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.
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!