Black wolves and coyotes are often the villains of cartoons and children's fairy tales, but it now appears that they inherited their color from a much more warm and fuzzy animal -- the dog.
True, dogs are descended from wolves, but research Friday in the journal Science indicates that black fur was bred into dogs by humans, then inadvertently introduced into the wild species.
The trait shows up in the wild primarily in North America, and it was probably brought to the continent about 15,000 years ago when the first immigrants crossed over the Bering land bridge, bringing their dogs with them.
The fact that the mutation has stayed in the wild population for so long suggests that it is beneficial in some way.
The gene responsible for the color, called beta-defensin, was discovered in 2007 by geneticist Greg Barsh of Stanford University.
It belongs to a family of genes thought to be involved in fighting infections.
When the gene appears in its normal form, the animal has a light or yellow-colored coat. But when one copy of the gene is missing three nucleotides, the animal develops a black coat.
Studying genes from a large number of wolves, coyotes and dogs, Barsh and his colleagues concluded that the current mutation first appeared in dogs about 50,000 years ago.
It may also have appeared in wild animals, then disappeared again, the researchers speculated.
They also concluded that the mutation appeared in wolves and coyotes some time after the first humans reached North America.
Its almost exclusive appearance in the New World is probably because it was much easier for dogs to mingle with the wild animals here than in Europe, said Barsh's graduate student Tovi Anderson.
Black coats occur in about 62% of wolves in the forested areas of the Canadian Arctic, compared with about 7% in the icy tundra. Researchers agree that the coat does not camouflage the animals from predators, but it may help them sneak up on prey.
The mutated gene might also provide a better immune defense against infectious agents that occur primarily in the warmer forests, Barsh said.