A fox with thick fur would have a survival advantage over other foxes

If it was cold weather and the other foxes didn't have as much fur then possibly their is a half half because the other wolfs could have food and no fur and the wolf with fur could only have fur and no food.

The fox has more so he can keep more heat in but in the summer he will get overheated. hunting with big fur is hard and other ones would have an advatange