Natural selection

• Conditions for natural selection


  • Reproduction
  • Inheritance
  • Variation in individual characters among members of the population
  • Variation in fitness or organism
• Selection


  Ecosystem are made up of various biotic (living) and abiotic (non-living) factors that contribute to selecting which variations will provide the individual with an increased chance of surviving over others
• Competition


  Rivalry between or among living things for territory, resources, goods, mates etc
• Biological resistance


  The natural or genetic ability of an organism to avoid or repel attack by biotic agents (pests, parasites, pathogens etc) or to withstand the effects of abiotic agents (chemicals, pesticides, salt, wind, heavy metals etc)
• Artificial selection (selective breeding)


  Process where humans identify desirable traits in animals and plants and use these traits to develop desirable phenotypic traits by breeding
• Advantages and disadvantages of artificial selection

  • Can result in better quality products and higher yields in plants and animals that have been bred from specific characteristics
  • Example: increased yield of milk by cows
  • Can reduce the genetic diversity
• Natural vs Artificial selection

  Natural

  • Process occurs naturally
  • Trait acquired increase chance for species survival
  • Example: animals in the wild (colour of peppered moth)

  Same

  • Traits are inherited from parents
  • Results in change in genetic trait of species
  • Change occurs over many generations

  Artificial

  • Desired trait selected by humans
  • Acquired traits don't always enhance the survival of species
  • Examples: dogs, livestock, or crops in agriculture
• Selection agents


  Any force in the environment that favours or disfavours traits
• Populations subjected to different selective agents


  May become so different that they are no longer able to breed with one another
• Types of selective agents


  • Predation
  • Disease
  • Availability of resources
  • Climate
  • Competition