Origin of the domestic dog

This article is about the origin of the domestic dog. For dog breeding, see Dog breeding.

DNA evidence indicates that the dog and the modern wolf (above) are both descendents of an extinct wolf-like canid that lived in Europe.
Some dog breeds, like this Tamaskan Dog, look very much like wolves due to admixture.
The 14,500 year old upper-right jaw found in Kesslerloch Cave, Switzerland is the sister to 2/3 of modern dogs (courtesy Hannes Napierala)

The origin of the domestic dog (Canis lupus familiaris or Canis familiaris) is not clear. Nuclear DNA evidence points to a single domestication 11,000–16,000 years ago that predates the rise of agriculture and implies that the earliest dogs arose along with hunter-gatherers and not agriculturists.[1] Mitochondrial DNA evidence points to a domestication 18,800–32,100 years ago and that all modern dogs are most closely related to ancient wolf fossils that have been found in Europe,[2][3] compared to earlier hypotheses which proposed origins in Eurasia as well as Eastern Asia.[4][5][6] The 2 recent genetic analyses indicate that the dog is not a descendant of the extant (i.e. living) gray wolf but forms a sister clade, that the ancestor is an extinct wolf-like canid and the dog's genetic closeness to modern wolves is due to admixture.[1][7]

The archaeological and morphological evidence from several ancient dog-like fossils, such as the 36,000 year old Goyet specimen from Belgium and the 33,000 year old Altai Mountains specimen from Central Asia, indicates that domestication may have begun earlier than the genetic evidence points to and arose in multiple locations.[8] It has been proposed that based on the morphological similarity between these and other early specimens compared to later prehistoric dogs dated to 15,000 years BP, that these specimens might have provided the stock from which dogs later evolved.[9]

Lineage

The direct ancestor of the dog has not yet been positively identified (see Genetic evidence below).
See under Wolf ancestry
See under Megafaunal wolf
See under Paleolithic dog

Genetic evidence

The development of molecular biology allows us to infer evolutionary relationships for species and to represent them in a phylogenetic tree, however these are not without their limitations.

There are three schools of thought on the origin of the dog.

Descendant of other canids that exist today

Within the Canidae, the results of allozyme and chromosome analyses suggest several phylogenetic divisions:

  1. The wolf-like canids, (genus Canis, Cuon and Lycaon) including the dog, gray wolf (Canis lupus), red wolf (Canis rufus), eastern wolf (Canis lycaon), coyote (Canis latrans), golden jackal (Canis aureus), Ethiopian wolf (Canis simensis), black-backed jackal (Canis mesomelas), side-striped jackal (Canis adustus), dhole (Cuon alpinus), and African wild dog (Lycaon pictus).[10]
  2. The fox-like canids, which include the swift fox (Vulpes velox), kit fox (Vulpes macrotis), red fox (Vulpes vulpes), Cape fox (Vulpes chama), Arctic fox (Alopex lagopus), and fennec fox (Fennecus zerda).[10]
  3. The South American canids, including the bush dog (Speothos venaticus), hoary fox (Lycalopex uetulus), crab-eating fox (Cerdocyon thous) and maned wolf (Chrysocyon brachyurus).[10]
  4. monotypic taxon, including the bat-eared fox (Otocyon megalotis), gray fox (Urocyon cinereoargenteus), and raccoon dog (Nycteruetes procyonoides).[10]

These phylogenetic relationships imply that the dog has several close relatives within its genus, in fact, all members of Canis can produce fertile hybrids and several species may have genomes that reflect hybridization in the wild.[11] Charles Darwin speculated in On the Origin of Species that given the vast morphological variation across numerous breeds, dogs must have had more than one wild ancestor.[12] Therefore, it was once thought possible that the dog could have been a descendant of a number of canids that exist today—similar to the Coyote-Wolf-Dog hybrid found among some Eastern Coyotes[13]—until DNA analysis indicated otherwise.

Descendant of a wolf that exists today

It has been thought for some time that "... the wolf is the most probable ancestor and closest relative of the domestic dog."[14]:54 By 1993 with advancements in molecular biology, the mitochondrial DNA mtDNA analysis of extant (i.e., living today) Canidea species indicated that "The domestic dog is an extremely close relative of the gray wolf, differing from it by at most 0.2% of mtDNA sequence.... In comparison, the gray wolf differs from its closest wild relative, the coyote, by about 4% of mitochondrial DNA sequence."[15] In the same year, the domestic dog Canis familiaris was reclassified as Canis lupus familiaris, a subspecies of the gray wolf Canis lupus in Mammal Species of the World.[16] In 1995, research indicated that the wolf may have been the ancestor of the dog.[17] By 1999, further genetic analysis indicated that the domestic dog may have emerged from multiple wolf populations.[18][19] Based on these pieces of research and the reference reclassification, Canis lupus familiaris is the name for the taxon listed by ITIS.[20] However, Canis familiaris is also accepted due to a nomenclature debate regarding the naming of wild and domestic sub-species.[21]

Descendant of an extinct wolf-like canid

The wolf-like canids that exist today comprise genus Canis, genus Cuon and genus Lycaon. These include the dog, gray wolf (Canis lupus), red wolf (Canis rufus), eastern wolf (Canis lycaon), coyote (Canis latrans), golden jackal (Canis aureus), Ethiopian wolf (Canis simensis), black-backed jackal (Canis mesomelas), side-striped jackal (Canis adustus), dhole (Cuon alpinus), and African wild dog (Lycaon pictus).[10]

Location of the first domestication

In 1997, a study determined that domestic dogs could have originated as much as 135,000 years ago.[22] This was determined by using mitochondrial DNA (mtDNA). However, this number could potentially be overinflated due to the possibility of unobserved multiple substitutions at hypervariable sites.[22] These hypervariable sites are mutational hotspots where somatic mitochondrial DNA and germline mutations usually take place.[23] Though this number of 135,000 years may not be completely accurate, it still gives the indication that domesticated dogs have been around for longer than 14,000 years, which was previously suggested by archaeological evidence.[22]

