Polar Bears Are Older than We Thought — and They Come from Ireland

Candice Gaukel Andrews May 15, 2012 18
Polar bear in willows

Recent DNA analyses show that the maternal ancestors of modern polar bears came from Ireland. ©Eric Rock

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 climate change and global warming?

A more ancient species

Two grizzly bears

It’s been long thought that polar bears started off as brown bears about 150,000 years ago. ©Eric Rock

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 forty 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 seventeen ancient brown bears that were found at eight cave sites across Ireland.

Polar bear on ice

Will today’s polar bears be able to deal with a rapidly warming planet? ©Eric Rock

Because the caves’ constant, cool temperatures preserved the genetic material within the bones, the researchers were able to study the mitochondrial DNA — which is 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), whatever the environment throws at them. The problem is, they haven’t experienced anything like the rapid warming that the world is likely to experience in the next thirty to fifty 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,

Candy

18 Comments »

  1. P.T. May 30, 2012 at 4:58 am - Reply

    I loved the thought of Polar Bears originating from Ireland – makes Foxes who like Glacier Mints more real (UK advert). Seriously though all animals come from some origin so why not Ireland. I know that many people believe that the current Canadian Polar Bears came from brown bears that crossed into the Arctic and adapted to the climate.

  2. Sandra H. May 26, 2012 at 10:28 am - Reply

    This is very interesting. Living in Yukon sub arctic, we have seen a change in range as polars are heading south during the summer to roam on the land instead of the ice and there has been a couple of documented cases of hybridized bears in the last few years. Bears who have reproduced with North American Grizzlies or Brown Bears. last year, a female was moved twice from Yukon’s interior back to the McKenzie Delta. Amazing to see them down here, and a little scary, as they have different behavior than Grizzlies or Blacks and have been known to actively hunt Humans, Not something we have had to worry about here.
    Being the eternal optimist, I feel they will survive. As they say in Jurassic Park, Nature always finds a way!

  3. Candice Gaukel Andrews May 26, 2012 at 10:20 am - Reply

    Michaela,

    Thank you for writing. Yes, I’ve loved animals since I was your age – and before! I grew up with a lot of dogs in my family, and I think I had every species of toy, plush animal ever made. I’m sure your love of animals will lead you to do great things to protect and conserve them.

    As for harp seals, there are many good books on them; just ask your teacher or librarian. You can also check out the World Wildlife Fund (http://wwf.worldwildlife.org) website and the National Geographic (http://animals.nationalgeographic.com) website.

    Good luck, Michaela,

    Candice Gaukel Andrews

  4. David May 23, 2012 at 3:25 pm - Reply

    On the other hand, there are polar bears living quite comfortably at he Phoenix Zoo. You see, their hollow fur also protects them from intense heat. Perhaps the question might be whether or not they can adapt to different prey or life on land as opposed to will they survive temperature increases.

  5. michaela martinez May 18, 2012 at 8:08 pm - Reply

    hey candice!very good article.have you been interesed in animals since you were a kid?im 10 years old and i love animals!and just to tell you something…..your my inspierer in animals knowledge.you get the latest details anaimals.do you think you can get details on harpseals?i dont blame you for being still worried about the polar bears, after this article im getting a little worried to.but just keep writting articles candice and i will try to keep up with all your details.

  6. Candice Gaukel Andrews May 17, 2012 at 8:46 am - Reply

    Andreas,

    Thank you for your thoughtful comment. My eco-issue and eco-ethical questions in these posts are meant to inspire exactly this kind of thought, reflection, and debate.

    The National Geographic Society (http://news.nationalgeographic.com/news/2007/09/070910-polar-bears.html), CBS News (http://www.cbsnews.com/2100-205_162-3243272.html), and FutureTimeline.net (http://www.futuretimeline.net/subject/energy-environment.htm) have all reported on government studies that state that polar bears could be at dangerously low population numbers or extinct by 2050 (thus, my question).

    You may also be interested in this recent post on Arctic sea ice: http://theadventurecorner.explorerscorner.com/2012/05/sea-ice-losing-in-the-arctic-but-gaining-in-the-antarctic/

    I, too, share your belief that polar bears are adaptable and perhaps can’t be counted out quite so quickly: see http://theadventurecorner.explorerscorner.com/2010/12/eating-goose-eggs-and-other-culinary-adventures/

    Thanks, again, for your interest in these issues and engaging in the discussion.

    C.G.A.

