Tag Archives: Pleistocene

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

Posted on May 30, 2023 | Comments Off

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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Posted in Book promotion, Evolution

Tagged climate change, genes, glacial cycles, hybridization, origins, Pleistocene, sea ice, speciation, thyroid hormone

Ancient polar bear remains explained by sea ice and polynyas: my peer-reviewed paper

Posted on May 6, 2022 | Comments Off

My open-access, peer-reviewed paper on the ecology of ancient polar bears in relation to sea ice has just been published in Open Quaternary. It’s called ‘Polar Bear Fossil and Archaeological Records from the Pleistocene and Holocene in Relation to Sea Ice Extent and Open Water Polynyas’.

A unique compilation of more than 104 polar bear skeletal records from the Holocene and late Pleistocene shows that most ancient remains are associated with existing or ancient open water polynyas or the expansion of sea ice during past cold periods. This big-picture analysis indicates that as they do today, polar bears were most commonly found near polynyas throughout their known historical past because of their need for ice-edge habitats.

Read my longer summary below and download the paper here. This is a much-updated and expanded analysis based on an informal study I did in 2012.

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Posted in Evolution, History, science, Sea ice habitat, Summary

Tagged archaeology, Clmatic Optimum, distribution, ecology, fossils, Holocene, Pleistocene, polynya, sea ice, Yamal, Zhokhov Island

Big announcement coming this week

Posted on May 1, 2022 | Comments Off

New peer-reviewed polar bear paper of mine coming out, likely Monday or Tuesday. Watch for it.

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Posted in Sea ice habitat, Summary

Tagged Pleistocene, polar bear, sea ice

Polar bears barely survived the sea ice habitat changes of the last Ice Age, evidence suggests

Posted on April 21, 2015 | Comments Off

While the polar bear is an Ice Age species, genetic and fossil evidence suggests it barely survived the profound sea ice changes associated with the Last Glacial Maximum, one of the most severe glacial periods of the Pleistocene.

A map of sea ice extent at the climax of the Last Glacial Maximum (both perennial and seasonal ice), prepared with the help of a colleague, makes it possible to discuss what genetic and fossil evidence can tell us about the probable effects of glacial conditions on polar bears and ringed seals.

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Posted in Evolution, Sea ice habitat

Tagged Arctic basin, genetic bottleneck, ice age, last glacial maximum, LGM, perennial ice, Pleistocene, polar bear, population bottleneck, population decline, ringed seal, sea ice, sea ice habitat, sea level, seasonal ice

Ancient Polar Bear Remains of the World

Posted on November 26, 2012 | Comments Off

How does the ancient distribution of polar bears – based on finds of natural-death remains (“fossils”) and bones found in archaeological sites – compare to the modern distribution of polar bears?

[Note: this post was updated 16 Feb. 2026 to indicate that an updated, published version of the data provided below is now available, and links are provided to my 2023 book on polar bear evolution that also includes more up-to-date information]

I have pulled together information from all of the reports I could find that listed ancient polar bear remains and summarized them into one table and one map. A low resolution copy of the map and a simplified version of the map notes are embedded in this post but a higher resolution version of the map and map notes (with pertinent details, including references) is available as a pdf. This document has been assigned an ISBN number (which means it is copyrighted and filed at Library and Archives Canada). The pdf can be downloaded below and will also be available on the PolarBearScience “references” page.

DOWNLOAD HERE: Ancient Polar Bear Remains_Crockford 2012
[small error fixed in yesterday’s version]

CITATION HERE:
Crockford, S.J. 2012. Annotated Map of Ancient Polar Bear Remains of the World. Electronic resource available at http://polarbearscience/references ISBN 978-0-9917966-0-1.

CITATION for the updated published version is below, announced and discussed in this blog post, which includes an updated copy of the map shown below: Ancient polar bear remains explained by sea ice and polynyas: my peer-reviewed paper, 6 May 2022.

Crockford, S. J. 2022. Polar bear fossil and archaeological records from the Pleistocene and Holocene in relation to sea ice extent and open water polynyas. Open Quaternary 8(7): 1-26. https://doi.org.10.5334/oq.107 [Open Access]

See also my polar bear evolution book published in 2023:

Crockford, S.J. 2023. Polar Bear Evolution: A Model for How New Species Arise. Amazon Digital Services, Victoria. https://www.amazon.com/dp/1778038328 Discussed here and here.

See map notes on pdf below for more details. Click to enlarge.

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Posted in Evolution, Sea ice habitat

Tagged archaeological, bones, fossil record, Pleistocene, polar bear history, sea ice extent

Is it plausible that polar bears are 4-5 million years old? Part 3, sea ice

Posted on August 23, 2012 | Comments Off

Last in a three-part series of my critique of Miller et al.’s (2012)
paper on the newest genetic evidence for the origin of polar bears. Part 1 here, Part 2 here.

Here is my final (I hope) comments on the claims made in that paper, suggesting why we might want to take them with a grain of salt.

These are the points regarding this paper that I think deserve a critical look. In this post, I’ll elaborate on Claims #3 and #4. [I’ve added one more to the original three listed].

Claim #1 Polar bears and brown bears (aka grizzlies) arose 4-5 million years old. [I countered with fossil evidence]

Claim #2 Hybridization in both directions occurred repeatedly throughout the evolutionary history of polar bears and brown bears. [I countered with full details on known hybrids]

Claim #3 Svalbard may have been an important refugium for polar bears during warm interglacial periods – and related sea ice issues related to the origin of polar bears as a species.

Claim #4 Polar bear population numbers (population size estimates) over the last one million years track changes in climate (warmer/colder periods).

Claim #3 Svalbard may have been an important refugium for polar bears during warm interglacial periods (and related sea ice issues related to the origin of polar bears as a species) [Which I’ll counter with evidence on paleo sea ice]

Comments Off on Is it plausible that polar bears are 4-5 million years old? Part 3, sea ice

Posted in Evolution, Sea ice habitat

Tagged genetics, interglacial, Miller, Miocene, Pleistocene, polar bear evolution, refugium