In 2002, a study examined the mitochondrial DNA sequence variation among 654 domestic dogs representing all major dog populations worldwide. All sequences belonged to three phylogenetic groups universally represented at similar frequencies, suggesting a common origin from a single gene pool for all dog populations. A larger genetic variation in East Asia than in other regions and the pattern of phylogeographic variation suggested an East Asian origin for the domestic dog around 15,000 years ago.[24]

In 2009, a study of African dogs sampled 318 village dogs from 7 regions in Egypt, Uganda, and Namibia, measuring genetic diversity >680 bp of the mitochondrial D-loop, 300 SNPs, and 89 microsatellite markers. This study found a high level of mtDNA diversity in African dogs.[25] Later in 2009, a study analyzed entire mitochondrial genomes for 169 dogs to obtain maximal phylogenetic resolution and the control region for 1,543 dogs across the Old World for a comprehensive picture of geographical diversity. The analyses showed that dogs universally share a common homogenous gene pool containing 10 major haplogroups. However, the full range of genetic diversity, all 10 haplogroups, was found only in southeastern Asia south of Yangtze River, and diversity decreased following a gradient across Eurasia, through seven haplogroups in Central China and five in North China and Southwest Asia, down to only four haplogroups in Europe. The mean sequence distance to ancestral haplotypes indicates an origin 5,400–16,300 years ago (ya) from at least 51 female wolf founders.[26]

In 2010, a study conducted an extensive genome-wide survey of more than 48,000 single nucleotide polymorphisms in dogs and their wild progenitor, the grey wolf. It showed that dog breeds share a higher proportion of multi-locus haplotypes unique to grey wolves from the Middle East, indicating that they are a dominant source of genetic diversity for dogs rather than wolves from East Asia, as suggested by mitochondrial DNA sequence. This indicates the Middle East as the source of domestication.[27] In 2011, a study analyzed 14 437 bp of Y-chromosome DNA sequence in 151 dogs sampled worldwide. It found 28 haplotypes distributed in five haplogroups. Two haplogroups were universally shared and included three haplotypes carried by 46% of all dogs, but two other haplogroups were primarily restricted to East Asia. Highest genetic diversity and virtually complete phylogenetic coverage was found within Asia south of the Yangtze. The 151 dogs were estimated to originate from 13–24 wolf founders, but there was no indication of post-domestication dog–wolf hybridisations. Thus, Y-chromosome and mtDNA data give strikingly similar pictures of dog phylogeography, most importantly that roughly 50% of the gene pools are shared universally but only Asia south of the Yangtze has nearly the full range of genetic diversity, such that the gene pools in all other regions may derive from Asia south of the Yangtze. This corroborates that Asia south of the Yangtze was the principal, and possibly sole region of wolf domestication, that many wolves were domesticated, and that later dog–wolf hybridisation contributed modestly to the dog gene pool.[28]

In 2011, a study looked at skulls from the Gravettian Předmostí site in the Czech Republic. Three were dated to 24,000 and 27,000 years old and identified as Palaeolithic dogs, characterized by short skull lengths, short snouts, and wide palates and braincases relative to wolves. One complete skull could be assigned to the group of Pleistocene wolves. Three other skulls could not be assigned to a reference group; these might be remains from hybrids or captive wolves.[29]

Wayne studies

33,000 year old skull of a dog-like canid found in the Altai Mountains. It has no descendants today

In 1934, an eminent paleontologist indicated that the ancestor of the dog lineage may have been an extinct Canis lupus.[30] In 1999, Robert K Wayne emphasized that while molecular genetic data seem to support the origin of dogs from wolves, dogs may have descended from a now extinct species of canid whose closest living relative was the wolf.[18] Between March 2013 and January 2014, three studies were released that undertook similar investigation using the same or similar samples and each had Wayne as a senior author. These studies appear to have validated Wayne's original hypothesis.

Druzhkova et al.

In March 2013, a study[31] isolated, sequenced and analysed 413 nucleotides of the mitochondrial control region of ancient DNA from the well-preserved 33,000-year old skull of a dog-like canid that was excavated from Razboinichya Cave in the Altai Mountains of southern Siberia (Central Asia) in 1975. The sample was deposited in GenBank with accession number JX173682 and classified as Canis lupus familiaris (dog). The sample was compared with those of 72 extant dogs and 30 wolves (17 Old World and 13 New World), 35 prehistoric New World canids (including 2 from the Beringian wolf), and 4 coyotes. The sample was also compared to 3 ancient wolf teeth also found in the cave (32,500 BP, 48,000 BP and 50,000 BP). "The analyses revealed that the unique haplotype of the Altai dog is more closely related to modern dogs and prehistoric New World canids than it is to contemporary wolves... This preliminary analysis affirms the conclusion that the Altai specimen is likely an ancient dog with shallow divergence from ancient wolves. These results suggest a more ancient history of the dog outside of the Middle East or East Asia." The haplotype groups closest to the Altai dog included such diverse breeds as the Tibetan Mastiff, Newfoundland, Chinese Crested, Cocker Spaniel and Siberian Husky. The study also stated "We stress the point that these analyses were limited to a single, maternally inherited locus and more sequence data would be needed to obtain a statistically well-supported phylogeny and unambiguously resolve the genetic relationship of the Altai specimen....More data of prehistoric wolves from the same region are needed to estimate the population diversity and obtain a more comprehensive picture of genetic relationships of the Altai canid."

