Not so long ago polar bears were to have diverged as a distinct species from brown bears just 130,000 years ago or so. That got pushed to about 600,000 years by more fossil and gene study. The latest: for more than FOUR MILLION YEARS their genome has been largely distinct from their close, landlubber relatives. But some cross-species mating recurred over that time, presumably mainly during warm periods that brought polar bears to dry land as ice floes ebbed, and drew brown bears range northward.
That's the news in the Proceedings of the Nat'l Academy of Science. The paper has 26 authors from Penn State U. , USGS, Univ. at Buffalo, and institutes in Norway, Iceland, Denmark, China, and Canada. The paper says it's not yet possible to say how long ice-adapted Arctic bears resembled the white giants of today, but the gene pool that led to them seems to have a long and largely distinct history.
Give the interest in the immediate future of polar bears during the current warming, unprecedented in speed and distinctly of our own making, naturally several reporters and their editors saw the deep history of the species through natural climate variations as news.
Stories:
- NYTimes – James Gorman: How Brown and Polar Bars Split Up, but Continued Coupling ; It says here that all brown bears' DNA has traces of polar bear genes, but it's five or ten percent in some islands along the Alaskan panhandle. Hmm – can't help wondering about the genealogy of the huge Kodiak Island brown bears near the base of the Aleution chain. Tag line: "One thing the evidence does suggest..is that there may be more interbreeding ahead."
- Science News – Devin Powell: Polar bears' ancient roots pushed way back /Genetic blueprints suggest the animals arose millions of years ago ;
- USA Today – Dan Vergano: Polar bears ancient and in decline ; The decline he notes is not a recent blip or our fault – it goes back half a million years.
- Live Science – Wynne Parry: Ancient Warming may Have Reunited Polar and Brown Bears, for a bit;
- Milwaukee Journal Sentinel – Amanda Alvarez: Polar bears' genome shows adaptability, study shows ; One source is worried that the public will take the news to mean that polar bears are therefore resilient to the present warming and should survive it. This period, compared to previous ones, is "off the charts."
- Alaska Dispatch – Doug O'Harra: Polar bears diverged 4 to 5 million years ago, but interbred with brown bears ;
- .. several more out there too
Grist for the Mill: U. Buffalo Press Release ;
– Charlie Petit
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