Tag Archives: hybridization

How grizzlies evolved into polar bears: The first book to tell the whole story is now available

Posted on June 11, 2023 | Comments Off on How grizzlies evolved into polar bears: The first book to tell the whole story is now available

Polar Bear Evolution: A Model for How New Species Arise is the fascinating story of the origin of polar bears. It reveals not just when and where the species came to be, but how it happened and why the bears were able to survive repeated cycles of sea ice change, some of unimaginable severity.

No other book like this exists. Despite decades of serving as an icon for the catastrophic climate change narrative, the polar bear has never had its evolutionary history explained so completely, never mind in a fully-referenced, plain-language style. And I couldn’t have done it without the financial help of my many supporters, so I thank you all again for your assistance in getting this important work completed.

One Amazon reviewer said this about Polar Bear Evolution:

The author of Polar Bear Evolution, Susan Crockford, is a good, credentialed scientist. Her writing is clear; her thinking is also. She has a broad understanding of biology and an informed paleo perspective. Crockford condenses a very large literature on polar bear biology and evolution in this book which will help readers understand the science related to the evolution of an Arctic species. Perhaps the most important aspect of this book is its synthesis of information from the fields of wildlife biology, molecular evolution, paleontology, and climate. Her original ideas and hypotheses on thyroid hormone’s role in evolution are very important and add a credible mechanism of phenotypic change which complements the literature on molecular genetic evolution. Polar Bear Evolution is an important contribution to science and its application in evolutionary biology and wildlife biology. Matthew A. Cronin, Ph.D.

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Grizzlies vs. grizzly X polar bear hybrids by appearance alone: a photo essay

Posted on June 2, 2023 | Comments Off on Grizzlies vs. grizzly X polar bear hybrids by appearance alone: a photo essay

Hybridization with grizzlies comes up repeatedly in genetic studies that aim to zero in on polar bear origins and is one of the issues I explore in detail in my upcoming new book, Polar Bear Evolution: A Model for How New Species Arise. Here is a photo essay to get you thinking about grizzly X polar bear hybrids, because understanding the topic is critical to unravelling the genetic evidence on how polar bears came to be.

For example, who can forget the hoopla over the bear shot near Arviat on the shore of Western Hudson Bay in 2016 (shown above) that everyone, including polar bear expert Ian Stirling, decided must be a hybrid–but it turned out to be a blonde grizzly.

Explaining all the ins and outs of why hybrids are important to polar bear evolution is an important part of my book.

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Posted in Book promotion, Evolution, Hybridization

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

Posted on May 30, 2023 | Comments Off on The story of polar bear evolution could not be told without discussing climate change

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 glacials. 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).

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Grizzly on the shore of W. Hudson Bay and two tagged polar bears still on sea ice at 17 August

Posted on August 21, 2022 | Comments Off on Grizzly on the shore of W. Hudson Bay and two tagged polar bears still on sea ice at 17 August

A tundra grizzly was again caught on the live cam set up for polar bears last week (15 August) but was too late for interspecies hankypanky, even as some polar bears lingered on invisible offshore sea ice.

A polar bear rests on the ice Aug. 23, 2009, after following the Coast Guard Cutter Healy for nearly an hour in the Beaufort Sea.

Polar bear specialist Andrew Derocher reported that two of his 23 tagged polar bears were still on the sea ice, a phenomenon that’s been happening since at least 2015 at breakup. Instead of heading to shore when the sea ice concentration dwindles below 50% coverage, some bears are choosing to lounge around on decaying bits of ice, sometimes into late July or well into August, until they must finally swim ashore. There is no evidence that the bears continue to successfully hunt seals under these conditions but no evidence either that their choice to stay on the ice rather than move to land at this time of year has had any negative impact on their health or survival.

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Posted in Hybridization, Life History, Sea ice habitat

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New genetics paper is not about whether climate change causes polar bear hybrids

Posted on April 20, 2017 | Comments Off on New genetics paper is not about whether climate change causes polar bear hybrids

A new paper on the evolutionary history of bears (Bears breed across species borders: Kumar et al. 2017) has concluded that hybridization is common and natural among all species of ursids. And while some media outlets (e.g. DailyMail) have framed this as surprisingly convincing proof that experts were wrong to claim that climate change is the cause of recent polar bear X grizzly hybrids, definitive evidence against that interpretation has been available for years to anyone who bothered to look: see my recent “Five facts that challenge hybridization nonsense.”