One of the team members of this study had conducted an earlier study,[8] which used Accelerator Mass Spectrometry radiocarbon dating independently conducted through 3 laboratories located in Tucson, Arizona (USA), Oxford (UK), and Groningen (the Netherlands) to derive an age of 33,000-years for the well-preserved skull and left mandible of the Altai dog. The morphology was compared to the skulls and mandibles of large Pleistocene wolves from Predmosti, Czech Republic dated 31,000 BP, modern wolves from Europe and North America, and prehistoric Greenland dogs from the Thule period (1,000 BP or later) to represent a large-sized but unimproved fully domestic dogs. The morphologies best matched the Greenland dogs and not the ancient nor modern wolves. However, the lower carnassial tooth fell within the lower range of values for prehistoric wolves and was only slightly smaller than modern European wolves, and the upper carnassial tooth fell within the range of modern wolves. "We conclude, therefore, that this specimen may represent a dog in the very early stages of domestication, i.e. an incipient dog, rather than an aberrant wolf... The Razboinichya Cave specimen appears to be an incipient dog that did not give rise to late Glacial – early Holocene lineages and probably represents wolf domestication disrupted by the climatic and cultural changes associated with the Last Glacial Maximum. The two earliest incipient dogs from Western Europe (Goyet, Belgium) and Siberia (Razboinichya), separated by thousands of kilometers, show that dog domestication was multiregional, and thus had no single place of origin (as some DNA data have suggested) and subsequent spread."

Thalmann et al.

In November 2013, a study[2] analysed the complete and partial mitochondrial genomes of 18 fossil canids dating from 1,000 to 36,000 years ago from the Old and New Worlds, and compared these with the complete mitochondrial genome sequences from 49 modern wolves and 77 modern dogs—including divergent dog breeds, such as the Basenji and Dingo—3 recently published Chinese indigenous dogs, and 4 coyotes totaling 148 mitochondrial genomes. Mitochondrial DNA was analyzed because there is a higher abundance of mitochondrial than nuclear DNA available from ancient specimens. The data indicate that 22% (17 of 77) of the dogs sampled are sister to modern wolves from Sweden and the Ukraine with a most recent common ancestor 9,200 years ago (else the mitochondrial genome introgressed from wolves, as dogs were clearly domesticated by this time), and 78% (60 of 77) are sister to one or more ancient canids from Europe. Some 12% (9 of 77) of the dogs are sister to two morphologically distinct ancient dogs from Germany, one 14,700 years old from Bonn-Oberkassel (GenBank accession number KF661093) and one 12,500 years old from the Kartstein cave (KF661094) with a most recent common ancestor 16,000–24,000 years ago. [Note: the study's Figure 1 shows the Phylogenetic relationships and indicates that this most recent common ancestor was also dog-like, and separated from what was to become the ancestor of many of the modern Eurasian wolf lines at 24,000–31,000 years ago.] Some 3% (2 of 77) of the dogs are sister to the 14,500 year old wolf sequence from the Kesslerloch cave in Switzerland (KF661087) with a most recent common ancestor 18,300 years ago. They are also distantly rooted in the same sequence as the Altai dog, however the study does not support its recent common ancestry with most modern dogs. Some 64% (49 of 77) of the dogs are sister to another 14,500-year-old wolf sequence also from the Kesslerloch cave in Switzerland (KF661091) with a most recent common ancestor 32,100 years ago. This group of dogs matches 3 fossil pre-Columbian New World dogs between 1,000 and 8,500 years old. Matching these 3 to the 49 relatives indicates a most recent common ancestor 18,800 years ago, which supports the hypothesis that pre-Columbian dogs in the New World share ancestry with modern dogs. Thus, these dogs likely arrived with the first humans to the New World. The early dog population appears to have undergone a population bottle-neck (decrease) between 5,000 and 2,000 years ago, followed by a sharp increase that parallels the trajectory of the human population.

Three haplotypes from ancient Belgium canids (Belgium 36,000 years BP cataloged as Canis species KF661079 and Belgium 30,000 and 26,000 years BP cataloged as Canis lupus KF661080 KF661078) form the most diverging group. Although the cranial morphology of the Goyet dog (Belgium 36,000) has been interpreted as dog-like, it's mtDNA relation to other canids places it as an ancient sister-group to all modern dogs and wolves rather than a direct ancestor. Belgium 26,000 has been found to be uniquely large and could be related to a distinct genetically and morphologically form of wolves from Late Pleistocene deposits in the High Arctic permafrost. However, none of the sequences from three northerly permafrost wolves (dated at 28,000 years BP, 21,000 years BP, and 20,800 years BP and classified as Canis lupus KF661088, KF661089, KF661090) fall within or are sister to this Belgium clade. The Belgium canids may represent a phenotypically distinct and not previously recognized population of gray wolf, or the 36,000-year-old Goyet dog from Belgium and the 33,000-year-old Altai Mountain dog from Russia (catalogued as Canis lupus familiaris – dog JX173682), may represent aborted domestication episodes.

The data from this study indicate an association of modern dogs with ancient European canids and some with modern European wolves, with no close affinity to modern wolves from the Middle East or East Asia. This suggests the origin of dogs from Europe, rather than the Middle East or East Asia, as previously suggested. Additionally, there are no ancient dog remains from these regions older than 13,000 years. Divergence times implies a European origin of the domestic dog dating 18,800–32,100 years ago, which supports the hypothesis that dog domestication preceded the emergence of agriculture and occurred in the context of European hunter-gatherer cultures. An evolutionary scenario consistent with these results is that dog domestication was initiated close to the Last Glacial Maximum when hunter-gatherers preyed on megafauna.[32][33]

The co-senior author of the study, Robert K Wayne, stated that:

"But if domestication occurred in association with hunter-gatherers, one can imagine wolves first taking advantage of the carcasses that humans left behind – a natural role for any large carnivore – and then over time moving more closely into the human niche through a co-evolutionary process. The idea of wolves following hunter-gatherers also helps to explain the eventual genetic divergence that led to the appearance of dogs. Wolves following the migratory patterns of these early human groups would have given up their territoriality and would have been less likely to reproduce with resident territorial wolves. We have an analog of this process today, in the only migratory population of wolves known existing in the tundra and boreal forest of North America. This population follows the barren-ground caribou during their thousand-kilometer migration. When these wolves return from the tundra to the boreal forest during the winter, they do not reproduce with resident wolves there that never migrate. We feel this is a model for domestication and the reproductive divergence of the earliest dogs from wild wolves. We know also that there were distinct wolf populations existing ten of thousands of years ago. One such wolf, which we call the megafaunal wolf, preyed on large game such as horses, bison and perhaps very young mammoths. Isotope data show that they ate these species, and the dog may have been derived from a wolf similar to these ancient wolves in the late Pleistocene of Europe....A dog from Belgium dates back approximately 36,000 years, and a group of dogs from Western Russia is approximately 15,000 years old." [3]
Freedman et al.

