Intra-hybridizations between dogs and other subspecies of gray wolves are the most common wolfdogs since dogs and gray wolves are considered the same species hence are genetically very close and have shared vast portions of their ranges for millennia. Such hybridizations in the wild have been detected in many populations scattered throughout Europe and North America, usually occurring in areas where wolf populations have declined from human impacts and persecutions.[1][2] At the same time, hybrids are also often bred in captivity for various purposes. Inter-hybridizations of dogs and two other North American wolf species have also occurred historically in the wild, although it is often difficult for biologists to discriminate the dog genes in the eastern timber and red wolves from the gray wolf genes also present in these wolf species due to their historical overlaps with North American gray wolves as well as with coyotes, both of which have introgressed into the eastern timber and red wolf genepools.[3] At the same time, because many isolated populations of the three wolf species in North America have also mixed with coyotes in the wild,[4] it has been speculated by some biologists that some of the coywolf hybrids in the northeastern third of the continent may also have both coydogs and wolfdogs in their genepool.[5] Hybrids between dogs and Ethiopian wolves discovered in the Ethiopian Highlands likely originated from past interactions between free-roaming feral dogs and Ethiopian wolves living in isolated areas.[6]
The term "wolfdog" is preferred by most of the animals' proponents and breeders because the domestic dog was taxonomically recategorized in 1993 as a subspecies of Canis lupus. The American Veterinary Medical Association and the United States Department of Agriculture refer to the animals as wolf–dog hybrids.[7] Rescue organizations consider any dog with wolf heritage within the last five generations to be a wolfdog, including some established wolfdog breeds.[8][unreliable source?]
Recognized wolfdog breeds by FCI are the Czechoslovakian Wolfdog and the Saarloos Wolfdog.