Evolution

• Species

  Group of similar individuals that can interbreed to produce fertile offspring under natural conditions. Smallest unit of biological classification.
• Taxonomy

  Science of classifying organisms
• Linnaean Classification


  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • species
• Understanding and grouping organisms important for agriculture, medicine and survival
• Evolution


  Change in characteristics of species over many generations
• Genetic diversity

  Range of genetic characteristics (and therefore alleles) within a single species
• What evolution can do

  • Lead to more complex species or less complex species
  • Increase or decrease genetic diversity
• Evolution depends on characteristics species needs to survive its environment
• Charles Darwin


  Biologist who proposed that species could change via Evolution (1809 - 1882)
• Alfred Russel Wallace


  Biologist who proposed that species could change via Evolution (1823 - 1913)
• Mutations


  Introduce new alleles and sometimes new advantageous characteristics to a species
• Artificial selection (or Selective Breeding)


  Process by which humans choose to breed particular organisms with desirable features
• Natural selection


  Process where an environmental factor acts on a population and results in some organisms having a greater chance of survival and producing more offspring than others
• Artificial Selection


  • Budgerigars and dogs were bred based on their desirable characteristics
• Different breeds of dogs are all one species and were produced by artificial selection
• Artificial Selection Process


  1. Variations in individuals are usually the result of mutations

  2. Can selectively cross an individual with a desirable feature with another individual which has a different desirable feature

  3. Can then continually selectively breed different offspring with desirable features
• Genetic diversity


  Decreased in artificial selection because only a small number of individuals with certain, desirable genes are selected to breed
• Undesirable genes disappear from the population in artificial selection
• Species with little variation in phenotypes due to lack of genetic diversity


  Is likely to go extinct when faced with disease or new environmental conditions
• Selection pressure

  Environmental factor that impacts an organism's ability to survive and reproduce
• Selection pressures

  • Disease
  • Predation
  • Climate change
  • Competition
• Natural Selection Example

  • Dark-brown mice easier to see on light brown ground colour and therefore eaten more by owls compared to dark-brown mice. More light-brown mice will survive and reproduce. Eventually, more of the mice population will be light brown.
• Natural selection can result in increased or decreased frequency of certain characteristics and alleles within a population
• Natural selection can only happen if there is an initial variation in characteristics or phenotypes of individuals in population
• Mutations


  Form new alleles which contribute to variation
• Individuals with beneficial phenotypes

  Are better equipped to survive, reproduce and therefore pass their alleles to offspring
• Example #1: Peppered Moths

  • In cities in England, almost all peppered moths were black because white moths resting on blackened trees due to pollution were easily seen and eaten by birds. In rural areas, almost all peppered moths were white because black moths resting on clean light coloured tree trunks were easily seen and eaten by birds.
• Example #2: Bacteria

  • Some fungi make special chemicals (named antibiotics) to defend themselves against bacteria (E.g. Penicillin). Some bacteria have become resistant to antibiotics by natural selection.
• Speciation

  Process by which one species splits into 2 or more separate species. Process by which new species are formed.
• Natural selection is the mechanism by which evolution and speciation occurs
• Steps in speciation

  1. Variation

  2. Isolation

  3. Selection
• Speciation can only occur if there is variation in the population because it depends on natural selection
• Isolation


  Different groups in population become isolated from each other due to geographical or climatic barriers, preventing interbreeding
• Change in Selection Pressure

  Natural selection affects genotype of each group and causes enough changes that prevent the groups breeding even if they come together again. Possible changes: Courtship behaviour, Breeding seasons, Sterility, Chemical barriers.
• Natural Selection

  1. Variation
  2. Selection pressure
  3. selection advantage
  4. Heritability