From Polar Bear Science
Susan Crockford
Polar bears arose as a brand new species as a result of the local weather modified and compelled some brown bears to colonize the ocean ice. Polar bears epitomize the story of how evolution works however maybe not fairly the way you imagined it.
Shifting from extremes in heat to extremes in chilly characterised the final million years of geological historical past, because the graph above reveals, the place odd-numbered Marine Isotope Phases (MIS) are heat interglacials and even-numbered levels alongside the underside are chilly interglacials. MIS 2 was the Final Glacial Most.
However the place and when throughout this era of change did polar bears come to be–and the way, precisely, did it occur? My new ebook tells the entire story, which has by no means been finished earlier than. Not lengthy to attend now, the discharge date is barely a couple of week away (1st week June).
Polar Bear Evolution: A Mannequin for How New Species Come up explains when and the place the species got here to be, in addition to how it occurred and why they have been capable of survive repeated cycles of sea ice change, a few of unimaginable magnitude.
Right here you’ll discover a detailed account of fossil proof, current hybridization occasions between brown bears and polar bears, and summaries of greater than a dozen genetic research which were finished on these bears to find out probably the most believable time and place for the origin of polar bears.
It’s logical to imagine this speciation occasion occurred throughout a chilly interglacial, however which one?
And should you’ve ever questioned whether or not polar bears might have arisen greater than as soon as or if hybridization with brown bears actually did play a big half in polar bear evolution–as some geneticists insist–this ebook is for you.
Distinctive to this account, a organic mechanism reveals how this fast transformation from a brown bear ancestor might have occurred.
Thyroid hormone, important for numerous coordinated physique capabilities together with stress responses, the expansion of embryos, and the activation of crucial genes, appears to have performed a significant function within the overwhelming majority of all fast speciation occasions.
A testable principle primarily based on thyroid hormone not solely explains how polar bears got here to be however does the identical for home canine, flightless birds like the dodo, and extinct dwarf proto-human from Indonesia generally known as “Hobbits.”
This evolutionary historical past of the polar bear additionally explains why the trendy species is actually pre-adapted to persist in a hotter world.
Every time the species first arose, its survival via the very heat early Eemian interglacial, an prolonged interval of about ten thousand years (at ca. 130-120k years in the past), when there was constantly a lot much less summer season and winter sea ice than at the moment, ensured the polar bear was eternally versatile sufficient to take care of profound variations in sea ice.
Or did lack of sea ice trigger it to go extinct and come up a second time?
It’s a superb story–you’re going to adore it.