Natural selection

• Natural selection


  • The mechanism driving evolutionary change
  • The process where organisms become better adapted to their environment tend to survive and produce offspring
• Natural selection


  • Proposed by Darwin and Wallace
• Genetic variation


  • Mutations generate new alleles
  • Meiosis produces gametes with variation due to crossing over and independent assortment of homologous chromosomes
  • Sexual reproduction generates new allele combinations
  • Random fertilization of gametes
• Factors that promote natural selection

  • Overproduction of offspring - intraspecific competition for resources
  • Populations increase until carrying capacity is reached
  • Carrying capacity is the max population size of a species that can be supported
• Natural selection


  1. Selective pressures

  2. Genetic variation due to mutations

  3. Intraspecific competition

  4. Favorable adaptations

  5. Survive and reproduce

  6. Genetic inheritance

  7. Allele frequency increase
• Natural selection


  • White peppered moth
  • Antibiotic resistant bacteria
• Sexual selection


  • Difference in physical/behavioral traits can affect success in attracting a mate
  • Arises through preference for certain traits
• Sexual selection


  • Plumage of Raggiana birds of paradise
  • Guppies
• Gene pool


  All genes and their different alleles in an interbreeding population
• Evolution


  Change in gene frequencies in a population's gene pool over time
• Neo Darwinism


  Modern evolutionary theory
• Types of selection


  • Stabilizing
  • Directional
  • Disruptive
• Hardy-Weinberg principle


  • Dominant + recessive allele frequency = 1
  • (dominant homozygous)^2 + (2*heterozygous) + (homozygous recessive)^2 = 1
• Assumptions of Hardy-Weinberg principle: large populations, no migration, no sexual selection, no mutations, no natural selection
• Artificial selection


  • Humans choose individuals with desired traits
  • Unintended consequences (e.g. antibiotic resistance) are due to natural selection
• Artificial selection


  • Corn with long ears and big kernels
• Genetic drift


  Mutation in a small population