Natural Selection & Evidence for Evolution

• Evolution – the gradual change of organisms over long periods of time (from simple to more complex)
• Natural selection - explains how features of the environment apply a selective force on the reproduction of individuals in a population
• A fossil is the remains or evidence of any organism that once lived on Earth.

  • Remains of a dead animal or plant

  • Imprint left from remains

  • Trace fossils – something that was made by the animal while it was living and hardened into stone (e.g. burrows, footprints)

  
• Darwin’s observations

  Four key observations:

  • Offspring generally appear similar to their parents
  • No two individuals are identical
  • Organisms have the ability to produce large numbers of offspring
  • Populations in nature tend to remain fairly stable in size
• Problems with Darwin’s theory

  • Fossil record incomplete
  • Earth was not thought to be old enough to support evolution
  • Couldn’t explain where the variation came from (no knowledge of genes/alleles in Darwin's time)
  • Couldn’t explain how characteristics were passed on to offspring
• Selection pressure - These are environmental factors that determine the direction of evolutionary change.

  e.g.;

  • Availability of food
  • Predators
  • Diseases
  • Physical factors such as climate
  • Chemical factors such as oxygen availability
• What evidence do we have for evolution?

  • fossils
  • molecular evidence
• Molecular evidence is evidence for evolution, how does molecular evidence show evolution?


  Organisms that diverged more recently have more similar DNA base sequences, as less time has passed for changes to occur
• What was Alfred Russell Wallace's theory on 'warning colours'?

  Wallace's theory was that warning colours (e.g. wasps, butterflies) aimed at deterring predators had evolved through natural selection