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Origin of the domestic dog

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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. Whole genome sequencing indicates that the dog, the gray wolf and the extinct Taymyr wolf diverged at around the same time 27,000-40,000 years ago.[1] These dates imply that the earliest dogs arose in the time of human hunter-gatherers and not agriculturists.[2] Modern dogs are more closely related to ancient wolf fossils that have been found in Europe than they are to modern gray wolves,[3] with nearly all genetic commonalities with the gray wolf due to admixture [2] but several Arctic dog breeds with the Taymyr wolf of North Asia due to admixture.[1]

Paleoecology

The last glacial period, commonly referred to as the 'Ice Age', spanned 125,000[4] to 14,500[5] years ago and was the most recent glacial period within the current ice age which occurred during the last years of the Pleistocene era.[4] The Ice Age reached its peak during the last glacial maximum, when ice sheets commenced advancing from 33,000 years BP and reached their maximum positions 26,500 years BP. Deglaciation commenced in the Northern Hemisphere approximately 19,000 years BP, and in Antarctica approximately 14,500 years BP which is consistent with evidence that this was the primary source for an abrupt rise in the sea level 14,500 years ago.[6]

A vast Mammoth steppe stretched from Spain across Eurasia and over the Bering land bridge into Alaska and the Yukon where it was stopped by the Wisconsin glaciation. This land bridge existed because more of the planet's water was locked up in glaciation than now and therefore the sea-levels were lower. When the sea levels began to rise this bridge was inundated around 11,000 years BP.[7] During the last glacial maximum, the continent of Europe was much colder and drier than it is today, with polar desert in the north and the remainder steppe or tundra. Forest and woodland was almost non-existent, except for isolated pockets in the mountain ranges of southern Europe.[8]

The fossil evidence from many continents points to the extinction mainly of large animals at or near the end of the last glaciation. These animals have been termed Pleistocene megafauna. The most common definition of megafauna is an animal with an adult body weight of over 44 kg. Across Eurasia, the staight-tusked elephant became extinct between 100–50 years BP. The hippopotamus, interglacial rhinoceros (Stephanorohinus), cave bear (Ursus spelaeus), and heavy-bodied Asian antelope (Spirocerus) died out between 50,000-16,000 years BP. The spotted hyena, woolly rhinoceros and mammoths died out between 16,000-11,500 years BP. The musk ox died out after 11,500 BP, as did the giant deer (Megaloceros) with the last pocket having survived until about 7,700 years BP in western Siberia.[9] A pocket of mammoths survived on Wrangel Island until 4,500 years BP.[10] Among the top predators, the sabre-toothed cat (Homotherium) died out 28,000 years BP,[11] the cave lion 11,900 years BP,[12] and the leopard in Europe died out 27,000 years BP.[13]

Modern human's ancestors first appeared in East Africa 195,000 years ago.[14] Some migrated out of Africa 60,000 years ago with one group reaching Central Asia 50,000 years ago.[15] From there they reached Europe, with human remains dated 43,000-45,000 years BP discovered in Italy,[16] Britain,[17] and in the European Russian Arctic 40,000 years ago.[18][19] Another group left Central Asia and reached the Yana River, Siberia, well above the Arctic circle 27,000 years ago.[20] Modern humans then made their way across the Bering land bridge and into North America between 20,000-11,000 years ago, after the Wisconsin glaciation had retreated but before the Bering land bridge became inundated by the sea.[21] These people then populated the Americas. In the Fertile crescent the first agriculture was developing 11,500 years ago.[22]

Into this environment came the dog with her two sisters - the gray wolf and the now-extinct Taymyr wolf.

First Divergence

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.

