As much as I find it interesting to have hybrid animals like ‘grolar bears’, their chances of being something we would come into contact with is extremely low. As the climate changes, the natural habitat of the polar bear decreases, and as their habitat decreases, Darwinism comes knocking in to give the polar bears a reality check.
I don’t find it unreasonable to think that there could be cross-breeding between the two species, but anything occurring would be rare. Polar bears and grizzly bears live in very different places, and to mate some type of travel would have to be involved. Due to the earth heating and ice melting, it wouldn’t be unreasonable to expect some polar bears to move in the direction of different land, but a large majority of them will die whether it be in the process of moving or just because of circumstances. These bears would face issues when trying to feed and live off of an unfamiliar and new habitat, decreasing their population even further.
Any bears that did manage to mate with the existing grizzly bears would be part of a minority, which would soon die regardless. Darwinism reflected the idea that only the fittest animals survive, and that their circumstances (both genetically and in their habitat) determine whether they will live or die. The polar bears couldn’t move fast enough, and if they did, they wouldn’t last terribly long. Any bears that mated with the grizzly bears would have merged features, but even those animals would face conflicts surviving in an environment they are not suited for. In this scenario, their breeding with the natural grizzly bear population would wean down the genes and traits from the polar bear over time, as the undesirable traits would be cut off.
Hybrids occurring would be more likely with other animals, such as birds, due to their access to different locations. Flying makes things easier in comparison to bears who have to walk, but even they will face difficulties when mating with pre-existing species. It does leave questions about how many animals will mate and form new hybrids, but after how long would they even be considered hybrids? I even wonder how compatible a polar bear and grizzly bear would be, and if their children would be capable of surviving past a few generations.