The early conservation movement evolved out of necessity to maintain natural resources such as fisheries, wildlife management, water, soil, as well as conservation and sustainable forestry. The contemporary conservation movement has broadened from the early movement's emphasis on use of sustainable yield of natural resources and preservation of wilderness areas to include preservation of biodiversity. Some say the conservation movement is part of the broader and more far-reaching environmental movement, while others argue that they differ both in ideology and practice. Chiefly in the United States, conservation is seen as differing from environmentalism and it is generally a conservative school of thought which aims to preserve natural resources expressly for their continued sustainable use by humans . Outside the U.S., the term conservation more broadly includes environmentalism.