North American gray wolves usually have mixed gray and white fur, but some members of the species have a version of a gene, or gene variant, that gives them a mostly black coat instead. Sarah Cubaynes and her team studied twelve populations of North American gray wolves. They found that the black-furred wolves are more common in areas where outbreaks of distemper virus happen regularly. The team also discovered that the black-furred wolves are more likely to be immune to distemper than the gray-furred wolves are. Taken together, these findings suggest that ______blank