In January 2014, a study[1] analysed using a number of tests the 10 million single-nucleotide variant sites from whole-genome data generated for six unique canid lineages. These data include whole-genome sequences of:

  • Three individual wolves (Canis lupus) to represent the broad regions of Eurasia where domestication has been hypothesized to have taken place – Croatia (Europe), Israel (Middle-East), and China (East/South-East Asia).
  • An Australian dingo and a basenji, being divergent lineages to the reference boxer genome (that is available from GenBank with accession number AAEX01000000) and so maximize the odds to capture distinct alleles present in the earliest dogs. These lineages are also geographically distinct, with modern basenjis tracing their ancestry to hunting dogs of western Africa, while dingoes are free-living semi-feral dogs of Australia that arrived there at least 3,500 years ago. The natural range of wolves has never extended this far south and due to geographic isolation, they are less likely to have overlapped and admixed with wolves in the recent past. For some analyses, data were leveraged from a companion study of 12 additional dog breeds.
  • A golden jackal (Canis aureus) to infer the ancestral state of variants arising in dogs and wolves.[1]

The data provided significant evidence of admixture between the Israeli wolf and the basenji, the Israeli wolf and the boxer, and between the Chinese wolf and dingo. The Chinese wolf with dingo likely represents ancient admixture in Eastern Eurasia, and the Israeli wolf with Basenji and Boxer likely represents ancient admixture in Western Eurasia. The fact that these lineages have been geographically isolated from wolves in the recent past suggests that this gene flow was ancestral and has likely affected most dog lineages. There was significant gene flow between the golden jackal and the Israeli wolf, as well as the population ancestral to the dog and wolf samples.[1]

One test indicated that dogs and modern wolves form monophyletic sister clades i.e. the dog is a sister to the modern wolf and they share a common ancestor. Supporting this, another test indicated that none of the sampled wolf populations is more closely related to dogs than any of the others, and dogs diverged from wolves at about the same time as wolves diverged from each other. This implies that the wolf population(s) from which dogs originated has gone extinct and the current wolf diversity from each region represents novel, younger wolf lineages.[1]

The data indicate that the golden jackal and the ancestor of the wolf/dog diverged 400,000 years ago. Dogs and wolves then diverged 14,900 years ago. The 3 wolf populations diverged from each other 13,400 years ago. The dog populations diverged from each other not long after, with the Dingo at 12,800 years ago and divergence between the boxer and the basenji at 12,100 years ago. There was a 16-fold population bottleneck for dogs since divergence.[1]

(Two studies have found evidence of a human population bottleneck (i.e. loss of genetic diversity) in Europe assessed as occurring somewhere between 17,000–43,000 years ago[34] and between 10,000–60,000 years ago[35] that the researchers attribute to a large human migration out of Europe towards Asia. This implies that humans migrated out of Europe at the end of the Last Glacial Maximum and may have taken dogs with them, resulting in a bottleneck being observed in both populations and the spread of dogs across Eurasia.)

There was a 3-fold population decline for the 3 wolf samples since divergence, and appears to have occurred well in advance of direct extermination campaigns by humans and within the timeframe of environmental and biotic changes associated with the ending of the Pleistocene era i.e. changes in climate and prey, including megafaunal extinctions. This indicates that before the divergence of dogs from wolves that there was much more wolf diversity. The results support a recent divergence between dogs and wolves followed by a dramatic reduction in population size.[1]

The AMY2B (Alpha-Amylase 2B) is a gene that codes a protein that assists with the first step in the digestion of dietary starch and glycogen. An expansion of this gene in dogs would enable early dogs to exploit a starch-rich diet as they fed on refuse from agriculture. Data indicated that the wolves and Dingo had just 2 copies of the gene, the Siberian Husky that is associated with hunter-gatherers had just 3–4 copies, whereas the Saluki that is associated with the Fertile Crescent where agriculture originated had 29 copies. The results show that on average, modern dogs have a high copy number of the gene whereas wolves and dingoes do not. The high copy number of AMY2B variants likely already existed as a standing variation in early domestic dogs, but expanded more recently with the development of large agriculturally based civilizations. This suggests that at the beginning of the domestication process, dogs may have been characterized by a more carnivorous diet than their modern-day counterparts, a diet held in common with early hunter-gatherers.[1]

The divergence time between dogs and wolves is estimated to have occurred between 11,000 and 16,000 years ago. Other recent studies place the divergence between 11,000 to 32,000 years ago (depending on the mutation-rate assumptions used), however all of the studies place the divergence prior to the adoption of extensive agriculture by humans. This finding raises questions regarding the hypothesis that the advent of agriculture created a novel niche that was the driving force for dog domestication.[1][36]

The co-senior author of the studies, Robert K Wayne, stated that:

"The common ancestor of dogs and wolves was a large, wolf-like animal that lived between 9,000 and 34,000 years ago. Based on DNA evidence, it lived in Europe."[7]

Morphological evidence

Institution specimens

Specimen references used under this topic relate to the following institutions:
MAE RAS – Museum of Anthropology and Ethnography (Kunstkamera), Russian Academy of Science, Saint-Petersburg
PM NASU – Palaeontological Museum National Academy of Science of Ukraine, Kiev
RBINS – Royal Belgian Institute of Natural Sciences
ZIN RAS – Zoological Institute of the Russian Academy of Science, Saint-Petersburg

Paleolithic "dog"

In 2002, a study looked at 2 fossil skulls of large canids (references: MAE RAS 447 and ZIN RAS 23781) dated at 13,905 years BP that had been found buried within metres of what was once a mammoth-bone hut at the Upper Paleolithic site of Eliseevichi 1 in the Brayansk region of central Russia, and using an accepted morphologically-based definition of domestication declared them to be "Ice Age dogs".[37]

