Origin of the Domestic Dog

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The dog, Canis lupus familiaris, nicknamed Man's Best Friend, is a domesticated subspecies of the Gray Wolf, a member of the Canidae family of the order Carnivora. The term is used for both wild and pet varieties. The domestic dog is one of the most widely kept working and companion animals in human history.

The dog soon became a familiar presence across cultures in all parts of the world, and was extremely valuable to early human settlements. For instance, sled dogs probably made the successful emigration across the Bering Strait possible. Dogs perform many roles for people, such as hunting, herding, protection, and assisting handicapped individuals. Currently, there are about 400 million dogs in the world.

Over the 15,000-year span that the dog has been domesticated, it evolved into only a handful of groups whose anatomy and behavior had been shaped by environmental factors and functional roles. As modern genetics developed, humans began to breed dogs for a wide range of specific traits, leading to the development of hundreds of varied breeds showing more behavioral and morphological variation than any other land mammal. For example, height ranges from a few inches in the Chihuahua to a few feet in the Irish Wolfhound; color varies from white through grays to black, and browns from light (tan) to dark ("red" or "chocolate") in a wide variety of patterns; coats can be short or long, coarse-haired to wool-like, straight, curly, or smooth. Most breeds commonly shed this coat, but non-shedding breeds are also popular.

Domestic dogs inherited a complex social hierarchy and behaviors from their wolf ancestors. They are pack animals who behave according to each dog's position in the social hierarchy, exhibiting postures and nonverbal communication that reveal their states of mind. These sophisticated forms of social behavior and communication explains their trainability, playfulness, and ability to fit into human households and social situations and have earned dogs a unique relationship with humans.

Although opinions differ over the details of dog domestication, it is agreed that human interaction played a significant role in shaping the dog. Shortly after domestication, dogs became ubiquitous in human populations, and spread throughout the world. Emigrants from Siberia likely crossed the Bering Strait accompanied by dogs, with some experts suggesting that use of sled dogs may have been critical to their success some 12,000 years ago. Dogs also carried much of the load in the migration of the Apache and Navajo tribes 1,400 years ago

While biologists and archaeologists cannot agree on exactly when domestication of dogs took place, there is conclusive evidence that dogs genetically diverged from their wolf ancestors at least 15,000 years ago. Although it’s not clear whether man domesticated the dog, or whether the dog evolved on its own, the latter view has recently been gaining supporters. The theory is that some wolves started gathering around the campsites of early humans to scavenge for refuse.

Scientific evidence for the evolution of the domestic dog comes from archaeological findings and mitochondrial DNA studies, indicating that the domestication of dogs from their wolf ancestors occurred more than 15,000 years ago in the late Upper Paleolithic period, between 17,000 and 14,000 years ago. However, a wide range of contradictory findings make this issue controversial. In 2008, archeological evidence that a large, toothy canine existed 31,700 years ago and ate a diet of horse, musk ox and reindeer was unearthed from Goyet Cave in Belgium. Prior to this, the earliest dog fossils were two large skulls from Russia and a mandible from Germany dating roughly 14,000 years ago. Remains of smaller dogs from Natufian cave deposits in the Middle East have been dated to around 10,000 to 12,000 years ago. Fossils uncovered in Germany, the French Alps, and Iraq, and cave paintings in Turkey show that dogs existed throughout Europe and Asia roughly 8,000 to 10,000 years ago, indicating that dogs could have diverged from wolves much earlier than 15000 years ago.

Genetic analyses indicate all dogs most likely descended from a small number of females, although evidence also shows that domesticated dogs interbred with local populations of wild wolves. Data suggests that dogs first diverged from wolves in East Asia and then spread throughout the world, reaching the North American continent around 8000 B.C. The oldest groups of dogs, which most resemble their wolf ancestors, are primarily Asian and African breeds, including the Basenji, Lhasa Apso, and Siberian Husky.

The theory that "man domesticated the wolf" is very controversial because the nature of the interaction between man and wolf that led to domestication is unknown. At least three early species of pre-humans began spreading out of Africa roughly 400,000 years ago, and thus lived for a considerable period in contact with canine species. Despite this, no evidence of any adaptation of canine species to the presence of the close relatives of modern man has been found.

The domestication of dogs roughly 15,000 years ago would have coincided with the development of agriculture and the expansion of human territory, leading some biologists to suggest that a shift in human lifestyle in the form of established settlements was one of the factors that led to it.