The world's living things have developed over hundreds of millions of years to be able to survive in the places where they have chosen to live. The most important influence on them has been the climate.

Rainfall, temperature, sunshine and other parts of the climate vary all over the world. At the Equator, for example, there is rain on most days and the temperature hardly varies from near 25°C through the year. But away from the Equator, the climate changes, with part of the year being dry. The further you go from the Equator, the longer this dry season becomes until, when you get to the Tropics, a dry season lasts all year and the land is desert. Polewards of this the effect of longer winters become most important until, when you get to the Arctic and Antarctic, it is cold throughout the year.

There are no plants that can survive in both a desert and at the Equator. Instead, plants have evolved and adapted to live either in a desert or in an Equatorial rainforest.

Because animals depend on plants for their food, different animal live in areas with different kinds of plant. Again, each animal has adapted to make use of a particular range of plants.

The world's biggest areas of natural vegetation are called biomes. As mentioned above, we tend to know each one by a more common name, such as desert, coniferous forest, rainforest, and ocean. In a general way, each biome matches a climate, and as a result, most biomes occur in bands around the world.