Dogs were probably the first tame animals. They have accompanied humans for at least 20,000 years and possibly as many as 40,000. Scientists generally agree that all dogs, domestic and wild, share a common wolf ancestor; at some point grey wolves and dogs went on their separate evolutionary ways.
Today humans have bred hundreds of different domestic dog breeds—some of which could never survive in the wild. Despite their many shapes and sizes all domestic dogs, from Newfoundlands to pugs, are members of the same species—Canis familiaris. Although they have domestic temperaments, dogs are related to wolves, foxes, and jackals.
Similarities to Wild Relatives
Domestic dogs still share many behaviors with their wild relatives. Both defend their territories and mark them by urinating on trees, rocks, fence posts, and other suitable sites. These scent posts serve notice to other dogs that an animal is occupying its territory.
Many pet dogs also bury bones or favorite toys for future use, just as their wild relatives sometimes bury a kill to secure the meat for later feasts.
Dogs communicate in several ways. Scent is one method, another is physical appearance. Body position, movement, and facial expression often convey a strong message. Many of these signals are recognizable even to humans, such as the excited tail-wagging of a happy dog or the bared teeth of an angry or threatened animal. Vocally, dogs communicate with a cacophony of sounds including barks, growls, and whines.
Domestic dogs serve as more than companions; many earn their keep by working hard. Dogs herd livestock, aid hunters, guard homes, and perform police and rescue work. Some special animals even guide the blind—a poignant symbol of the dog's longstanding role as man's best friend.