B2 Revision Cards Natural Selection

B2 revision cards for natural selection

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  • Created by: Eleanor.1
  • Created on: 18-04-14 09:05

Charles Darwin and Natural Selection

  • Over 150 years ago Charles Darwin wrote his theory of natural selection.
    • This explained how evoulution might happen.
    • It says that if animals and plants are better adapted to their environment, they and the following genarations are more likely to survive.
  • He didn't know exactly how adaptions were passed on. When organisms reproduce, their genes are passed on to the next generation.
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Charles Darwin and Natural Selection 2

  • The modern version can be summarised like this:
    • Within any species there is a variation.
    • Organisms produce far more live young than will survive, so their is competition for limited recources such as food.
    • Only the best adapted will survive, which is called survival of the fittest.
    • Those that suvive pass on successful adaptations for the next generation in their genes.
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Charles Darwin and Natural Selection 3

  • Over time, the changes produced by natural selection may result in a new species.
    • This only happens if different groups of organisms cannot mate for a long time.
    • The organisms might be prevented from mating because they live in different areas. This is called geographical isolation.
      • They might be prevented from mating because of behavioural isolation.
    • If each group evolves differently they might over time become different enough to be classified as separate species.
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Modern Examples of Natural Selection

  • Natural selection is difficult to study because it usually takes thousands of years to see the effect. Some examples have been studied over shorter time spans:
    • More and more bacteria are developing resistance to antibiotics.
    • Peppered moths are dark or pale in colour. Dark moths are better camouflaged in polluted areas, so more of them survive.
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Arguments over Natural Selection

  • At first many people disagreed with Darwin's ideas:
    • Some people thought he did not have enough evidence to back up his theory.
    • Many people disagreed because they thought God created all species.
  • Now Darwin's theoryis much more widely accepted. This is because:
    • It explains lots of observations.
    • It has been discussed and tested and tested by a wide range of scientists.
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Arguments of Natural Selection 2

  • There have been other attempts to explain evoulution.
    • Before Darwin, Jean Baptiste de Lamarck had a different theory, called the law of required characteristics. This said, for exmaple, that giraffes aquired long necks to feed, and this characteristic was passed on.
  • As we have discovered more about how genes are passed on, theories like Lamarck's have been proved incorrect and Darwin's theory has become more widley accpected.
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