Arctic Bears
How Grizzlies Evolved into Polar Bears

The icon of the Arctic, the polar bear, is the ultimate survivor in one of the harshest areas on Earth. Reigning over a world of ice, tundra, and snow, this carnivore would seem to have a lineage that traces back to some mammoth creature of the icy regions.

But in fact, the polar bear’s closest ancestor is a land carnivore we associate more strongly with our forests. Over the years, scientists have uncovered an evolutionary path suggesting that polar bears are a relatively new species, and actually a subspecies, of Ursus arctos, more widely known as the brown bear. Scientific evidence has found that the brown bear, a species that also includes grizzly bears, was a “precursor” to polar bears, which then went on to develop specializations for inhabiting the harsh Arctic.

Proving their genetic compatibility, brown bears and polar bears can mate and produce viable, or fertile, offspring. It is this reproductive viability that establishes that an animal belongs within a given species. In 2006, a hybrid grizzly/polar bear, which some call a “pizzly,” was discovered in the Canadian Arctic, providing researchers proof that polar bears and grizzly bears can interbreed, even in the wild. And when researchers in Alaska compared the DNA of brown bears from around the world, looking for genetic links, they made an interesting discovery about one population of brown bears in particular. Analysis of the DNA of a distinct population of brown bears living on Alaska’s ABC islands, 900 miles south of the nearest polar bear, revealed that the ABC bears were even more closely related to polar bears genetically than they were to other brown bears.

So just when did polar bears arise as a separate subspecies? Genetic models show that the emergence of the polar bear could have taken place as recently as 70,000 years ago or as many as 1.5 million years ago. For many years, a fossil found at Kew Bridge in London was considered the oldest polar bear specimen. The fossil then placed the evolution around 70,000 years ago. But recently, scientists uncovered a fossilized jawbone from an island in the Arctic Ocean midway between Norway and the North Pole, dated to be at least 100,000 years old. Scientists believe this jawbone may represent the remains of the oldest-known polar bear, thus marking the appearance of the polar bear earlier than previously thought.

Relying on the fossil record and DNA analysis, scientists have been able to arrive at a clearer picture of the polar bear’s evolutionary path over the millennia. Some 200,000 years ago, when glaciers covered much of Eurasia, the Arctic Ocean was completely frozen. It was during this challenging period that brown bears began to wander in search of food. Approximately 125,000 years ago a population of brown bears in the far north of their range was likely split off from their brown bear ancestors, perhaps because of competition for food. The population likely became isolated by massive glaciers and, while most died in the harsh environment, those bears with an evolutionary advantage — ideal coat color and thickness for extreme cold — survived and bred. Over thousands of years, this population of bears underwent further evolutionary change, adapting even more specialized traits for surviving the harsh polar environment. When life in the North demanded teeth better shaped for ripping apart seals than munching berries, the polar bear’s molar teeth changed significantly from those of the brown bear. The bears also grew white fur, which camouflaged them in their snow-covered surroundings and gave them a hunting advantage. Scientists believe that at first these bears scavenged seal carcasses that had washed ashore, and gradually began to hunt the seals by waiting at the water’s edge as the seals surfaced to breathe. This is believed to be an important step in the evolution of a new subspecies of bear — Ursus maritimus or the polar bear.

Nature once exerted such extreme pressure on the brown bear that it eventually gave rise to a new, better-adapted subspecies, the polar bear. Now, once again, evolutionary forces are acting on this long-enduring species. As the Arctic warms, the polar bear’s unique specializations that once lent it an evolutionary edge, may now be the creature’s downfall. A changing climate may name a new king of the Arctic — the fierce and opportunistic brown bear.

  • Mickey

    I’m crying. How sad

  • Sam

    waw! u know i never new that grizzlies evolved into polar bear! this is great info! thank you nature.

  • Kurtz

    This isn’t sad– it shows the amazing adaptability of life! Nothing is permanent: not animals, not continents, not planets, not stars. There is nothing that isn’t changing in this world, least of all life. That we so lament change is the greatest failure of modern thought; that we pretend to so radically effect change on global scales is the greatest absurdity. This fixation on stasis hints that homo sapiens may be at an evolutionary dead end. Hopefully, this is not so, but rather, only a temporary cultural obsession. Hopefully it is not an indication that the brain which has carried us so far has assumed its final form to which no further change is possible. Otherwise our species will have no further evolutionary prospect than that of the cockroach. Ironically, our wish for permanence will have been granted, at least in the freezing of our own minds.

