Mechanisms for Mechanisms for EvolutionEvolution

Lamark vs. DarwinLamark vs. Darwin

Differing Viewpoints…Differing Viewpoints…

Charles DarwinCharles Darwin CharacteristicsCharacteristics among members of a among members of a

species species varyvary.. Only individuals with the characteristics Only individuals with the characteristics best best

suitedsuited to the environment will survive to to the environment will survive to reproducereproduce..

Over time characteristics will Over time characteristics will increaseincrease in the in the population.population.

(Now called Natural Selection)(Now called Natural Selection)

Differing ViewpointsDiffering Viewpoints

Jean LamarkJean Lamark EvolutionEvolution occurs through the occurs through the use and use and

disusedisuse of physical features. of physical features. Over an organisms lifetime features will Over an organisms lifetime features will

increases by useincreases by use or or decrease by disuse.decrease by disuse. These traits are than These traits are than passed downpassed down to their to their

offspring.offspring.

Lamark vs. DarwinLamark vs. Darwin

Natural Selection Natural Selection

Process by which Process by which populationspopulations change in change in response to their environments.response to their environments.

Key components of natural selection:Key components of natural selection: Genetic VariationGenetic Variation Competition and Struggle for existenceCompetition and Struggle for existence Survival of the fittest (Variation is Selected)Survival of the fittest (Variation is Selected) Increased frequency of best traits (Variation is Increased frequency of best traits (Variation is

inherited)inherited)

Requirement #1: Genetic VariationRequirement #1: Genetic Variation

Exists within a population Exists within a population throughthrough MeiosisMeiosis – genetic variation – genetic variation

is increased during is increased during crossing crossing overover

Mutations-Mutations- spontaneous spontaneous changes in DNAchanges in DNA

Genetic RecombinationGenetic Recombination – – occurs during sexual occurs during sexual reproduction and provides reproduction and provides endless source of endless source of new new variationsvariations

Requirement #2: Requirement #2: Struggle for ExistenceStruggle for Existence

Every organism must Every organism must constantly fight for constantly fight for limited resourceslimited resources (food, water, mates) (food, water, mates) and escape from and escape from predatorspredators in order to in order to survive long enough survive long enough to to reproducereproduce..

Requirement # 2Requirement # 2Reproduction Leads to CompetitionReproduction Leads to Competition

When conditions are When conditions are favorablefavorable organisms organisms tend to produce many tend to produce many offspring.offspring.

When resources When resources become scarce: become scarce: competitioncompetition occurs. occurs.

Requirement #3Requirement #3Survival of the FittestSurvival of the Fittest

Individuals Individuals bestbest suited/adaptedsuited/adapted to their to their environments have the environments have the best chances for best chances for survival survival Those individualsThose individuals

Reproduce more oftenReproduce more often and pass those good and pass those good traits that allowed traits that allowed survival on to their survival on to their offspring.offspring.

End Result:End Result:Increased frequency of best traitsIncreased frequency of best traits

Over time, good Over time, good traits appear traits appear more in a more in a population population because more because more individuals individuals survive and survive and reproduce.reproduce.

Examples of Natural SelectionExamples of Natural Selection

Sickle Cell AnemiaSickle Cell Anemia Hereditary disease that Hereditary disease that

affects hemoglobinaffects hemoglobin• Protein in our blood that Protein in our blood that

carries oxygencarries oxygen 1/500 have Sickle Cell 1/500 have Sickle Cell

Anemia in USAnemia in US 1/100 have Sickle Cell 1/100 have Sickle Cell

Anemia in Central AfricaAnemia in Central Africa

Malaria is a warm climate Malaria is a warm climate disease caused by a parasite disease caused by a parasite that is transmitted by that is transmitted by mosquitoes.mosquitoes.

Causes death if not treated.Causes death if not treated. People with sickle cell anemia People with sickle cell anemia

are more resistant to malariaare more resistant to malaria

•AA = normal blood (no resistance)AA = normal blood (no resistance)•Aa = both normal and sickle Aa = both normal and sickle shaped blood (resistance)shaped blood (resistance)•aa = all sickle shaped blood aa = all sickle shaped blood (resistance)(resistance)

Types of Natural SelectionTypes of Natural Selection

1)1) Balancing SelectionBalancing Selection (Stabilizing Selection)(Stabilizing Selection)

* When selective pressures * When selective pressures select againstselect against the the two extremestwo extremes of a trait. of a trait.

AA Aa aa

Another ExampleAnother Example

The Peppered Moth The Peppered Moth White or black and White or black and

sits on the bark of sits on the bark of treestrees

Pray to birdsPray to birds

Industrial revolutionIndustrial revolution Increased pollutionIncreased pollution Killed lichens on treesKilled lichens on trees

• Trees covered in lichens Trees covered in lichens appear more white while trees appear more white while trees without lichens appear darkwithout lichens appear dark

What Happened?What Happened?

