Unit 6 Concept 1

• Principles of natural selection

  1. Overproduction of offspring

  2. Variation

  3. Adaptation

  4. Descent with modification
• Genetic variation


  Different traits arise from genetic mutations, recombination, and migration, enabling adaptation to changing environments
• Niche specialization


  Individuals with varied adaptations can exploit different resources, reducing competition and maximizing survival
• Disease resistance


  Genetic diversity provides some individuals with resistance or immunity to diseases, increasing survival during outbreaks
• Environmental adaptability


  Diverse traits allow for adaptation to various environmental conditions, facilitating colonization and reducing the risk of population decline
• Factors contributing to genetic variation

  • Random genetic mutations
  • Genetic recombination during meiosis
  • Migration (gene flow)
• Mutations are the primary source of new alleles and genetic diversity, providing the raw material for natural selection to act upon
• Directional selection


  Increases the expression of an extreme version of a trait in a population
• Disruptive selection


  A process that splits a population into two groups; removes individuals with average traits and favors the 2 extremes
• Stabilizing selection


  Eliminates extreme expressions of a trait when the average expression leads to higher fitness
• Mechanisms of microevolution


  • Mutations
  • Natural selection
  • Genetic drift
  • Gene flow
  • Sexual selection
• What was believed before?

  • Creationism
  • Catastrophism (Cuvier)
  • Gradualism (Hutton)
  • Struggle for Existence (Malthus)
  • Uniformitarianism (Lyell)
  • Inheritance of Acquired Traits (Lamark)
  • Intelligent Design
• Conditions for evolution to not occur

  • Population is very large
  • Random mating
  • No mutation
  • No natural selection
• Charles Darwin


  Went on a voyage to the Galapagos islands, saw differences in species on different islands, and developed the theory of natural selection
• Microevolution


  Evolution can occur on a small scale, affecting a single population
• Macroevolution


  Evolution on a large scale, affecting changes in species across populations
• Natural selection


  Organisms with the "best" traits (adaptations) will live longer and reproduce more than others, causing changes in the population over time by acting on traits that are heritable
• Fitness

  A measure of how well you can survive in your environment
• Adaptation


  A feature that allows an organism to survive in its environment. Beneficial traits (adaptations) will become more common over time because organisms should live longer and thus be able to reproduce more.
• Gene pool


  The combined alleles of all individuals in a given population
• Genetic drift


  Random change in the frequency of alleles in a population over time
• Gene flow


  Movement of genes into and out of a population, occurring during migration and resulting in an increase in genetic variation
• Sexual selection

  The selection of traits that aren't necessarily good for survival fitness, but without them, you can't pass on your genes at all because you can't reproduce
• Genetic equilibrium


  When there are no changes in the allele frequencies in a population over time