Scientists—and those of us who are polar bear enthusiasts—have long thought that polar bears started off as brown bears about 150,000 years ago, adapting to their cold environment by developing smaller ears, thicker fur and teeth ideally shaped to tear into seal flesh. But a new, international study coming out of Germany states that polar bears may be a lot older: about 600,000 years old.
And while it was also widely believed that polar bears are most closely related to brown bears living on islands off the coast of Alaska, United Kingdom scientists have recently uncovered evidence that they share the most genetic traits with ancient brown bears from Ireland.
It surely makes us wonder how much we truly know about one of the Earth’s largest land predators. But more than that, how will this new information change our thinking about how polar bears will deal with the current challenges of rapid climate change?
A more ancient species
Until recently, scientists—relying on their examinations of mitochondrial DNA, the fragments of genetic material contained within tiny cell components called mitochondria—believed that polar bears genetically split from brown bears about 150,000 years ago, suggesting that the mammals adapted very rapidly to Arctic life. But the results of a new study published in the April 2012 edition of Science magazine—where scientists analyzed genetic information from the cell nucleus of more than 40 brown, black and polar bears—indicate that polar bears actually evolved in the mid-Pleistocene, about 600,000 years ago.
This new finding means that polar bears had more time to colonize and adapt to life in the high Arctic than we previously thought. It also means that they would have lived through a couple of cycles of warming and cooling; although only two periods noticeably warmer than today, with still most of their existence spent in cooler times. And, the researchers say, the polar bear’s lack of genetic diversity suggests that changes in the environment, such as warm phases, most likely led to periodic dramatic falls in their population numbers. Add in today’s human stressors, such as habitat destruction and environmental pollutants, and the impact of current climate change compared to past episodes will be magnified, posing a novel and probably profound threat to polar bear survival.
An Irish connection
Another recent polar bear study published in Current Biology magazine reports that the maternal ancestors of modern polar bears came from Ireland. In this study, researchers from Ireland, the United Kingdom and the United States examined the teeth and skeletons of 17 ancient brown bears that were found at eight cave sites across Ireland.
Because the caves’ constant, cool temperatures preserved the genetic material within the bones, the researchers were able to study the mitochondrial DNA—passed from mother to child—which showed that extinct Irish brown bears are the ancestors of today’s polar bears. While the two bear species split from a common ancestor to become separate perhaps 600,000 years ago, polar bear males and Irish brown bear females mated opportunistically during the past 10,000 years or more, just before or during the last Ice Age.
The University of Oxford’s Dr. Ceiridwen Edwards, the research paper’s lead author, sequenced the mitochondrial DNA from the bones recovered from the eight sites and from different time depths. She found that the older bears in Ireland—from between 43,000 and 38,000 years ago and before the last Ice Age arrived—had the same genetic signature as brown bears living today in Eastern Europe. But DNA from bears that roamed Ireland in cooler times, 38,000 to 10,000 years ago, had sequences that are the closest match yet to modern polar bears.
These new studies mean that polar bears need more time than thought to adapt to changes in their environment and that hybridization occurs between polar bears and brown bears during times of environmental stress (such as Ice Ages and warming periods) when their home ranges overlap. In fact, recent instances of hybridization in the wild have already been documented where grizzly bears have encroached on polar bear territories.
The reports also demonstrate that polar bears are adaptable if given enough time. They will do—and are already doing—their best to survive; whether that’s by finding new food sources or hybridizing. The problem is, they haven’t experienced anything like the rapid warming that the world is likely to experience in the next 30 to 50 years.
With these two new studies in mind, do you think polar bears will be able to make it through the next several decades?
Here’s to finding your true places and natural habitats,