The dog (Canis lupus familiaris)is a domesticated form of the Wolf, a member of the Canidae family of the order Carnivora. The domestic dog has been one of the most widely kept working and companion animals in human history.
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 developed, humans began to intentionally breed dogs for a wide range of specific traits. Through this process, the dog has developed into hundreds of varied breeds, and shows more behavioral and morphological variation than any other land mammal.