Although
it is closely related to the brown bear, it has evolved to occupy a
narrow 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, it spends most of its time at sea, hence its
name meaning "maritime bear", and can hunt consistently only from sea
ice, spending much of the year on the frozen sea.