Charles Darwin's theory of evolution

Charles Darwin's theory of evolution by natural selection states: all living thigs that exist today, and many more than are now extinct, evolved from simple life forms that first developed more than three billion years ago. 

It took a long time to be accepted because:

  • it challenged the idea that God made all the animals and plants that live on Earth
  • there was insufficient evidence at that time (1859 when it was published) to convince many scientists
  • the mechanism of inheritance and variation wasn't discovered until 50 years later 
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Natural Selection

The key points of natural selection are:

  • individuals in a species show a wide range of variation
  • the variation is because of differences in genes 
  • individuals with characteristics most suited to the environment are more likely to survive and reproduce
  • the genes that allowed the individuals to be successful are passed onto the offspring in the next generation

Individuals that are poorly adapted to their environment are less likely to survive and reproduce. This means that their genes are less likely to be passed to the next generation. Given enough time, a species will gradually evolve.

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Lamarck's Theory

Jean-Baptiste Lamarck's theory involved two ideas:

  • A characteristic which is used more and more by an organism becomesbigger and stronger, and one that is not used eventually disappear
  • Any feature of an organism that is improved through use is passed to its offspring.
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