Tuesday, 4 February 2014


Polar bears have evolved from brown bears.  But they are white, not brown.  So why did they change colour?

The reason for the change is the difference in habitat of the two bears. The polar bear differs from its brown cousin as it lives and hunts on sea ice.  The snow and ice are white so the bears blend in with their surroundings.  Most Arctic animals such as the Arctic fox and hare are white in the winter, but the polar bear is white all year round.  

However, think again.  It is not the fur that is white.  The hairs are actually transparent and it is the light bouncing off them that makes them appear white.  In addition the hair follicle is hollow so there is no melanin present to determine colour.. Even more fascinating is the fact that the skin colour of the polar bear is black.

Polar bears have two layers of hairs that help to insulate them against temperatures as cold as -50F.  Next to the skin is a layer of soft, downy colourless hairs which trap warm air to insulate the skin.  Above these are thick, coarse guard hairs which repel water and are also colourless.

Polar bears have previously turned green in some zoos.  Further investigation by scientists found that algae from pond water inside the enclosure was growing inside the hollow hair fibres and giving the green appearance.

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