The story of polar bear evolution could not be told without discussing climate change

From Polar Bear Science

Susan Crockford

Polar bears arose as a new species because the climate changed and forced some brown bears to colonize the sea ice. Polar bears epitomize the story of how evolution works but perhaps not quite how you imagined it.

Moving from extremes in warmth to extremes in cold characterized the last million years of geological history, as the graph above shows, where odd-numbered Marine Isotope Stages (MIS) are warm interglacials and even-numbered stages along the bottom are cold interglacials. MIS 2 was the Last Glacial Maximum.

But where and when during this period of change did polar bears come to be–and how, exactly, did it happen? My new book tells the whole story, which has never been done before. Not long to wait now, the release date is only about a week away (1st week June).

Polar Bear Evolution: A Model for How New Species Arise explains when and where the species came to be, as well as how it happened and why they were able to survive repeated cycles of sea ice change, some of unimaginable magnitude.

Here you’ll find a detailed account of fossil evidence, recent hybridization events between brown bears and polar bears, and summaries of more than a dozen genetic studies that have been done on these bears to determine the most plausible time and place for the origin of polar bears.

It’s logical to assume this speciation event happened during a cold interglacial, but which one?

And if you’ve ever wondered whether polar bears could have arisen more than once or if hybridization with brown bears really did play a significant part in polar bear evolution–as some geneticists insist–this book is for you.

Unique to this account, a biological mechanism reveals how this rapid transformation from a brown bear ancestor could have happened.

Thyroid hormone, essential for countless coordinated body functions including stress responses, the growth of embryos, and the activation of critical genes, seems to have played a vital role in the vast majority of all rapid speciation events.

A testable theory based on thyroid hormone not only explains how polar bears came to be but does the same for domestic dogs, flightless birds like the dodo, and extinct dwarf proto-human from Indonesia known as “Hobbits.

This evolutionary history of the polar bear also explains why the modern species is essentially pre-adapted to persist in a warmer world.

Whenever the species first arose, its survival through the very warm early Eemian interglacial, an extended period of about ten thousand years (at ca. 130-120k years ago), when there was consistently much less summer and winter sea ice than today, ensured the polar bear was forever flexible enough to deal with profound variations in sea ice. 

Or did lack of sea ice cause it to go extinct and arise a second time?

It’s a fabulous story–you’re going to love it.  

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May 31, 2023 3:26 am

Polar bears survive in zoos all over the planet so they adapt very rapid I would say.

Reply to  Robertvd
May 31, 2023 12:30 pm

But they seem to suffer from mental health problems when so incarcerated. Not surprising – could many of us survive being imprisoned for years with no mental stimulation? So cruel!

May 31, 2023 3:40 am

The even-numbered cold stages are glacials, not interglacials.

Polar bears’ main prey species, ringed seals, survived the Eemian and prior warm interglacials, so so did the bears dependent on them. Ringed seals breed in snow lairs on land fast ice in early spring, which never went away even in the balmiest of Pleistocene interglacials, just as it has always been around during the present Holocene, even in its Climatic Optimum, 5.2 to 8.0 Ka.

Rich Davis
Reply to  Milo
May 31, 2023 4:00 am

So I think technically it’s stadials (even MIS, cold) and interstadials (odd MIS, warm)

Reply to  Rich Davis
May 31, 2023 4:28 am

Stadials and interstadials are during glacials. Interglacials are between glacials.

Reply to  Milo
May 31, 2023 4:50 am

In the UK, the Eemian Interglacial is called the Ipswichian, MIS 5e. The interglacial(s) of MIS 7 are there named the Aveley. It was a double dip, with two warm stages separated by a cool snap.

MIS 9 was the Purfleet, MIS 11 the hot, long-lasting Hoxnian and MIS 13 the Cromerian.

Susan Crockford
Reply to  Milo
May 31, 2023 9:06 am

Typo fixed, thanks!


Reply to  Susan Crockford
May 31, 2023 10:05 am

De nada!

May 31, 2023 3:50 am

It’s dreadfully cliche, but life finds a way. 5 mass extinctions are surely a testament to that. 

But all the hype about polar bears – either dying for lack of ice, or attacking humans for lack of food, is just an attempt to reinforce a sense of alarm. As are alleged threats to any icy environment

For example:

“Experts say this is likely to be one of the deadliest years on record on Mount Everest, with variable weather caused by climate change being blamed as one of the main reasons for the deaths of up to 17 people.

The figure was confirmed by Yuba Raj Khatiwada, the director of Nepal’s tourism department. “Altogether this year we lost 17 people on the mountain this season,” he said. “The main cause is the changing in the weather. This season the weather conditions were not favourable, it was very variable. Climate change is having a big impact in the mountains.”

