DOG

(species Canis familiaris), domestic mammal of the family Canidae (order Carnivora); it is related to wolves, foxes, and jackals. Dogs are the first animal to have been domesticated. They probably originated somewhere in Eurasia approximately 12,000 to 14,000 years ago. The association may have developed gradually as wild dogs took to hanging around encampments to pilfer scraps, and humans began to rely on the dogs for warning of any approaching danger. Through the centuries many breeds were developed for specific tasks, such as hunting, herding, or guarding. Today, however, most dogs are kept chiefly for companionship. Selective breeding by humans has had great effect on the natural variation present in one species. The smallest dog, the chihuahua, may weigh less than 2 pounds (0.9 kg), while 150 pounds (68 kg) is not uncommon for a mastiff or a Saint Bernard. Selective breeding has also altered the physical form of many breeds of dog. Early in domestication a mutation occurred for the upcurved tail; this trait occurs in most dog populations, but it is not found among wolves. Other variations from the original wolflike body-form include the very short legs of breeds such as dachshunds and Welsh corgis; the foreshortened face of bulldogs, mastiffs, and Pekingese; and the drooping ears that are more typical of domestic dogs than are the ancestral erect ears still found on some of the most wolflike breeds, such as German shepherds and malamutes. Coat colour also has been modified and includes solid black, black and tan, piebald (mottled), and white. Coat texture may be wolflike (as in German shepherds), curly (poodles), wiry (Airedale terriers), long (briards), short (Labrador retrievers), or even nonexistent (Mexican hairless). Selective breeding has also enhanced particular behavioral patterns. Hounds, such as bloodhounds, foxhounds, and beagles, have been developed to hunt by scent; bloodhounds can follow a faint trail that is days old. The herding instinct, part of the hunting behaviour of the wolf and wild dog, has been highly developed in such breeds as border collies (used by shepherds) and Welsh corgis (used by cowherds). Some breeds, including the Great Pyrenees and komondors, live with flocks of sheep and protect them from predators. Terriers, such as fox terriers and miniature schnauzers, were developed to follow small game and verminsuch as foxes and ratsinto their burrows and to trap and kill them. Sporting breeds are used to find game birdssetters and pointers to stand on point (i.e., stop and wait) when they locate a bird, spaniels to rush in and flush the bird, and retrievers to collect dead and wounded birds and bring them to the hunter. Mastiffs, originally used as guard dogs and watchdogs, have been superseded by more agile breeds, such as Doberman pinschers and German shepherds. Breeds like the husky, malamute, and Bernese mountain dog were developed mainly as draft animals. Members of all these breeds also serve as companions, as do the various toy or miniature dogs and breeds that are categorized as nonsporting dogse.g., the Lhasa apso (originally a temple dog), the poodle (bred as a water retriever), and the Dalmatian (originally a hunting dog and later used to escort and guard horse-drawn carriages). The dog's best-developed senses are smell and hearing. Its nasal passages can process large amounts of air, and the olfactory centre in the brain is enlarged. The dog's hearing is also acute; it can respond to frequencies of up to 35,000 vibrations per second (human hearing stops at 20,000). Sight is relatively poorly developed, although certain hounds (e.g., greyhounds and Afghans), known as gazehounds, or sight hounds, have been bred to follow their preyusually antelopes or haresvisually. All dogs lack colour vision. Wild dogs are highly social animals and, like wolves, tend to run in groups and follow a leader. In domestic dogs, this characteristic makes possible the transference of pack loyalties to human owners. They are also fairly intelligent animals, and, when motivated, many can learn a large number of commands. German shepherds, Labrador retrievers, and poodles are among the most amenable to extended training, although individuals of almost any breed may excel in obedience. Domestic dogs are mature by about one year of age, and females, called bitches, may come into their first heat, or estrus, before six months of age. Most bitches have two heats yearly, about six months apart. To avoid unwanted puppies, females can be spayed (removing the ovaries) and males castrated. After mating, dogs are attached in a copulatory tie for up to half an hour. Gestation lasts approximately nine weeks. An average litter consists of 4 to 6 puppiesborn blind, deaf, and helplessbut the tiny breeds may have only 1 or 2 and the large breeds more than 10. Puppies should be allowed to nurse for at least six weeks before they are weaned. Between six and eight weeks is the ideal age at which to transfer the pup's social allegiance from dogs to humans, but this usually can be accomplished any time up to 12 weeks. Puppies that interact only with other dogs for a longer period of time may never become fully adapted to humans. Simple training may begin at six to eight weeks, but complex training generally is not successful until the dog is about six months old. The reward