Post on 17-Jan-2018
description
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