The polar bear (Ursus maritimus) is a carnivorous bear whose native range lies largely within the Arctic Circle (Northern Hemisphere). It is a large bear, approximately the same size as the omnivorous Kodiak bear (Ursus arctos middendorffi). Although it is the sister species of the brown bear, it has evolved to occupy a narrower ecological niche, with many body characteristics adapted for cold temperatures, for moving across snow, ice, and open water, and for hunting the seals which make up most of its diet. Although most polar bears are born on land, they spend most of their time at sea. Their scientific name means "maritime bear", and derives from this fact. Polar bears hunt their preferred food of seals from the edge of sea ice, often living off fat reserves when no sea ice is present.
For thousands of years, the polar bear has been a key figure in the material, spiritual, and cultural life of Arctic indigenous peoples, and polar bears remain important in their cultures. Constantine Phipps was the first to describe the polar bear as a distinct species in 1774. Phipps chose the scientific name Ursus maritimus, Latin for 'maritime bear', due to the animal's native habitat. The Inuit refer to the animal as nanook. The Yupik also refer to the bear as nanuuk in Siberian Yupik. In the Norway-administered Svalbard archipelago, the polar bear is referred to as Isbjørn (ice bear).
The polar bear was previously considered to be in its own genus, Thalarctos. However, evidence of hybrids between polar bears and brown bears (i.e. grolar or pizzly), and of the recent evolutionary divergence of the two species, does not support the establishment of this separate genus, and the accepted scientific name is now therefore Ursus maritimus, as Phipps originally proposed.
The bear family, Ursidae, is believed to have split off from other carnivorans about 38 million years ago. The Ursinae sub-family originated approximately 4.2 million years ago. The oldest known polar bear fossil is a 130,000 to 110,000-year-old jaw bone, found on Svalbard-Norway in 2004. Fossils show that between 10 to 20 thousand years ago, the polar bear's molar teeth changed significantly from those of the brown bear. Polar bears are thought to have diverged from a population of brown bears that became isolated during a period of glaciation in the Pleistocene epoch.
The evidence from DNA analysis is more complex: The mitochondrial DNA (mtDNA) of the polar bear diverged from the brown bear, Ursus arctos, roughly 150,000 years ago. Further, some clades of brown bear, as assessed by their mtDNA, are more closely related to polar bears than to other brown bears, meaning that the polar bear would not be a true species according to some species concepts. The mtDNA of Irish brown bears is particularly close to polar bears. A comparison of the nuclear genome of polar bears with that of brown bears revealed a different pattern, the two forming genetically distinct clades that diverged approximately 603,000 years ago, although the latest research is based on analysis of the complete genomes (rather than just the mitochondria or partial nuclear genomes) of polar, brown and black bears, and establishes the divergence of polar and brown bears at 4-5 million years ago.
However, the two species have mated intermittently for all that time, most likely coming into contact with each other during warming periods, when polar bears were driven onto land and brown bears migrated northward. Most brown bears have about 2 percent genetic material from polar bears, but one population residing in Alaska's Alexander Archipelago has between 5 percent and 10 percent polar bear genes, indicating more frequent and recent mating. Polar bears can breed with brown bears to produce fertile grizzly–polar bear hybrids, rather than indicating that they have only recently diverged, the new evidence suggests more frequent mating has continued over a longer period of time, and thus the two bears remain genetically similar. However, because neither species can survive long in the other's ecological niche, and because they have different morphology, metabolism, social and feeding behaviors, and other phenotypic characteristics, the two bears are generally classified as separate species.
Unlike grizzly bears, polar bears are not territorial. Polar bears don't hibernate in the strict sense of the word. True hibernators experience a marked drop in heart rate and body temperature and generally stay for a long period in a den. Adult males and non-pregnant females don't den up at all. The polar bear is an excellent swimmer and individuals have been seen in open Arctic waters as far as 200 miles from land. Despite what tenderfoots think, a polar bears' fur is not white—it just looks that way. Each hair shaft is pigment-free and transparent with a hollow core that scatters and reflects visible light, much like what happens with ice and snow. Scientists used to think that polar bears' hollow hairs acted like fiber optic tubes and conducted light to their black skin; In 1988, a physicist at St. Lawrence University proved this theory false.
When the polar bear was originally documented, two sub-species were identified: Ursus maritimus maritimus by Phipps in 1774, and Ursus maritimus marinus by Peter Pallas in 1776. This distinction has since been invalidated. One fossil sub-species has been identified. Ursus maritimus tyrannus — descended from Ursus arctos — became extinct during the Pleistocene epoch. Ursus maritimus tyrannus was significantly larger than modern bears.
The polar bear's range includes the territory of 5 nations: Greenland (Denmark), Norway (Svalbard), Russia, the United States (Alaska) and Canada. These 5 nations are the signatories of the International Agreement on the Conservation of Polar Bears, which mandates cooperation on research and conservation efforts throughout the polar bear's range. If polar bears came from brown bears then why do we still have brown bears? Professor Webb Miller of Pennsylvania State University knows the answer. Ken Ham's Creation Museum teaches pseudo-science.