Grizzly–polar bear hybrid

A grizzly–polar-bear hybrid (also named grolar bear, pizzly bear, zebra bear, grizzlar, or nanulak) is a rare ursid hybrid that has occurred both in captivity and in the wild. In 2006, the occurrence of this hybrid in nature was confirmed by testing the DNA of a unique-looking bear who had been shot near Sachs Harbour, Northwest Territories, on Banks Island in the Canadian Arctic. The number of confirmed hybrids has since risen to eight, all of them descending from the same female polar bear.

Possible wild-bred polar bear–grizzly bear hybrids have been reported and shot in the past, but DNA tests were not available to verify the bears' ancestry.

Genetic analysis has revealed multiple instances of introgressive hybridization between bear species, including introgression of polar bear DNA into brown bears during the Pleistocene ("grizzly bear" is a local common name for Ursus arctos whereas "brown bear" is used internationally and in science to refer to the species as a whole).

Occurrences in the wild

With several suspected sightings and eight confirmed cases, theories of how such hybrids might naturally occur have become more than hypothetical. Although these sister species often occupy adjacent regions, direct contact has not been the norm because polar bears hunt, breed, and sometimes even make maternity dens on sea ice, whereas brown bears have an overwhelmingly terrestrial lifestyle.

Scientists have been unable to give an exact explanation for the phenomenon. One theory suggests that as the grizzly population increases, male bears leave their dens sooner while females stay with their cubs. This means that to the male grizzlies, female polar bears have become viable mates.