This genetic evidence is just a cherry on top of the rest but will help get the paper the media attention the authors crave.

Polar bear X grizzly hybrids were known long before climate change and sea ice decline became an issue. See also previous posts here, here, and here. In fact, as I’ve pointed out, “most polar bear hybrids said to exist have not been confirmed by DNA testing” (including virtually all of the bears specialist Andrew Derocher claimed were hybrids, including the latest one from 2016 that prompted such gems as “Love in the time of climate change”).

pizzly_andrewderocher_300dpi_2017 paper

A polar bear X grizzly hybrid, see Kumar et al. 2017. Photo by A. Derocher.

In my opinion, the most important conclusion of this paper is that occasional but widespread hybridization among bears is why it has been so hard to say with confidence when polar bears arose (which I addressed years ago, in my Polar bear evolution series: Part 1, Part 2, and Part 3). You cannot use traditional methods of pinpointing the timing of speciation events from genetic data if one or more of the species have hybridized (traded genes). See the long, fuzzy “divergence times” for bears in the image below from the Kumar paper.

Kumar et al 2017 hybridization in bear evolution_fig 5

From Kumar et al. 2017, Fig. 5: “The scale bar shows divergence times in million years and 95% confidence intervals for divergence times [speciation events] are shown as shadings.”

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Polar bear hybrid update: samples sent for DNA testing to rule out blonde grizzly

Posted on May 24, 2016 | Comments Off on Polar bear hybrid update: samples sent for DNA testing to rule out blonde grizzly

That putative polar bear hybrid shot in Arviat last week has been sent for DNA testing.

hybrid-bear_didji-ishalook-15 May2016_facebook

Just out from NunatsiaqOnline (24 May 2016): Nunavut biologist sends possible “grolar” bear DNA for analysis: Unusual bear killed in Arviat could just be a blonde grizzly bear

Additional details confirm the animal shot was a female, which could account for the fact it was described as “small”. The Nunavut biologist who sent in the sample for testing warned it could also be a blonde grizzly, as I pointed out last week.

UPDATE 24 May 2016: Comments added below from a Toronto Star news report below on the hybrid identity of this animal.

UPDATE 28 May 2016: See this 27 May 2016 follow-up post (Most polar bear hybrids said to exist have not been confirmed by DNA testing) for details on unconfirmed sightings or reports of hybrids.
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Posted in Conservation Status, Hybridization, Sea ice habitat

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Challenging NOAA’s “Arctic Report Card 2014” on polar bears

Posted on December 19, 2014 | Comments Off on Challenging NOAA’s “Arctic Report Card 2014” on polar bears

NOAA’s list of purported evidence for harm being caused to polar bears by Arctic warming is short and weak. It puts the gloomiest spin possible on the current well-being of an animal with all the earmarks of a healthy, well-distributed species.

Arctic report card 2014 screencap_Dec 18 2014

This year, polar bears are virtually the only species that NOAA mentions in their Arctic Report Card – they’ve put all their icon-eggs in one leaky basket [what happened to walrus??]. But polar bears are doing so well that to make an alarming case for polar bears as victims of Arctic warming, many important caveats had to be left out or misrepresented. Some details given are simply wrong.

This year’s polar bear chapter was penned by IUCN Polar Bear Specialist Group chairman Dag Vongraven (you might recall his email to me earlier this year) and a polar bear conservation activist from Polar Bears International (whose battle cry for donations is “Save Our Sea Ice!”), Geoff York.

I challenge their four weak talking points one by one below.

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Ancestor of the polar bear by any name: grizzly vs. brown bear monikers explained

Posted on May 8, 2014 | Comments Off on Ancestor of the polar bear by any name: grizzly vs. brown bear monikers explained

Apparently, all media outlets (except Fox News) so confused the distinction between the two common names used for the ancestor of polar bears, Ursus arctos, that they got the point of a recent news story totally wrong. An Alaskan journalist explains.

Coastal brown bears from Admiralty Island, southeast Alaska. See previous post here.

