The thin surface layer of our planet known as the biosphere, where all life on earth takes place, has been adapted and altered beyond recognition by human activities since the end of the last ice age, about 10,000 years ago. Landuse patterns of Homo sapie ns can be seen clearly from space. Forests have given way to farm land, grasslands to ranches, rivers have been dammed and coastlines tamed, lakes have appeared and seas have shrunk. As our numbers grew, so villages, roads, ports and cities broke up the l andscape. Even the air and the water are not the same. Pollution from cars, factories and towns has spread from pole to pole, and changed even the chemical composition of the atmosphere.

Some places, although they are few, remain virtually untouched. These are frequently those areas that have been protected as national parks, nature reserves, or marine reserves. Nowhere is utterly undisturbed, but the protected areas of the world are some of the most important surviving reservoirs of biodiversity - the fantastic wealth of natural ecosystems, plants and animals that once covered the earth.