All members of the Canis genus within the wolf-like canids can produce fertile hybrids and several species may have genomes that reflect hybridization in the wild.[23] 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.[24] 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.[25]

It has been thought for some time that "... the wolf is the most probable ancestor and closest relative of the domestic dog."[26]:54 By 1993 with advancements in molecular biology, the mitochondrial DNA analysis of extant (i.e. living today) Canis 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."[27] 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.[28] By 1999, further genetic analysis indicated that the domestic dog may have emerged from multiple wolf populations.[29][30] Based on these pieces of research and the reference reclassification, Canis lupus familiaris is the name for the taxon listed by ITIS.[31] However, Canis familiaris is also accepted due to a nomenclature debate over the naming of wild and domestic sub-species.[32]

Time of divergence

The ancestral dog and the ancestral modern gray wolf diverged from a common ancestor at least 27,000 years ago

In May 2015, a study was conducted on a partial rib-bone of a wolf (named Taimyr-1) found near the Bolshaya Balakhnaya River in the Taimry Penensula, North Asia, that was AMS radiocarbon dated to 34,900 years BP. The sample provided the first draft of the entire nuclear genome of a Pleistocene carnivore and the sequence was deposited in the ENA with accession number PRJEB7788 and classified as Canis lupus because the genome sequence was found to be substantially closer to modern gray wolves than it was to modern coyotes. The data was compared to the genotypes of 532 dogs from 48 breeds and 15 gray wolves from Europe, the Middle East, China, and North America.[1]

Using the Taimyr-1 specimen's radiocarbon date, its genome sequence and that of a modern wolf, a direct estimate of the genome-wide mutation rate in dogs/wolves could be made to calculate the time of divergence. The data showed that the Taimyr-1 lineage was separate to modern wolves and dogs and indicated that the Taimyr-1 genotype, gray wolves and dogs triverged from a now-extinct common ancestor before the peak of the Last Glacial Maximum 27,000-40,000 years ago. The separation of the dog and wolf did not have to coincide with selective breeding by humans.[1]:page3

This derived mutation rate was much slower than that assumed in previous studies. Such an early divergence is consistent with several paleontological reports of dog-like canids up to 36,000 years old, as well as evidence that domesticated dogs most likely accompanied early colonizers into the Americas.[1]

The ancestral fossils have not yet been found.

Place of divergence

Modern dogs show a closer genetic association with ancient, extinct European canids than with modern gray wolves, which suggests they originated in Europe.[3]

A number of mitochondrial DNA studies have searched for the time and place that the dog first diverged from the extant gray wolf, including 135,000 years ago,[33] in East Asia 15,000 years ago,[34] in Africa,[35] in southeastern Asia south of Yangtze River 5,400–16,300 years ago,[36] in the Middle East,[37] in East Asia south of the Yangtze River,[38] and in Europe.[39] Genetic studies comparing the dog to the extant gray wolf did not result in agreement among researchers.

In 1934, an eminent paleontologist indicated that the ancestor of the dog lineage may have been the extinct Canis lupus variabilis.[40]

In November 2013, a study 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 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 admixture with 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.[3]

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.[3]

Ancestral dog

In 1999, a study 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.[29]

Goyet dog - 36,000 BP

Genus Canis, species indeterminate

In 2009, a study looked at 117 skulls of recent and fossil large canids. None of the 10 canid skulls from the Belgian caves of Goyet, Trou du Frontel, Trou de Nutons, and Trou de Chaleux could be classified, so the team took as their basic assumption that all of these canid samples were wolves.[41] The DNA sequence of 7 of the skulls indicated 7 unique haplotypes that represented ancient wolf lineages lost until now. The osteometric analysis of the skulls showed that one large canid fossil from Goyet (RBINS 2860) was clearly different from recent wolves, resembling most closely the Eliseevichi-1 dogs (15,000 years BP) and so was identified as a Paleolithic dog (see below).[39]

In November 2013, a DNA study sequenced 3 haplotypes from the ancient Belgium canids (the Goyet dog - Belgium 36,000 years BP cataloged as Canis species KF661079, and with Belgium 30,000 years BP KF661080 and 26,000 years BP KF661078 cataloged as Canis lupus) and found they formed the most diverging group. Although the cranial morphology of the Goyet dog has been interpreted as dog-like, it's mitochondrial DNA 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 but was found not to be related to the Beringian wolf. This Belgium canid clade may represent a phenotypically distinct and not previously recognized population of gray wolf or the Goyet dog may represent an aborted domestication episode.[3]