Changes in [daily] weather are in fact a change of climate, a trend is no longer required!

There is a real problem on Everest, but it isn’t weather or climate.

comment image

Reply to  strativarius
May 31, 2023 4:11 am

Wow, that’s ugly.

Reply to  Scissor
May 31, 2023 4:29 am

Just like Glastonbury next month

It’s so ludicrous I should have made it a story tip.

Richard Page
Reply to  strativarius
May 31, 2023 5:24 am

We’ve mentioned them as being the ‘chattering class’ perhaps now we should refer to them as the ‘littering class’.

Reply to  Richard Page
May 31, 2023 5:27 am

Definitely an accurate monicker.

Natural variability it would seem is the real killer, here.

May 31, 2023 4:13 am

Bears (genus Ursiadae) have existed since roughly late Eocene to early Miocene, up to 38 MYA. They have evolved into numerous species, of which 8 still exist today. Polar bears split off from brown bears in the late Pleistocene. Dr. Crockford can go into far greater detail in her book, obviously, than this paragraph can convey.

The point being that bears are extremely adaptable, and over millennia are capable of specializing their characteristics to fit a particular set of environmental conditions. Considering that the earth has gone through approx. 26 glaciations/interglacials in the last 2.6 MY of the Pleistocene/Holocene, bear species, like most species, do indeed adapt to just about any range of temperature conditions.

Common species with which we are very familiar, such as horses and various breeds of domesticated dogs and cats, and cattle and such, are relatively recent speciations of various genera that date back to the rise to dominance of mammals and feathered birds. They all adapt, or else are selectively bred to produce dominant characteristics.

Nothing stays stagnant. The old Indian saying, “Only the rocks live forever” is of course not even true, as we’ve known since the birth of geological science a few hundred years ago.

Reply to  Duane
May 31, 2023 4:31 am

You mean Early Oligocene. The Miocene came after the Oligocene Epoch. But 38 Ma is still Eocene.

Reply to  Milo
May 31, 2023 5:07 am

I stated a range, and what I stated is correct.

Reply to  Duane
May 31, 2023 5:20 am

The Oligocene follows the Eocene. The Miocene follows the Oligocene. The Ursidae evolved around the Oligocene-Miocene boundary, c. 25 Ma. Back in the Late Eocene and Early Oligocene, bears had not yet evolved. At 38 Ma, their ancestral carnivorans existed but not true bears.

The Eocene ancestors of bears, raccoons and pinnipeds were small, badger-sized caniform carnivorans. By a stretch they could be called ursids, but modern bears in Family Ursidae date from the Late Oligocene.

Reply to  Milo
May 31, 2023 5:43 am

Ursidae is a family, not a genus. Living bears are in the subfamily Ursinae.

Phylogenetic taxonomists sometimes place the bear-dog ancestors of bears in Ursidae but more often in their own family. There are always lumpers and splitters.

Reply to  Milo
May 31, 2023 9:07 am

Lumpers have sweeter tea, but the splitters keep it warm.

Reply to  Milo
May 31, 2023 11:14 am

Pinnipeds used to be thought closer to mustelids (weasel family) than bears and raccoons, but DNA shows their relationship with bears.

Order Carnivora has two main suborders, felids and canids. Within the later, dogs appear to be the outgroup to the other main lineages, ie weasels, seals, raccoons and bears. Dogs have dewclaws, the vestigial fifth forepaw digit, and four rear paw digits. Bears and kin still retain five fingers and toes.

Weasels and seals also have five clawed toes.

Pandas famously have a wrist bone repurposed as a sixth finger or “thumb” for holding bamboo. A vegetarian carnivoran. Other bears of course are omnivores.

Hyenas are felids.

Richard Page
Reply to  Duane
May 31, 2023 5:35 am

That range may not be enough. Recent studies have given different ranges from 150,000 to 600,000 years ago, depending on the fossil remains dated. It seems as though the divergence of the bears from Brown to Polar may have been something that occurred several times, with the different subgroups then interbreeding. As Susan Crockford has hinted, it’s likely a far more complex story than we have considered up to now. A parallel might be drawn between the bears and our hominid/homo sapiens ancestors where we, homo sapiens sapiens, are in fact an amalgamation of various hominid and early homo sapiens subgroups rather than a single continuous line of evolution.

Peta of Newark
May 31, 2023 5:20 am

Ha, ain’t that so lovely. Thank you hun

It is that, as I understood, vast areas of this globe/world are to all intents uninhabitable, certainly by humans – exactly because of Iodine

In particular because a lack of Iodine in the environment and even more especially, all of North America is totally devoid of the stuff.
Uninhabitable UNLESS, as a human you take on a diet revolving around animal consumption. You then rely upon the animals you eat to get the Iodine you need as they can filter immense amounts of stuff and ‘concentrate’ it for you.

