Over many tens of thousands of years, polar bears evolved to be uniquely well-adapted for a very narrow ecological niche. Their physical features provide superb protection from the cold: they have extremely dense fur and almost no exposed skin, their thick layer of fat provides excellent insulation, and their low surface-area-to-volume ratio helps retain heat. In addition, they are well-designed to walk on ice and snow, and swim in frigid waters. Huge feet function like snowshoes and make good paddles for swimming; bumpy foot pads provide traction on slippery surfaces; short, curved, sharp claws grab the ice effectively; and a blubber-wrapped body has excellent buoyancy.
Evolution has honed polar bear physique, dentition, and metabolism for maximum exploitation of a completely carnivorous, high-fat, marine-mammal diet. A narrow skull, long muscular neck and flesh-grabbing teeth all facilitate plunging head-first deep into a seal’s breathing hole or birth lair to grab prey. Clutching a captured seal in its powerful jaws, a polar bear then uses its incredible strength to drag prey upward and out onto a sea-ice platform where the quarry can be devoured. Polar bears are able to satisfy their enormous energy needs and thrive in the Arctic because they are able to digest and assimilate 84% of the protein and 97% of the fat from their blubbery prey.