Biology - B1.7 - Evolution

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B1.7.1 - Theories of Evolution

  • Scientist estimate life began 3 billion years ago and before 18th century, few ideas about how evolution works
  • Jean-Baptiste Lamarck - 'inheritance of aquired characteristcs' - characteristcs that develop in organisms lifetime are passed onto offspring, people found this hard to believe
  • Charles Darwin - 'natural selection' - small changes take place in organisms over long period of time, all organisms vary, so some are more likely to survive and they breed and pass on the characteristics - he didn't know about genes, so couldn't prove it
  • We now say that best adapted organisms survive to breed and then pass on their genes to their offspring
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B1.7.2 - Accepting Darwin's Ideas

  • Darwins idea was only gradually accepted, because:
  • Challenged religious views
  • Many scientists didn't hink there was sufficient evidence
  • Darwin couldn't explain why there was variety or how inheritence worked - scientists didn't know about genes until around 50 years ago
  • Darwin had tried to show how environmental conditions could change animals, but he couldn't explain, in terms of genes, why the offspring inherited the useful adaptations
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B1.7.3 - Natural Selection

  • Most organisms have large numbers of offspring
  • Individual organisms show wide range of variation beacue of different genes
  • All organisms compete for food, sheltor (from predators) and mates
  • Organisms with with best suited characteristics survive - eg. camouflage, eysight, strongest, quickest, best suited to a climate etc. - the 'fittest' will survive and are more likely to successfully breed and pass on genes
  • Mutations - genes accidentally chane and become a new form of the gene, if the mutated gene controls a characteristic that means it's better adapted it will be passed on
  • Mutations are important in natural selection - eg. can become immune to a disease and therefore survive to breed and pass on the mutation while others die
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B1.7.4 - Classification and Evolution

  • Millions of different organisms - classification groups similar organisms
  • Biologists study similarities and differences between organisms to classify them - natural classification system - large groups that split into smaller ones
  • Largest: kingdoms - animal, plant and kingdoms containing microorganisms
  • Smallest: species - organisms in same species can breed together
  • Evolutionary trees - models drawn to show relationships between different groups of organisms
  • New evidence can change evolutionary relationship
  • Ecological relationships show us how species evolved together in an environment
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