Domestication of the dog

The domestication of the dog was the process which led to the domestic dog. This included the dog's genetic divergence from the wolf, its domestication, and the emergence of the first dogs. Genetic studies suggest that all ancient and modern dogs share a common ancestry, descending from an ancient, now-extinct wolf population – or closely related wolf populations – which was distinct from the modern wolf lineage. The dog's similarity to the grey wolf is the result of substantial dog-into-wolf gene flow, with the modern grey wolf being the dog's nearest living relative. An extinct Late Pleistocene wolf may have been the ancestor of the dog.

The dog is a wolf-like canid. The genetic divergence between the dog's ancestor and modern wolves occurred between 20,000 and 40,000 years ago, just before or during the Last Glacial Maximum (20,000–27,000 years ago). This timespan represents the upper time-limit for the commencement of domestication because it is the time of divergence but not the time of domestication, which occurred later.

One of the most important transitions in human history was the domestication of animals, which began with the long-term association between wolves and hunter–gatherers more than 15,000 years ago. The dog was the first species and the only large carnivore to have been domesticated. The domestication of the dog occurred due to variation among the common ancestor wolf population in the fight-or-flight response where the common ancestor with less aggression and aversion but greater altruism towards humans received fitness benefits. As such, the domestication of the dog is a prominent example of social selection rather than artificial selection. The archaeological record and genetic analysis show the remains of the Bonn-Oberkassel dog buried beside humans 14,200 years ago to be the first undisputed dog, but there are other disputed remains occurring 36,000 years ago. The oldest known dog skeletons were found in the Altai Mountains of Siberia and a cave in Belgium, dated ~33,000 years ago. According to studies, this may indicate that the domestication of dogs occurred simultaneously in different geographic locations.

The domestication of the dog predates agriculture, and it was not until 11,400 years ago in the Holocene era that people living in the Near East entered to relationships with wild populations of aurochs, boar, sheep, and goats. Where the domestication of the dog took place remains debated; however, literature reviews of the evidence find that the dog was domesticated in Eurasia, with the most plausible proposals being Central Asia, East Asia, and Western Europe. By the close of the most recent Ice Age 11,700 years ago, five ancestral lineages had diversified from each other and were represented through ancient dog samples found in the Levant (7,000 years before present YBP), Karelia (10,900 YBP), Lake Baikal (7,000 YBP), ancient America (4,000 YBP), and in the New Guinea singing dog (present day).

In 2021, a literature review of the current evidence infers that domestication of the dog began in Siberia 26,000-19,700 years ago by Ancient North Eurasians, then later dispersed eastwards into the Americas and westwards across Eurasia. This hypothesis is derived from when genetic divergences are inferred to have happened. Ancient dog remains dating to this time and place have not been discovered, but archaeological excavation in those regions is rather limited.

Genetic studies indicate that the grey wolf is the closest living relative of the dog. Attempting to reconstruct the dog's lineage through the phylogenetic analysis of DNA sequences from modern dogs and wolves has given conflicting results for several reasons. Firstly, studies indicate that an extinct Late Pleistocene wolf is the nearest common ancestor to the dog, with modern wolves not being directly ancestral to it. Secondly, the genetic divergence (split) between the dog's ancestor and modern wolves occurred over a short period of time, so that the time of the divergence is difficult to date (referred to as incomplete lineage sorting). This is complicated further by the cross-breeding that has occurred between dogs and wolves since domestication (referred to as post-domestication gene flow). Finally, there have been only tens of thousands of generations of dogs since domestication, so few mutations between dog and wolf have occurred; this sparsity makes the timing of domestication difficult to date.

The Late Pleistocene era was a time of glaciation, climate change, and the advance of humans into isolated areas. During the Late Pleistocene glaciation, a vast mammoth steppe stretched from Spain eastwards across Eurasia and over Beringia into Alaska and the Yukon. The close of this era was characterized by a series of severe and rapid climate oscillations with regional temperature changes of up to 16 °C (29 °F), which has been correlated with megafaunal extinctions. There is no evidence of megafaunal extinctions at the height of the Last Glacial Maximum (26,500 YBP), indicating that increasing cold and glaciation were not factors. Multiple events appear to have caused the rapid replacement of one species by another one within the same genus, or one population by another within the same species, across a broad area. As some species became extinct, so too did the predators that depended on them (coextinction).

The grey wolf is one of the few large carnivores to survive the Late Pleistocene megafaunal extinctions, but similar to many other megafaunal species it experienced a global population decline towards the end of this era, which was associated with extinctions of ecomorphs and phylogeographic shifts in populations. Grey wolf mitochondrial genomes (excluding the Himalayan wolf and the Indian plains wolf) indicate that the most recent common ancestor for all C. lupus specimens studied – modern and extinct – dates to 80,000 YBP, and this is more recent than the time suggested by the fossil record. The fossil record suggests that the earliest grey wolf specimens were found in what was once eastern Beringia at Old Crow, Yukon, in Canada and at Cripple Creek Sump, Fairbanks, in Alaska. The age is not agreed but could date 1 million YBP. All modern wolves (excluding the Himalayan wolf and the Indian plains wolf) show a most recent common ancestor dating to 32,000 YBP, which coincides with the commencement of their global demographic decline.