U. of Calif Davis Professor Matthew Cronin has published a peer reviewed paper suggesting that polar bears and brown bears diverged as different species 1.2 million years ago and black bears diverged from the polar/brown bear lineage 2.3 million years ago.............Based on these findings, the polar bear was an independent species for about 1 million years...........It therefore survived previous cold and warm periods where sea ice was non-existent----------------The Professor theorizes that if Polar Bears previously survived without ice flows to hunt seals on, that perhaps they will survive into the future even if our polar caps completely melt out.......What variables if any, is Cronin not taking into account with this outlook?

Link: http://snras.blogspot.com/2014/03/bear-species-genetic-relationships.html

Bear species' genetic relationships determined

Matthew Cronin, professor of animal genetics with the UAF School

 of Natural Resources and Extension and colleagues at the University

 of California Davis and Delta G Co. published a paper on bear

 genetics in the Journal of Heredity online in January. The paper,

 which will be printed in the next few months, describes the research

 involving genome sequence comparisons of the three bear species.

brown bear

Cronin also published papers on the relationships of the bears

 with different genetic analyses in 2012 with a collaborator at the 

U.S. Department of Agriculture in the Journal of Heredity, and in

 2013 with co-workers at Texas Tech University in the Canadian

 Journal of Zoology.

The 2014 paper replicates other research on bear genomes but 

includes analysis of genetic variation in more than 300 bears from

 Alaska and genetic elements not assessed previously in bears. 

These are known as ultra-conserved elements, and show the polar

 and brown bears to be more closely related than either is to black

 bears.

The data was used in a “molecular clock” that uses the numbers

 of differences (mutations) in DNA sequences to estimate when

 the sequences, and hence the species, diverged. The data suggest

 that polar bears and brown bears diverged as different species 

1.2 million years ago, and black bears diverged from the

 polar/brown bear lineage 2.3 million years ago.  These estimates 

are within the ranges in other studies.

Utilizing labs at the University of California Davis, Cronin and

 technology experts pored over huge datasets. He also analyzed

 tissue samples from Montana and from Alaska’s Admiralty,

 Baranof and Chichagof islands, obtained from state and

 federal wildlife agencies. In recent years DNA science has 

improved so much that Cronin is able to study billions of 

nucleotides of DNA rather than the thousands he used to

 be limited to. “It’s very advanced because of the applications

 in medicine and agriculture,” Cronin said.

“The ramifications are that if the polar bear was an independent 

species for about 1 million years it survived previous cold and 

warm periods,” Cronin said. “This means the polar bear has 

been an independent lineage a long time through glacial and

 interglacial and warm periods.”

The last glacial period was at maximum extent about 22,000

 years ago, and was preceded by a warm interglacial period

 about 130,000 years ago. Other warm and cold periods

 preceded that. Cronin thinks that if polar bears survived

 previous warm periods in which there was little or no arctic 

summer sea ice, this should be used in  models predicting

 the species’ response to current climate change.

“It seems logical that if polar bears survived previous warm, 

ice-free periods, they could survive another. This is of course 

speculation, but so is predicting they will not survive, as the

 proponents of the endangered species act listing of polar 

bears have done.”

Cronin has been studying animal genetics for 25 years. 

He recently researched wood bison and plains bison. 

Comparing wolves in Southeast Alaska to species across

 the country is his next area of research.