Grizzly bears are a subspecies of brown bear, set apart by their size, their silver-tipped fur and their trademark hump of upper-back muscles. Scientists think North American grizzlies (Ursus arctos horribilis) evolved from Asia's Ussuri brown bears, which migrated into Alaska from Siberia some 100,000 years ago.
They eventually spread as far as Mexico and the Great Lakes, but European settlers and U.S. pioneers later wiped them out across most of the Lower 48 states, leaving only a few pockets in Idaho, Montana, Wyoming and Washington. All U.S. grizzlies were added to the endangered species list in 1975 except those in Alaska, where they're still abundant.
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