People care about saving species for their beauty and the thrill of see them, for scientific and educational purposes, and for their ecological, historic, and cultural values. A compelling reason to preserve species is that each one plays an important role in an ecosystem-an intricate network of plant and animal communities and the associated environment. When a species becomes endangered, it indicates that something is wrong with the ecosystems we all depend on. Like the canaries used in coal mines whose deaths warned miners of bad air, the increasing numbers of endangered species warn us that the health of our environment has declined. The measures we take to save endangered species will help ensure that the planet we leave for our children is as healthy as the planet our parents left for us.
Some species provide more immediate value to humans.
For example, cancer fighting drugs have been derived from the bark of a yew that is native to the Pacific Northwest. Chemicals used to treat diseases of nerve tissue were found in an endangered plant in Hawaii. Valuable resources such as these could be lost forever if species go extinct. Habitat destruction is the single most serious worldwide threat to wildlife and plants, followed by exploitation for commercial or other purposes. Disease, predation, inadequate conservation laws, pollution, and introduction of non-native species, or a combination of these, can contribute to a species' decline.