It may not always sound like it but I like science. Really. I just don’t like the term ‘the science is settled’ or long-term predictions about stuff or computer models… you get the picture.
The problem is that science has a way of being ‘unsettled’… especially when it comes to polar bears. Until very recently, the polar bear was thought to have deviated from a large Brown Bear ancestor about 160,000-200,000 years ago – fairly recently when speaking about evolution.
Basically, this theory showed that a glacial maximum around 150,000 years ago – the Wisconsin – resulted in brown bears increasingly venturing out onto the sea ice and hunting seals. As the ice retreated during the Eemian warming period (125,000 years ago), this basically stranded the resident brown bears in the high arctic and increased the speed of their evolution into polar bears. As the planet cooled again, the polar bear population grew.
The problem is that DNA evidence now seems to show that polar bears have existed for about 4 million years. This basically up-ends much of what we believe about the evolution of this species. Neat!
So through four million years of warming and cooling trends – what were the polar bears up to back then? Retreating to little enclaves of cold? Or do polar bears – as a species – come and go with global warming/cooling patterns…?
Does the polar bear essentially ‘return’ to being a brown bear when the climate warms – the result of habitat overlap and interbreeding? Then when the planet cools, does the same evolutionary process begin anew – with a new polar bear species the inevitable result?
If it is the case that polar bears come and go as a species, then our polar bear books are still mostly true – the latest polar bear emerged at a time when the planet reached a glacial maximum… on the other hand, if polar bears survived periods of warming that were much more significant than today, well that’s a tough one to figure out!
We’ll probably never know for sure but it keeps you on your toes anyway…
http://www.sciencedaily.com/releases/2012/07/120723151028.htm
Pingback: August 23, 2012 | Another Slow News Day
Polar bears are carnivores, Grizzles are omnivores. Look at their teeth as evidence of this. Their fur is also different to reflect the differing climates each species endures. Carnivores follow their prey, in this case the seal, which prefer to pup on sea ice but at times of low sea ice the seals pup on land. Either way the PB will follow. The Grizzly will eat meat if available but fruits as well which are a summer/autumn harvest. winter gives very little food so they fatten up during the autumn and then hibernate to the next year’s food bonanza.
I have no doubt that both species came from the same root but the timing of 120,000 years seems too short to me for such diversity to develop.