system seems to be the best basis for training a dog; most work willingly for a pat and a fond word. Various competitions are held by groups interested in dogs and dog breeding. During dog shows animals are judged on how closely they match the breed standards set by the ruling organization. In the United States these rules are formulated by the American Kennel Club, in Britain by the Kennel Club of England. Other competitions include field trials (for hunting and shepherd dogs) and obedience trials. (species Canis familiaris), domestic mammal of the family Canidae (order Carnivora). It is related to wolves, foxes, and jackals. The dog is one of the two most ubiquitous and popular domestic animals in the world (the cat is the other). For more than 12,000 years it has lived with humans as a hunting companion, protector, object of scorn or adoration, and friend. The dog has evolved from similar (that is, undifferentiated) fur-bearing animals into more than 400 distinct breeds. Human beings have played a major role in creating dogs that fulfill distinct societal needs. Through the most rudimentary form of genetic engineering, dogs were bred to accentuate instincts that were evident from their earliest encounters with humans. Although details about the evolution of dogs are uncertain, the first dogs were hunters with keen senses of sight and smell. Humans developed these instincts and created new breeds as need or desire arose. Dogs are regarded differently in different parts of the world. Western civilization has given the relationship between human and dog great importance, but, in some of the developing nations and in many areas of Asia, dogs are not held in the same esteem. In some areas of the world, dogs are used as guards or beasts of burden or even for food, whereas, in the United States and Europe, dogs are protected and admired. In ancient Egypt during the days of the pharoahs, dogs were considered to be sacred. Characteristics of loyalty, friendship, protectiveness, and affection have earned dogs an important position in Western society, and in the United States and Europe the care and feeding of dogs has become a multibillion-dollar business. Dogs have played an important role in the history of human civilization and were among the first domesticated animals. They were important in hunter-gatherer societies as hunting allies and bodyguards against predators. When livestock were domesticated about 7,000 to 9,000 years ago, dogs served as herders and guardians of sheep, goats, and cattle. Although many still serve in these capacities, dogs are increasingly used for social purposes and companionship. Today, dogs are employed as guides for the blind and disabled or for police work. Dogs are even used in therapy in nursing homes and hospitals to encourage patients toward recovery. Humans have bred a wide range of different dogs adapted to serve a variety of functions. This has been enhanced by improvements in veterinary care and animal husbandry. Additional reading The American Kennel Club, The Complete Dog Book, 18th ed. (1992), comprehensively illustrates every breed that is registerable in the AKC stud book and includes a chapter on health care and puppy management. David Taylor and Connie Vanacore, The Ultimate Dog Book (1990), is an illustrated overview of most of the breeds registered in the United States and Great Britain, with brief histories and descriptions of each.Fernand Mry, The Life, History, and Magic of the Dog (1970; originally published in French, 1968), traces the beginnings of the domestication of the dog and recites legends concerning the dog and its ancestors throughout the world. Stanley J. Olsen, Origins of the Domestic Dog (1985), is an anthropological study of fossils, primarily in the United States. Maxwell Riddle, The Wild Dogs in Life and Legend (1979), describes many wild canids that exist in different parts of the world and relates the stories natives tell about them.A vastly important contribution to the understanding of canine behaviour is John Paul Scott and John L. Fuller, Genetics and the Social Behavior of the Dog (1965, reissued as Dog Behavior: The Genetic Basis, 1974), describing the genetic structure of personality based on original research by the authors. The foundational work describing the development of personality in puppies is Clarence J. Pfaffenberger, The New Knowledge of Dog Behavior (1963), based on research done by Scott and Fuller in the 1950s. Jack Volhard and Melissa Bartlett, What All Good Dogs Should Know (1991), is a basic primer for obedience training. Carol Lea Benjamin, Mother Knows Best: The Natural Way to Train Your Dog (1985), uses a commonsense approach to teaching basic manners and solving problems.William J. Kay and Elizabeth Randolph, The Complete Book of Dog Health (1985), gives detailed descriptions of the major organ systems of the dog and describes common ailments and symptoms that dog owners can identify. Harold R. Spira, Canine Terminology (1982), definitively describes canine anatomy, illustrated from nose to tail. Terri McGinnis, The Well Dog Book (1991), is a basic veterinary manual for dog owners. Also helpful is Malcolm B. Willis, Practical Genetics for Dog Breeders (1992), which studies the genetic structure of the dog, including anatomy, coat colour, and breed differentiation. Constance B. Vanacore