Evolution

• Evolution


  Change in living populations over time
• Change is apparent from FOSSILS (organisms are different now than they used to be)
• Evolution has been observed and recorded in many present-day populations (birds, bacteria, insects, etc.)
• Darwin’s theory has been added to and modified into modern evolutionary theory
• Theory


  A well-supported, testable explanation for something that happens in the natural world
• Theories are about as far as we get in science: Newton’s theory of gravitation, Einstein’s theory of relativity
• Descent With Modification


  By measuring genetic similarity, you can figure out how long ago 2 organisms had a common ancestor
• Darwin drew the first “evolutionary tree” to show common descent—the idea that organisms share ancient common ancestors
• Darwin’s Two Big Ideas

  • The more recently two species have shared a common ancestor, the more alike they are genetically
  • The more recently two groups have shared a common ancestor, the more alike they are genetically
• Pleiotropy


  When one gene influences multiple, seemingly unrelated phenotypic traits
• Natural Selection


  • Proposes one of the mechanisms for evolution
  • Inspired by “artificial selection”
• How Natural Selection Works

  Genetic variation, overproduction, competition lead to survival and reproduction of those with helpful variations, passing the variations on to their kids. Over time, helpful variations become more common, harmful ones become less common, and the population changes (evolves)
• Natural Selection is the environment acting on a population’s phenotypes, but the change it causes (evolution) is a change in allele frequency, and happens between generations
• How do we get information about how life has changed over time? The fossil record—all the fossils that have been found so far
• Most of the species that have existed are extinct
• When new fossils are found, theories are modified (fern fossils in Antarctica, dinosaurs with feathers)
• You have to be pretty lucky to get fossilized…
• Evidence for Evolution: Homologous structures, Analogous structures, Vestigial structures
• Homologous structures are body structures which have different mature forms but arise from the same embryonic tissues, suggesting common ancestry
• Analogous structures are structures that are similar because of similar environments, leading to convergent evolution
• Vestigial structures are inherited structures that have lost most/all function, remnants of evolutionary past
• The “Molecular clock” uses DNA and proteins to calculate time since common ancestor
• Find a protein that just about all species make, pick your 2 groups, and start counting differences to determine descent with modification
• Calculating time since common ancestor

  Measure how different the same gene (or protein) is in 2 groups
• Descent with modification
• Finding rate of evolution

  Measure how different the same gene (or protein) is in 2 groups
• Gene Pool
• For any gene, different alleles occur at different frequencies in a population
• Wolf gene pool allele frequencies

  • A=aggressive, a=tamer
• Living by a human garbage dump affects allele frequencies in wolf gene pool
• Evolution is a change in allele frequency
• Sources of Genetic Variation

  • Mutations
  • Errors in DNA replication
  • Sex
• Mutations are the ultimate source of new traits
• Sex leads to gene shuffling which increases diversity in populations
• Most traits are polygenic and determined by more than one gene (protein)
• Populations typically show a bell curve for polygenic traits
• Directional Selection


  Critters at one end of curve have higher fitness, curve tends to shift one direction (L or R)
• Stabilizing Selection


  Critters at center of curve have higher fitness, curve narrows, center increases
• Disruptive Selection


  Orgs. at BOTH ends of curve have higher fitness than middle, population can split into 2 distinct phenotypes
• Speciation occurs when a population evolves to become different enough from its ancestors