NATURE: Arctic Bears

Polar bears are living on borrowed time. They are the descendents of grizzlies, long-ago evolved to live and hunt on the frozen ice of the Arctic, eating a specialized diet of seal meat.

But the winters have become increasingly warmer, the ice is disappearing and raising a family becomes a much more difficult proposition when hunting time is short and food is scarce.

Grizzlies, on the other hand, are masters at living off the land, making a meal from a wide variety of foods--meats, seeds, berries, insects, fruit and honey. Their world is bountiful and expanding northward, converging with what once was the icy domain of the polar bear.

As the two worlds meet, are the polar bears fated to become grizzlies once again? If the changing world proclaims the grizzly the new king of the Arctic, what will become of the polar bear? NATURE tracks both species at close range in "Arctic Bears." Learn more about how grizzlies evolved into polar bears.

NATURE is on Facebook, and you can follow @PBSNature on Twitter.