Black Wolves the Result of Interbreeding With Dogs

Biologist Tovi Anderson of Stanford University and her team compared the genes of wolves from Yellowstone National Park and the Canadian Arctic to those of domestic dogs and coyotes. They found that, in each species, the black individuals have the same mutation, which first arose about 45,000 years ago. And molecular-clock analysis showed the mutation was oldest in dogs, suggesting it originated with them and then spread to wolves and coyotes through interbreeding.

This all happened in North America, because there are no black wolves in Europe or Asia (except for an Italian population that has hybridized very recently with dogs). And wolves picked up the black-coat mutation in the distant past, perhaps 12,000-15,000 years ago, when people first crossed the Bering Land Bridge from Asia.

The black coat seems to provide an advantage to forest-dwelling wolves, meaning dogs passed on some useful genetic diversity to their wild cousins.

Source