Evolutionary ThoughtEvolutionary ThoughtTheories of EvolutionTheories of Evolution

Questions about the world that Questions about the world that started to set the stage for modern started to set the stage for modern

evolutionary thoughtevolutionary thought

GEOLOGYGEOLOGY Age of earth?Age of earth? Changing earth?Changing earth?

POPULATIONSPOPULATIONS Competition?Competition? Change over time?Change over time? Extinction of species?Extinction of species?

GEOLOGYGEOLOGYHutton and Lyell (geologists)Hutton and Lyell (geologists)

James Hutton (1785) James Hutton (1785) hypothesized earth to be very old when he examined hypothesized earth to be very old when he examined

geologic features such as rock layers and erosiongeologic features such as rock layers and erosion

Charles Lyell (1833) Charles Lyell (1833) Hypothesized that complex geologic processes like Hypothesized that complex geologic processes like

erosion, volcanoes, etc. shaped the earth as we erosion, volcanoes, etc. shaped the earth as we currently see it.currently see it.

CONCLUSIONS:CONCLUSIONS: EARTH IS VERY VERY OLD!EARTH IS VERY VERY OLD! Today’s best guess??? Today’s best guess??? 4.6 Billion Years 4.6 Billion Years

1809:Lamarck’s Theory1809:Lamarck’s Theory

Use and DisuseUse and Disuse::Body parts that are used more Body parts that are used more

grow stronger and bigger.grow stronger and bigger.Body parts not used will Body parts not used will

deteriorate. deteriorate. Inheritance of Acquired CharacteristicsInheritance of Acquired Characteristics::

Physical changes that occur in an Physical changes that occur in an organism are inherited by its organism are inherited by its offspring.offspring.

Example: Giraffe’s neck gets Example: Giraffe’s neck gets longer as it stretches to reach longer as it stretches to reach food in trees. food in trees.

But was Lamarck correct?But was Lamarck correct?NONO

According to genetics…According to genetics…

only variations that occur in only variations that occur in the genes of ____________ the genes of ____________ are passed to offspring.are passed to offspring.

variations that occur in variations that occur in _____________ (body cells) _____________ (body cells) are NOT inherited.are NOT inherited.

gametesgametes

somaticsomatic cells

Thomas Malthus (1798)Thomas Malthus (1798)

Observed human population Observed human population growth will eventually hit a limit growth will eventually hit a limit due to living space and available due to living space and available food. Darwin would later apply this food. Darwin would later apply this to all organisms where these limits to all organisms where these limits result in competition.result in competition.

While Lamarck's reasoning behind While Lamarck's reasoning behind why change happened was why change happened was flawed, Lamarck and Malthus both flawed, Lamarck and Malthus both greatly influenced the thinking of greatly influenced the thinking of Mr. Charles Darwin.Mr. Charles Darwin.

Charles DarwinCharles Darwin English scientist born in 1809English scientist born in 1809 1831 famous voyage around world on HMS 1831 famous voyage around world on HMS

Beagle where he examined numerous Beagle where he examined numerous different types of animals and the wide different types of animals and the wide diversity of life he founddiversity of life he found

Noted that organisms seemed to be Noted that organisms seemed to be uniquely adapted to their environmentsuniquely adapted to their environments

Galapagos Galapagos Similar organisms on different Similar organisms on different islands had unique characteristics that islands had unique characteristics that suited their specific habitatsuited their specific habitat

On the Origin of SpeciesOn the Origin of Species Published 1859Published 1859

Summarized his ideas on causes of Summarized his ideas on causes of speciationspeciation

Darwin's On the Origin of Species by Darwin's On the Origin of Species by Means of Natural Selection, made several Means of Natural Selection, made several points that had major impact on points that had major impact on nineteenth-century thought: nineteenth-century thought:

Main Principles of NATURAL Main Principles of NATURAL SELECTIONSELECTION

I.I. Competition.Competition.

