Polar bear

The polar bear (Ursus maritimus) is a large predatory mammal native to the Arctic and surrounding regions. Closely related to the brown bear, with which it can hybridise, the species represents a highly specialised lineage adapted to life on sea ice and dependence on marine prey. It is the largest extant bear and the most powerful land-based carnivore, occupying a central position in Arctic ecosystems and cultures.

Naming and Classification

The modern common name polar bear was introduced by Thomas Pennant in 1771. Historically, Europeans referred to the species as the white bear, sea bear or Greenland bear. The Norse called it by terms meaning “ice bear”, while Inuit languages preserve a rich vocabulary distinguishing the bear by age, sex and behaviour.
Carl Linnaeus initially classified the polar bear as a variety of the brown bear in his Systema Naturae. Constantine John Phipps recognised it as a distinct species in 1774 following exploratory work in the high Arctic. Although some taxonomists once placed the species in the separate genus Thalarctos owing to its marine specialisations, the consensus now retains Ursus as the valid genus, reflecting fossil continuity and the ability to interbreed with brown bears. Numerous historical subspecies have been proposed, but none is currently recognised; the species is considered monotypic.
One putative fossil form, Ursus maritimus tyrannus, described in 1964 from an oversized ulna fragment, was once thought to represent a giant ancestral polar bear. Later analyses suggest the bone more likely belonged to a very large brown bear.

Evolutionary History

The polar bear is one of six living species in the subfamily Ursinae. The fossil record for the species is sparse, but a jawbone dating to 130,000–110,000 years ago from Prince Charles Foreland in Norway is the oldest secure find. Early interpretations based on mitochondrial DNA suggested that polar bears diverged from brown bears relatively recently, and that certain brown bear populations—such as those from the ABC Islands of Alaska—were descended from polar bears.
More comprehensive genomic studies have clarified this picture. They show that polar and brown bears form distinct sister lineages, with evidence of ancient hybridisation events rather than direct descent. Divergence estimates vary: some studies suggest a split around 600,000 years ago, others more than one million years ago. Gene flow between the species occurred episodically, particularly during glacial cycles, and appears to have ceased approximately 200,000 years ago. Genetic exchange from polar bears into brown bears is detectable in several populations, including the ABC bears and some ancient Irish bears.
Genome analyses highlight adaptations associated with the polar bear’s carnivorous lifestyle and Arctic environment. These include reduced diversity in olfactory receptor genes, fewer copies of amylase genes, enhanced pathways for lipid metabolism and cardiovascular efficiency, and expanded gene families involved in keratin production contributing to dense fur.

Physical Characteristics

The polar bear is the largest living bear species. Adult males typically measure between 2.4 and 3 metres in body length and weigh between 350 and 700 kilograms, though individuals heavier than 1,000 kilograms have been recorded. Adult females are roughly half this size. The species shows pronounced sexual dimorphism, with males possessing proportionally larger heads.
Polar bears have elongated bodies, longer necks and narrower skulls than brown bears. Their snout profile is curved, and their dentition is specialised for a primarily carnivorous diet, featuring long, sharp canines and pointed cheek teeth. A noticeable diastema separates the canines from the premolars, likely aiding in gripping large prey.
Adaptations for Arctic living include thick insulating fat layers and a heavy double-layered coat composed of dense underfur and protective guard hairs. The skin beneath the fur is black, maximising heat absorption. Large, furry paws distribute weight on snow and ice and aid in swimming; claws are sharp, curved and comparatively short.

Ecology and Behaviour

Polar bears are both terrestrial and pagophilic, spending significant time on sea ice and serving as specialised apex predators of the Arctic marine ecosystem. As strong and capable swimmers, they are classified as marine mammals. Their seasonal distribution largely follows the extent of annual sea ice.
Their diet is dominated by pinnipeds, especially ringed seals. Hunts frequently involve waiting beside seal breathing holes or approaching hauled-out seals by stealth. The bears target blubber-rich tissues, which provide high-energy food essential for survival in extreme cold. They may also prey opportunistically on walruses, beluga whales, fish, birds and terrestrial mammals, though these items constitute minor dietary components.
Polar bears are generally solitary. Interactions occur during the breeding season, when males compete for females, and occasionally on land at food sources. Females give birth in winter maternity dens, typically to one to three cubs, which remain with their mothers for up to two and a half years.

Distribution and Habitat

The species is distributed throughout the circumpolar Arctic, including northern Canada, Alaska, Greenland, Svalbard, Russia and adjacent ice-covered seas. Its habitat preference is strongly tied to the seasonal formation and disappearance of sea ice, which provides platforms from which to hunt seals. During summer ice retreat, bears may remain on land, where food availability is much lower.

Conservation Status

The polar bear is listed as Vulnerable by the International Union for Conservation of Nature. Global population estimates range from approximately 22,000 to 31,000 individuals. The primary threat to the species is climate change, which is driving rapid Arctic sea ice decline. Reduced ice cover limits hunting opportunities, increases energetic costs and raises the incidence of malnutrition and starvation. Increasing time spent on land also heightens conflict with humans.
Secondary threats include pollution, industrial development, shipping and historical hunting. Indigenous peoples have long hunted polar bears for subsistence and cultural purposes, and controlled hunting continues in some regions.

Cultural Significance

Polar bears have held an important place in Arctic cultures, featuring in folklore, art and traditional religious practices among Inuit and other circumpolar peoples. In the modern era they have become powerful symbols of the Arctic environment, frequently appearing in conservation messaging. The species has also been displayed in zoos, immortalised in literature and used in scientific and artistic representations of wildlife and climate change.