Origin of the domestic dog
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. These dates imply that the earliest dogs arose in the time of human hunter-gatherers and not agriculturists. Modern dogs are more closely related to ancient wolf fossils that have been found in Europe than they are to modern gray wolves, with nearly all genetic commonalities with the gray wolf due to admixture, but several Arctic dog breeds have commonalities with the Taymyr wolf of North Asia due to admixture.
- 1 Dog evolution
- 1.1 Paleoecology
- 1.2 Wolf-like lineage
- 1.3 Probable ancestor
- 1.4 First divergence
- 1.5 Ancestral dog
- 1.6 Second divergence
- 2 Dog domestication
- 3 References
Dog evolution (from the Latin evolutio: "unrolling") is the biological descent with modification that led to the domestic dog. This process encompasses small-scale evolution (changes in gene frequency in a population from one generation to the next) and large-scale evolution (the descent of different species from a common ancestor over many generations).
- The dog came into being towards the last glacial maximum in very cold and dry climatic conditions.
During the last glacial maximum a vast mammoth steppe stretched from Spain across Eurasia and over the Bering land bridge into Alaska and the Yukon. 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. The Late Pleistocene was characterized by a series of severe and rapid climate oscillations with regional temperature changes of up to 16 °C, which has been correlated with Pleistocene megafaunal extinctions. There is no evidence of megafaunal extinctions at the height of the LGM, indicating that increasing cold and glaciation were not factors. Multiple events appear to also involve the rapid replacement of one species by one within the same genus, or one population by another within the same species, across a broad area. As some species became extinct, so too did their predators. Modern humans' ancestors first reached Europe with their remains dated 43,000-45,000 years BP discovered in Italy and in Britain.
Into this environment came the dog.
- See further: Paleoecology at this time
- Early DNA studies indicated that the dog is descended from a wolf-like lineage.
In 1868, Charles Darwin proposed that domestic dogs were phenotypically so diverse that they likely had originated from two or more wild canis species.:16 All species within the Canis genus, the wolf-like canids, are phylogenetically closely related with 78 chromosomes and can potentially interbreed. Later, others thought that "the wolf is the most probable ancestor and closest relative of the domestic dog.":54
The development of molecular biology allows the inference of evolutionary relationships about species and to represent them in a phylogenetic tree; however, these are not without their limitations. DNA studies may give unresolvable results due to the specimens selected, the genome technology used, and the assumptions made by the researchers. A panel of genetic markers can be chosen, for example from mitochondrial Cytochrome b. The techniques used to extract, locate and compare sequences can be applied using advances in genome technology to observe longer lengths of base pairs that give better phylogenetic resolution. These techniques can be applied to the maternal mitochondrial control region, mitochondrial D-loop, mitochondrial genome, paternal Y chromosomes, microsatellites, single nucleotide polymorphisms, nuclear DNA and the whole genome.
In June 1993, a study of 736 base pairs of the mitochondrial Cytochrome b gene of the wolf-like canids found that there was a close kinship between domestic dogs, gray wolves, coyotes and Simien jackals, but with a distance from the African wild dog and from the golden, side-striped and black-backed jackals. The domestic dog was "an extremely close relative of the gray wolf, differing from it by at most 0.2% of Mitochondrial DNA [mDNA] sequence. In comparison, the gray wolf differs from its closest wild relative, the coyote, by about 4% of mDNA sequence." Therefore, the study concluded that the molecular genetic evidence did not support theories that dogs arose from jackal ancestors. The study warned of "the need for caution in the interpretation of phylogenies based on mDNA; such gene trees are not necessarily species trees and may not accurately reflect the phylogenetic affiliations or divergence time." The study proposed the hypothesis that because of the diversity of dog remains found in archaeological sites, dogs may be derived from several different ancestral gray wolf populations.
In the same year 1993, 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. However, Canis familiaris is also accepted due to a nomenclature debate over the naming of wild and domestic sub-species.
In 1995, a researcher found that the archaeological record did not show any distinctive dog breeds until 3,000–4,000 years ago and that most breeds had been developed over the past seven hundred years.
In 1997, a study was conducted of 261 base pairs on the control region of 140 dogs across 67 breeds and 162 wolves across 27 populations. The control region of the dogs and wolves was highly polymorphic, with dogs revealing 26 haplotypes, and wolves revealing 27 haplotypes, of which four had a widespread distribution. Dog haplotypes could not be partitioned into breeds: for example, eight German shepherds revealed five distinct sequences, and six golden retrievers revealed four sequences. No dog sequence differed from any wolf sequence by more than 12 substitutions but differed from coyote sequences by at least 20 substitutions and 2 insertions, clearly supporting a wolf ancestry for dogs. The 26 dog haplogroups formed four distinct clades; Clade 1 included 19 haplotypes, Clade 2 included one haplotype, Clade 3 included three haplotypes, and Clade 4 included three haplotypes which were identical or very similar to a wolf haplotype found in Romania and western Russia and which suggests recent hybridization. A further analysis of 1,030 base pairs on the control region of 24 dogs provided greater phylogenetic resolution and supported four monophyletic clades. The wolf and coyote ancestral lines diverged one million years ago based on the fossil record, and comparing their sequence divergence with those of the dog implies that dogs diverged 135,000 years ago. The estimate may be inflated as it is based on some assumptions, but it implies that the origin of dogs is more ancient than 14,000 YBP as suggested by the archaeological record. The study proposed the hypothesis that because dog haplotypes form four monophyletic clades, early domestic dogs may not have been morphologically distinct from their wild relatives until the change 10,000-15,000 years ago when humans moved from nomadic hunter-gatherer societies into agricultural societies and imposed selective regimes that resulted in marked phenotopic divergence from wolves. After the origin of dogs from a wolf ancestor, dogs and wolves may have continued to exchange genes.
