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Unit 1 - Theories of Evolution

Evolution forms a major part of GCSE Biology. Not only will students look at Charles Darwin's theory of evolution by natural selection, they will also examine the evidence supporting it and take a look at some shorter-lived theories, like that of evolution's earlier proponent, Jean-Baptiste Lamarck.

The best known of the evolution theories is Charles Darwin's theory of evolution by natural selection. It states that all species of living organisms have evolved from simpler life forms. Variation within populations leads to different adaptations, some of which may give an organism a survival advantage. Examples of such variation could be longer claws, which would make an animal a more efficient hunter, or larger leaves, which would mean that a plant would get more light and shade out its competitors. Organisms with these adaptations are more likely to survive longer and will therefore pass on their successful characteristics to the next and subsequent generations. Those organisms who are less well adapted are more likely to die and can even become extinct.

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Text books often give the impression that Darwin came up with his natural selection theory after he had visited the Galapagos Islands during a sea voyage on a ship called the Beagle. This is only partly true and slightly misleading. He took over 20 years to come up with the theory and his observations during the month or so that he was at the Galapagos Islands formed only a small part of the story. The turning point came after he read an essay about human population. The population of Great Britain in the mid 19th Century was increasing rapidly, particularly in cities. The essay claimed that the trend would continue up to the point where there would not be enough food to go round, then the population would decline rapidly as people starved. He realised that the same would apply in the natural world which would only allow the 'survival of the fittest'.

Darwin was very reluctant to publish his theory because it contradicted the teachings and beliefs of religion - the 'Church' was very powerful at the time. Despite this, he was eventually persuaded to publish his book but was then ridiculed by both the press and fellow scientists. There just wasn't enough evidence for evolution and besides, how could we possibly have evolved from apes? We now call the 'apes' primates and there is plenty of evidence to show that all organisms have undergone evolution. You need to be aware that this wasn't the first or only theory of evolution. In the exam, you could be asked about these others.

See if your knowledge of evolution theories is evolved enough to get 10 out of 10 in this quiz!

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  1. Darwin's theory was not accepted at first because of objections by which organisation?
    The press and other scientists were also very harsh towards Darwin's theory
  2. What does evolution mean?
    Variation is caused by genetic mutation or a change in behaviour in response to a change in the habitat or environment
  3. What is a fossil?
    The fossil record of the horse is particularly complete and provides evidence for evolution that is difficult to deny
  4. Evidence for evolution comes from where?
    The fossil record gives a picture of the evolutionary process
  5. What did Lamark's theory of evolution state?
    Knowledge of genetics was many years in the future. Without knowing about genes and inheritance, any theory of evolution is hard to understand and explain
  6. Evolution leads to the formation of which of the following?
    Variation in each successive generation can create so many new adaptations that an organism is deemed to be a new species, as it has little in common with its ancestors
  7. In natural selection, the individuals which survive are described as being which of the following?
    If an organism is better adapted, it can survive and pass on its genes (or new behaviour) to the next and future generations
  8. The organisms which survive can then breed and pass on what?
    Alleles are alternative forms of a gene that arise by mutation and are found at the same place on a chromosome
  9. Why are there gaps in the fossil record?
    This can occur for many reasons but, despite these gaps, other evidence can be used to support an evolutionary pathway, such as DNA
  10. Variation which leads to new forms of organisms is caused by what?
    Mutation of genes can be caused by environmental factors and by mistakes arising when DNA copies itself during cell reproduction

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