II.II. Survival of the fittestSurvival of the fittest

III.III. Descent with modificationDescent with modification

Natural Selection: CompetitionNatural Selection: Competition

Members of the same species are in Members of the same species are in competition with each other for food competition with each other for food and space.and space.

Over production:Over production: In a population, more offspring are produced In a population, more offspring are produced

than can survivethan can survive. .

““Struggle for existence”Struggle for existence” Individuals with traits that give them an advantage Individuals with traits that give them an advantage

make better competitors.make better competitors.

Natural Selection: Survival of the Natural Selection: Survival of the FittestFittest

VariationVariation::There is variation within a population There is variation within a population

and and variations are inherited.variations are inherited. AdaptationAdaptation::

Traits that are favorable and improve Traits that are favorable and improve the organism’s ability the organism’s ability to function and to function and reproducereproduce. .

Survivors pass on their Survivors pass on their variationsvariations. Therefore a larger . Therefore a larger proportionproportion in the next in the next generationgeneration will have those variations. will have those variations.

““Fitness” in evolution is a Fitness” in evolution is a measure of an individual’s ability measure of an individual’s ability to survive and pass on genes to survive and pass on genes (reproduce!)(reproduce!)measure of an individual’s measure of an individual’s genetic genetic contributioncontribution to the next generation. to the next generation.

Natural Selection: Descent with Natural Selection: Descent with ModificationModification

As new desirable characteristics become As new desirable characteristics become established within a population, the established within a population, the species as a whole changes over long species as a whole changes over long periods of time. periods of time.

Evolution is the development of new Evolution is the development of new organisms from preexisting organisms organisms from preexisting organisms over time.over time.

Speciation:Speciation: Over time, small changes Over time, small changes accumulateaccumulate

and and populationspopulations change. change. Species: a group of organisms that can Species: a group of organisms that can

matemate and produce and produce fertile offspringfertile offspring.. Sometimes, two populations diverge Sometimes, two populations diverge

(change differently) and become two (change differently) and become two separate separate speciesspecies..

Each of the Hawaiian honeycreeper species has a Each of the Hawaiian honeycreeper species has a bill specialized for eating certain foods. Scientists bill specialized for eating certain foods. Scientists suggest that all 23 honeycreeper species suggest that all 23 honeycreeper species apparently arose from a single species that apparently arose from a single species that migrated to Hawaii. migrated to Hawaii.

Lamarck vs DarwinLamarck vs Darwin

Lamarck Darwin

Use / disuse Variation

Transmission of acquired

characteristics

Inheritance

Increasing complexity

Differential survival

No extinction Extinction

Principle of Common DescentPrinciple of Common Descent All species (living and extinct) have evolved from All species (living and extinct) have evolved from

common ancestors for a very long time.common ancestors for a very long time.

Evidence of Evolution• Fossil Record• Geographic Distribution• Transitional Species• Comparative Anatomy• Vestigial Organs• Comparative Embryology • Comparative Biochemistry

Fossil RecordFossil Record

Preserved remain of ancient Preserved remain of ancient life in rock support change life in rock support change over time.over time.

Fossils found in lower levels Fossils found in lower levels of rock older than ones of rock older than ones above. (relative age)above. (relative age)

Majority of species (over Majority of species (over 99%) that have existed on 99%) that have existed on this planet are extinct!this planet are extinct!

Very hard for an organism Very hard for an organism to become a fossilto become a fossil..

How is the age of fossils and rocks How is the age of fossils and rocks determined?determined?

Radiometric dating – using half-lives of Radiometric dating – using half-lives of radioactive isotopesradioactive isotopes Radioactive isotopes decay at a constant rateRadioactive isotopes decay at a constant rate Half Life Half Life length of time for ½ of an isotope length of time for ½ of an isotope

to decayto decayEx. Carbon-14 decays to Nitrogen-14Ex. Carbon-14 decays to Nitrogen-14Half-life = 5,730 yearsHalf-life = 5,730 yearsCarbon 14 can only be uses to date fossils Carbon 14 can only be uses to date fossils

less than 50,000 years old! less than 50,000 years old!

