The polar bear (Ursus maritimus) is a bear species found in the Arctic region of the northern hemisphere. Along with the domestic bear, it is the largest bear and the largest carnivore living on land.
The polar bear is descended from the brown bear. Genetic studies have given different timings of polar bear birth. According to a study on mitochondrial DNA published in 2010, a polar bear separated from a brown bear about 150,000 years ago and quickly adapted to life on Arctic sea ice. According to an nDNA study published in the journal Science in 2012, the difference occurred 600,000 years ago. According to a study published in the Proceedings of the National Academy of Sciences in the same year, the difference occurred 4 to 5 million years ago, but even then there was a cross between species. The oldest known polar bear fossil is the jawbone, which is 110,000 to 130,000 years old.
Polar bears live in northern Russia, western and northern Alaska, the Canadian Arctic, Greenland, the Svalbard, and northern Siberia. In 2018, the total number of polar bears was estimated at 39,000 (range 26,000–58,000), of which 60–80 per cent in Canada. There are 19 populations, one of which is declining, two are growing, seven are stable and there is insufficient data on nine. In 1960, the total number of polar bears was estimated at 10,000, so their population has multiplied over the decades. Remains of prehistoric polar bears have been found in Sweden and Denmark, for example. The species is thought to have lived in Finland at the time, although there is no definite evidence. The ABC islands of Alaska are home to a crossbreeding population of polar bears and brown bears. It was born when male Brown Bears swam to the islands from the mainland and mated with female polar bears.
The polar bear is longer and slimmer than other bears in its body structure to facilitate movement in the water. Polar bears range in length from more than two meters up to 2.8 meters, and their withers reach from 120 centimeters to 150 centimeters in height. The tail is about 18 inches long. Females weigh 175 to 300 kilograms and males 350 to 700 kilograms, although the largest individuals can weigh as much as 800 kilograms. The polar bear’s skin is black, the hairs are bright (i.e., they have no pigment at all), although they look white in different shades. The hairs are tubular and reflect and absorb sunlight, folding it to white. The eyes, nose and nails are dark. Between the forefeet of a polar bear there are fin-like folds and skin bumps on the trails that improve grip on the ice. In the wild, polar bears live for about 30 years, even longer in captivity. The oldest was Doris (1948–1991) at the Detroit Zoo, who was 43 years old and eight months old.
The polar bear feeds mainly on seals. In their absence, it also eats other animals. Sometimes, rarely does a polar bear prey on walks up to half its weight, preferably young or wounded, and young milk whales from their vents. Most terrestrial animals in the Arctic run harder than polar bears and marine animals are more agile in the water. The interface between ice and water is the polar bear's own predatory terrain. On the ice, it approaches its prey by creeping and attacking after reaching a distance of about 10 meters. The polar bear often lurks at the breathing holes in the seals ’ice. It can be virtually stationary for several hours. When a seal rises to breathe, the bear bites it on the head or upper body and rips it to the ice.
In the spring, female polar bears in particular look for nestlings of seals in the snow. If the bear hears a seal or cub in the nest, it will rise