Are grizzly bears just dirty polar bears?

We went to the San Diego Zoo last month. It's a fantastic zoo, and we keep coming back. This time I was amused to find this dirty polar bear and its inmate, who was a nice clean white. Click images for (much) larger versions.

I recall reading somewhere that the genetic difference between Ursus maritimus (polar) and Ursus arctos horribilis (grizzly) is really quite small, and hybrids do occur in captivity as well as in the wild.

So, tongue in cheek, I wonder if the genetic difference isn't just normal variation, and we have been fooled all this time by dirty polar bears.

It could be one of those infamous attempts of the damned treehuggers to split up the wild population into many small ones, having us all believe that they need protection because there are only a few polar/grizzly/brown bears left in the wild. But they won't fool me, and one day someone will go into the wild and point a hose at those grizzlies and rub that ink off Gorbachev's forehead while they're at it.