Many of us own or have owned a dog. Some, like the miniature dachshund, are a far cry in appearance from the dog ancestor in comparison with other breeds, like the Siberian husky. But all dog breeds -- about 400 -- share a common ancestry with gray or timber wolves of North America, Europe and Asia.

The oldest remains of domestic dogs, found in England, Idaho, Iran, Iraq, Israel, Japan and western Asia, were thought to be 10,000 to 12,000 years old. Recent evidence, however, has confirmed that dogs originated from wolves about 135,000 years ago. This clearly gives dogs the distinction of being the first mammal domesticated by humans, and the animals rapidly spread throughout the world with nomadic human family groups. Yet despite a long history of domestication, wolf-like dogs probably became different from wolf relatives as "dog breeds" only around 10,000 to 15,000 years ago, as humans reverted from a nomadic, hunter-gatherer to a more sedentary, farming way-of-life.

Gray wolves were not the only canids found in close contact with early humans. Humans lived with coyotes in North America, jackals in Africa and Asia, and Falkland Island wolves in South America. The Falkland Island wolf, in particular, was a very tame canid that was taken to the island from South America by Native Americans. Although Charles Darwin encountered this wolf species in his journeys, it was extinct by 1876.

Gray wolves were the "best" ancestors of domestic dogs for several reasons. Gray wolves are genetically similar to dogs. Wild gray wolves also hunt cooperatively in packs, which closely resembled the hunting style of early human social groups. Once domesticated, dogs readily accompanied early humans during hunts and assisted them in finding and capturing prey because of excellent senses of hearing and smell in dogs.

In addition, both early humans and wolves each lived in small groups, consisting of related individuals from more than one generation. Human groups existed as dominance hierarchies, with men and women caring for and providing necessities for the young children. Wolves easily adapted to this human hierarchy because its structure was similar to that of wolf packs. Domestication of dogs was assured when humans raised wolf pups within the human family group. These young "dogs" imprinted on a human as the group leader. Humans determined the amount of food given to these submissive adult animals and their young, which is thought to have led to the evolution of two litters per year in dogs, versus one litter in wolves. Early humans presumably selected individual "watch dogs" that barked frequently in response to danger; selection for barking is a major reason why today dogs bark whereas wolves howl.

It's also interesting that brains of dogs are only about two-thirds the size of those of wolves in similarly sized animals. Humans provided dogs with food, shelter and other necessities over many generations and, thus, natural selection no longer favored the evolution of large brain size. A smaller brain in domesticated dogs was a benefit because energy otherwise diverted for maintenance of a larger brain could be used for growth or rearing of young.

Domestic dogs gone wild, termed feral dogs, are commonplace throughout the world today. The most famous feral dog is the dingo of Australia, which was brought to the continent by humans about 8,000-9,000 years ago. Another feral or semi-domesticated dog, closely related to dingos, is the pariah of southeast Asia, northern Africa and the Balkans.

In summary, the domestic dog has become our "best friend" because of its ancestral ability to coexist and adapt to human society. Values of dogs to humans -- as companions, guardians, and helpers -- are unsurpassed in the animal world. Also, keep in mind what Groucho Marx said: "Outside of a dog, a book is probably man's best friend; inside of a dog, it's too dark to read."