’t interbreed due to isolation, their

allele frequencies can become more and more allele frequencies can become more and more different from each otherdifferent from each other

Each population will adapt to its environment, Each population will adapt to its environment, eventually preventing breeding with members of eventually preventing breeding with members of other populations (reproductive isolation)other populations (reproductive isolation)

Changes in chromosome number causes Changes in chromosome number causes instantaneous speciationinstantaneous speciation

Most speciation happens gradually Most speciation happens gradually

Types of IsolationTypes of Isolation

Geographic- geographic barriers form that Geographic- geographic barriers form that separate two populations.separate two populations.

Ecological- different environmental factors Ecological- different environmental factors may cause isolation (wet vs. dry, soil may cause isolation (wet vs. dry, soil conditions, etc.)conditions, etc.)

Reproductive- mating structures and Reproductive- mating structures and behaviors may isolate two populations behaviors may isolate two populations

Temporal- two populations may reproduce at Temporal- two populations may reproduce at different times different times

Types of EvolutionTypes of Evolution

Divergence (ex: adaptive radiation); Divergence (ex: adaptive radiation); Single populations splits to adapt to different Single populations splits to adapt to different

environmentsenvironments ConvergenceConvergence

Unrelated species become similar as they Unrelated species become similar as they adapt to a similar environment. adapt to a similar environment.

Analogous structuresAnalogous structures• Same use, different formSame use, different form• Not evidence of a common evolutionary Not evidence of a common evolutionary

ancestorancestor

Rate of SpeciationRate of Speciation

Fossil record suggests the rate is variableFossil record suggests the rate is variable Gradualism: slow, steady process of Gradualism: slow, steady process of

changechange Punctuated equilibrium: long periods of Punctuated equilibrium: long periods of

genetic stability punctuated by rapid genetic stability punctuated by rapid changes to new environmental changes to new environmental conditionsconditions

Pace of EvolutionPace of Evolution

Gradualism- the pace of natural selection Gradualism- the pace of natural selection is gradual change. is gradual change.

Punctuated Equilibrium- model of Punctuated Equilibrium- model of evolutions that states there are differing evolutions that states there are differing periods of rapid change and periods of periods of rapid change and periods of little to no change. little to no change.

Why? What could cause this?Why? What could cause this?