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Why Do Polar Bears Have White Colored Fur?

Polar bears (Ursus maritimus) evolved transparent colored fur as opposed to black or brown for camouflage. Although the fur appears white, it actually is colorless. In the polar bear's home in the Arctic Circle, most of the landscape consists of snow and ice. White animals blend in with the white background, hiding the bear from its prey and from other bears. This adaptation is similar to a green snake who lives in grass or a brown doe who lives in the forest.

Hair Anatomy
- Polar bear fur consists of two layers -- the outer and the inner. Each hair in a polar bear's outer layer or guard hairs is hollow. None of the hairs contain pigment. This construction reflects light rather than absorbs it. When the human eye looks upon the fur, it appears white. The soft, dense inner hair is not hollow, but still transparent enough to appear snowy white. Hollow hair shafts are thought to trap warm air inside the bear's coat, according to "Encyclopedia of Adaptation in the Natural World."
Evolution
- Polar bears evolved from brown bears or Ursus arctos, a species which still survives in North America and Eurasia. One of the best known subspecies of brown bear is the grizzly or Ursus arctos horribilis. DNA of brown bears on Alaska's ABC Islands more closely matches polar bear DNA than any other population of brown bears in the world. The two species separated anywhere from an estimated span of 1.5 million to 70,000 years ago, according to the PBS series "Nature." Brown bears gradually turned white and became leaner when some migrated to the Arctic Circle.
Speculation
- Both grizzlies and polar bears can interbreed, creating what is called a "pizzly" or "grolar." One such bear was shot in the Canadian wilderness in 2006. It had the coloring of a polar bear. Unlike most other hybrid species, such as the mule, pizzly bears are fertile. The bear shot in 2006 had a pizzly mother and a grizzly father, according to the Northwest Territories Environment and Natural Resources Department. Grizzly bears progressively push north into polar bear territory in order to find food. If climate change and more grizzlies enter the Arctic Circle, future generations of "pizzlies" or polar bears may change color.
Fun Fact
- During the 1970s, some polar bears kept in captivity turned green during summer months. Their fur becomes host to algae, which take up residence inside the bear's individual hollow hair shafts. The algae came from the moats or swimming ponds in their enclosures. Polar bears at the Higashiyama Zoo and Botanical Gardens turned green due to algae in 2008. Since zoos are located much further south than the Arctic Circle, algae growth does not bother wild polar bears.

Animals & Science