Ancestry:
Paleontologists and archaeologists have determined that about 60 million years ago a small mammal, rather like a weasel, lived in the environs of what are now parts of Asia. It is called Miacis, the genus that became the ancestor of the animals known today as canids: dogs, jackals, wolves, and foxes. Miacis did not leave direct descendants, but doglike canids evolved from it. By about 30 to 40 million years ago Miacis had evolved into the first true dog—namely, Cynodictis. This was a medium-size animal, longer than it was tall, with a long tail and a fairly brushy coat. Over the millennia Cynodictis gave rise to two branches, one in Africa and the other in Eurasia. The Eurasian branch was called Tomarctus and is the progenitor of wolves, dogs, and foxes.
Genetic evidence suggests that dogs descended directly from wolves (Canis) and that the now-extinct wolf lineages that produced dogs branched off from the line that produced modern living wolves sometime between 27,000 and 40,000 years ago. The timing and location of dog domestication is a matter of debate. There is strong genetic evidence, however, that the first domestication events occurred somewhere in northern Eurasia between 14,000 and 29,000 years ago. In this region wolves likely facilitated their own domestication by trailing nomadic people in northern Eurasia and consuming the remains of game animals that hunters left behind
Most studies agree that domestication was not a single discrete event. It was a process that unfolded over thousands of years—likely involving dog populations that appeared in different parts of Eurasia at different times, with dogs and wild wolves continuing to interbreed with one another and with early dog populations being replaced by later ones. Some genetic studies have documented evidence of early domestication events in specific regions. One study contends that wolves were domesticated 16,300 years ago to serve as livestock in China, whereas another reports that early dogs dating from about 12,000 to 14,000 years ago came from a small strain of gray wolf that inhabited India. Genetic evidence also reveals that dogs did not accompany the first humans to the New World more than 15,000 years ago, suggesting instead that dogs came to the Americas only some 10,000 years ago. One study even suggested that some dogs have descended not from the wolf but rather from the jackal. These dogs, found in Africa, might have given rise to some of the present native African breeds.
Role in human societies
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 mainly 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.
In ancient Egypt dogs were thought to possess godlike characteristics. They were pampered by their own servants, outfitted with jewelled collars, and fed the choicest diet. Only royalty was permitted to own purebred dogs, and upon the death of a ruler his favourite dog was often interred with him to protect him from harm in the afterlife.
Illustrations of dogs dating from the Bronze Age have been found on walls, tombs, and scrolls throughout Europe, the Middle East, and North America. Often the dogs are depicted hunting game with their human counterparts. Statues of dogs guard the entrances to burial crypts. In many cases these dogs clearly resemble modern canines. Such relics are indelible testimony to the importance that humans have given to the dog throughout the ages.
Origin of breeds:
Once it became evident that dogs were faster and stronger and could see and hear better than humans, those specimens exhibiting these qualities were interbred to enhance such attributes. Fleet-footed sight hounds were revered by noblemen in the Middle East, while in Europe powerful dogs such as the mastiff were developed to protect home and traveler from harm.
As society changed and agriculture—in addition to hunting—became a means of sustaining life, other breeds of dogs were developed. Herding and guarding dogs were important to farmers for protecting their flocks. At the same time, small breeds became desirable as playthings and companions for noble families. The Pekingese in China and fragile breeds such as the Chihuahua were bred to be lapdogs. The terrier breeds were developed, mainly in England, to rid granaries and barns of rodents. Pointing and retrieving breeds were selected for special tasks related to aiding the hunter to find and capture game. Many breeds are extremely ancient, while others have been developed as recently as the 1800s.
Physical traits and functions:
General characteristics
Dogs come in a wide range of shapes and sizes. It is difficult to imagine that a large Great Dane and a tiny poodle are of the same species, but they are genetically identical with the same anatomic features. All dogs have 78 chromosomes, or 39 pairs of chromosomes (humans have 23 pairs), and one member of each pair comes from each parent. The normal temperature (rectal) of an adult dog is 100–102.5 °F.
Teeth
Dogs have two sets of teeth. Twenty-eight deciduous teeth erupt by six to eight weeks of age, and by the time puppies are six to seven months old these deciduous teeth are all replaced by 42 adult teeth. The permanent teeth include incisors, which are used to nip and bite; canines, which tear and shred flesh; and premolars and molars, which shear and crush. In short, a dog’s teeth serve as weapons and as tools for cutting or tearing food. The canines are the upper and lower fangs for which the dog family was named. As in most carnivores, the teeth are high-crowned and pointed, unlike the broad, grinding teeth of many herbivorous animals.
The teething process can be difficult for puppies. Their gums hurt and become swollen, they may lose their appetites, and they may have mild intermittent diarrhea.
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