The dog (Canis lupus familiaris,pronounced /ˈkeɪnɨs ˈluːpəs fəˈmɪli.ɛərɨs/) is a domesticated form of the wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The domestic dog has been one of the most widely kept working and companion animals in human history. The word "dog" may also mean the male of a canine species, as opposed to the word "bitch" for the female of the species.

The dog quickly became ubiquitous across culture across the world, and was extremely valuable to early human settlements. For instance, it is believed that the successful emigration across the Bering Strait might not have been possible without sled dogs. Dogs perform many roles for people, such as hunting, herding, protection, assisting police and military, companionship, and, more recently, aiding handicapped individuals. This versatility, more than almost any other known animal, has given them the nickname "Man's best friend" in the western world. Currently, there are estimated to be 400 million dogs in the world.

Over the 15,000 year span that the dog had been domesticated, it diverged into only a handful of landraces, groups of similar animals whose morphology and behavior have been shaped by environmental factors and functional roles. As the modern understanding of genetics deve