Biology B1 Evolution


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7.1 Theories of Evolution

  • The theory of evolution states that all the species which are alive today evolved from simple life forms that first developed more than 3 billion years ago
  • Darwin's theory is that evolution takes place through natural selection

Sequence for natural selection:

mutation ---> variation ---> best adapted ---> survival ---> breed ---> genes passed on

(a mutation is a change in the genetic material of an organism)

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7.2 Accepting Darwin's ideas

Darwin's theory of evolution by natural selection was only gradually accepted for a number of reasons:

  • it conflicted with the widely held belief that God made all the animals and plants on Earth as they are today
  • insufficient evidence
  • no mechanism for explaining variety and inheritance - genetics were not yet understood
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7.3 Natural Selection

  • Natural selection works by selecting the organisms best adapted to a particular habitat
  • Different organisms in a species show a wide range of variation because of differences in their genes
  • The individuals with the characteristics most suited to their envirnonment are most likely to survive and breed successfully
  • The genes that have produced these successful characteristics are then passed onto the next generation
  • Mutation is a change in the genetic material (DNA) which results in a new form of a gene
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7.4 Classification and Evolution

  • Classification is the organisation of living things into groups according to their similarities
  • Biologists study the similarities and differences between organisms in order to classify them
  • The system used is called the natural classification system
  • The NCS starts with large groups (kingdoms) and splits off into smaller groups called species)

The main kingdoms are:

  • The animal kingdom
  • The plant kingdom
  • The kingdoms which contain microorganisms

Members of a species are very similar and can breed together to produce fertile offspring

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