“Gene pool” is wrong. “Gene river” is more like it. That’s what Richard Dawkins was trying to tell us in “River Out of Eden.”
Sometimes, tributaries of the river rejoin.
In 2006 a hunter killed an animal that was found to be half grizzly and half polar bear, the first known “grolar bear.” Another grizzly-polar hybrid was killed in April: DNA tests showed that not only was it a hybrid, it was a second-generation mix.
This makes conservation tricky. Polar bear, polar bear, wherefore art thou “Polar,” bear? It makes it so hard to protect polar bears when they turn half grizzly and we have to re-write our tidy legal definitions. Of course, if we just stopped overheating the planet, that would help.