Bear is a group of mammals (哺乳动物) distinguished by a large, strong body powerful limbs dense fur and a short tail. Bears live in North America, South America, Europe, and Asia, where they occupy a wide range of habitats, including mountain, forest, and Arctic wilderness. Over the last century bear populations have steadily declined as humans have overhunted bears and occupied their habitat (栖息地). Zoologists (scientists who study animals) classify eight species of bears: giant panda, spectacled bear, sun bear, sloth bear (长毛熊), Asiatic black bear, American black bear, brown bear, and polar bear. All of these species, with the exception of some populations of spectacled bears and sun bears, live north of the equator. Bears are not currently found in Africa, Australia, or Antarctica. All bears are similar, but individual species vary in size, diet, and type of habitat. For example, polar bears live in frozen Arctic wilderness, where they feed primarily on seals, while sun bears live in Asian iron forests and dine on insects, fruits, nuts, and small animals. Reaching weights of 800 kg, polar bears may grow 12 times larger than their smaller cousins the sun bears, which rarely exceed 66 kg in weight. Despite the considerable division of its range, the brown bear is still the most widespread member of its family. It persists in scattered pockets from Spain to Japan and' in the northern Rocky Mountains of the United States. Populations are more continuous in Russia, Alaska, and Canada. This broad range encompasses (包含) much variation, from enormous coastal brown bears in Alaska and Kamchatka to much smaller bears in Southern Europe, where large, erous individuals (and their genes) were eliminated long ago. There are pale cream brown bears and almost black brown bears. Because of their frosted coats, brown beam of the North American interior are universally called grizzlies (灰熊). Bears have long fascinated humans. Ancient cave art and more recent paintings and sculpture illustrate the fear as well as admiration with which people regard the awesome power and acute intelce of bears. In fairy tales, bears are the symbolic image of brave deeds. In folk literature, the bear's habit of disappearing in winter months and emerging in spring evokes a theme of spiritual renewal, the supply of food, and the return of prosperity. In modem times, as the recreational use of parks and wilderness areas has grown dramatically, humans have experienced increased contact with bears. Bear attacks on humans are rare, however. American black bears killed fewer than 40 people during the 20th century. Grizzly bears, a type of brown bear, are more erous, but attacks on humans are still rare. In United States national perks that are home to grizzlies, injury rates from grizzly bears are about one person per 2 million visitors. Bears prefer to avoid humans, but when attacks do occur, they are usually the result of humans surprising these nervous, shy, and easily frightened animals. Bears are giant animals with wide shoulders, a short back, short and thick legs, broad paws, and a short tail. They have a lengthened head, rounded ears that stand straight up, small eyes, and a long snout (嘴). Bears hunt for food using an acute sense of hearing and an extremely keen sense of smell—some can detect odors from more than a mile away. Bear eyesight is probably similar in sharpness to human vision. Black bears, and likely other bears, have color vision, which helps them identify ripe fruits and nuts. Bears have 32 to 42 teeth, depending on the species, and these teeth reflect a varied diet of both plants and animals. Although all bears are meat eaters, all but polar bears have become omnivorous—that is, they eat many types of foods, including roots, nuts, fruits, berries, seaweed, grasses, honey and ants. Bear teeth are not as sharp or specialized for shearing (剪毛) meat as are those o