Dinosaurs, saber-tooth tigers and the dodo bird are
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famous examples of animals that have become extinct. In
case of the dinosaurs, it seems likely that a catastrophic
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event alters the global climate enough to lead to their
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disappearance. More recent extinctions and near-extinctions—such
as the blue whales, tiger, panda, and North American
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bison—have been the direct result of human activity. By
the early 1990s, species were becoming extinct at a rate of
three per hour, or 27,000 every year—a figure quoted by the
American biologist Edward O. Wilson of Harvard University,
based on his most conservative estimates. This rate of
extinctions carries with it some terrible consequences. Each
plant that becomes extinct, for example, may take with it as
much as 30 insects and animals that depend on it for food.
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Habitat loss is one of the most important causes of extinction.
For rising populations in many countries lead to the
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clearing of more land, habitats such as raining forests and
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grasslands disappear.
In the East Africa, once renowned for its wildlife, few
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wild animals remain living outside the boundaries of
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national parks and game reserves. In other parts of the world,
coastal ecosystems are clearing for development. Wetland
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areas are drying out as a result of water extraction to support
farming and tourism. Bird species are among the worst affected
by the loss of wetlands.