In 2009, a study looked at these 2 prehistoric dog skulls in comparison to much earlier Late Pleistocene but morphologically similar fossil skulls that had been found across Europe, and proposed the much earlier specimens were "Paleolithic dogs" that were morphologically and genetically distinct from the Pleistocene wolves living in Europe at that time. The study looked at 117 skulls of recent and fossil large canids. Several skulls of fossil large canids from sites in Belgium, the Ukraine and Russia were examined using multivariate techniques to look for possible evidence of the presence of Paleolithic "dogs" that were separate from Pleistocene wolves. Reference groups constituted of the prehistoric dogs, and recent wolves and dogs. The osteometric analysis of the skulls indicated that the Paleolithic dogs fell outside the skull ranges of the Pleistocene wolf group and the modern wolf group, and were closer related to those of the prehistoric dog group. The fossil large canid from Goyet, Belgium (RBINS 2860), dated at 31,700 BP was clearly different from the recent wolves, resembling most closely the Eliseevichi 1 prehistoric dogs. Thus it is identified as a Paleolithic dog, suggesting that dog domestication had already started during the Aurignacian. The two Epigravettian Mezin, Ukraine (PM NASU 5490) and Mezhirich, Ukraine (PM NASU 4493) skulls are also identified as being Paleolithic dogs. Collagen analysis indicated that the Paleolithic dogs associated with human camp-sites (Eliseevichi 1, Mezin and Mezhirich) had been specifically eating reindeer, while other predator species in those locations and times had eaten a range of prey.[9]

In 2013, a study recalibrated the age of the Eliseevichi 1 specimens to 15,000 BP with the genetic analysis of one skull deposited in GenBank with accession number KF661082 and classified as Canis lupus familiaris (dog). The Goyet specimen was recalibrated to 36,000 years BP and cataloged as Canis species KF661079.[2]

Morphology

In comparison to the Pleistocene wolf, the Paleolithic dog had a short skull length, short snout, a wide palate and braincase, relatively short and massive jaws, and a shorter carnassial length but these were larger than the modern dog. The mandible of the Paleolithic dog is more massive compared to the elongated mandible of the wolves, and presents a high frequency of crowded premolars and of a hook-like extension of the caudal border of the coronoid process. The Paleolithic dog had a mean body mass of 36–37 kg compared to Pleistocene wolves 42–44 kg and recent European wolves 41–42 kg.[9]

Relationship to the domestic dog

Recently, a major Mitochondrial DNA study has found that divergence times from wolf to dog implies a European origin of the domestic dog dating 18,800–32,100 years ago, which supports the hypothesis that dog domestication preceded the emergence of agriculture and occurred in the context of European hunter-gatherer cultures.[2]

It has been proposed that based on the genetic evidence of the timeline and European location, the archaeological evidence of the Paleolithic dog remains being found at known European hunting camp-sites, and based on morphology and collagen analysis that their diet had been restricted, the Paleolithic dog was domesticated. It has been further proposed that the Paleolithic dog may have provided the stock from which early dogs came from.[9]

There has been an ongoing debate in the scientific press about what the fossil remains of the Paleolithic "dog" might be, with some commenters declaring them as either wolves or a unique form of wolf. These include a first article proposing the Paleolithic dog,[9] its refutation,[38] a counter to the refutation,[39] a second article,[40] its refutation,[41] a third article that includes a counter to the refutation,[42] its refutation,[43] a counter to the refutation,[44] and another refutation.[45]

As the ancestor of the dog has not been positively identified by scientists, this debate continues.

Archaeological evidence

Archaeology locates the first dog and human remains together in the Gravettian period (i.e. somewhere between 32,000–22,000 BP), however dog-like canid fossils have also been found at Goyet (36,000 BP) and Altai (33,500 BP) in the Aurignacian period.

