Natural selection

• What is evolution?


  The process of change in the inherited traits of a population of organisms from one generation to the next
• What is the theory of natural selection?

  The theory that all species have evolved from simple life forms over a period of time.
• What are the key points to natural selection?


  • individuals in a species show a wide range of variation because of their different genes
  • individuals with characteristics most suited to their environment are more likely to survive and reproduce (survival of the fittest) the helpful genes are passed on to their offspring which results in those specific genes becoming more common.
  • Those that are poorly adapted to their environment are less likely to survive and reproduce. Their genes are less likely to be passed on to the next generation.
  • This causes the species to gradually evolve over time.
• What can cause variation?

  both genes and environment. but only genetic variation can be passed on to the next generation.
• What can cause the formation of two species?

  if two populations of one species become increasingly different in phenotype that they can no longer interbreed to form fertile offspring.
• What is a phenotype?

  The visible characteristics of an organism which occur as a result of its genes.
• What are fossils?

  The preserved remains of a dead organism from millions of years ago. They are found in rocks.
• What can fossils be formed from?

  • hard body parts , such as bones and shells, which do not decay easily or are replaced by minerals as they decay.
  • parts of organisms that have not decayed because one or more of the conditions needed for decay are absent
  • preserved traces of organisms , such as footprints, burrows and rootlet traces - these become covered by layers of sediment which eventually become rock.
• What are the three key factors needed for decay?

  Temperature, water and oxygen availability
• What is Darwin's theory of evolution?

  simple life forms evolved into more complex ones (natural selection)
• Who created the theory of natural selection?

  Charles Darwin and Alfred Russel Wallace
• What can scientists learn from studying fossils?

  how much (or little) organisms have changed as life developed on earth
• Why are there gaps in the fossil record?

  many early forms of life were soft-bodied so they have left few traces behind. Any traces that may have been left behind have been destroyed by geological activity. This is why scientists cant be sure how life began.
• What are evolutionary trees?

  They are used to represent the relationships between organisms. Branches show places where specification has occurred and a new species has evolved.
• What do dead animals and plants get preserved in?

  amber, peat bogs, tar pits or in ice
• What is amber?

  a substance that is formed from hardened tree sap or resin. This means when animals or plants get reserved in it the whole organism can be seen clearly.
• What are peat bogs?


  a wetland that accumulates peat as a deposit of dead plant materials.
• What is peat?


  Decomposed plant material.
• Why can bacteria evolve quickly?

  because it reproduces at a fast rate
• What are the 4 stages of development of resistance?

  1. random mutations occur in the genes of individual bacteria cells
  2. some mutations protect the bacterial cell from the effects of the antibiotic
  3. bacteria without the mutation die or cannot reproduce when the antibiotic is present
  4. resistant bacteria can reproduce with less competition from normal bacterial strains
• Why has the number of resistant strains increased?

  overuse and misuse of antibiotics - this resulted in more infections that are difficult to control
• What is MRSA


  methicillin - resistant staphy aureus and it is very dangerous because it is resistant to most antibiotics
• How can we reduce the rate of development of antibiotic resistant strains?

  • doctors should not prescribe antibiotics inappropriately , such as treatment of non-serious infections
  • patients should always complete the full course of antibiotics to ensure all bacteria are killed and none do not survive to mutate and form resistant strains
  • the agricultural use of antibiotics should be restricted.
• When does extinction occur?


  When there are no remaining individuals of a species alive.
• Animals that are well adapted to their environment are less likely to go extinct. Extinction has a role in evolution as some species disappear. others survive and continue to evolve.
• What can cause a species to become extinct?

  • new diseases
  • new predators
  • new , more successful competitors
  • changes to the environment over geological time - such as climate change
  • a single catastrophic event - such as volcanic eruption or collision between an asteroid and earth