Ancient

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 carnivore. Most important to the ancestry of the dog was the Canoidea line that led 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 began to expand throughout the world ^[1].

Wolf

In terms of their molecular biology, dogs are wolves (Canis lupus) and the wide variation in their adult morphology probably results from simple changes in developmental rates and timing ^[2].

The assessment that the wolf is the progenitor of the dog is a working hypothesis that currently is supported by several lines of independent evidence behaviour, morphology and genetics. The parallel conclusions of these investigations strongly suggest, given current knowledge and understanding of evolutionary process, that the wolf is the domestic dog's most recent ancestor ^[3]. The earliest proven association between the two species is from the Natufian burial at Ein Mallaha in Israel. At Ein Mallaha, a 12,000 year old site, a burial of an old woman with a puppy contained in her left hand, was found. The next appearance of the domestication of the dog is from 8.5-9,000 years ago with the Zarzian culture of the Zagros Mountains, in Iraq. The Mesolithic Star Carr settlement in Yorkshire shows dogs were widely present part of their culture.

Specialization

As humans migrated around the planet a variety of dog forms migrated with them. The agricultural revolution and subsequent urban revolution led to an increase in the dog population and a demand for specialization. These circumstances would provide the opportunity for selective breeding to create specialized working dogs and pets

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 domesticaion of the dog:

1. Orphaned wolf-cubs: Studies have shown that wolf pups taken at an early age and reared by humans are easily tamed and socialized ^[4]. 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 be attracted to the bones and refuse dumps of human camping sites as scavengers. 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 adoptee became tame wolves dependent on humans for their source of food. The Papua New Guinean "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 inheritable, making these wolves more likely to be domesticated. The wolves hypothetically 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 their pulling of 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, and their uses as beasts of burden.
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 ^[5].

The adaptation to living with humans changed these once wild animals. At the genetic point, which tame wolves could no longer compete successfully in the wild, a subspecies of the wolves (Canis lupus) was created called the domestic dog (Canis lupus familiaris). Archaeology has placed the earliest known domestication at potentially 10,000 BCE-12,000 BCE and with certainty at 7,000 BCE ^[6]. 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, that have been retained through neoteny, throughout the dog's life. Certain wolf-like behaviours, such as the regurgitation of half 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 ^[7] 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, became 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 sexual 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 socialsation 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 whimpiering and tail wagging is a holdover from puppyhood, as are the foreshoretened 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 ^[1], 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 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 up to 100,000 years ago. At such an early time span, according to the Out-of-Africa hypothesis Homo sapiens was confined to Africa, and it would be estimated that at this time a sub-species of extinct African Saharan wolf would have been the original dog ancestor. 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 would capture. The dogs-in-process probably would 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.

The influx of new genes from those crossings could very well explain the extraordinarily high number of dog breeds that exists today, the researchers suggest. Dogs have much greater genetic variability than other domesticated animals, such as cats, says Vilà. Once farming started dogs would have been selected for different tasks, their wolf-like nature being a handicap as dogs became herders, guards, and used for other different tasks. Ostrander is of the view that "When we became an agricultural society, what we needed dogs for changed enormously, and a further and irrevocable division occurred at that point." That may be the point -- at which dogs and wolves were noticeably different physically -- that stands out in the fossil record.

1  Wayne, R. K., (1993). Molecular evolution of the dog family. Trends in Genetics.
2 Brewer, D., et al. (2001). Dogs in Antiquity.
3  Brewer, D, op cit.
4 Scott, J.P. et al. (1965). Dog Behavior: the Genetic Basis.
5 http://www.thepetprofessor.com/articles/article.aspx?id=265
6 Scott, J.P. op cit
7 Trut, L.N. (1999). Early Canid Domestication: The Farm-Fox Experiment, American Scientist, 87: 160-169.