Polar Bear Jawbone gives Clues to Evolution of Polar Bear Species

Scientists have known for some time that the Polar Bear (Ursus maritimus) is most closely related to the Brown Bear (Ursus arctos) or a sub-species thereof.  However, the timing of the evolution of a bear adapted to the cold and subsequently being named and described as a new species has been debated.

Polar Bear Jawbone

In a research paper published by a team of Scandinavian scientists, on the study of a fossilised jawbone from an ancient Polar Bear, one of the conclusions drawn is that Polar Bears evolved as recently as 150,000 years ago, in response to dramatic climate change in the northern hemisphere.  The jawbone is the oldest Polar Bear fossil found to date and it suggests that Brown Bears trapped on remote islands at the onset of a period of global cooling adapted to the cold conditions and over many thousands of years they evolved into a new species – the Polar Bear.

Affinity Between the Polar Bear and the Brown Bear

The close affinity between the Polar Bear and the Brown Bear is well known, with genetic studies indicating how closely related these two species are.  There have also been several reports of “hybrid” bears being discovered in the wild and bred in zoos, natural crosses between a Brown Bear and a Polar Bear.  This has caused certain difficulties for hunters in the Canadian frozen wastes, as although they may have had the correct hunting permit to shoot Polar Bears (around 500 such bears are shot legally each year), sometimes a hybrid is shot a “pizzly” as they are referred to by the locals and this can get the hunter into trouble with the Canadian authorities.

Discovery on an Arctic Island

The bone was discovered at Poolepynten on the Arctic island of Svalbard by Professors Olafur Ingolfsson, of the University of Iceland, and Oystein Wiig, of the University of Oslo.

In a research paper the researchers concluded:

“The Poolepynten subfossil mandible, which we argue is from a fully grown male, is probably the oldest Polar Bear find discovered so far.  Its true age is interpreted to be 110,000-130,000 years old.”

Academics have debated the Polar Bear lineage for many years, some believe that it evolved as recently as 50,000 years ago, whilst other scientists have argued that this species evolved more than a million years in the past.

Svalbard Fossil

The existence of the Svalbard fossil indicates that polar bears were already a distinct species by about 130,000 years ago.  But anatomical and DNA evidence from the fossil indicate a closeness between Polar Bears and Brown Bears of the time — suggesting the species diverged no more than about 200,000 years ago and probably about 150,000 years ago.

This sharply narrows the “window” during which Polar Bears might have emerged to a period when the Northern Hemisphere was being drawn into an ice age that lasted from approximately 190,000 to 130,000 years ago.  This period of dramatic climate change would have put pressure on the northerly enclaves of Brown Bears, especially those on isolated islands such as Admiralty Island and its neighbours Baranof Island and Chichagof Island (known locally as the ABC islands).

Examining DNA

One research group, led by Gerald Shields, of the University of Alaska Fairbanks, used DNA from 61 Brown Bears taken from three populations in Alaska and 55 Polar Bears from Arctic Canada and Siberia.  The scientists wanted to work out not only when Polar Bears evolved but also, potentially, where from and from which population of Brown Bears.

The researchers discovered that the DNA of the ABC island bears was closer to that of the Polar Bear than any other Brown Bear population studied.

In a paper they research team concluded:

“Brown Bears of the ABC islands may be descendants of ancient ursids [bears] that diverged from other lineages of Brown Bears and subsequently founded the Polar Bear lineage.”

This view is expected to get support from new research, out this week, based on DNA extracted from the Poolepynten jawbone.

It means polar bears have already survived a global warming that affected the northern hemisphere from 130,000 to 115,000 years ago, when the Greenland ice sheet and the Arctic ice cap were smaller than now.  Professor Chris Stringer, of the Natural History Museum in London, an expert in ice age mammals and the evolution of hominids, commented:

“Early Polar Bears would not have had all the specialisations of modern animals and we know nothing about their behaviour.”

Reflecting on the current plight of Polar Bear (listed as vulnerable under the Endangered Species Act), Professor Stringer said:

“Living through a warm period back then does not mean they are resilient to climate change now.”

For models and replicas of prehistoric animals: Prehistoric Animal Models and Figures.