Altai dog - 33,000 BP

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

In 2011, a study looked at the well-preserved 33,000-year old skull and left mandible of a dog-like canid that was excavated from Razboinichya Cave in the Altai Mountains of southern Siberia (Central Asia). 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 Razboinichya Cave cranium is virtually identical in size and shape to prehistoric 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...and probably represents wolf domestication disrupted by the climatic and cultural changes associated with the Last Glacial Maximum".[42]

In March 2013, a DNA study sequenced the Altai dog with the data 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 same 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."[43]

In November 2013, a study looked at 18 fossil canids and compared these with the complete mitochondrial genome sequences from 49 modern wolves and 77 modern dogs. A more comprehensive analysis of the complete mtDNA found that the phylogenetic position of the Altai dog as being either dog or wolf was inconclusive and cataloged its sequence as Canis species (KF661092). The sequence strongly suggests a position at the root of a clade uniting two ancient wolf genomes, two modern wolves, as well as two dogs of Scandinavian origin, however the study does not support its recent common ancestry with the great majority of modern dogs. The study suggests that it may represent an aborted domestication episode.[3]

Paleolithic dog - 27,000 BP

Detailed DNA analysis yet to be conducted

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".[44] 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).[3] It is the oldest known specimen recognized as belonging to a dog.

In 2009, a study proposed that there was a low frequency of recognized dog skulls in Upper Paleolithic sites because existing specimens had not yet been recognized as dogs. The 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 Eliseevichi-1 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 Eliseevichi-1 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. 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.[39]

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.[39]

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.[39] 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,[39] its refutation,[45] a counter to the refutation,[46] a second article,[47] its refutation,[48] a third article that includes a counter to the refutation,[49] its refutation,[50] a counter to the refutation,[51] and another refutation.[52]

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

See also Paleolithic dog

A leading evolutionary biologist has stated:

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.[53]
See also Megafaunal wolf

Second divergence

Gray wolf admixture

There was admixture between the ancestral dog, the ancestral modern gray wolf, and the golden jackal
The ancestral dog triverged into the Dingo, Basenji and Boxer lineages, and the ancestral modern gray wolf split into today's gray wolves

In January 2014, a study analysed the whole-genome sequences of 3 wolves (Canis lupus) to represent the regions of Eurasia where domestication has been hypothesized to have taken place – Croatia (Europe), Israel (Middle-East), and China (East/South-East Asia), plus 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.[2]

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.[2]

One test indicated that dogs and modern wolves form 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.[2]

The data indicate that the golden jackal and the ancestor of the wolf/dog diverged 400,000 years ago. Dogs and wolves then diverged into the ancestral dog and the ancestral modern gray wolf. The ancestral modern gray wolf population triverged into the 3 populations studied. Not long after, the ancestral dog populations diverged into the dingo lineage, the basenji lineage and the reference boxer lineage. There was a 16-fold population bottleneck for dogs since this divergence.[2]

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.[2]

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.[2]

Greenland sled dog carries 3.5% shared genetic material with the 35,000 years BP Taymyr wolf specimen.

Taimyr wolf admixture

There was admixture between Taimyr-1 and those breeds associated with high latitudes

In May 2015, a study compared the ancestry of the Taimyr-1 wolf lineage to that of dogs and gray wolves.

Comparison to the gray wolf lineage indicated that Taimyr-1 was basil to gray wolves from the Middle East, China, Europe and North America but sharing a substantial amount of history with the present-day gray wolves after their divergence from the coyote. This implies that the ancestry of the majority of gray wolf populations today stems from an ancestral population that lived less than 35,000 years ago but before the inundation of the Bering Land Bridge with the subsequent isolation of Eurasian and North American wolves.[1]:21

A comparison of the ancestry of the Taimyr-1 lineage to the dog lineage indicated that some modern dog breeds have a closer association with either the Gray wolf or Taimyr-1 due to admixture. The Sarloos wolfdog showed more association with the Gray wolf and this is in agreement with the documented historical crossbreeding with gray wolves in this breed. Taimyr-1 shared more alleles (i.e. gene expressions) with those breeds that are associated with high latitudes - the Siberian husky and Greenland dog that are also associated with arctic human populations, and to a lesser extent the Shar Pei and Finnish spitz. An admixture graph of the Greenland dog indicates a best-fit of 3.5% shared material, however an ancestry proportion ranging between 1.4% and 27.3% is consistent with the data. This indicates admixture between the Taimyr-1 population and the ancestral dog population of these 4 high-latitude breeds. These results can be explained either by a very early presence of dogs in northern Eurasia or by the genetic legacy of Taimyr-1 being preserved in northern wolf populations until the arrival of dogs at high latitudes. This introgression could have provided early dogs living in high latitudes with phenotypic variation beneficial for adaption to a new and challenging environment. It also indicates the ancestry of present-day dog breeds descends from more than one region.[1]:3-4

