Authorities agree that the dog was the first of man's domesticated animals. How and when this domestication took place, however, remains unknown. A 50,000-year-old cave painting in Europe seems to show a doglike animal hunting with men. But most experts believe the dog was domesticated only within the last 15,000 years. Moreover, fossil remains that would substantiate the presence of dogs with humans have not yet been unearthed for periods earlier than about 10,000 BC. One theory holds that humans took wolf pups back to their camp or cave, reared them, allowed the tame wolves to hunt with them, and later accepted pups of the tame wolves into the family circle. Another theory suggests that dogs were attracted to food scraps dumped as waste near human living sites. As they scavenged and kept the site clean, the dogs rendered a service to the humans. In turn, the humans would accept the presence of the scavengers and would not drive them away. Still other theories maintain that the dog was domesticated to pull sleds and other conveyances bearing the heavy game killed by humans, to provide a ready source of food, or to act as a sacrificial animal for magical or religious purposes.

Studies of primitive human societies still in existence tend to substantiate some of these theories. Whatever the ultimate reason for the domestication of the dog, however, the final submission must have been the consequence of thousands of years of caution and "deliberation" by the dog before it would cast its lot with humans. Also, the dog, itself a hunter, had to suppress its desire to kill the other animals domesticated by humans. Instead, it had to learn to protect them.

Some feral dogs live today; that is, they have returned to the wild state. The dingo of Australia, for example, spends only a portion of its time with humans. When the mating urge seizes it, the dog runs off to the wild. Another, the dhole of India, is reputed to be a fierce, untamable dog.

The partnership between dog and master has long been shown in paintings and other art forms and in writings. Prehistoric paintings done about 15,000 years ago on the walls of Spanish caves show doglike animals accompanying humans on a hunt. Dogs are amply illustrated in the sculptures and pottery of ancient Assyria, Egypt, and Greece. The ancient Egyptians worshiped Anubis as the god of death. Anubis was portrayed with the head of a jackal or a dog. The Egyptians were great lovers of dogs and were responsible for developing many breeds by crossing dogs with jackals, wolves, and foxes.

Homer, the Greek author of the 'Odyssey' in the 9th century BC, is believed to be one of the first to write about dogs. They were mentioned often in his classic epic. The ancient Greeks believed that the gates of the underworld were guarded by a savage three-headed dog named Cerberus. The belief might have been derived from the widespread practice in Greece of using watchdogs. The ancient Romans relied on watchdogs, too. So many dogs were kept in the larger Roman cities that any house with a watchdog was required to have a sign warning "Cave Canem" (Beware the Dog). The Romans also used dogs for military purposes, some as attack dogs and some as messengers.

During the 400 years of the Han Dynasty of China, which began in the 3rd century BC, dogs were portrayed in many pieces of pottery. These were effigy pieces that symbolized the burial of favored dogs with their masters. Toy dogs were also popular among the ancient Chinese: the little animals were used to provide warmth when carried in the wide sleeves of their gowns.

Many of the European hound breeds were developed in the Middle Ages, when coursing was popular with the nobility. In coursing, the prey is pursued until exhausted. Then it is killed. Coursing was eventually replaced by fox hunting, which was considered less cruel.

Throughout the years dogs have been bred for many reasons, such as for hunting, for herding, and for guarding. Breed histories and pedigrees, however, were not methodically compiled until the 19th century with the establishment of the first kennel clubs. The world's first dog show took place in Great Britain in 1859.