Except for red wolves (Canis rufus), all living North American wolves are considered to be Canis lupus -- a total (as of 1997) of 32 recognized subspecies.

Gray wolves are widely recognized to be the ancestor of all domestic dog breeds (Canis lupus familiaris), including feral forms such as dingos (Canis lupus dingo) and New Guinea singing dogs (Canis lupus halstromi). Genetic evidence suggests that gray wolves were domesticated at least twice, and perhaps as many as 5 times, by humans. Artificial selection by humans for particular traits, including size, appearance, aggressiveness, loyalty, and many desirable, specialized skills, has resulted in an astonishing array of domestic dog morphologies. Domestic dogs vary in size from diminutive, 1.5 kg chihuahuas to 90 kg giant mastiffs.