Geographic DistributionGeographic Distribution BiogeographyBiogeography

study of the distribution of plants and study of the distribution of plants and animals throughout the worldanimals throughout the world

Some fossils found on different continents Some fossils found on different continents nearly identical supporting movement of nearly identical supporting movement of continents. continents.

There are patterns in how species occur There are patterns in how species occur geographically, based on such factors as geographically, based on such factors as where they evolved, how far they where they evolved, how far they dispersed, and how changes in the Earth dispersed, and how changes in the Earth affected their distribution.affected their distribution.

Transitional SpeciesTransitional Species

While theoretically, all species are While theoretically, all species are “transitional”, we use this term to classify “transitional”, we use this term to classify certain species as almost “stepping certain species as almost “stepping stones” from one type of organism to stones” from one type of organism to another.another.

Ex. Ex.

Fish Fish AmphibianAmphibian

Homologous Structures Homologous Structures (Comparative Anatomy)(Comparative Anatomy)

Scientists note Scientists note similarities among similarities among physiology of physiology of organismsorganisms

Morphologically Morphologically similar structures similar structures that perform that perform different functions different functions are called are called homologous homologous structuresstructures. .

Analogous StructuresAnalogous Structures Serve similar function but have a much Serve similar function but have a much

different structuredifferent structure Ex. Insect wing and bird wingEx. Insect wing and bird wing Ex. Squid eye and human eyeEx. Squid eye and human eye Ex. Whale fin and fish finEx. Whale fin and fish fin

Vestigial OrgansVestigial Organs

Rudimentary structures that are of marginal Rudimentary structures that are of marginal or no use to an organism, or structures in or no use to an organism, or structures in which the shared form appears to be which the shared form appears to be inefficient. inefficient.

ExamplesExamples Skeletons of some snakes retain the vestiges of Skeletons of some snakes retain the vestiges of

pelvic girdle and leg bones of walking pelvic girdle and leg bones of walking ancestors. ancestors.

Some blind, cave-dwelling fish have eye-Some blind, cave-dwelling fish have eye-sockets but no eyes. sockets but no eyes.

Comparative Embryology Comparative Embryology

closely related organisms go closely related organisms go through similar stages during their through similar stages during their embryonic development embryonic development

Biochemical SimilaritiesBiochemical Similarities

What we all useWhat we all use DNADNA ATP (energy molecule)ATP (energy molecule) similar enzymes, similar enzymes, same codons for protein synthesissame codons for protein synthesis same 20 amino acids etc.same 20 amino acids etc.

Remember, at the cell level we are very Remember, at the cell level we are very close to most other eukaryotic organisms!close to most other eukaryotic organisms!

Evolution in ActionEvolution in Action

All inheritable physical traits that appear in an All inheritable physical traits that appear in an organisms can be looked at as changes in an organisms can be looked at as changes in an organism’s geneticsorganism’s genetics

Darwin did not understand genetics and therefore Darwin did not understand genetics and therefore could not explain how traits were passed down could not explain how traits were passed down through generations.through generations.

We now can apply our understanding of genetics We now can apply our understanding of genetics and apply them to evolutionary theory.and apply them to evolutionary theory.

PhylogenyPhylogeny

the connections between all groups of the connections between all groups of organisms as understood by organisms as understood by ancestor/descendant relationships.ancestor/descendant relationships.

Express relationships using a Express relationships using a CLADOGRAMCLADOGRAM

CladogramCladogram

Gene PoolGene Pool is combined genetic information of is combined genetic information of all the members of a particular populationall the members of a particular population

In a given gene pool, there will typically be two In a given gene pool, there will typically be two or more different alleles for a given gene. or more different alleles for a given gene.

