The Theory of EvolutionThe Theory of Evolution

Earth’s HistoryEarth’s History

The Earth was formed about 4.6 The Earth was formed about 4.6 billion years agobillion years ago

by 2.2 billion years ago, the Earth by 2.2 billion years ago, the Earth probably looked like it looks todayprobably looked like it looks today

oxygen was not believed to be in oxygen was not believed to be in abundant supply in Earth’s early abundant supply in Earth’s early atmosphereatmosphere

Earth’s HistoryEarth’s History

oldest known cellular fossil (3.5 oldest known cellular fossil (3.5 billion years old) traces back to a billion years old) traces back to a place in Australiaplace in Australia

- were probably cyanobacteria = - were probably cyanobacteria = photosynthetic unicellular prokaryotesphotosynthetic unicellular prokaryotes

- first prokaryotes were probably - first prokaryotes were probably anaerobic – Why?anaerobic – Why?

Earth’s HistoryEarth’s History

uniformitarianism = a principle that uniformitarianism = a principle that states the same geographical states the same geographical processes that occur today occurred processes that occur today occurred in the pastin the past

- these processes occur very - these processes occur very slowly, requiring organisms to change slowly, requiring organisms to change as well (very slowly) as well (very slowly)

UniformitariansimUniformitariansim

Charles DarwinCharles Darwin

Charles DarwinCharles Darwin did most of his research on the did most of his research on the Galapagos IslandsGalapagos Islands

Charles DarwinCharles Darwin

- collected 13 similar but separate - collected 13 similar but separate species of finchesspecies of finches

- each had a distinct type of beak for - each had a distinct type of beak for feedingfeeding

- overwhelming similarities showed - overwhelming similarities showed they came from a common ancestorthey came from a common ancestor

Charles DarwinCharles Darwin

Charles DarwinCharles Darwin

Charles DarwinCharles Darwin

Darwin’s TheoriesDarwin’s Theories1) New species descend from one or a few 1) New species descend from one or a few original typesoriginal types

- similar organisms arise in the same - similar organisms arise in the same geographic locationgeographic location

2) Species were modified and evolution 2) Species were modified and evolution occurred because of natural selection = occurred because of natural selection = organisms best suited for the environment organisms best suited for the environment survive better (or have higher fitness) and survive better (or have higher fitness) and reproduce more successfully than othersreproduce more successfully than others

Darwin’s TheoriesDarwin’s Theories3) The process of natural selection 3) The process of natural selection drives evolutiondrives evolution

4) The environment “selects” the traits 4) The environment “selects” the traits that will be increase a populationthat will be increase a population

- adaptation = when an organism - adaptation = when an organism becomes better suited for its becomes better suited for its environmentenvironment

Evidence of EvolutionEvidence of Evolution

1) Homologous Structures = similar features 1) Homologous Structures = similar features that originated in a common ancestorthat originated in a common ancestor

ex) forelimbs of a cat, whale, bat, and ex) forelimbs of a cat, whale, bat, and

humanhuman

- look different and vary in function, but - look different and vary in function, but

very similar in skeletal structuresvery similar in skeletal structures

- indicates they share a common - indicates they share a common

ancestorancestor

Homologous StructuresHomologous Structures

Evidence of EvolutionEvidence of Evolution2) Analogous Structures = serve 2) Analogous Structures = serve

identical functions and look identical functions and look somewhat alikesomewhat alike

- ex) wing of a hummingbird and - ex) wing of a hummingbird and wing of a mothwing of a moth

- indicates they show a remote - indicates they show a remote ancestor but evolved ancestor but evolved independently and differentlyindependently and differently

Analogous StructuresAnalogous Structures

Evidence of EvolutionEvidence of Evolution

3) Vestigial Structures = structures that 3) Vestigial Structures = structures that are found in an organism but are not are found in an organism but are not useful to themuseful to them

- were useful to a common - were useful to a common ancestor ancestor

- ex) human tailbone, appendix, - ex) human tailbone, appendix, tiny tiny limb bones in snakes, pelvic limb bones in snakes, pelvic bones in whalesbones in whales

