Domestic Dog

Lore & Background

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 Erralla dog 17,500 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 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 17,500 years ago.

Reader's Guide

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. The origin of dogs is couched in the biogeography of wolf populations that lived during the Late Pleistocene. The fossil record shows evidence of changes in the morphology and body size of wolves during the Late Pleistocene, which may be due to differences in their prey size.

Wolf skeletal development can be changed due to a preference for larger prey which results in larger wolves. Considerable morphological diversity existed among grey wolves by the Late Pleistocene. These are regarded as having been more cranio-dentally robust than modern grey wolves, often with a shortened rostrum, the pronounced development of the temporalis muscle, and robust premolars. It is proposed that these features were specialized adaptations for the processing of carcass and bone associated with the hunting and scavenging of Pleistocene megafauna.

Compared with modern wolves, some Pleistocene wolves showed an increase in tooth breakage that is similar to that seen in the extinct dire wolf. This suggests that these either often processed carcasses, or that they competed with other carnivores and needed to quickly consume their prey. The frequency and location of tooth fractures found in these wolves compared with the modern spotted hyena indicates that these wolves were habitual bone crackers.

These ancient wolves carried mitochondrial lineages which cannot be found among modern wolves, which implies that the ancient wolves went extinct. Grey wolves suffered a species-wide population bottleneck (reduction) approximately 25,000 YBP during the Last Glacial Maximum. This was followed by a single population of modern wolves expanding out of a Beringia refuge to repopulate the wolf's former range, replacing the remaining Late Pleistocene wolf populations across Eurasia and North America as they did so.

This source population probably did not give rise to dogs, but it admixed with dogs which allowed them to gain coat colour genes that are also related to immunity. There is little genetic information available on the ancient wolves that existed prior to the bottleneck.