Dogs are domesticated mammals, originally bred from wolves and were the first animals ever to be domesticated. Today, about 20% of dogs are used as pets. Some of them help humans do their work, including police dogs, army dogs, service dogs, fire dogs, messenger dogs, hunting dogs, sled dogs, herding dogs, or rescue dogs. This influence on human society has given them the nickname "man's best friend". It is estimated that 75% of the world's dog population lives in the developing world as feral, village, or community dogs. Most of these dogs live their lives as scavengers and have never been owned by humans.
Interestingly that Dingo and New Guinea singing dog are considered a dog, nevertheless they have become wild animals again and live independently of humans. To the contrast African wild dog and Dhole (Asian wild dog) do not belong to dog family from a scientific point of view.