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.