Polar bears as with all bears alive today evolved from the Ursavus who inhabited Asia 22 million years ago, and was the ancestor of all bears. Polar bears began evolving from brown or grizzly bears about 300,000 yrs ago. Evolution of Polar Bear can easily be traced by the fossil transitions, which confirms our knowledge of development of the Polar Bear species. The polar bears of this time period were much larger than they are today, as were many other species. Scientists now believe that the polar bear evolved from a group of brown bears which became isolated by glaciers in an area near Siberia.
The polar bear's silhouette is very different from that of the brown bear: its body is more elongated and it lacks a shoulder hump. The polar bear's sense of smell and eyesight is much keener than that of the brown bear. The polar bear also has excellent hearing as well. The polar bear's teeth are also different than those of the brown bear, which lives on a largely vegetarian diet. The polar bear's cheek teeth are sharper, this adaptation allows the bears to shear off chunks of meat. Other differences include a longer neck, useful in keeping the polar bear's head above water when swimming; warm, thick fur which insulates them from the cold and huge paws, which help spread the bear's weight on thin ice and are very useful when swimming. Brown bears hibernate in winter, polar bears do not although pregnant female polar bears do den, however, as cubs require a shelter from the weather conditions until they are three or four months old.
The polar bear lives in the most extreme weather conditions and is the biggest bear among the various species, because these dimensions allow it to keep better the heat into his body. Its color allows the bear to hide itself in the ice and not being seen by its potential preys, but also to reflect the solar light at least partially toward its skin that is still black, and better to absorb this heat, but in any case this is not necessary to the polar bear to live. The polar bears existence is now threatened by global warming as his ice fields from which he hunts are shrinking and the ice is becoming too thin to support his weight. I am sure the polar bear will adapt and change as he has done over the past 300,000 years and will still be with us in the future.