During the course of millions of years, animals have adapted to various environments on Earth. Although animals have evolved over geologic time to Earth's constantly changing environments, and although the extinctions of certain species are normal, in no other time in the planet's history has the extinction rate climbed as high as it is today. Causes of this unprecedented extinction rate include destruction of wildlife habitat, pollution, overfishing, and poaching. ""Animals"" illustrates these urgent issues in a manner accessible to middle and high school readers.