Claire biology tips

• Theory of evolution by natural selection

  The theory that organisms better adapted to their environment are more likely to survive and reproduce, passing on their traits to offspring
• Wallace worked with Darwin on the theory of natural selection for a number of years and they produced scientific journals together
• Darwin's Origin of the Species is the book that explains the theory of natural selection
• Darwin's observations on the Galapagos Islands


  • Noticed unusual species very similar to mainland species
  • Saw clear variation between members of the same species
  • Offspring like their parents, no two individuals are identical
  • Organisms have the ability to produce a large number of offspring
  • Populations tend to remain fairly stable despite producing large numbers of offspring, suggesting some offspring die off
• Competition for food and resources


  Leads to some offspring dying off, with those better adapted to the environment more likely to survive and reproduce
• Adaptation and speciation

  Beneficial variations arise over time, leading to organisms becoming so different they can no longer interbreed and are classified as different species (e.g. Darwin's finches)
• Evidence for evolution by natural selection

  • Fossils
  • Comparison of DNA and biological molecules
  • Observation of changes in organisms over time (e.g. horse evolution, human skull development)
• Fossils


  Can show how old organisms are, links between organisms, and intermediate forms
• DNA and biological molecules

  Similarities in base sequences or amino acid sequences indicate close evolutionary relationships, differences indicate distant relationships
• Archeopteryx is an example of an intermediate form between birds and reptiles
• Natural Selection


  A theory proposed by Darwin where a series of events allow the evolution of a species over time
• Key aspects of Natural Selection

  • Genetic variation within a population
  • Random mutations
  • Advantageous mutations that increase survival
  • Passing on advantageous mutations to offspring
  • Selection pressures (e.g. predation, weather, disease)
• Natural Selection

  1. Genetic variation within a population

  2. Random mutations occur

  3. Advantageous mutations increase survival

  4. Advantageous mutations passed on to offspring

  5. Selection pressure acts on population
• Selection pressures

  • Competition for food
  • Predators
  • Diseases
  • Chemical or physical factors
• Black peppered moth example

  • Originally white moths
  • Industrial revolution darkened trees
  • White moths more visible to predators
  • Darker winged moths more likely to survive
  • Darker wing allele increases in frequency
• When answering exam questions on natural selection, include the specific details from the question (e.g. type of selection pressure)