An attempt to explore admixture between Taimyr-1 and gray wolves produced unreliable results.[1]:23

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".[40]:15 More recent researchers have proposed that Canis lupus variabilis may be an ancestor of the dog lineage.[54][55]:7 At the site, the small wolf's remains were in close proximity to Homo erectus pekinensis or Peking man.
42,000 Europe First anatomically modern humans migrate into Europe.
40,000 Bolshaya Balakhnaya River in the Taymyr Peninsula, North Asia Partial rib-bone of a wolf AMS radiocarbon dated to 35,000 years BP. The mDNA analysis shows that the Taymyr wolf lineage was separate to modern wolves and dogs, which indicates that the Taymyr wolf, gray wolves and dogs all diverged at around this time.[1] The remains of the common ancestor have yet to be found.
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.[39] No descendants, genetic classification of species is inconclusive.[3]
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.[43] 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.[3]
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.[47][56]
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.[57]
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".[44] 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.[39] Genetic analysis of one skull was deposited in GenBank with accession number KF661082 and classified as Canis lupus familiaris (dog).[3] 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.[58] Genetic analysis deposited in GenBank with accession number KF661093 and classified as Canis lupus familiaris (dog).[3]
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.[39]
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.[39]
12,500 Karstein cave, Germany Ancient dog skull. Genetic analysis deposited in GenBank with accession number KF661094 and classified as Canis lupus familiaris (dog).[3]
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.[59]
12,000 Ain 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.[60]
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.[61]
7,800 Jiahu site, China Eleven dog internments. Jaihu is a Neolithic site 22 kilometers north of Wuyang in Henan Province.[62]
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.[63]
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.[64]

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.[55] Another study proposed that the ancestor of Canis familiaris was a wild "Canis familiaris".[65] 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.[3] Another found the same thing and that the dog, the Gray wolf and the now-extinct Taymyr wolf all diverged from a common ancestor 40,000 years ago i.e. without human intervention.[1] Readers should be aware of these inconsistencies 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.[66] 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.[67]

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.[68][69][70]

Natural selection against aggression without human intevention

Dogs can infer the name of an object and have been shown to learn the names of over 1,000 objects. Dogs can follow the human pointing gesture; even nine week old puppies can follow a basic human pointing gesture without being taught. New Guinea Singing dogs, a half-wild proto-dog endemic to the remote alpine regions of New Guinea, as well as Dingoes in the remote outback of Australia are also capable of this. These examples demonstrate an ability to read human gestures that arose early in domestication and did not require human selection. "Humans did not develop dogs, we only fine-tuned them down the road."[71]:92 Similar to the chimpanzee, Bonobos are a close genetic cousin to humans. Unlike the chimpanzee, bonobos are not aggressive and do not participate in lethal intergroup aggression or kill within their own group. The most distinctive features of a bonobo are its cranium, which is 15% smaller than a chimpanzee's, and its less aggressive and more playful behavior. Dogs mirror these differences relative to wild wolves: a dog's cranium is 15% smaller than an equally heavy wolf's, and the dog is less aggressive and more playful. The guinea pig's cranium is 13% smaller than its wild cousin the cavie and domestic fowl show a similar reduction to their wild cousins. Possession of a smaller cranium for holding a smaller brain is a telltale sign of domestication. Bonobos appear to have domesticated themselves.[71]:104 In the "farm fox" experiment, humans selectively bred foxes against aggression which caused a domestication syndrome. The foxes were not selectively bred for smaller craniums and teeth, floppy ears, or skills at using human gestures but these traits were demonstrated in the friendly foxes. Natural selection favours those that are the most successful at reproducing, not the most aggressive. Selection against aggression made possible the ability to cooperate and communicate among foxes, dogs and bonobos. Perhaps it did the same thing for humans.[71]:114

