Evolution

• Evolution is very important. Without it we wouldn't have the great variety of life we have on Earth today.
• Theory of Evolution


  All of today's species have evolved from simple life forms that first started to develop over three billion years ago
• Charles Darwin's theory of evolution by natural selection


  • He used the observations he made on a huge round-the-world trip, along with experiments, discussions and new knowledge of fossils and geology, to suggest the theory
• Darwin's theory of evolution by natural selection

  1. Organisms in a species show wide variation in their characteristics (phenotypic variation)

  2. Organisms have to compete for limited resources in an ecosystem

  3. Organisms with the most suitable characteristics for the environment would be more successful competitors and would be more likely to survive

  4. Successful organisms that survive are more likely to reproduce and pass on the genes for the characteristics that made them successful to their offspring

  5. Organisms that are less well adapted would be less likely to survive and reproduce, so they are less likely to pass on their genes to the next generation

  6. Over time, beneficial characteristics become more common in the population and the species changes - it evolves
• Darwin's theory wasn't perfect. Because the relevant scientific knowledge wasn't available at the time, he couldn't give a good explanation for why new characteristics appeared or exactly how individual organisms passed on beneficial adaptations to their offspring.
• Phenotype


  Controlled by genes
• Mutations


  Changes in DNA that produce new phenotypic variations
• Beneficial variations are passed on to future generations in the genes that parents contribute to their offspring.
• Speciation


  The development of a new species
• Speciation


  1. Over a long period of time, the phenotype of organisms can change so much because of natural selection that a completely new species is formed

  2. Speciation happens when populations of the same species change enough to become reproductively isolated-this means that they can't interbreed to produce fertile offspring
• Extinction


  When no individuals of a species remain
• Reasons for species extinction

  • The environment changes too quickly (e.g. destruction of habitat)
  • A new predator kills them all (e.g. humans hunting them)
  • A new disease kills them all
  • They can't compete with another (new) species for food
  • A catastrophic event happens that kills them all (e.g. a volcanic eruption or a collision with an asteroid)
• Dodos


  • Humans not only hunted them, but introduced other animals which ate all their eggs, and we destroyed the forest where they lived-they really didn't stand a chance
• When Darwin proposed his theory in his book "On the Origin of Species" in 1859, his idea was very controversial for various reasons.
• Darwin couldn't explain why these new, useful characteristics appeared or how they were passed on from individual organisms to their offspring. But then he didn't know anything about genes or mutations, which weren't discovered 'til 50 years after his theory was published.
• There wasn't enough evidence to convince many scientists, because not many other studies had been done into how organisms change over time.
• Lamarck's hypothesis


  Changes that an organism acquires during its lifetime will be passed on to its offspring
• Lamarck's hypothesis


  • If a characteristic was used a lot by an organism, then it would become more developed during its lifetime, and the organism's offspring would inherit the acquired characteristic (e.g. a rabbit's legs getting longer from running a lot)
• Lamarck's hypothesis was eventually rejected because experiments didn't support it.
• The discovery of genetics supported Darwin's idea because it provided an explanation of how organisms born with beneficial characteristics can pass them on (i.e. via their genes).
• The relatively recent discovery of how bacteria are able to evolve to become resistant to antibiotics also further supports evolution by natural selection.
• There's so much evidence for Darwin's idea that it's now an accepted hypothesis (a theory).