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Fossil turtle, Cretaceous PeriodFossil turtle, Cretaceous Period Over geological time—millions, or even hundreds of millions of years—the fossil record tells us that living things (organisms) have, very gradually, changed. Animals, for example, may have grown a fin or a tail, developed wings, or lost teeth. This is all part of a process by which living things adapt to their environment. This process is known as evolution. Variations within species mean that some individuals are better suited to their lifestyle than others. These individuals are more likely to survive and reproduce, passing on the features that helped them survive. However, conditions change naturally with time: some foods may become scarcer or the climate may change. Evolution may allow some living things to survive in the new conditions.


Evolution of elephantsEvolution of elephantsWhy does evolution happen? Life is a continual struggle to avoid predators and bad weather, to find food and shelter, and to breed. Living things that survive the struggle are those best suited or adapted to the conditions. However these conditions change naturally with time. Some kinds of food may become more scarce. The climate may become colder or warmer. New diseases may appear. Living things must evolve to suit the new conditions or die out.

For thousands of years, humans have bred domestic animals or crops with “desirable” features to emphasize those features in the next generation. This is called “artificial selection”.

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