The graphic we see is only a tiny part of what iodine does inside of us:
Iodine Controls Everything inside the human body and without it we totally fall apart physically and mentally.
It’s been known for ages – hence why ‘Iodised salt’ is de-rigueur in many parts of the world.

(In the UK, we get our Iodine again from animals but not directly. It has been and still is the practice among dairy farmers to use Iodised Teat Dips and washes on their cows before and especially after milking.
We get along without Iodised Salt in that way.
(Mrs Thatcher thus did a lot more harm than anyone imagined when she stopped ‘Free School Milk’ here in the UK. In schools of all places. sigh)

Manufactured Iodised salt didn’t need to be a requirement because The Pioneers got their salt from the Salt lakes and Salt flats dotted across the continent.
Or if they were near the coast, from sea water. We didn’t settle beside the sea just because of the nice predictable/stable climate all that water creates

Would anyone like to imagine the damage that might start showing up by a trend away from eating animals to vegetarianism AND – the perfectly insane war on Salt in all our diets

You don’t need to imagine – just look around you.

Richard Page
Reply to  Peta of Newark
May 31, 2023 5:38 am

Time to persuade vegetarians and vegans to include seaweed in their diet?

Reply to  Richard Page
May 31, 2023 7:36 am

No no no. Let the vegetarians die and the Vegans go back to Vega (it’s only 40 light-years away).

Jeff Alberts
May 31, 2023 5:30 am

I’m picturing a brown bear and a polar bear. They find each other attractive. Go on a few dates. Then over a nice Aurora-lit dinner one evening, one says to the other, “Say baby, how ’bout we have a little, y’know, hybridization event.” That’s when the magic happens.

Richard Page
Reply to  Jeff Alberts
May 31, 2023 5:59 am

If it’s a male Polar Bear, likely the Brown Bear was the dinner!

Reply to  Jeff Alberts
June 1, 2023 4:49 am

Things could get fraught if a relative starts speculating what colour fur the cubs might have…

More Soylent Green!
May 31, 2023 6:15 am

This is a model and needs to be treated as such. It does not explain or show how polar bears evolved, it explains how polar bears *may* have evolved.

Unlike other models we discuss at WUWT, this model is testable. It is an hypothesis.

Richard Page
Reply to  More Soylent Green!
May 31, 2023 7:59 am

It does seem to fit with the different dating evidence from archaeological remains and the different subgroup’s having slightly different dna though. It may not be the definitive answer but it will move the conversation forward.

Susan Crockford
Reply to  More Soylent Green!
May 31, 2023 9:16 am

Exactly so. It’s the testable hypothesis that best fits the facts. I wrote my PhD dissertation on this topic back in 2004 and almost twenty years later, it’s still the hypothesis that best fits the facts. It may not be exactly right, but it is likely something close to it.

Until the testing is done, we won’t know. It’s not my job to do that part, as I’m not a bench scientist. But it will happen eventually regardless because the ‘genes-rule-everything’ folks are running out of excuses. As Richard points out below, testing it will, at the very least, move the discusion forward–and that is real progress.

Reply to  Susan Crockford
June 1, 2023 7:11 pm

Tell me when ringed seals evolved and I’ll give you my guess as to when polar bears evovled.

When early spring shore fast ice became a reliable feature of the Arctic, the stage was set for ringed seals. Did that happen in the Pliocene, early Pleistocene or after the Mid-Pleistocene Transition? I don’t know.

The standard model of polar bear evolution is that Arctic brown bears started scavenging marine mammal carcasses before evolving traits better to exploit these resources as predators.

Today, brown bear-polie hybrids live as brown bears, because lacking white coats, needed to ambush ringed and other ice seals. So the model goes.

May 31, 2023 6:59 am

What about Pandas? Are Pandas in the bear family? Do Pandas exist in the wild anymore? China has little wild habitat….birds are noticeably in short supply……wildlife is in short supply. It is a good thing that the short nosed bear became extinct because it would make the grizzly look like a Panda in comparison.

Reply to  antigtiff
May 31, 2023 10:09 am

Pandas are bears. It and the Andean spectacled bear however split off earlier and lie outside the Ursinae. A few pandas still live in the wild.

The spectacled bear is the last surviving species of the short-faced bear lineage, much smaller than its extinct relatives.

Richard Page
Reply to  antigtiff
May 31, 2023 1:23 pm

Bats are very plentiful in China, apparently!

Reply to  Richard Page
May 31, 2023 1:57 pm

I’m sure that with the proper seasoning bats can be a sought after delicacy.

Richard Page
Reply to  AndyHce
May 31, 2023 11:22 pm

Ozzy Osbourne might well agree!

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