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How Do Species Change in Nature?

During Earth's 4.6 billion year history, many different kinds of plants and animals have changed over time. Scientists call this evolution — or descent with modification.

Here's how it works: Species evolve through a process called Natural Selection. Individuals inherit traits, or features, from their parents. No two organisms in a population (except twins) are exactly alike. This is called individual variation. The inherited variation may come from a mixture of genetic information from parents, or very occasionally from mutations. There is a limit to the number of individuals that can survive in any particular environment. Those individuals that have traits that allow them to survive better will tend to pass those characteristics to their offspring. For example, saddleback tortoises have longer necks and can reach high food more easily. On islands that lack food close to the ground, animals with this trait have a better chance of surviving and reproducing compared to their short-necked cousins. So over time, the long-necked tortoises are naturally selected compared to the short-necked tortoises in this environment. This is an example of how a population or species can evolve.

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