Coastal brown bears from Admiralty Island, southeast Alaska (courtesy Jim Baichtal, US Forest Service, Alaska). See previous post here.

Tundra grizzly from the Yukon (courtesy Government of Yukon Territory). These bears also occur across the north slope of Alaska and are the bears that occasionally hybridize with polar bears, as explained here.

Tundra grizzly bear from the Yukon (courtesy Government of Yukon Territory). These bears also occur across the north slope of Alaska and are the bears that occasionally hybridize with polar bears this time of year, as explained here.

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Polar bears have not been harmed by sea ice declines in summer – the evidence

Posted on August 18, 2013 | Comments Off on Polar bears have not been harmed by sea ice declines in summer – the evidence

PB logo colouredThe polar bear biologists and professional activists of the IUCN Polar Bear Specialist Group (PBSG) continue to insist that since 1979 increasingly smaller amounts of Arctic sea ice left at the end of summer (the September ice minimum) have already caused harm to polar bears. They contend that global warming due to CO2 from fossil fuels (“climate warming” in their lexicon) is the cause of this decline in summer ice.

In a recent (2012) paper published in the journal Global Change Biology (“Effects of climate warming on polar bears: a review of the evidence”), long-time Canadian PBSG  members Ian Stirling and Andrew Derocher (both of University of Alberta) summarized their position this way:

“Climate warming is causing unidirectional changes to annual patterns of sea ice distribution, structure, and freeze-up. We summarize evidence that documents how loss of sea ice, the primary habitat of polar bears (Ursus maritimus), negatively affects their long-term survival”

I’ve spent the last year examining their evidence of on-going harm, but in addition, I’ve looked at the evidence (much of it not mentioned in the Stirling and Derocher paper1) that polar bears have either not been harmed by less sea ice in summer or have thrived in spite of it.

This is a summary of my findings. I’ve provided links to my original essays on individual topics, which are fully referenced and illustrated. You are encouraged to consult them for complete details. This synopsis (pdf with links preserved, updated; pdf with links as footnotes, updated) complements and updates a previous summary, “Ten good reasons not to worry about polar bears” (pdf with links preserved; pdf with a foreword by Dr. Matt Ridley, with links as footnotes).

Update 8 September 2013: to include links to my post on the recently published Chukchi population report; updated pdfs have been added above.

Update 22 January 2014: added figure comparing March vs. September sea ice extent using the same scale, from NOAA’s “2014 Arctic Report Card,” discussed here.
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Biologists spreading misinformation: hybridization with grizzlies not due to polar bears moving inland

Posted on August 3, 2013 | Comments Off on Biologists spreading misinformation: hybridization with grizzlies not due to polar bears moving inland

A paper published last week in the journal Science, written by a team of biologists and atmospheric scientists, expounds on a possible dire future for a range of Arctic animals. It’s called, “Ecological consequences of sea-ice decline” and surprisingly, polar bears are discussed only briefly.

However, with the inclusion of one short sentence, the paper manages to perpetuate misinformation on grizzly/polar bear hybridization that first appeared in a commentary essay three years ago in Nature  (Kelly et al. 2010)1. The Post et al. 2013 missive contains this astonishing statement (repeated by a Canadian Press news report):

“Hybridization between polar bears and grizzly bears may be the result of increasing inland presence of polar bears as a result of a prolonged ice-free season.”

Lead author of the paper, Professor of Biology Eric Post, is quoted extensively in the press release issued by his employer (Penn State University, pdf here). In it, Post re-states the above sentence in simpler terms, removing any doubt of its intended interpretation:

“… polar and grizzly bears already have been observed to have hybridized because polar bears now are spending more time on land, where they have contact with grizzlies.”

Both statements are patently false. All recent hybridization events documented (2006-2013) occurred because a few male grizzlies traveled over the sea ice into polar bear territory and found themselves a polar bear female to impregnate (see news items here and here, Fig. 1 below). These events did not occur on land during the ice-free season (which is late summer/early fall), but on the sea ice in spring (March-May).

Grizzlies have been documented wandering over the sea ice of the western Arctic since at least 1885 (Doupe et al. 2007; Fig. 2, below) and the presence in this region of hybrid grizzly/polar bear offspring is not an indicator of declining summer sea ice, whether due to global warming or natural causes, or some combination thereof.

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