ORIGIN AND HISTORY OF DOGS

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.

It is believed that the early dogs dating from about 12,000 to 14,000 years ago came from a small strain of gray wolf that inhabited what is now India. Thereafter, this wolf—known as Canis lupus pallipes—was widely distributed throughout Europe, Asia, and North America. It is also possible that some of the dogs of today 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.

No matter what their origins, all canids have certain common characteristics. They are mammals that bear live young. The females have mammary glands, and they suckle their offspring. The early breeds had erect ears and pointed or wedge-shaped muzzles, similar to the northern breeds common today. Most of the carnivores have similar dental structures, which is one way paleontologists have been able to identify them. They develop two sets of teeth, deciduous (“baby”) teeth and permanent teeth.

Canids walk on their toes, in contrast to an animal like the bear, which is flat-footed and walks on its heels. Dogs, like most mammals, have body hair and are homeothermic—that is to say, they have an internal thermostat that permits them to maintain their body temperature at a constant level despite the outside temperature.

Fossil remains suggest that five distinct types of dogs existed by the beginning of the Bronze Age (about 4500 BC). They were the mastiffs, wolf-type dogs, sight hounds (such as the Saluki or greyhound), pointing dogs, and herding dogs.

Domestication

It is uncertain when the first dog became a companion of humans, but it is likely that wild canids were scavengers near tribal campsites at the same time that ancient humans discovered a hunting partner in the animals that ventured close by. In ancient Egypt, dogs were thought to possess godlike characteristics. They were pampered by their own servants, outfitted with jeweled 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.

By Constance B. Vanacore, extracted from Enciclopedia Britannica,2007. Adapted and illustrated to be posted by Leopoldo Costa.