Final answer:
The sister taxon to the polar bear is the brown bear (Ursus arctos). The brown bear is the closest living relative of the polar bear based on genetic analysis and shared physical characteristics. The existence of grizzly-polar bear hybrids further supports their close genetic connection.
Step-by-step explanation:
The sister taxon to the polar bear is the brown bear (Ursus arctos). Scientists consider the brown bear to be the closest relative of the polar bear based on genetic analysis and their shared physical characteristics. Both species belong to the genus Ursus and share a common ancestor.
One key piece of evidence for the evolutionary relationship between polar bears and brown bears is the existence of grizzly-polar bear hybrids, also known as grolar bears or pizzly bears. These hybrid bears are the result of mating between polar bears and brown bears, further substantiating their close genetic connection.
Overall, the brown bear serves as the closest living relative to the polar bear, forming the sister taxon of this iconic Arctic species.