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Natural selection

How does a species evolve? Occasionally, changes (DNA mutations) will occur in a gene as it passes from one generation to the next. Some of them affect an animal's appearance, behaviour or the way its body works. Sometimes, an animal with a new version of a gene survives better than an animal with the old version - 'the survival of the fittest': then that animal is likely to have more offspring. They will inherit the new version of the gene, and in turn pass it on to their young.

Charles Darwin, who rocked the world with his theory of natural selection.
Charles Darwin, who rocked the world with his theory of natural selection.
Science & Society Picture Library

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