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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