According to the textbooks, these two species aren’t supposed to inhabit the same environments. Polar bears are marine mammals; Grizzlies are terrestrial. But as the Arctic warms, sea ice is shrinking, and the tundra is expanding, the bears’ disparate populations are meeting, mating and creating a new breed that’s capable of reproducing: Meet the pizzly or the grolar. This new phenomenon highlights the big impact of global warming. Yet, intraspecies mixing has been part of evolution for thousands of years.