Behavioral and anatomical adaption to habitat–including climate–becomes an isolating mechanism that keeps resulting subspecies living and evolving apart and hence, genetically isolated.
But when the climate changes–when warm zones move north, so do grizzlies; and when sea ice hunting forces polar bears more often onto land–formerly isolated populations find new mates.
And apparently, they are still “post-zygotically” compatible so that hybrids–like this “pizzly bear” result. Polar meets grizzly. They share more than sperm and egg: both are on the US Endangered Species list. And in this way of blended genomes, both species as they’ve been known, are “lost.”
I’ve heard of pizzly bears before, and the little girl in me thinks it’s hilarious. The grown up in me thinks that something like that up there makes me happy I live in the desert.
But the fact is, adapt or die, baby. Nature threw us into the mix, and we’re mucking it up, and they’re either adapting or dying.
I have been following this new adaptation. It does keep the DNA of both species alive and in the active gene pool which may allow for similar species to evolve in the distant future when cold climates dominate again. And they will.