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Polar bears are the largest carnivorous land mammals on Earth. They are about seven to eight feet long, measured from the nose to the tip of their very short tail. Male polar bears are much larger than the females. A large male can weigh more than 1,700 pounds, while a large female is about half that size (up to 1,000 pounds). Bears can weigh about 50 percent more after a successful hunting season than they do at the start of the next; most of this additional weight is accumulated fat. A newborn polar bear weighs only about 1.5 pounds.
Many of the polar bear's physical adaptations help it maintain body heat and deal with its icy habitat. The bear's outer layer of fur is hollow and reflects light, giving the fur a white color that helps the bear remain camouflaged. The skin under the polar bear's fur is actually black; this black is evident only on the nose. Polar bears also have a thick layer of fat below the surface of the skin, which acts as insulation on the body to trap heat. This is especially important while swimming and during the frigid Arctic winter. The bear's large size reduces the amount of surface area that's exposed to the cold per unit of body mass (pounds of flesh), which generates heat.
The polar bear's footpads have a kind of “non-slip” surface, allowing them to get traction on slippery ice. Polar bears have strong legs and large, flattened feet with some webbing between their toes, which helps with swimming and walking on ice. The wide paws prevent sea ice from breaking by distributing the polar bear's weight as it walks. The webbed feet results in making polar bears, unlike other bear species, considered to be “marine mammals” along with seals, sea lions, walruses, whales, and dolphins. However, they are still bears. The polar bear evolved one to three million years ago from the brown bear, which still ekes out a marginal life along the northern shore of the Arctic oceans. Unlike the massive polar bear, which can grow huge on a diet of abundant seals, its ancestor in the Arctic is small, has very lower reproductive rates, and eagerly eats almost anything that exists in its environment.
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