Years BP Location Finding
200,000 Zhoukoudian cave system, China Small, extinct wolf skulls – Canis lupus variabilis. The skull differs from the typical wolf in much smaller size with a more slender muzzle and noticeably reduced or absent sagittal crest. In addition, the lower border of some Canis lupus variabilis mandibles is "strongly convex as in the dog".[30]:15 More recent researchers have proposed that Canis lupus variabilis may be an ancestor of the dog lineage.[46][47]:7 At the site, the small wolf's remains were in close proximity to Homo erectus pekinensis or Peking man.
36,000 Goyet Cave, Samson River Valley, Belgium Dog-like skull (RBINS 2860). The skull was found in a side gallery of the cave, together with remains from mammoth, lynx, red deer and large canids. The Goyet skull is very similar in shape to Eliseevich I dog skulls (15,000 BP) and to the Epigravettian Mezin 5490 and Mezhirich dog skulls (13,500 BP), which are about 18,000 years younger. Palaeolithic artifacts in this system of caves date from the Mousterian, Aurignacian, Gravettian, and Magdalenian, which indicates recurrent occupations of the cave from the Pleniglacial until the Late Glacial.[9] No descendants, genetic classification of species is inconclusive.[2]
33,500 Razboinichya Cave, Altai Mountains, Central Asia (Russia) Dog-like skull, mandibles (both sides) and teeth. Specimen is unlike ancient and modern wolves but similar to fully domesticated prehistoric dogs from Greenland (about 1,000 years BP) and the putative dogs from Eliseevichi I site in central Russia.[31] No modern descendants, the morphological classification is that of a dog, the genetic classification of the species is inconclusive – it is not clear if it is a dog or a wolf.[2]
32,500 Western Europe Based on genetic analysis, the estimated date that the line of most modern dogs and the ancient wolf remains found in Kesslerloch Cave, near Switzerland’s northern border with Germany and dated 14,500 BP, parted from the most recent common ancestor – a large, wolf-like canid.[2] The fossil of this ancestor has yet to be found.
32,000–22,000 Predmostí, Moravia, Czech Republic Three skulls. Predmostí is a Gravettian site (32,000–22,000 BP). The skulls were found in the human burial zone and identified as Palaeolithic dogs, characterized by – compared to wolves – short skulls, short snouts, widepalates and braincases, and even-sized carnassials. For one skull, "a large bone fragment is present between the upper and lower incisors that extends several cm into the mouth cavity. The size, thickness and shape of the fragment suggest that it could be a fragment of a bone of a large mammal, probably from a mammoth. The position of the bone fragment in the mouth and the articulated state of the lower jaw with the skull indicate that this mammoth bone fragment was inserted artificially into the mouth of the dog post-mortem." Wolf skulls were also found at the site. The presence of dogs buried with humans at this Gravettian site corroborates the hypothesis that domestication began long before the Late Glacial.[29][48]
26,000 Chauvet cave, Vallon-Pont-d'Arc, Ardèche region, France 50-metre trail of footprints made by a boy of about ten years of age alongside those of a large canid. The size and position of the canid's shortened middle toe in relation to its pads indicates a dog rather than a wolf. The footprints have been dated by soot deposited from the torch the child was carrying. The cave is famous for its cave paintings.[49]
15,000 Eliseevich I site, Russian Plain, Russia Two fossil dog skulls (references: MAE RAS 447 and ZIN RAS 23781). In 2002, a study looked at the fossil skulls of 2 large canids that had been found buried within metres of what was once a mammoth-bone hut at the Upper Paleolithic site of Eliseevichi 1 in the Brayansk region of central Russia, and using an accepted morphologically-based definition of domestication declared them to be "Ice Age dogs".[37] The most complete dog skull was found in a hearth deposit, near a concentration of mammoth skulls. Its braincase has been perforated on the left and right side. Cut marks are present on the zygomatic and frontal bones. With exception of the canines and some premolars, all its teeth are missing. In addition the left and right carnassials were apparently removed by damaging the alveoli. The Eliseevich I skulls are very similar in shape to the Goyet skull (36,000 BP) and to the Epigravettian Mezin 5490 and Mezhirich dog skulls (13,500 BP). The remains of at least eight mammoth bone complexes and large quantities of worked ivory were discovered at this site.[9] Genetic analysis of one skull was deposited in GenBank with accession number KF661082 and classified as Canis lupus familiaris (dog).[2] See Paleolithic dog.
14,700 Bonn-Oberkassel, Germany Ancient dog mandible. Directly associated with a human double-grave of a 50-year-old man and a 20-25-year-old woman.[50] Genetic analysis deposited in GenBank with accession number KF661093 and classified as Canis lupus familiaris (dog).[2]
13,500 approx Mezin, Ukraine Ancient dog skull (PM NASU 5490) as well as ancient wolf specimens found at the site. Dated to the Epigravettian period (17,000–10,000 BP). The Mezin skull is very similar in shape to the Goyet skull (36,000 BP), the Eliseevich I dog skulls (15,000) and Mezhirich dog skull (13,500 BP). The Epigravettian Mezin site is well known for its round mammoth bone dwelling.[9]
13,500 approx Mezhirich, Ukraine Ancient dog skull (PM NASU 4493). Dated to the Epigravettian period (17,000–10,000 BP). The Mezhirich skull is very similar in shape to the Goyet skull (36,000 BP), the Eliseevich I dog skulls (15,000) and Mezin dog skull (13,500 BP). The Epigravettian Mazhirich site has four mammoth bone dwellings present.[9]
12,500 Karstein cave, Germany Ancient dog skull. Genetic analysis deposited in GenBank with accession number KF661094 and classified as Canis lupus familiaris (dog).[2]
12,000 Yakutia, Siberia Mummified carcass. The "Black Dog of Tumat" was found frozen into the ice core of an oxbow lake steep ravine at the middle course of the Syalaah River in Ust-Yana region. DNA analysis confirmed it as an early dog.[51]
12,000 Bin Mallaha (Eynan) and Hayonim terrace, Israel Three canid finds. A diminutive carnassial and a mandible, and a wolf or dog puppy skeleton buried with a human during the Natufian culture.[52]
9,200 Texas, USA Dog bone fragment. Found in Hinds Cave in southwest Texas. DNA analysis confirms the bone was from a dog whose ancestry was rooted in Eurasia.[53]
7,800 Jiahu site, China Eleven dog internments. Jaihu is a Neolithic site 22 kilometers north of Wuyang in Henan Province.[54]
7,425 Baikal region, Siberia, Russia Dog buried in a human burial ground. Additionally, a human skull was found buried between the legs of a "tundra wolf" dated 8,320 BP (but it does not match any known wolf DNA stored in Genbank). The evidence indicates that as soon as formal cemeteries developed in Baikal, some canids began to receive mortuary treatments that closely paralleled those of humans. One dog was found buried with four red deer canine pendants around its neck dated 5,770 BP. Many burials of dogs continued in this region with the latest finding at 3,760 BP, and they were all buried laying on their right side, and faced towards the east as did their humans. Some were buried with artifacts, e.g., stone blades, birch bark and antler bone.[55]
5,250 Skateholm, Sweden Cemeteries contained dogs among humans. A dog burial with an antler headdress and three flint blades was recovered at one of the sites.[56]

Domestication

See also differences from wolves
Polychrome cave painting of a wolf-like canid painted 17,000 years ago, Font-de-Gaume, France.

Theory

The theory of dog domestication is based on a comparison between the dog and extant (i.e. living today) gray wolves, however one study highlighted a number of inconsistencies with this comparison and proposed that the ancestor of the dog appears more likely to have been a generalist canid and not the specialized gray wolf.[47] Another study proposed that the ancestor of Canis familiaris was a wild "Canis familiaris".[57] A genetic study recently indicated that the ancestor of the dog was not the extant gray wolf and that the fossil remains of the "wolf-like canid" ancestor have yet to be found.[2] Readers should be aware of this inconsistency with the theory before progressing further into this topic.