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

We can oftentimes see that different alleles We can oftentimes see that different alleles have different frequencies in different parts of have different frequencies in different parts of the world. Why do you think this is so?the world. Why do you think this is so?

Ex. Frequency of B allele for blood typeEx. Frequency of B allele for blood type

Genetic Change basis of EvolutionGenetic Change basis of Evolution

Natural selection acts on Natural selection acts on phenotypes phenotypes NOT genotypesNOT genotypes, however, this process , however, this process determines the relative frequencies of determines the relative frequencies of alleles.alleles.

Ex. Sickle cell anemiaEx. Sickle cell anemia Phenotype (blood cell shape) Phenotype (blood cell shape) because because

heterozygous individuals are resistant to heterozygous individuals are resistant to malaria. malaria.

Malaria resistance causes sickle-cell allele to Malaria resistance causes sickle-cell allele to be selected for in the population.be selected for in the population.

Mechanisms of EvolutionMechanisms of Evolution

Introduce new AllelesIntroduce new Alleles Sources of Genetic VariationSources of Genetic Variation

MutationsMutations Sexual ReproductionSexual Reproduction

External factors affect the allele External factors affect the allele frequencyfrequency

Remember, it is mutation that proposes Remember, it is mutation that proposes and selection that disposesand selection that disposes

What can change allele frequencies What can change allele frequencies besides natural selection?besides natural selection?

Genetic DriftGenetic Drift Evolutionary Change can also happen without Evolutionary Change can also happen without

natural selectionnatural selection In large populations, the laws of probability In large populations, the laws of probability

help predict allele frequencies.help predict allele frequencies. In smaller populations random change in In smaller populations random change in

allele frequency (genetic drift) may occur.allele frequency (genetic drift) may occur. Chance occurrences may increase/decrease Chance occurrences may increase/decrease

frequency of allelesfrequency of alleles

Mass ExtinctionsMass Extinctions

There have at least 5 mass extinctions.There have at least 5 mass extinctions. Permian Permian – 250 mya, over 90% of marine and – 250 mya, over 90% of marine and

terrestrial species disappeared; maybe due terrestrial species disappeared; maybe due to volcanoes, Pangeae, glaciationto volcanoes, Pangeae, glaciation

CretaceousCretaceous – 65 mya; ½ marine and many – 65 mya; ½ marine and many terrestrial forms, including dinosaurs; due to terrestrial forms, including dinosaurs; due to environmental changes or asteroidsenvironmental changes or asteroids hitting hitting the earththe earth

Genetic EquilibriumGenetic Equilibrium

In order for there to be no evolution (allele In order for there to be no evolution (allele frequencies remain constant) five frequencies remain constant) five conditions must be met;conditions must be met; Random matingRandom mating Large populationLarge population No migration in or out of populationNo migration in or out of population No mutationsNo mutations No natural selectionNo natural selection

Is this ever the case?Is this ever the case?

TWEEKING DARWINISMTWEEKING DARWINISM

Traditionally, it was believed that evolution Traditionally, it was believed that evolution happened in small steps over long period happened in small steps over long period of time. This is called gradualismof time. This is called gradualism

More recently, scientists like Stephen Gould, More recently, scientists like Stephen Gould, proposed the idea of punctuated equilibrium proposed the idea of punctuated equilibrium which is that a species may remain relatively which is that a species may remain relatively stable with sudden periods of rapid evolution stable with sudden periods of rapid evolution due to some environmental factor.due to some environmental factor. CHANGES IN SPURTS!CHANGES IN SPURTS!

What is a theory?What is a theory?

Evolution is an observable fact (bird beak Evolution is an observable fact (bird beak size changing, antibiotic resistance in size changing, antibiotic resistance in bacteria, etc.) but the term theory allows it bacteria, etc.) but the term theory allows it to grow and develop. to grow and develop.

Misconceptions About Misconceptions About EvolutionEvolution