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What is evolution?

Fossil turtleFossil turtleOver geological time—millions, or even hundreds of millions of years—living things have, very gradually, changed. We know this from studying fossils that belong to different periods in prehistory. Animals, for example, may have grown a fin or a tail, developed wings, or lost teeth. This is all part of a gradual process by which they adapt to their environment. It happens over many, many generations. This process is known as evolution. The animals and plants we see today have all evolved from ancestors that lived long ago.

A woolly mammoth A woolly mammoth


Why does evolution happen? For many animals, life is a continual struggle to avoid predators and bad weather, to find food and shelter, and to breed. Living things that survive this struggle are those best suited, or adapted, to the conditions. However these conditions change naturally over long periods of time. Some kinds of food may become more scarce. The climate may become colder or warmer. Living things must adapt to the new conditions or die out. They survive by evolving.

In 1840s England, industrial pollution turned tree trunks a sooty black. Darker pepper moths were better camouflaged on the dark trunks. Within 50 years, they became commoner than lighter moths, which were more easily spotted and preyed upon by birds. Now that trees are cleaner, the lighter kinds are commoner again. This is an example of evolution working quickly.

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