© Eric V. Regehr / USGS Change… Following on the well-traveled path of the Greek philosopher Heraclitus and others since, Isaac Asimov once said:
“It is change, continuing change, inevitable change that is the dominant factor in society today. No sensible decision can be made any longer without taking into account not only the world as it is, but the world as it will be…”
Alternatively – change is the only constant.
The planet we call home has been changing since it all began some four billion years ago. From the formation of our current atmosphere to the position, shape, and size of the continents that support us, change has indeed been a constant. Therefore, while the world is certainly a very different place today than it was say a thousand years ago, the questions that haunt us now have to do more with the rate, magnitude, and drivers of that change. Answers to those questions are providing some troubling, if not alarming, data regarding human driven changes. Some scientists have even coined a new term for our current era: the anthropocene: the time when human activities became the dominant drivers of key global systems and biodiversity.
Nowhere are these questions more acute, and the transformative affects more apparent than in the Arctic, a region that is warming at more than twice the global average. The face of that change for many is the iconic polar bear. A warming Arctic is rapidly eroding the very sea ice that polar bears need to be- well- to be polar bears as we know them today. While polar bears have clearly survived warming events in the past, there is no reason to infer the bears we have today will be as fortunate. A host of scientific research has clearly laid out those concerns and the measurable impacts of warming to date on some management units like Western Hudson Bay. However, some new observations of hybrid bears in the wild and fresh data on polar bear genetics have some people asking questions.
First, let’s look at the important recent genetic study (overview | original study) that resets our collective understanding of bear evolution and relatedness. This paper was several years in the works and required the collaboration of many scientists from around the world. It will not be the last word on polar bear evolution, but it provides a significant new dataset and several new hypotheses that reshape our understanding of this species. The essence of this first full look into the polar bear genome is that they split from a common bear ancestor with brown bears much longer ago than currently thought (up to 4.5 MYA) and that the two are sister species that have interbred historically. Polar bears likely co-evolved with brown bears, but did not evolve fromthem as previously thought. Researches also theorize that past changes in climate likely brought these two species into closer proximity that allowed for this hybridization. While some of their genes may carry on through cross breeding, there is no reason to believe the animals we know as polar bears would endure.
Genetic data also suggest that polar bears occur in much smaller numbers today than in prehistory. There is also no evidence that early polar bears resemble the highly specialized animals we know today. These historical population estimates appear to track changes in climate, showing a long-term decline in numbers since the last ice age. One result of this decline is that polar bears likely possess far less genetic diversity today than they had historically, making them more vulnerable to recent and projected changes.
At the end of the day, whether polar bears are 150,000 years old or 5 million, in the face of current persistent and rapid climate warming, the world around them (and us) will be unlike anything they have experienced by the end of this century, if not earlier.