Did you know that dogs are descended from a 15-million-year-old species?
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.
In fact, dogs come in a wide range of shapes and sizes and all dogs have 78 chromosomes, or 39 pairs of chromosomes (while us humans only have 23 pairs).
Below is a brief history of the origin of dogs and how they have come to be:
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.
Domestication of Dogs
The timing and location of dog domestication is less clear and has been a matter of significant debate, but there is strong genetic evidence that the first domestication events occurred somewhere in Central Asia before 15,000 years ago.
Some genetic studies have suggested that wolves were domesticated 16,300 years ago to serve as livestock in China. Other genetic studies, however, have suggested that dog domestication began as early as 18,800–32,100 years ago in Europe or that 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. However, one genetic study that compared the DNA of dogs and wolves inhabiting areas thought to have been centres of dog domestication suggests that dogs and modern wolves belong to separate lineages that share a common ancestor.
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.
A genetic study examining the migration of dogs to the Americas revealed evidence that dogs did not accompany the first humans to the New World more than 15,000 years ago; the study suggested that dogs came to the Americas only 10,000 years ago.
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 BCE). They were the mastiffs, wolf-type dogs, sight hounds (such as the Saluki or greyhound), pointing dogs, and herding dogs.
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.