Lots of Pollution:Lots of Pollution: No pollution:No pollution:

Try It….Try It….

http://www3.district125.k12.il.us/faculty/nfihttp://www3.district125.k12.il.us/faculty/nfischer/Moth/default.htm scher/Moth/default.htm

2) 2) Directional SelectionDirectional Selection

* When selective pressures are * When selective pressures are against against one extreme.one extreme.

White Moths Black Moths

Another ExampleAnother Example

Imagine rabbits with fur that can either be black, Imagine rabbits with fur that can either be black, grey, or white (due to incomplete dominance)grey, or white (due to incomplete dominance)

The environment consists of black rock The environment consists of black rock outcroppings, and white snowy tundra.outcroppings, and white snowy tundra.

Animals that are born with the heterozygous Animals that are born with the heterozygous grey coats are going to be spotted easily by their grey coats are going to be spotted easily by their predators. Animals with black or white fur are predators. Animals with black or white fur are likely to survive and reproduce more offspring likely to survive and reproduce more offspring than gray rabbits.than gray rabbits.

3) Disruptive Selection3) Disruptive Selection

* When selection acts * When selection acts againstagainst individuals individuals in the in the middlemiddle of the trait. of the trait.

White rabbits Grey rabbits Black Rabbits

AdaptationsAdaptations

An adaptationAn adaptation is an physical structure, is an physical structure, physiological process or behavioral trait of physiological process or behavioral trait of an organism that has an organism that has evolvedevolved over a over a period of time by the process of period of time by the process of natural selectionnatural selection..

Adaptations increase the Adaptations increase the reproductive successreproductive success of the of the organismorganism. .

AdaptationsAdaptations

Organisms that are adapted to their Organisms that are adapted to their environment are able to:environment are able to: obtain air, water, food and nutrients obtain air, water, food and nutrients cope with physical conditions such as cope with physical conditions such as

temperature, light and heat temperature, light and heat defend themselves from their natural enemies defend themselves from their natural enemies reproduce reproduce respond to changes around them respond to changes around them

Types of AdaptationsTypes of Adaptations

1) 1) MorphologicalMorphological – structures are adapted – structures are adapted to specific needs and environments.to specific needs and environments.

Floating LeavesTurtles shell

Floating Leaves

2) 2) Behavioral AdaptationsBehavioral Adaptations – based on – based on behaviorbehavior

Bird MigrationLiving in herds/schools

3) 3) Physiological AdaptationsPhysiological Adaptations – Adaptations – Adaptations on a molecular levelon a molecular level

* Things inside the body vs. outside* Things inside the body vs. outside

Bioluminescent –deep sea Poisons- Dart Frog

SpeciationSpeciation

If a species changes enough that it If a species changes enough that it can no longer interbreed with the can no longer interbreed with the original species a original species a new speciesnew species can can form.form.

Types of Reproductive Isolation:Types of Reproductive Isolation:

Reproductive Isolation-If a population becomes isolated Reproductive Isolation-If a population becomes isolated and can’t interbreed, changes can accumulate and a new and can’t interbreed, changes can accumulate and a new species can formspecies can form

Three Types…Three Types…

1. Geographical Isolation1. Geographical Isolation

2. Temporal Isolation2. Temporal Isolation

3. Behavioral Isolation3. Behavioral Isolation

1) Geographical Isolation1) Geographical Isolation

Separation by land forms or physical Separation by land forms or physical featuresfeatures Examples: Rivers, mountains, islandsExamples: Rivers, mountains, islands

Darwin’s FinchesDarwin’s Finches•Galápagos Islands – had different Galápagos Islands – had different environmentsenvironments•14 species of finches arose by 14 species of finches arose by speciation from a single South speciation from a single South American species. American species. •Populations of finches can no Populations of finches can no longer interbreed.longer interbreed.

Finches BeaksFinches Beaks

2) Temporal Isolation2) Temporal Isolation

Separated by time of day or year reproduction occursSeparated by time of day or year reproduction occurs Examples: gamete exchange during different Examples: gamete exchange during different

seasonsseasons

Frogs:Rana aurora - breeds January - March Rana boylei - breeds late March - May

Fruit Flys:Drosophila persimilis - breeds in early morning Drosophila pseudoobscura - breeds in the afternoon

3) Behavioral Isolation3) Behavioral Isolation

Separated by behaviorSeparated by behavior Examples: Bird/frog calls, different courtship Examples: Bird/frog calls, different courtship

behaviors, lighting patterns of lightning bugs.behaviors, lighting patterns of lightning bugs.

Patterns in EvolutionPatterns in Evolution

ConvergenceConvergence – Unrelated organisms develop similar – Unrelated organisms develop similar traits. traits. Different geographical areas sometimes exhibit groups of plants and animals of strikingly similar appearance, even though the organisms may be only distantly related.

Patterns in EvolutionPatterns in Evolution

DivergenceDivergence – – two related species become two related species become increasingly different. Organisms evolve to fill increasingly different. Organisms evolve to fill diverse ecological niches. (In the broadest diverse ecological niches. (In the broadest sense, all current species are the result of sense, all current species are the result of divergent evolution.)divergent evolution.)