Vestigial StructuresVestigial Structures

Vestigial StructuresVestigial Structures

Vestigial StructuresVestigial Structures

Vestigial StructuresVestigial Structures

Types of Natural SelectionTypes of Natural Selection- a population is the smallest unit in - a population is the smallest unit in

which evolution can occurwhich evolution can occur

- bell curve = a graph that illustrates - bell curve = a graph that illustrates that most members of a population that most members of a population show show the average form a given the average form a given measurable traitmeasurable trait

- only a few individuals will show the - only a few individuals will show the extremes of a traitextremes of a trait

Bell CurveBell Curve

Types of Natural SelectionTypes of Natural Selection (cont) (cont)

1) Stabilizing Selection = individuals 1) Stabilizing Selection = individuals with the average form of a trait have with the average form of a trait have higher fitnesshigher fitness

- the most common kind of selection- the most common kind of selection

- results in very similar morphology - results in very similar morphology of a speciesof a species

Stabilizing SelectionStabilizing Selection

Stabilizing SelectionStabilizing Selection

Types of Natural SelectionTypes of Natural Selection (cont) (cont)

2) Directional Selection = 2) Directional Selection = individuals with the more extreme individuals with the more extreme form of a trait have greater fitness form of a trait have greater fitness than the average formthan the average form

Directional SelectionDirectional Selection

Directional SelectionDirectional Selection

Types of Natural SelectionTypes of Natural Selection (cont) (cont)

3) Disruptive Selection = individuals 3) Disruptive Selection = individuals with either extreme variation of a with either extreme variation of a trait have greater fitness than trait have greater fitness than individuals with the average formindividuals with the average form

Disruptive SelectionDisruptive Selection

Disruptive SelectionDisruptive Selection

Types of Natural SelectionTypes of Natural Selection (cont) (cont)

4) Sexual Selection = females tend to 4) Sexual Selection = females tend to chose the males they mate with chose the males they mate with based on certain traitsbased on certain traits

- the genes of successful - the genes of successful reproducersreproducers, rather than those of , rather than those of merely successful merely successful survivorssurvivors, are , are amplified through natural selectionamplified through natural selection

Sexual SelectionSexual Selection

Sexual SelectionSexual Selection

Sexual SelectionSexual Selection

New SpeciesNew Species

- speciation = the process of - speciation = the process of species formationspecies formation

- Speciation begins with isolation- Speciation begins with isolation

- 2 ways for this to occur- 2 ways for this to occur

New SpeciesNew Species (cont) (cont)

1) Geographic Isolation = the 1) Geographic Isolation = the physical separation of members of physical separation of members of a populationa population

- ex) fish in ponds in Death Valley- ex) fish in ponds in Death Valley

- fish diverged enough to be - fish diverged enough to be considered separate speciesconsidered separate species

Geographic Isolation – Death ValleyGeographic Isolation – Death Valley

Geographic Isolation - PupfishGeographic Isolation - Pupfish

New SpeciesNew Species (cont) (cont)

2) Behavioral Isolation2) Behavioral Isolation

- ex) different mating times and - ex) different mating times and calls of frogs reduce the chance calls of frogs reduce the chance of interbreeding among the of interbreeding among the different speciesdifferent species

Behavioral Isolation - FrogsBehavioral Isolation - Frogs

Rates of SpeciationRates of Speciation

1) Gradualism = species evolve at a 1) Gradualism = species evolve at a steady, stable ratesteady, stable rate

2) Punctuated Equilibrium = species 2) Punctuated Equilibrium = species arise abruptly and are quite different arise abruptly and are quite different from the species they came fromfrom the species they came from

- seen in the fossil record where - seen in the fossil record where large gaps seem to appear from one large gaps seem to appear from one to anotherto another

Rates of SpeciationRates of Speciation

Rates of SpeciationRates of Speciation

Rates of SpeciationRates of Speciation

Rates of SpeciationRates of Speciation

Basic Definition of EvolutionBasic Definition of Evolution

= Earth’s present day species = Earth’s present day species developed from earlier, developed from earlier, distinctly different species distinctly different species through the process of natural through the process of natural selectionselection