Evolution

• Charles Darwin


  Scientist and naturalist who put forward the theory of evolution
• Theory of Evolution


  1. Supported by experimentation and his knowledge of geology and fossils from a round the world expedition

  2. Published 'On the Origin of Species' in 1859
• Theory of Evolution


  • Variation exists within species as a result of mutations in DNA
  • Organisms with characteristics most suited to the environment are more likely to survive to reproductive age and breed successfully - called survival of the fittest
  • The beneficial characteristics are then passed on to the next generation
  • Over many generations the frequency of alleles for this advantageous characteristic increase within the population
• There was lots of controversy surrounding Darwin's ideas for many reasons:
• Lamarck's theory


  • Changes that occurred during the lifetime of an organism were passed onto offspring
  • If an individual continually repeated an action, the characteristic that allowed it to do this would develop further
  • For example, if a giraffe stretched to reach leaves on a tree high up, its neck would become longer allowing it to do this more easily. This characteristic would then be passed on to its offspring
• Lamarck's theory was proven wrong when it was understood that changes caused by the environment were not passed on in the sex cells
• Darwin's theory was supported by genetics as it provided a mechanism for beneficial characteristics caused by mutations to be passed on. Fossil evidence showed how developments in organisms arose slowly
• Speciation


  The process of a new species developing through the selection of different alleles. This increases the genetic variation until the new population cannot breed with those in the old population to produce fertile offspring
• Alfred Russel Wallace


  • Developed the theory of speciation, and therefore evolution by natural selection
  • On his travels, he had the idea that the individuals who did not have characteristics to help them survive a change in the environment would die out
  • He published joint studies with Darwin, but Darwin received the credit for the theory
• The process of speciation

  1. Variation exists within a population as a result of genetic mutations.

  2. Alleles which provide a survival advantage are selected for through natural selection.

  3. Populations of a species can become isolated, for example through physical barriers such as a rock fall preventing them from breeding together.

  4. Different alleles may be advantageous in the new environment, leading to them being selected for.

  5. Over time the selection of different alleles will increase the genetic variation between the two populations.

  6. When they are no longer able to breed together to produce fertile offspring, a new species has formed.
• Gregor Mendel


  • Trained in mathematics and natural history in Vienna
  • Worked in the monastery gardens and observed the characteristics passed on to the next generations in plants
  • He carried out breeding experiments on pea plants
  • He used smooth peas, wrinkled peas, green peas and yellow peas and observed the offspring to see which characteristics they had inherited
  • He came to the conclusions that: Offspring have some characteristics that their parents have because they inherit 'hereditary units' from each, one unit is received from each parent, and units can be dominant or recessive, and cannot be mixed together
• Mendel was not recognised till after his death as genes and chromosomes were not yet discovered, so people could not understand
• In the late 19th century chromosomes as a part of cell division were observed, and in the 20th century, it was understood that chromosomes and units had similar behaviours. It was decided that units (now known as genes) were on the chromosomes
• The structure of DNA was determined in 1953, which meant we were able to understand how genes worked
• Evidence for Evolution


  • Fossils: the remains of organisms from many years ago, which are found in rocks
  • Antibiotic resistance in bacteria: the selection pressure of antibiotics leads to advantageous mutations being selected for in bacteria populations so they are no longer killed when exposed to antibiotics
• Extinction


  When an entire species has died out
• Factors which can contribute to extinction

  • Changes in environment which the species cannot adapt fast enough to
  • New predators may have evolved or migrated to the area
  • A new disease arises and there are no resistant alleles to it
  • They have to compete with a species which has advantageous mutations for the same food source
  • A catastrophic event can wipe out a species
  • Destruction of habitat
• Resistant Bacteria


  Bacteria are labelled resistant when they are not killed by antibiotics which previously were used as cures against them
• How resistant bacteria develop

  1. Bacteria reproduce at a fast rate

  2. Mutations during reproduction can result in new genes, such as the gene for antibiotic resistance. This the creation of a new strain

  3. Exposure to antibiotics creates a selection pressure, as those with antibiotic resistant genes survive and those without die

  4. As a result those with antibiotic resistance can reproduce and pass on the advantageous gene to their offspring

  5. This population of antibiotic resistant bacteria increases
• Bacterial diseases spreads rapidly because people are not immune to these new resistant bacteria and there is no treatment for it
• MRSA


  Called a 'superbug' as it is resistant to many different types of antibiotics
• How to slow the development of resistance in bacteria

  • Antibiotics should not be given for viral or non-serious infections
  • Specific antibiotics should be given for specific bacteria
  • Patients should complete their course of antibiotics - if they do not some bacteria may survive and mutate to become antibiotic resistant
  • Antibiotics should be used less in agriculture - farmers currently use them to prevent their livestock dying from disease, but this overuse leads to antibiotic resistant bacteria which are then transferred to humans when they consume the meat
• How to slow the transmission of the bacteria

  • Maintain high standards of hygiene in hospitals
  • Medical staff and visitors should wash hands regularly
  • Medical staff should wear disposable clothing or clothing that is regularly sterilised
• As the development of antibiotics is expensive and slow, it is difficult to keep up with the development of resistant strains