Evolution

Geologic change

• Catastrophism: natural disasters shaped landforms and caused species to become extinct• Gradualism: landform shaping is the result

of gradual changes.• Uniformitarianism: processes that shape

Earth are uniform through time

Early Ideas

• Buffon: shared ancestor theory• Erasmus Darwin: common ancestor• Lamarck: inheritance of acquired

characteristics

Darwin’s Observations

• Variation: not all members of a species or a population are identical• Adaptation: a feature that allows an

organism to better survive over time

Artificial Selection

• Organisms are bred to produce desirable traits

Natural Selection

• Organisms with unfavorable traits will die out, so the favorable traits are passed on

How Natural Selection Works

• Variation within a population• Many more young are born than can survive• Individuals best suited to the environment will

survive to pass their genes on.• Descent with modification: Over time, small

changes build up

Evidence for Evolution

• Fossils• Geography• Embryology• Anatomy• Vestigial structures

Population Evolution

• Gene pool: all the alleles of all the individuals in the population• Allele frequency: how common a specific

allele is in the population

Genetic variation

• Mutation: random change in DNA• Recombination: like in meiosis of sexual

reproduction• Hybridization: crossing two different

species that contain common genes.

Natural selection in populations

• Normal distribution: most are average, few are extreme. The bell curve.

Disruptive selection: The mean is selected against

Stabilizing selection: Both extremes are selected against

Directional selection: an extreme is selected against

Comparison of selection models

Other mechanisms

• Gene flow: migration moves alleles between populations• Genetic drift: when some alleles become fixed or

disappear due to small population size. Allele frequencies are different.• Bottleneck effect: when a population size decreases

rapidly, genetic diversity also decreases. When the population rebounds, it has less diversity.

• Founder effect: when a small number of individuals colonize a new area, the new gene pool is different from the original.• Sexual selection: how females choose their mate• Intrasexual: competition among the males• Intersexual: primping

Sexual selection

Winner gets the girl Ain’t I pretty