Evolution

• Charles Darwin


  Developed a theory of evolution that is important in modern biology
• Natural selection


  • Individuals of a species show variation
  • Some individuals will be better able to survive in their environment and produce more healthy offspring than others
  • The environment (including climate and other organisms) selects which individuals pass on their alleles to the next generation
• Darwin's theory


  1. Adults usually produce more young than the environment can support

  2. This produces a 'struggle for existence' by the young

  3. Some individuals have inherited advantageous variations in characteristics that are better adapted to the environment

  4. These individuals will have a better chance of survival to adulthood

  5. Individuals with variations that are not as well adapted to the environment will be less likely to survive

  6. Individuals with advantageous variations will pass their genes on to their young

  7. The young may inherit the advantageous variations

  8. More individuals will have these advantageous variations in the next generation
• One example of Darwin's theory

  • Development of antibiotic resistance in bacteria
• This is an example of where you may be asked to apply your understanding to a specific example that you may not be familiar with
• Evidence for evolution leading to modern humans (Homo sapiens)


  • Fossils of bones and teeth
  • Stone tools
• Ardi


  • Height 120cm
  • Brain size 350 cm³
  • Tree climber, also walked upright
• Lucy


  • Height 107 cm
  • Brain size 400 cm³
  • Walked upright, face ape-like
• Homo habilis


  • Height <130cm
  • Brain size 500-600 cm³
  • Walked upright, used simple stone tools
• Homo erectus


  • Height about 175 cm
  • Brain size 850-1100 cm³
  • Long-distance walker, strongly built
• Homo sapiens


  • Height wide variety
  • Brain size approx. 1200 cm³
  • User of complex tools
• You do not need to remember details such as brain sizes but you do need to remember the names and the general trends
• Stone tools


  • Earliest stone tools around 2.4 million years old
  • Over time more complex tools were made, and a greater range of tool types
• Selective breeding


  Plants or animals with certain desirable characteristics are bred together, so that offspring will be produced that inherit these characteristics
• Reasons for selective breeding

  • Disease resistance
  • Increased yield
  • Better ability to cope with difficult conditions
  • Faster growth
  • Better flavour
• The increase in milk yield per cow is mainly the result of selective breeding
• Genetic engineering


  Changing the genome (the DNA) of an organism, often by introducing genes from another to create genetically modified organisms (GMOs)
• How genetic engineering works

  1. Genes can be transferred from any kind of organism to any other kind of organism

  2. The gene for a characteristic is 'cut out' of a chromosome using enzymes

  3. The gene is inserted into a chromosome inside the nucleus of a cell in a different organism

  4. The cell of this organism now produces the characteristic from the gene
• GM crops


  • Resistance to attack by insects
  • Resistance to herbicides, so that fields can be sprayed to kill weeds, but not the crop
  • These characteristics can help the crop grow better and produce more food (an increased yield)
• Evaluating something means identifying advantages and disadvantages, then comparing them to draw a conclusion about whether the example is worth doing
• Stages in genetic engineering

  1. DNA from a human cell is cut into pieces using restriction enzymes

  2. Bacteria cells contain small circles of DNA called plasmids, which are cut open using the same restriction enzymes

  3. The pieces of DNA containing the insulin gene are mixed with the plasmids, and DNA ligase links them back into a continuous circle

  4. The plasmids are inserted into bacteria, which can now be grown in fermenters to make human insulin