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.[3]

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.[72] 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.[73][74]

Against this proposition, wolves have been scavenging around human living areas, noted in Israel and Italy for centuries, without demonstrating any move towards domestication.[75]

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.[70][76][77][78][79] The most docile or interesting animals could have been permitted to reproduce.[77][78][80] After several generations of unconscious and later of conscious selection of human-defined behavioral traits, the first dogs emerged.[81]

Orphaned wolf-pups

Studies have shown that some wolf pups taken at an early age and reared by humans are easily tamed and socialized,[26]:140 and one study has demonstrated that adult wolves can be socialized.[26]:141 Some researchers propose that humans adopted orphaned wolf pups and breastfed them alongside human babies.[73][82] 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.[26]:pages55-56

Against this proposition, at the time of domestication near the LGM humans were already the top predator and had no need for wolves that would grow to eat 5 kilograms of meat per wolf per day at a time when food was very scarce. Starvation would have been a real threat to many carnivores in the Ice Age and competition for food would have been fierce.[71]:29 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.[83]

Human selection

See also: Dog breeding

The "farm fox" experiment attempted to reenact how domestication may have occurred.[84] 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.[85] 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.[75] When humans restrict dog's breeding diversity, another variable also comes into play that may have contributed to the change – inbreeding.[73]:30

Convergent evolution

Behavioral evidence

Convergent evolution is when distantly related species independently evolve similar solutions to the same problem. For example, fish, penguins and dolphins have each separately evolved flippers as solution to the problem of moving through the water. What has been found is something less frequently demonstrated: psychological convergence. Dogs have independently evolved to be cognitively more similar to humans than we are to our closest genetic relatives.[71]:60 Dogs have evolved specialized skills for reading human social and communicative behavior. These skills seem more flexible – and possibly more human-like – than those of other animals more closely related to humans phylogentically, such as chimpanzees, bonobos and other great apes. This raises the possibility that convergent evolution has occurred: both Canis familiaris and Homo sapiens might have evolved some similar (although obviously not identical) social-communicative skills – in both cases adapted for certain kinds of social and communicative interactions with human beings.[86]

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.[87] 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.[88]

Later studies support coevolution in that dogs can discriminate the emotional expressions of human faces,[89] most people can tell from a bark whether a dog was alone or being approached by a stranger, playing or being aggressive,[90] and able tell from a growl how big the dog is.[91]

From[75]:40
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 n 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.

Biological evidence

In 2013, a DNA sequencing study indicated that parallel evolution in humans and dogs is most apparent in the genes for digestion and metabolism, neurological process and cancer, likely as a result of shared selection pressures.[92][93]

In 2014, a study compared the hemoglobin levels of village dogs and people on the Chinese lowlands with those on the Tibetan plateau. It found the hemoglobin levels higher for both people and dogs in Tibet, suggesting that Tibetan dogs might share similar adaptive strategies as the Tibetan people. A population genetic analysis then showed a significant convergence between humans and dogs in Tibet.[94]

In 2015, a study found that 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.[95]

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?[96]

Bison surrounded by gray wolf pack

In 2002, a study argued that immediate human 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.[97]

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.[97]

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.[97]

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.[97]

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.[96]

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.[96]

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.[96]

From a biologist's vantage point, the interwining process of hominization and canization makes sense only if viewed in terms of coevolution.[96]

Further reading

  • Derr, Mark. How the Dog Became the Dog: From Wolves to Our Best Friends (Penguin Group; 2011); book extensively cites research papers to support its propositions.
  • Hare, Brian & Woods, Venessa. The Genius of Dogs (2013 Penguin Publishing Group) Part 1, Chapters 2-5, pages 17–121; these several chapters focus on the cognitive evolution of the dog.
  • Morey, Darcy. Dogs: Domestication and the Development of a Social Bond (Cambridge University Press; 2010) 384 pages; uses zooarchaeology to explores ties between humans and canines over the past 15,000 years with a focus on the New World and Arctic regions.

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