Evolution

• Extinction


  When there are no remaining individuals of a species still alive
• Factors that may contribute to a species' extinction

  • New predators
  • New diseases or pathogens
  • Increased competition for resources or mates
  • Catastrophic events (e.g., asteroid impacts, volcanic eruptions, earthquakes)
  • Changes to the environment (e.g., climate change, destruction of habitats)
• Classification of living organisms

  Carl Linnaeus developed a system to classify living things into groups, based on their structure and characteristics
• New models of classification were proposed as understanding of biochemical processes developed and improvements in microscopes led to discoveries of internal structures
• Three-domain system


  Organisms divided into Archaea (primitive bacteria usually living in extreme environments), Bacteria (true bacteria), and Eukaryota (including protists, fungi, plants, and animals)
• Evolutionary trees


  Use current classification data for living organisms and fossil data for extinct organisms to show how scientists believe organisms are related
• Evolution


  The gradual change in the inherited characteristics of a population over time
• Natural selection


  The theory of evolution by natural selection states that organisms within species show a wide range of variation in phenotype, individuals with characteristics most suited to the environment are more likely to survive and breed successfully, and these characteristics are then passed on to their offspring
• Bacteria can evolve rapidly because they reproduce very quickly, leading to many strains developing antibiotic resistance
• The development of antibiotic resistance in bacteria is evidence for the theory of evolution by natural selection
• To reduce the rise of antibiotic-resistant strains


  • Doctors should only prescribe antibiotics for serious bacterial infections
  • Patients should complete their courses of antibiotics so all bacteria are killed and none survive to form resistant strains
  • The use of antibiotics in farming and agriculture should be restricted
• Fossils


  The remains of organisms from millions of years ago, which are found in rocks, and can be formed from parts of an organism that do not decay, hard parts of an organism replaced by minerals, or preservation of traces of organisms
• The theory of evolution by natural selection is now widely accepted because there is evidence from it being shown that characteristics are passed on to offspring in genes, the fossil record, and the evolution of antibiotic resistance in bacteria
• Benefits of the fossil record

  • Can tell scientists how individual species have changed over time
  • Fossils allow us to understand how life developed over the Earth's history
  • Fossils can be used to track the movement of a species or its ancestors across the world
• Problems with the fossil record

  • Many early organisms were soft-bodied, so most decayed before producing fossils
  • There are gaps in the fossil record as not all fossils have been found and others have been destroyed by geological or human activity - this means scientists cannot be certain about how life began on Earth