Certain animals and plants have died out and new ones have appeared ever since life began on Earth. This is a natural part of evolution. Sometimes an endangered species has been able to build up its numbers again and become common. At other times the endangered species has become extinct. Probably the best-known animals to become extinct by natural causes are the dinosaurs, which died out about 65 million years ago.
Today far more species are endangered than ever before. In the early 21st century more than 4,600 species of animals and plants were listed as endangered all over the world. Many more are considered vulnerable, or likely to become endangered.
Animals and plants rely on each other and their environment to survive. But human activities cause most of the environmental changes that affect plants and animals today. Animals and plants need clean air, soil, and water, but people pollute the environment with garbage, car fumes, and factory wastes. Animals and plants also need places to live, but the human population is increasing fast and taking over natural areas for houses, roads, factories, and farmlands. People clear forests, swamps, and other wild places, causing the death of many animals and plants. Some animals and plants are endangered simply by human greed. Some people still wear coats made from the furs of rare mammals; others collect rare species of flowers and butterflies.
The list of endangered mammals includes many large, well-known animals. African and Indian elephants have been killed for their tusks, which are used to make ivory earrings and other art objects. Whales are no longer hunted as widely as they once were, but many decades of slaughter greatly reduced the numbers of some species. The giant panda survives only in remote parts of China and in zoos. Other threatened mammals include the tiger and various species of deer, antelopes, and primates.
Until fairly recent times few people were concerned about the impact of human activities on animals and plants in the wild. As people began to worry about such changes they tried to come up with ways to conserve the environment. Today several international and national agencies maintain lists of endangered species. They work to protect and preserve natural habitats and to promote programs for the recovery of threatened species.