Definition

Domestication is an evolutionary process in which one population of a species is reproductively isolated from another intentionally by humans.[58] This reproductive isolation leads to an divergent adaptation and results in a specialization process. As a result of the changes in the selection pressures on the given species, the process of domestication produces evolutionary changes in certain aspects of the characteristic behavior of the domesticated species just as it affects the anatomy and morphology of the certain species as well. For example, such behavioral change in dogs is the decreased level of aggression, which is manifested in morphological changes such as teeth size.[59]

Self domestication

The first of the two main hypotheses of dog domestication is self-domestication by wolves. Some wolves moved into a symbiotic relationship with prehistoric humans. They scavenged on the remains of the prey animals left by the prehistoric people at the human settlements or the kill sites. Those wolves that were less anxious and aggressive thrived, continued to follow the prehistoric humans and colonized the human-dominated environments, generation after generation. Gradually, the first primate dogs emerged from this group.[60][61][62]

Free will and powerful emotions

"The dog could have arisen only from animals predisposed to human society by lack of fear, attentiveness, curiosity, necessity, and recognition of advantage gained through collaboration....were not biological Audio-Animatronics born with a preprogrammed response...It is fair, I think, to say that the humans and wolves involved in the conversion were sentient, observant beings constantly making decisions about how they lived and what they did, based on the perceived ability to obtain at a given time and place what the needed to survive and thrive. They were social animals willing, even eager, to join forces with another animal to merge their sense of group with the others' sense and create an expanded super-group that was beneficial to both in multiple ways. They were individual animals and people involved, from our perspective, in a biological and cultural process that involved linking not only their lives but the evolutionary fate of their heirs in ways, we must assume, they could never have imagined. Does this thesis project too much self-awareness into the past? I doubt it. Powerful emotions were in play that many observers today refer as love – boundless, unquestioning love."[63]:40

Cooperation

A genetic study has found a dog-wolf divergence time of greater than 15,000 years ago. An evolutionary scenario consistent with these results is that dog domestication was initiated close to the Last Glacial Maximum when hunter-gathers preyed on megafauna. Conceivably, proto-dogs might have taken advantage of carcasses left on site by early hunters, assisted in the capture of prey, or provided defense from large competing predators at kills.[2]

Socialisation

Some researchers argue that those wolves that were more successful at interacting with humans would pass these traits on to their offspring, eventually creating wolves with a greater propensity to be domesticated. The behavioral characteristic called "flight distance" represents how close an animal will allow humans (or anything else it perceives as dangerous) to get before it runs away. Animals with shorter flight distances will linger and feed when humans are close by. This behavioral trait would have been passed on to successive generations, and amplified, creating animals that are increasingly more comfortable around humans. To be able to eat in the presence of human beings is something that wild wolves can't do.[64] The "most social and least fearful" wolves were the ones who were kept around the human living areas, helping to breed those traits that are still recognized in dogs today.[65][66]

Against this proposition, wolves have been scavenging around human living areas, noted in Israel and Italy for centuries, without demonstrating any move towards domestication.[63]

Human domestication

The second of the two main hypotheses of dog domestication is domestication by humans. Paleolithic people actively selected wolf pups for several reasons: they could be used as pets, they could be kept for utilitarian, ceremonial and symbolic uses, as social storage, or combat and/or as living tools.[62][67][68][69][70] The most docile or interesting animals could have been permitted to reproduce.[68][69][71] After several generations of unconscious and later of conscious selection of human-defined behavioral traits, the first dogs emerged.[72]

Orphaned wolf-pups

Studies have shown that some wolf pups taken at an early age and reared by humans are easily tamed and socialized,[14]:140 and one study has demonstrated that adult wolves can be socialized.[14]:141 Some researchers propose that humans adopted orphaned wolf pups and breastfed them alongside human babies.[65][73] In Alaska and other northern areas where people still live close to wolves, wolf pups are sometimes captured and some become acceptable as pets or sled dogs, and once these breeding over generations would become more dog-like.[14]:pages55-56

Against this proposition, other researchers attempting to socialize wolf pups after they reach 21 days of age found it very time-consuming and seldom practical or reliable in achieving success.[74]

Human selection

See also: Dog breeding

The "farm fox" experiment attempted to reenact how domestication may have occurred.[75] Researchers, working with farmed silver foxes selectively bred over 35 generations and 40 years for "tameability". The "domestic elite" foxes were tamer to humans than others but they also showed new physical traits even though the physical traits were not originally selected for. These include spotted or black-and-white coats, floppy ears, tails that curl over their backs, the barking vocalization and earlier sexual maturity. One researcher found that the migration of certain melanocytes (which determine colour) was delayed, resulting in a black and white 'star' pattern.

One criticism of this experiment was later made by the author, who stated that the living conditions of the foxes in the farm would have been very different to those of wolf puppies in Paleolithic camps.[76] A further criticism based on information obtained after the experiment's publication is that the definition of "tame" was changed at least once during the experiment, and that some of the foxes that were classified as neither tame nor aggressive also exhibited these changes, indicating that some factor other than human selection for tameness may have been at work during domestication.[63] When humans restrict dog's breeding diversity, another variable also comes into play that may have contributed to the change – inbreeding.[65]:30

Human–dog coevolution

Related fields

Human-dog co-evolution is based on the proposal that humans and dogs have undergone behavioral change since domestication. Conceptually, the field is related to behavioural genetics, behavioral ecology, behavioral epigenetics, evolutionary biology, evolutionary psychology and neuroethology.

