Ancient history. The earliest fossil carnivores that can be linked with some certainty to canids are the Eocene Miacids some 55 to 38 million years ago. From the miacids evolved the cat-like (Feloidea) and dog-like (Canoidea) carnivores. Most important to the ancestry of the dog was the canoid line, leading from the coyote-sized Mesocyon of the Oligocene (38 to 24 million years ago) to the fox-like Leptocyon and the wolf-like Tomarctus that roamed North America some 10 million years ago. From the time of Tomarctus, dog-like carnivores have expanded throughout the world.
About Domestication. Human hunter-gatherers and wolves experienced several overlaps as both are social species, they shared habitat and hunted the same prey. There are four theories to explain possible routes for domestication of the dog:
1. Orphaned wolf-cubs: Studies have shown that some wolf pups taken at an early age and reared by humans are easily tamed and socialized.  Once these early adoptees started breeding amongst themselves, a new generation of tame “wolf-like" domestic animals would result which would over generations of time, become more dog-like.
2. The Promise of Food: Early wolves would, as scavengers, be attracted to the bones and refuse dumps of human campsites. Once there, they would recognise specific humans as “ours" and in protecting their range from strangers, would be useful to prevent surprise attack. These early adoptees became tame wolves, dependent on humans for their source of food. The New Guinea “singing dogs" have such a function today, as do the pariah dogs of India. Dr. Raymond Coppinger of Hampshire College, Massachusetts, argues that such wolves over time would become less fearful of humans than most wild wolves, and this trait may have been heritable, making these wolves more likely to be domesticated. Hypothetically, wolves separated into two populations - the village-oriented scavengers and the packs of hunters. The next steps have not been defined, but selective pressure must have been present to sustain the divergence of these populations.
3. As a beast of burden: North American Indians used dog-sized travois before adapting the horse for this purpose, and huskies are famous for pulling sleds for Inuit communities. It is very probable that the dog was the original beast of burden before the domestication of the horse or ox.
4. Dogs as a source of food and fur: Whilst Westerners have difficulty thinking of dogs (or wolves) as a source of meat, wolf fur is a highly prized commodity.
Archaeology has placed the earliest known domestication at potentially 10,000 BCE-12,000 BCE and with certainty at 7,000 BCE . Domestication of the wolf over time has produced a number of physical changes typical of all domesticated mammals. These include: a reduction in overall size; changes in coat colouration and markings; a shorter jaw initially with crowding of the teeth and, later, with the shrinking in size of the teeth; a reduction in brain size and intelligence and thus in cranial capacity (particularly those areas relating to alertness and sensory processing, necessary in the wild); and the development of a pronounced “stop”, or vertical drop in front of the forehead (brachycephaly). Behaviourally, the wagging of tails and barking are behaviours only found in wolf puppies, retained via neoteny throughout the dog's life. Certain wolf-like behaviours, such as the regurgitation of partially digested food for the young, have also disappeared.
As an experiment in the domestication of wolves, the “farm fox" experiment of Russian scientist Dmitry Belyaev  attempted to reenact of how domestication may have occurred. Researchers working with selectively breeding wild silver foxes over thirty-five generations and forty years for the sole trait of friendliness to humans, created more dog-like animals. The “domestic elite" foxes are much more friendly to humans and actually seek human attention, but they also show new physical traits that parallel the selection for tameness, even though the physical traits were not originally selected for. They include spotted or black-and-white coats, floppy ears, tails that curl over their backs, and earlier *** maturity. It was reported “On average, the domestic foxes respond to sounds two days earlier and open their eyes one day earlier than their non-domesticated cousins. More striking is that their socialisation period has greatly increased. Instead of developing a fear response at 6 weeks of age, the domesticated foxes don't show it until 9 weeks of age or later. The whimpering and tail wagging is a holdover from puppyhood, as are the foreshortened face and muzzle. Even the new coat colours can be explained by the altered timing of development. One researcher found that the migration of certain melanocytes (which determine colour) was delayed, resulting in a black and white ‘star’ pattern. "
DNA Evidence. Prior to the use of DNA researchers were divided into two schools of thought: 1. most supposed that these early dogs were descendants of tamed wolves, which interbred and evolved into a domesticated species. 2. other scientists, whilst believing wolves were the chief contributor, suspected that jackals or coyotes contributed to the dog's ancestry.
Carles Vilà of UCLA, , who has conducted the most extensive study to date, has shown that DNA evidence has ruled out any ancestor canine species except the wolf. Vila's team analyzed 162 different examples of wolf DNA from 27 populations in Europe, Asia, and North America. These results were compared with DNA from 140 individual dogs from 67 breeds gathered from around the world. Using blood or hair samples, DNA was extracted and genetic distance for mitochondrial DNA was estimated between individuals.
Based on this DNA evidence, most of the domesticated dogs were found to be members of one of four groups. The largest and most diverse group contains sequences found in the most ancient dog breeds, including the dingo of Australia, the New Guinea singing dog, and many modern breeds, like the collie and retriever. Other groups such as the German shepherd showed a closer relation to wolf sequences than to those of the main dog group, suggesting that such breeds had been produced by crossing dogs with wild wolves. It is also possible that this is evidence that dogs may have been domesticated from wolves on different occasions and at different places. Vilà is still uncertain whether domestication happened once - after which domesticated dogs bred with wolves from time to time - or whether it happened more than once.
The most puzzling fact of the DNA evidence is that the variability in molecular distance between dogs and wolves seems greater than the 10-20,000 years assigned to domestication. Based upon the molecular clock studies conducted, it would seem that dogs separated from the wolf lineage approximately 100,000 years ago. Although clear evidence for fossil dogs becomes obscure beyond about 14,000 years ago, there are fossils of wolf bones in association with early humans from well beyond 100,000 years ago.  Tamed wolves might have taken up with hunter-gatherers without changing in ways that the fossil record could clearly capture. These dogs-in-process would possibly have dallied with wolves as packs of humans and canines traveled out of Africa and around the world. Since evidence of dogs is not found elsewhere before 14,000 years ago, it may be that the “Sahara pump" associated with the Glacial Maximum was responsible for the spread of the dogs out of Africa. Such a thesis is compatible with the spread of languages associated with the Nostratic hypothesis.
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