  • Pat Dolan

    The author of this section plainly understands how evolution works- the bears that happen to have traits that enable them to survive the new conditions live, the rest die. However, he/she lapses into confusing language that could be interpreted to mean that the species- or even individuals- reacted to the new conditions by somehow creating structures that met the need. “When life in the North demanded teeth better shaped for ripping apart seals… the polar bear’s molar teeth changed significantly from those of the brown bear.” Please be more careful about this! There are many people in the US who have no understanding of evolution and resist teaching about it in schools- lets not confuse them further.
    I hear people say that animals like these should, basically, pull up their socks and adapt, as if this were a choice individuals could make. Some species have genes that allow a wide range of behavior response; otherwise, individuals are stuck with the morpholgy and behavioral constraints they are born with and if these don’t work in the new conditions they die (or at least fail to reproduce). If species could react to specific pressures, evolution would happen faster and there would be more hope for animals caught in the rapid change our planet is experiencing.

  • Celia Garrett

    As sad as it is, perhaps grizzlies and polar bears will be forced to become interbreed again and (if humans ever get global warming under control) then the bears will become two varieties again.

    I hope we can prevent global warming in time to prevent the extinction of bears.

  • Mike Mills

    You provide no proof or scientific statements or sources for your speculation.
    Until it is verified I take it with a grain of salt.

  • Sammy

    This is sad! I’m gonna cry!

  • Keenen Fahtwa

    I like polar bears. With my pie.

  • Annie

    awwwww poor babiess.

  • look in front of you

    hello agnes

  • agnes loves mikey’s french accent

    lolll. you guys are ridonculous.
    i love yer french accent mikey [:

  • Michael

    Thedentition of polar bears has evolved smoothly from brown bears to U. maritimus tyrannus, the first polar bear, to the present day dentition of modern polar bears. These changes are consistent with the evolution of many species over the millions of years life has been present. It’s not a new concept Pat
    Dolan. And a simple google search on the evolution of polar bears will lead anyone to many papers confirming the relationship of brown bears and polar bears. Unless of course you can’t read or wish to revel in your own opinions despite the facts.

  • Michael

    BTW, adaption and evolution via species variation is a well known concept. Brown bears have a great deal of variation in hair color etc. With intense pressure of selection on a small population of animals you can see very rapid changes in a relatively short period of time.

    One particular finch on the Galopolus Islands was greatly diminished in population by the recent arrival of another species of Finch with a larger beak. The larger beaked animal was able to eat certain berries better than the one with a smaller one. The population of the larger one exploded too much resulting in fierce competition for the larger berries which became much less common. This forced a great reduction in the larger beaked population of birds allowing the smaller beaked Finch to flourish again. It had adapted to other sources of food from diverse sources as a result of the initial pressures from the larger beaked bird. This happened since the time of Darwin’s expedition and actually really very recently.

    A related principle applies to the emregence of antibiotic resistant bacteria over a short period of time. Evolution is not always something that happens slowly over millions of years. It can be quick.

  • Matt

    Kurtz-

    You’re not nearly as insightful as you perceive. Your notion that change in the biosphere, such as evolution, extinction, etc., are inevitable is obviously true, but your suggestion that humans have not 1) physically altered every component of the biosphere, which includes the atmosphere, and 2) increased the rates of species extinctions is simply absurd.

  • York

    Every living thing on the earth changes after years, even humans. The reason why we change is so that we can survive better or adapt.

  • Laura

    I agree with Pat Dolan that the language is confusing. The above description sounds more like a
    demonstration of Larmarck’s evolutionary theory of inheritance of acquired traits than like Darwin’s
    theory involving survival of those members of the species with traits best suited to live in a particular environment. The language used implies that a species or individual may react to new conditions by creating structure that meet a need. It would follow that these acquired traits could then be passed on to offspring.

  • dawn

    It is not a speculation they spend years and hard work uncovering this information. They understand the pieces to the puzzle unlike those who speculate they are not doing the research to back up their theories.

  • khezi – november 21th, 2009 @ 346pm

    wow this is so harsh poor bears whish i could do somethiing

  • Kenneth Evers

    you can, khezi. Every time you put something that is supposed to go into the recycling bin into it, you’re saving them

  • Hugh G. Rection

    Thank you for posting this, i now know how the polar bears came about, it makes a lot of sense to me. I think its sad how they are all going to be extinct soon.

