How Evolution WorksHow Evolution WorksGenes, Geography and SexGenes, Geography and Sex

Early Idea: Lamarckian Evolution

Early Idea: Lamarckian Evolution

Fossil record indicated increasing complexity

Reasoned traits are passed via use and disuse

e.g. the giraffe’s neck

Fossil record indicated increasing complexity

Reasoned traits are passed via use and disuse

e.g. the giraffe’s neck

Step 1: Raw MaterialStep 1: Raw Material

Genes are raw materialForms of genes = allelesPolygenic vs. Single gene trait

Genes are raw materialForms of genes = allelesPolygenic vs. Single gene trait

Selection on a Single Gene: The Peppered Moth

Selection on a Single Gene: The Peppered Moth Before Industrial

Revolution

After Industrial Revolution

Before Industrial Revolution

After Industrial Revolution

Single gene controlling a trait will have only a few (usually 2 or 3 phenotypes)

Single gene controlling a trait will have only a few (usually 2 or 3 phenotypes)

Variation and SelectionVariation and Selection

Variation from two sources 1) New mutations = new allele

types 2) Gene shuffling = new allele

combinationsAny change in allele frequency =

EvolutionPeppered Moth Simulation

Variation from two sources 1) New mutations = new allele

types 2) Gene shuffling = new allele

combinationsAny change in allele frequency =

EvolutionPeppered Moth Simulation

Polygenic TraitsPolygenic Traits

More than one gene controls a trait

More than one gene controls a trait

Selection and Changing the Norm

Selection and Changing the Norm

Most traits are polygenicThe normal trait is the average or

mean in the populationSelection changes the mean,

usually lowers variationSelection will adjust mean

Most traits are polygenicThe normal trait is the average or

mean in the populationSelection changes the mean,

usually lowers variationSelection will adjust mean

Stabilizing SelectionStabilizing Selection

Disruptive SelectionDisruptive Selection

Can lead to new speciesCan lead to new species

Does Evolution Ever Stop?Does Evolution Ever Stop?

YES, but only if the following conditions are met

1) Random mating 2) Large Population 3) No movement in or out of

population 4) No Mutations 5) No Natural SelectionHardy Weinberg Equilibrium

YES, but only if the following conditions are met

1) Random mating 2) Large Population 3) No movement in or out of

population 4) No Mutations 5) No Natural SelectionHardy Weinberg Equilibrium

How New Species Are Formed

How New Species Are Formed

Two populations must become reproductively isolated

Two populations must become reproductively isolated

Behavioral IsolationBehavioral Isolation

Groups differ in mating, feeding, sleep/awake cycles so members of populations do not meet to mate

Groups differ in mating, feeding, sleep/awake cycles so members of populations do not meet to mate

Rana aurora (Red-legged frog)Rana aurora (Red-legged frog)

Breeds in fast moving streams

Breeds in fast moving streams

Rana catesbiana (Common bullfrog)Rana catesbiana (Common bullfrog)

Breeds in still ponds Breeds in still ponds

Geographic IsolationGeographic Isolation

Geological Time and Evolution

Geological Time and Evolution

First fossils 3.5 bya

Stromalites

550 mya = Cambrian Explosion (by fossil evidence)

First fossils 3.5 bya

Stromalites

550 mya = Cambrian Explosion (by fossil evidence)

Dating Fossil AgeDating Fossil Age

Relative Dating Relative Dating Radioisotope Dating

Known decay times of isotopes can be used

Radioisotope Dating

Known decay times of isotopes can be used

Extinction and Adaptive Radiation

Extinction and Adaptive Radiation

Most species cannot adapt

Those that can radiate into open niches

Most species cannot adapt

Those that can radiate into open niches

Evolution PatternsEvolution Patterns

Convergent EvolutionConvergent Evolution CoevolutionCoevolution