  7. Andreas Fischlin May 17, 2012 at 5:41 am - Reply

    Why do you even ask this question “With these two new studies in mind, do you think polar bears will be able to make it through the next several decades?”? These studies don’t make a difference for the next several decades, since there is very little evidence that polar bears as a species wouldn’t make it through the next several decades. The real issue with the survival of this species is: Will it survive the end of this and most of all the next century? There is still a lot of Arctic sea ice around and even if more recent trends of summer sea ice loss should continue as fast as some may have feared 2007 (year of the greatest loss so far and/or perhaps instigated by Stroeve et al., 2007) this would not mean near future extinction. There are 19 subpopulations spread over a large part of the Arctic experiencing still considerable differences in terms of temperatures and presence of sea ice and polar bear prey. Finally one has to consider that polar bears are not short-lived and survival of individuals will consequently drag on, even if the reproduction of the species should have come to a halt and extinction should be around the corner.

    Cited References:
    ————————
    Stroeve, J., Holland, M. M., Meier, W., Scambos, T., & Serreze, M. C., 2007. Arctic sea ice decline: Faster than forecast. Geophys. Res. Lett., 34L09501. http://dx.doi.org/10.1029/2007GL029703 Str034

    • michaela martinez May 18, 2012 at 8:13 pm - Reply

      Just for the record Andreas, you don’t have to be so rude about it! And there isn’t that much ice out there for the polar bears because of humans starting GLOBAL WARMING and polluting. People need more trees because the trees suck up all that pollution.

  8. Candice Gaukel Andrews May 16, 2012 at 6:44 pm - Reply

    Literacki,

    Thanks for commenting. Polar bears and brown bears do produce fertile offspring since they separated not that long ago. There are some good explanations here:

    http://www.pbs.org/wnet/nature/episodes/arctic-bears/how-grizzlies-evolved-into-polar-bears/777/

    http://www.slate.com/articles/news_and_politics/explainer/2010/05/pizzly_bears.html

    C.G.A.

    • Literacki May 18, 2012 at 1:38 pm - Reply

      Candice,

      These articles are based on the assumption that Polar Bears diverged from living brown bears, recently “The prevailing theory holds that polar bears diverged from brown bears at the end of the last ice age (the Pleistocene), when a population followed retreating ice northward.” which would make more sense in respect to producing fertile hybrids but this contradicts the findings of your article, since the Irish brown bear is extinct – not available for breeding – and the divergence occurred some 600k years ago– not very recent.

      It would seem more likely that polar bears are a subspecies of the first or early bears – that became isolated for short periods of time due to temporary glacier barriers – during the time that bears were migrating from their origin(s) but have made intermittent contact with other species that descended from the same early bear(s). This would explain why there is strong genetic similarities with an ancient bear species but polar bears can still produce fertile offspring with other modern species.

      Thanks for the response,
      Literacki

  9. Literacki May 16, 2012 at 6:26 pm - Reply

    Since hybrids are sterile and cannot produce offspring, how could hybridization be a factor in preventing the loss of genetic diversity, let alone a mechanism to counteract population declines during times of environmental stress?

  10. John D. May 16, 2012 at 2:34 pm - Reply

    Very interesting article.

  11. K. W. May 15, 2012 at 10:52 am - Reply

    Terrific article! Thanks for sharing it!

  12. Candice Gaukel Andrews May 15, 2012 at 8:16 am - Reply

    Zenda,

    I am still worried, but good to learn that polar bears are giving survival their best shot.

    And, interesting point you make about deer.

    Thanks for commenting!

    C.G.A.

  13. UWINEZA JEAN DE DIEU May 15, 2012 at 8:11 am - Reply

    Your information is really interesting. Really interested to see you are interested in doing research to animals.Do you know there is an other magnificent creature giant one “gorillas”. They seem to be as old as polar bears.They have some resemblance.They live in family.They are available in Rwanda at least in 8 groups .It should be a great experience to spot it.

  14. Candice Gaukel Andrews May 15, 2012 at 8:10 am - Reply

    Thank you, James! I appreciate it.

  15. Zenda Iannetti May 15, 2012 at 7:14 am - Reply

    Very interesting! What a great way to begin my day. I suppose that with other species of animals which hybridize (such as deer, etc) it may also be a coping mechanism as well? Maybe we shouldn’t worry as much?

    What do you think Candice?

  16. James Beard aka Noodin May 15, 2012 at 6:36 am - Reply

    Very nice information Candice. Always enjoy the information that you gather.

Leave A Response »