Evidence

Bison surrounded by gray wolf pack

In 2002, a study argued that our immediate ancestors and wolves may have domesticated each other through a strategic alliance that would change both respectively into humans and dogs. The effects of human psychology, hunting practices, territoriality and social behavior would have been profound.[77]

Marking of territory with signs such as pecked cupules, hand stencils and prints, abraded grooves, and finger impressions in once-soft mud are enduring signs used to mark occupation. They also became the first symbolic objects i.e. art. Wolves mark their territory with urine, however humans do not have the keen sense of smell as wolves and would have needed to use something more easily recognizable and enduring to mark their territory. Humans learned to mark their territory after watching wolves and dogs.[77]

Hunting large animals in packs is a distinctive wolf behavioral trait. There is no evidence of big game hunting in pre-sapiens groups, but big-game hunting is very typical of homo sapiens that, in addition to climate change, may have contributed to the extinction of many large mammals. Early humans moved from scavenging and small-game hunting to big-game hunting by living in larger, socially more-complex groups, learning to hunt in packs, and developing powers of cooperation and negotiation in complex situations. As these are characteristics of wolves, dogs and humans, it can be argued that these behaviors were enhanced once wolves and humans began to cohabit. Communal hunting lead to communal defense. Wolves actively patrol and defend their scent-marked territory, and perhaps humans had their sense of territoriality enhanced by living with wolves.[77]

New forms of bonding might assist in living in large, complex and varied social groups. One of the keys to recent human survival has been the negotiation of situations by forming partnerships. Strong bonds exist between same-sex wolves, dogs and humans – bonds less-fickle than exists between other same-sex animal pairs. Today, the most widespread form of inter-species bonding occurs between humans and dogs. The concept of friendship has ancient origins, but it may have been enhanced through the inter-species relationship to give a survival advantage.[77]

The pointing gesture is a human-specific signal, is referential in its nature, and is a foundational building-block of human communication. Human infants acquire it weeks before the first spoken word.[78] In 2009, a study compared the responses to a range of pointing gestures by dogs and human infants. The study showed little difference in the performance of 2-year-old children and dogs, while 3-year-old children’s performance was higher. The results also showed that all subjects were able to generalize from their previous experience to respond to relatively novel pointing gestures. These findings suggest that dogs demonstrate a similar level of performance as 2-year-old children that can be explained as a joint outcome of their evolutionary history as well as their socialization in a human environment.[79]

Later studies support coevolution in that dogs can discriminate the emotional expressions of human faces,[80] most people can tell from a bark whether a dog was alone or being approached by a stranger, playing or being aggressive,[81] and able tell from a growl how big the dog is.[82]

When dogs and their owners interact, extended eye contact (mutual gaze) increases oxytocin levels in both the dog and its owner. As oxytocin is known for its role in maternal bonding, it is considered likely that this effect has supported the coevolution of human-dog bonding.[83]

In 2013, a DNA sequencing study suggested that some genes have evolved in parallel in humans and their canine companions, likely as a result of shared selection pressures.[84]

Lupification of humans

Isn’t it strange that, our being such an intelligent primate, we didn’t domesticate chimpanzees as companions instead? Why did we choose wolves even though they are strong enough to maim or kill us?[85]

In 2003, a study compared the behavior and ethics of chimpanzees, wolves and humans. The sociality of humans' closest relative, the chimpanzee, appears as a frightful caricature of human egoism. Even in their maternal behavior, warmth and affection are reduced to nursing and the occasional comforting hug. Cooperation among group members is limited to occasional hunting episodes or the persecution of a competitor, always aimed for one's own advantage. The closest approximation to human morality they can find in nature is that of the gray wolf, Canis lupus. Wolves ability to cooperate in well-coordinated drives to hunt prey, carry items too heavy for an individual, provisioning not only their own young but also the other pack members, babysitting etc. are rivalled only by that of human societies. Similar forms of cooperation are observed in two closely related canids, the African Cape hunting dog and the Asian dhole, therefore it is reasonable to assume that canid sociality and cooperation are old traits that in terms of evolution predate human sociality and cooperation. Today's wolves may even be less social than their ancestors, as they have lost access to big herds of ungulates and now tend more toward a lifestyle similar to coyotes, jackals, and even foxes.[85]

There are a number of behavioral adaptions that make communal life possible:

Reindeer moved in large herds across the Mammoth steppe and were preyed upon by carnivores
  1. Social pack-forming canids are essentially monogamous. One pair breeds, but all members share food and parental care generously.
  2. They are aware of where the other pack members are and what they are doing, especially when running as a single group. When canids hunt in a pack, close attention and close cooperation allow them to operate as an integrated system.
  3. In wolves, each pack member can accept greater risks when attacking, because if injured the needy will be fed by the other pack members. Cooperation and risk sharing is not only among close relatives or mated pairs, but also lasting friendships among the same gender, which is a central feature of canid pack living.
  4. "Wolfing down" prey as quickly as possible by the pack ensures that other predators get no advantage. They later regurgitate large chunks for the pups and their baby-sitters.
  5. They constantly watch each other – they know who is who, who is where, and what they are doing.
  6. They deal with hierarchy with minimal bloodshed, with dominance and submission treated as a low-key affair.[85]

The Mammoth steppe was the Eurasian tundra and grass steppe ecosystem which once stretched from Spain to the far east of Siberia, and at times continued into North America. On this steppe the wolves ability to hunt in packs, to share risk fairly among pack members, and to cooperate moved them to the top of the food pyramid above lions, hyenas and bears. Some, but not all, wolves followed the great reindeer herds, eliminating the unfit, the weaklings, the sick and the aged and therefore improved the herd. These wolves had become the first pastoralists hundreds of thousands of years before humans also took to this role. The wolves advantage over their competitors was that they were able to keep pace with the herds, move fast and enduringly, and make the most efficient use of their kill by their ability to "wolf down" a large part of their quarry before other predators had detected the kill. The authors of the study propose that during the last ice age, some of our ancestors teamed up with those pastoralist wolves. Many of our ancestors remained gatherers and scavengers, or specialized as fish-hunters, hunter-gatherers, and the hunter-gardeners. However, some ancestors adopted the pastoralist wolves' lifestyle as herd followers and herders of reindeer, horses, and other hoofed animals. They harvested the best stock for themselves while the wolves kept the herd strong. These pastoralists later became herders and the dog.[85]

From a biologist's vantage point, the interwining process of hominization and canization makes sense only if viewed in terms of coevolution.[85]

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