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The domestic dog (Canis lupus familiaris or Canis familiaris), based on nuclear DNA evidence as of January 2014, began from a single domestication 11 to 16 thousand 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 as of November 2013 indicates that all modern dogs are most closely related to the extant and extinct canids of Europe[2][3] compared to earlier writers who proposed the origins from Eurasia as well as Eastern Asia.[4][5][6]
The analysis indicates that the dog is not a descendant of the extant (i.e. living) Gray wolf but forms a sister clade, and that dogs were originally domesticated from a now-extinct wolf population that was more genetically diverse than today’s wolf population. The dog's genetic closeness to modern wolves is due to admixture.[1][7]
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. Furthermore, several ancient dogs may represent failed domestication events, such as the 36,000 year old Goyet specimen of Belgium and the 33,000 year old Altai Mountains specimen from Russia, as they have no descendents today.[2][8]
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, three distinct phylogenetic groupings are apparent:- The fox-like canids, which include species closely related to the red fox (Vulpes vulpes), and the arctic fox (Vulpes lagopus), and the fennec fox (Vulpes zerda or Fennecus zerda, disputed).
- The wolf-like canids, including dog, wolf, coyote, Ethiopian wolf or Simien jackal, and three other species of jackals (genus Canis), and the African hunting dog (genus Lycaon) and the dhole (genus Cuon).
- The South American canids, including fox-sized canids, such as the pampus fox, crab-eating fox, and small-eared dog (genus Pseudalopex, Lycalopex, Atelocynus) and the maned wolf (genus Chrysocyon) and bushdog (genus Speothos).
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.[9] 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.[10] 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[11]—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."[12]: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."[13] 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.[14] In 1995, research indicated that the wolf may have been the ancestor of the dog.[15]By 1999, further genetic analysis indicated that the domestic dog may have emerged from multiple wolf populations.[16][17] Based on these pieces of research and the reference reclassification, canis lupis familiaris is the name for the taxon listed by ITIS.[18] However, canis familiaris is also accepted due to a nomenclature debate regarding the naming of wild and domestic sub-species.[19]
Descendant of a wolf that no longer exists today
Location of the first domestication
In 1997, a study determined that domestic dogs could have originated as much as 135,000 years ago.[20] 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.[20] These hypervariable sites are mutational hotspots where somatic mitochondrial DNA and germline mutations usually take place.[21] 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.[20]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.[22] In 2008, a study of several skulls of fossil large canids from sites in Belgium, Ukraine and Russia were examined to look for possible evidence of the presence of Palaeolithic dogs. The fossil large canid from Goyet (Belgium), dated at c. 31,700 BP was identified as a Palaeolithic dog, suggesting that dog domestication had already started in Europe during the Aurignacian.[23][24][25]
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.[26] 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.[27]
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.[28] 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.[29]
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.[30]
"Wayne" studies
In 1934, an eminent paleontologist indicated that the ancestor of the dog lineage may have been an extinct Canis lupus.[31] 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.[16] 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[32] 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,[33] 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 indicates 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.