  • i am a scientist

    i wish i was a polar bear

  • swana man

    i lilke to eat polar bears and pizzly bears!!!!

  • nerdy bof

    i think the polar bears look like garfield on the loo

  • Hugh Jass

    Regardless of global warming, I can’t help but think that ultimately the survival of these species will be dependent upon our custodianship of the wild and how committed we humans are to the concept of conservation. Human populations have difficulty living in close proximity to any species of bear, as they do with any other powerful predatory animal. Fortunately for Polar Bears, these animals live in an area with minimal human populations due to the extreme harshness of their habitat. Other bear species have been decimated by human hunters to control their populations. Just last week on the first day of bear hunting season in the state of New Jersey 257 Black Bears were killed. I’ve seen wild Black Bears a few times and it has always been a thrill. To see a Polar Bear or a Grizzly would be even more exciting. As to the genetic link claimed in this article, I would say that at this time it is a fairly well substantiated theory but I am not totally convinced that the DNA did not display a case of genetic convergence that was not linear but rather a lateral and parallel case of development. Good theory though and the concept of environmental pressures forcing adaptive change has been well enough established to make it more than plausible.

  • Brad

    This is completely wrong for example how could the beaver evolve. The beaver has eye lids that he can see through. So debris does not get in. And its back teeth are covered by a layer of skin. This protects the beavers sensitive molars from cold water. Its front teeth are not sensitive because it can swim through cold water, and bite through trees. It also can drag logs and branches up river, Through currents and across rivers. If the beaver did evolve what possibly could of the beaver evolved. This shows that it has a creator and is not evolved

  • Brandon

    Another interesting aspect of this is that the polar bear’s skin is black while the brown bear’s skin is white. I would imagine that since black skin allows the animal to absorb more of the sun’s energy and thus warm it more that those animals who were born with black skin would require less energy to warm themselves and therefore be able to maintain a higher body weight than other bears with lighter skin. This in turn would allow the heaviest of the bears to become alpha males and of course reproduce.

    The thing is though that none of this is evolution.

    People are born with all different hair colors, skin colors, teeth shapes, skull shapes, etc and we do not call them a new species. We already have all of these characteristics inherent in our DNA and it just needs to be sequenced correctly to attain a specific result.

    In the end, we must redefine what makes polar bears and brown bears a different species otherwise we must begin to classify humans as different species based on skin color and we all know how well that goes….

  • John McCue

    Perhaps the bears should be thought of as breeds rather than species just as we do with dogs,

  • Doug

    Technically then since polar bears are a subspecies of the brown bear they would be Ursus arctos maritimus
    —just as the grizzly is Ursus arctos horribilis. Ursus arctos would encompass any subspecies that can interbreed and produce viable offspring.

  • Shwetadari Bhandari

    I’m not agree with you @Brandon. this is all about evolution. every brown bears are not of exactly same weight, height. and many more difference you can see. it is also eligible for polar bear. just what you say about humans.. but the evolution is, human comes from the apes. here is the same..

  • Taylah Dalton

    Polar bears didnt really evolve from brown bears, if you look at some sites like http://www.gizmodo.com.au/…/polar-bears-arent-descended-from-brown-b and
    http://www.nytimes.com/…/polar-bears-did-not-descend-from-brown-bears, you can see that eairly last year they discovered that the polar bears didnt evolve from the brown bear, but both the brown bear and polar bear evolved from black bears

  • Taylah Dalton

    The assignment at hand asks me to identify which theory is correct in regards to the evolution of polar bears from brown bear, but with further research into it I have discovered that polar bears never descended from brown bears. Both bears have a common ancestor that dates back over 600,000 years ago but, the polar bears branched off shortly before the brown bear, the ancestor of both bears is the black bear. The reason for polar bears being older than once thought is thanks to the breeding between brown bears and polar bears, which made hybrid polar bears. This is what scientists found, a few years back and didn’t research further, but early last year, researchers found DNA (Deoxyribo Nucleic Acid), of a deceased polar bear, which showed the true history of polar bears and how they descended from black bears.

  • James Bond

    You just gave me a heap of info and answers towards my assignment.

    Thanks

  • Isaac Clarke

    hey I’m doing the same assignment as Taylah and this website really helps!

  • James Bond FTW

    Im doing the same assignment as Taylah, and i find that this website and Taylahs comment helps alot!

    THANKS

  • Leah

    Are polar bears and Grizzlies the same speices

  • Jack

    I LOVE IT !!! AND I LOVE BEARS <3333

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