The Animal Wife.
In this novel by the author of Reindeer Moon, set in the Paleolithic age, Kori lives among his hunter-gatherer people, guilty with the knowledge that his unborn child is being carried by his shaman father's new wife. Then, Kori impulsively seizes another woman, from a different tribe, after seeing her swimming in a pond—putting his group in danger. He calls the woman Muskrat, and her customs, beliefs, and language are utterly alien to him.