How Evolution Works

How Evolution WorksGenes, Geography and Sex

Early Idea: Lamarckian Evolution

Fossil record indicated increasing complexity

Reasoned traits are passed via use and disuse

e.g. the giraffe’s neck

Step 1: Raw MaterialGenes are raw materialForms of genes = allelesPolygenic vs. Single gene trait

Selection on a Single Gene: The Peppered Moth

Before Industrial Revolution

After Industrial Revolution

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

Variation and SelectionVariation from two sources 1) New mutations = new allele

types 2) Gene shuffling = new allele

combinationsAny change in allele frequency =

EvolutionPeppered Moth Simulation

Polygenic TraitsMore than one gene controls a

trait

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

Stabilizing Selection

Disruptive SelectionCan lead to new species

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

How New Species Are Formed

Two populations must become reproductively isolated

Behavioral IsolationGroups differ in mating, feeding,

sleep/awake cycles so members of populations do not meet to mate

Rana aurora (Red-legged frog)

Breeds in fast moving streams

Rana catesbiana (Common bullfrog)

Breeds in still ponds

Geographic Isolation

Geological Time and Evolution

First fossils 3.5 bya

Stromalites

550 mya = Cambrian Explosion (by fossil evidence)

Dating Fossil Age Relative Dating Radioisotope

Dating Known decay

times of isotopes can be used

Extinction and Adaptive Radiation

Most species cannot adapt

Those that can radiate into open niches

Evolution PatternsConvergent Evolution Coevolution