natural selection

• Darwin's theory 


  genetic variation - characteristics in individuals vary (due to differences in genes)

  environmental change - change in conditions of an area causes competition between organisms

  natural selection - the variations make some individuals better at coping with the change - more likely to survive

  inheritance - the survivors breed and pass on their variations - next generation have more individuals with them

  evolution - if the conditions remain changed, natural selection occurs over and over and a new species evolves with all individuals having the variation
• Classification


  Genetic analysis has changed how we classify organisms. DNA changes over time, so looking at these changes, scientists can work out how closely related organisms are.

  The three domain systems have now been proposed to incorporate these ideas.

  Archaea - cells with no nucleus, genes contain unused sections of DNA

  Bacteria - cells with no nucleus, genes contain no unused sections of DNA

  Eukarya - cells with a nucleus, contain unused sections of DNA, e.g. animals, plants, fungi, protists with cilia, protist with flagella
• Breeds and varieties (artificial selection and selective breeding)


  Artificial selection is when humans choose certain organisms because they have useful characteristics an breed them.

  By repeating artificial selection many times we end up with new varieties. This is selective breeding.

  Reasons plants and animals are selectively bred:

  • disease resistance
  • increased yield
  • coping with certain environmental conditions
  • fast growth
  • better / different flavour
• Breeds and varieties (genetic engineering)


  Genetic engineering involved changing the DNA of one organism often by inserting genes from another.

  This process is faster than artificial selection but is more expensive.

  This process creates genetically modified organisms (GMOs).
• Biological control

  Using organisms to control pests is known as biological control. It can also be used for weeds.

  Biological, GMOs, and selective breeding can all help yield but as the human population grows we need to use all the available methods, including fertilisers.
• Fertilisers


  Fertilisers contain metal ions (nitrogen, potassium, and phosphorus) needed by plants for healthy growth.

  If not all the fertiliser is absorbed by the crop, some may get into streams, rivers and lakes, pollution.

  This can lead to the death of organisms in the water and health problems for humans and animals if they drink the water.
• Evidence for evolution


  Fossil evidence - skulls increasing in size.

  Pentadactyl limb - most animals have this but it has turned into different things.

  Stone tools - the time of these are worked from where they are found in stones, they have be seen to improve over time.