Dog

I

Introduction

Dog, mammal generally considered to be the first domesticated animal. This trusted work partner and beloved pet learned to live with humans more than 14,000 years ago. A direct descendant of the wolves that once roamed Europe, Asia, and North America, the domestic dog belongs to the dog family, which includes wolves, coyotes, foxes, and jackals. Dog ancestry has been traced to small, civet-like mammals, called miacis, which had short legs and a long body and lived approximately 40 million years ago.

The evolving relationship between the domestic dog and humans has been documented in fossil evidence, artifacts, and records left by earlier civilizations. Prehistoric dog skeletal remains, excavated from sites in Denmark, England, Germany, Japan, and China, indicate the early coexistence of dogs with people. An ancient Persian cemetery, dating to the 5th century bc, contained thousands of dog skeletons. Their formal burial and the positioning of the dog remains reveal the esteem in which the ancient Persians held their dogs. The relationship shared by dogs and humans also is evident in cave drawings, early pottery, and Asian ivory carvings that depict dogs. A statue of Anubis, the half dog, half jackal Egyptian god, was discovered inside King Tutankhamen’s tomb, constructed in about 1330 bc.

Literary references to the dog include those found in the Bible and in the Greek classic the Odyssey by Homer. In 1576 an English physician and dog fancier, John Caius, wrote a detailed text on dog breeds, Of English Dogges. Dogs are featured in tapestries that were created in the Middle Ages (5th century to 15th century), and in the work of many artists, including 17th- and 18th-century European painters Peter Paul Rubens and Thomas Gainsborough.

Although it is not known how humans and dogs first learned to coexist, people soon discovered the many ways dogs could enrich their lives. Dogs have been used to hunt for food, herd animals, guard livestock and property, destroy rats and other vermin, pull carts and sleds, perform rescues, and apprehend lawbreakers. They have been used during wartime as sentinels and message carriers. Today trained dogs are used to alert deaf people to common household sounds, such as the ringing telephone or doorbell; guide the blind; or retrieve objects for quadriplegics. Perhaps the most common of the many roles served by the domestic dog, however, is that of companion. As animals with strong social tendencies, dogs typically crave close contact with their owners. And people tend to form loving bonds with dogs. This companionship often helps to ease the pain and isolation of the elderly or people whose physical or mental health requires long-term convalescence or institutionalization.

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II

Physical Characteristics

Domestic dogs vary widely in appearance, particularly in size. The Shih Tzu, for example, is 20 to 28 cm (8 to 11 in) in length and weighs 4 to 7 kg (9 to 15 lb). The Irish wolfhound is at the other end of the scale, measuring about 71 to 94 cm (about 28 to 37 in) at the shoulder and weighing up to about 61 kg (about 135 lb). Coat color, length, texture, and pattern also vary greatly. The muzzle may appear shortened, as in the Pekingese, or elongated, as in the Doberman pinscher. Limbs are relatively short in the basset hound and dachshund, but long in the greyhound. Ear shape and carriage also vary, but these characteristics may be influenced by a dog owner’s decision to crop, or cut, the ears to make them stand up. Some dogs, notably the chow chow, even have a naturally blue-black tongue.

Despite these differences, all breeds of the domestic dog are essentially identical in anatomy. The skeleton of the domestic dog has an average of 321 bones, with variation reflecting differences in the number of bones in the tail and the presence of a dewclaw, an extra digit on the paw that not all breeds have. The rib cage consists of 13 pairs of ribs; the spine has 7 cervical vertebrae, 13 thoracic vertebrae, 7 lumbar vertebrae, and 3 sacral vertebrae. Rear paws have four complete digits and front paws have four or five digits. Most puppies have 28 temporary teeth, which are replaced with 42 permanent teeth at about six months of age.

Some breed differences evolved to help dogs survive in their native environment or occupation. For example, dogs that lived and worked outdoors, such as the Komondor of Hungary, needed a thick, weather-resistant coat to protect them from the elements and, perhaps, the biting teeth of predatory animals. Similarly, the Labrador retriever developed an oily coat, webbed feet, and a rudder-like tail to help it perform better in recovering downed waterfowl.

Just as distinct physical characteristics became trademarks in some breeds, unusual sensory abilities characterize others. Most dogs are able to detect scents and hear high-pitched sounds that are beyond human perception, but some breeds have especially acute sensory skills. The bloodhound, for instance, can follow a four-day-old track using its highly developed sense of smell. Other breeds with a keen sense of smell include the German shepherd, golden retriever, beagle, and Newfoundland. These dogs have been trained for such varied duties as detecting hidden drugs, explosives, termites, and even a decomposing body immersed in deep water.

III

Reproduction, Birth, and the Young

Dogs generally reach sexual maturity at about six months of age, with small breeds often maturing earlier than large breeds. Female dogs, or bitches, become sexually receptive to mating during a period called estrus (also called season or heat), which occurs about twice a year for 6 to 12 days. After a gestation period of about 63 days, an average litter of three to six puppies is born.

Blind and unable to stand, newborn puppies are helpless and spend 90 percent of their time sleeping and 10 percent nursing. Becoming chilled is the greatest danger facing a healthy newborn puppy because its immature circulatory system cannot sustain an adequate body temperature. For this reason, newborn puppies tend to stay close to their mother or cuddle together for warmth. Mothers clean, nurse, and defend their pups until they can live on their own, but fathers do not involve themselves in the care of the young.

IV

Dog Breeds

Of the more than 300 breeds of dogs that exist worldwide, 150 are recognized by the American Kennel Club (AKC), the primary kennel club in the United States. Since its founding in 1884 the AKC registers purebred dogs—dogs whose parents and ancestors were of the same breed since the breed was first recognized. More than one million such dogs are registered annually. Kennel clubs in other countries, such as the Canadian Kennel Club, the Kennel Club of England, and the Japanese Kennel Club, use their own standards in recognizing dog breeds.

The AKC organizes the 150 breeds it recognizes into seven groups (plus a miscellaneous category), based on physical and temperamental characteristics and the purpose for which the breed was originally developed. The club classifies breeds as terrier, working, sporting, hound, herding, toy, and nonsporting.

The terriers often have wiry coats and possess a feisty personality, which reflects their original use in catching prey such as foxes, badgers, and rabbits. Working dogs, such as the boxer or Alaskan Malamute, are muscular, even-tempered, and obedient, a necessary quality in dogs that serve as working partners with humans. Many of the sporting dogs, such as pointers and retrievers, are active dogs that respond instinctively when spotting game. Hounds such as the beagle are known for their stamina, acute sense of smell, and baying bark, qualities that are an invaluable aid to hunters and trackers. Other tireless helpers of humans are herding dogs, recognized for their innate ability to drive livestock and keep farm animals from straying. The low-to-the-ground Pembroke or Cardigan Welsh Corgi can drive a herd of cows many times its size. Toy dogs, on the other hand, are known for their diminutive size and function as companionable house pets. The papillon, named for the French word for butterfly because it has ears that resemble butterfly wings, is a happy, friendly dog, suitable for small living spaces. The final dog group, nonsporting , includes a wide variety of purebreds that differ in size, coat, overall appearance, and personality, from the shorthaired spotted dalmatian to the curly-haired poodle.

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