Belgium 26,000 - Pleistocene wolf skull from the Trou des Nutons cave in Belgium dated to be 26,000 years old (courtesy Royal Belgian Institute of Natural Sciences)
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 indicates 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.[34][8]
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 was 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]
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 infers 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 indicates 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[35] and between 10,000-60,000 years ago[36] 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][37]
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]
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".[31]:15 More recent researchers have proposed that Canis lupus variabilis may be an ancestor of the dog lineage.[38][39]: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. 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 dogs and to the Epigravettian Mezin 5490 and Mezhirich dog skulls, 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.[23] No descendants, genetic classification of species is contentious.[2] |
| 33,500 | Razboinichya Cave, Altai Mountains, Russia | Dog-like skull, mandibles (both sides) and teeth. Specimen is similar to fully domesticated dogs from Greenland (about 1000 years old), and unlike ancient and modern wolves, and putative dogs from Eliseevichi I site in central Russia.[32] No descendants, genetic classification of species is contentious.[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] |
| 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.[30][40] |
| 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.[41] |
| 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.[42] |
| 13,900 | Eliseevich I site, Russian Plain, Russia | Two ancient dog skulls. 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 remains of at least eight mammoth bone complexes and large quantities of worked ivory were discovered at this site.[23] |
| 13,500 approx | Mezin, Ukraine | Ancient dog skull - Mezin 5490 - as well as ancient wolf specimens found at the site. Dated to the Epigravettian period (17,000-10,000 BP). The Epigravettian Mezin site is well known for its round mammoth bone dwelling.[23] |
| 13,500 approx | Mezhirich, Ukraine | Ancient dog skull. Dated to the Epigravettian period (17,000-10,000 BP). The Epigravettian Mazhirich site has four mammoth bone dwellings present.[23] |
| 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.[43] |
| 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.[44] |
| 7,800 | Jiahu site, China | Eleven dog internments. Jaihu is a Neolithic site 22 kilometers north of Wuyang in Henan Province.[45] |
| 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.[46] |
| 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.[47] |
Domestication
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Theory
The current theory of dog domestication is based on the comparison between the dog and extant gray wolves, and although it has been claimed that "man domesticated the wolf", 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.[39] Another study proposed that the ancestor of Canis familiaris was the wild "Canis familiaris".[48] A genetic study recently found that the ancestor of the dog is not the extant gray wolf and the fossil remains of the "wolf-like canid" ancestor has yet to be found.[2] (Readers should be aware of this inconsistency with the theory before progressing through this section.)Domestication of the wolf over time has produced a number of physical or morphological changes. These include: a reduction in overall size; changes in coat coloration and markings; a shorter jaw initially with crowding of the teeth and, later, with the shrinking in size of the teeth; a reduction in brain size and thus in cranial capacity (particularly those areas relating to alertness and sensory processing, necessary in the wild); and the development of a pronounced “stop”, or vertical drop in front of the forehead (brachycephaly). Certain wolf-like behaviors, such as the regurgitation of partially digested food for the young, have also disappeared.[49]
Although experts disagree over the details of domestication, it is agreed that human interaction played a significant role in shaping the subspecies. At least three early species of the Homo genus began spreading out of Africa roughly 400,000 years ago, and thus lived for a considerable time in contact with canid species.[50]:pages95-136
Method
How domestication arose is unknown but the theories proposed include one, or all, of the following: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."[51]:40Cooperation
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]Access to food/self-domestication
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.[52] 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.[53][54]Against this proposition, wolves have been scavenging around human living areas, noted in Israel and Italy for centuries, without demonstrating any move towards domestication.[51]
Orphaned wolf-pups
Studies have shown that some wolf pups taken at an early age and reared by humans are easily tamed and socialized,[12]:140 and one study has demonstrated that adult wolves can be socialized.[12]:141Some researchers propose that humans adopted orphaned wolf pups and breastfed them alongside human babies.[53][55] 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.[12]: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.[56]
Human selection
The "farm fox" experiment attempted to reenact how domestication may have occurred.[57] Researchers, working with wild silver foxes selectively bred over 35 generations and 40 years for the sole trait of friendliness to humans, created more dog-like animals. The "domestic elite" foxes are much more friendly to humans and actually seek human attention, but they also show new physical traits that parallel the selection for tameness, even though the physical traits were not originally selected for. They include spotted or black-and-white coats, floppy ears, tails that curl over their backs, the barking vocalization and earlier sexual maturity. It was reported "On average, the domestic foxes respond to sounds two days earlier and open their eyes one day earlier than their non-domesticated cousins. More striking is that their socialization period has greatly increased.
Instead of developing a fear response at 6 weeks of age, the domesticated foxes don't show it until 9 weeks of age or later. The whimpering and tail wagging is a holdover from puppyhood, as are the foreshortened face and muzzle. Even the new coat colours can be explained by the altered timing of development. One researcher found that the migration of certain melanocytes (which determine colour) was delayed, resulting in a black and white 'star' pattern.
A criticism of this experiment that has been made based on information obtained after its 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.[51] When humans restrict dog's breeding diversity, another variable also comes into play that may have contributed to the change - inbreeding.[53]:30
A criticism of this experiment that has been made based on information obtained after its 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.[51] When humans restrict dog's breeding diversity, another variable also comes into play that may have contributed to the change - inbreeding.[53]:30
