In the case of the polar bear, the differing estimates also rely, on the one hand, on fossil information about when the panda bear became an independent species and, on the other, the mutation rate of primates, including humans. By calibrating what scientists call the molecular clock—the hypothesis that mutation occurs at a predictable rate—to the panda separation 12 million years ago, one group of researchers suggests the polar bear's appearance as a species is a relatively recent phenomenon. By suggesting that bears undergo mutation at roughly the same rate as humans, who also may have interbred with closely related hominins like the Neandertals, the other group finds a much older lineage. "One can already suspect that the mutation rate of carnivores, especially bears, will be most likely different from that of primates," argues bioinformaticist Axel Janke of the Biodiversity and Climate Research Center in Germany, one of the researchers behind the study published in Science.
Regardless of how old the polar bear is as a species, or whether it's a species at all, the purpose of such studies is to gain a better understanding of the great white bear's ability to survive in the Arctic, which is now rapidly transforming as a result of accelerated global warming. Understanding how the bears weathered past climate changes or sea ice–free conditions might help identify what could be done to help the unique animal survive.
The new analysis suggests that the key may be refuges with suitable environmental conditions. For example, the polar bear specimen from roughly 120,000 years ago survived in Svalbard during a warm interglacial period because that Arctic archipelago remained more frozen than other areas. "It is possible that Svalbard may have provided one such important refuge during warming periods, in which small polar bear populations survived and from which founder populations expanded during cooler periods," argues biologist Charlotte Lundqvist of the University at Buffalo, The State University of New York, who is a co-author of the new study. That could also explain modern polar bear's relative lack of genetic diversity, which appears to have been declining for 500,000 years. The new genetic analysis found less difference between polar bears living on opposite sides of the Arctic than between Asians and Europeans.
But places like the ancient icy oasis of Svalbard, should they endure relatively unchanged through human-induced global warming, may not be enough to save the polar bear this time. After all, the bear faces the impacts of human pollution, hunting and increased activity in the Arctic, such as shipping and oil drilling as well as the changes in its sea ice habitat. "There is no species that deserves careful study at this time more than the polar bear," Miller says. "I want my great-grandchildren to be able to see them."