In 1999, a review of the scientific literature regarding the genetic origin of the dog proposed a number of hypotheses. The molecular data indicated that dogs have protein alleles in common with wolves, share highly polymorphic microsatellites, and have mitochondrial DNA sequences similar or identical to those found in gray wolves. The mitochondrial control region DNA sequences show an average divergence between dogs and wolves of 1.5%, compared to dogs and coyotes, their next-closest relative, at 7.5%. Therefore, this indicated that the origin of the dog was from wolves. The archaeological record suggests that dogs were in Europe and the Middle East approximately 14,000 years ago, but the genetic record shows 135,000 YBP, which indicates that the morphological change was associated with artificial selection as humans shifted from hunter-gatherer to agrarian societies. Alternately, dogs may have had a more recent origin but are descended from a now extinct species of canid whose closest living relative was the gray wolf. The DNA sequences of dogs form four distinct clades, each with a separate ancestry from wolves that indicates four separate domestication events. One of the clades shows a wolf sequence that is identical to a dog sequence, suggesting a very recent interbreeding or domestication event. Once dogs were domesticated and spread over a wide area, occasional interbreeding would have transferred wolf mDNA to them.
- During the LGM, there were two types of wolf. A large, heavily-built megafaunal wolf spanned the cold north of the Holarctic that specialised in preying on megafauna. Another more gracile form lived in the warmer south in refuges from the glaciation. When the planet warmed and the LGM came to an end, whole species of megafauna became extinct along with their predators, leaving the more gracile form to dominate the Holarctic. This wolf we know today as the modern gray wolf, which is the dog's sister but not its ancestor - the dog shows a closer genetic relationship with the extinct megafaunal wolf.
In 2010, a study compared the mDNA haplotypes of 947 modern gray wolves from across Europe with the published sequences of 24 Pleistocene wolves from western Europe dated between 1,200-44,000 years BP. The study found that phylogenetically the haplotypes represented two haplogroups and referred to these as haplogroup 1 and 2. The 947 European wolves revealed 27 different haplotypes with haplogroup 1 forming a monophyletic clade, and all other haplotypes forming haplogroup 2. Comparison with gray wolves from other regions revealed that haplogroups 1 and 2 could be found spread across Eurasia, but only haplogroup 1 could be found in North America. The Pleistocene wolf samples from western Europe all belonged to haplogroup 2, which suggested a long-term predominance in this region. A comparison of current and past frequencies indicated that in Europe haplogroup 2 became outnumbered by haplogroup 1, but in North America haplogroup 2 became extinct and was replaced by haplogroup 1 after the Last Glacial Maximum. Access into North America was available between 20,000-11,000 years ago, after the Wisconsin glaciation had retreated but before the Bering land bridge became inundated by the sea. Therefore, haplogroup 1 was able to enter into North America during this period.
Analysis of stable isotopes, which offer conclusions about the diet and therefore the ecology of the extinct wolf populations, suggest that the Pleistocene wolves from haplogroup 2 mainly preyed on Pleistocene megafaunal species, which became rare at the beginning of the Holocene 12,000 years ago.:2 "Thus, Pleistocene wolves across Northern Eurasia and America may actually have represented a continuous and almost panmictic population that was genetically and probably also ecologically distinct from the wolves living in this area today.":R610 "The Pleistocene Eurasian wolves are morphologically and genetically comparable to the Pleistocene eastern-Beringian wolves.":791 Some of the ancient European and Beringian wolves shared a common haplotype (a17).:8 The specialized Pleistocene wolves, thus, did not contribute to the genetic diversity of modern wolves. Rather, modern wolf populations across the Holarctic are likely be the descendants of wolves from populations that came from more southern refuges as suggested previously for the North American wolves.:R611
The fossil remains of the direct ancestor of the dog have yet to be found, and so the probable ancestor is not yet confirmed.
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 Taymyr Peninsula, 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 European Nucleotide Archive 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.
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.: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.
The ancestral fossils have not yet been found.
Place of divergence
- Modern dogs show a closer genetic association with ancient, extinct canids from Europe and Arctic north-east Siberia.
In 2002, a study looked at 582 base pairs on the mitochondrial DNA of 654 dogs and 38 Eurasian wolves. The study found that 96% of the dogs formed three major clades, which were composed of 71 haplotypes. There was a total number of 44 haplotypes found in East Asia, of which 30 were unique to the region. The total number of haplotypes found in Europe was 20. The study assumed that the number of haplotypes would be higher in the ancestral population, and therefore the dog originated from one domestication event in East Asia and spread from there across Eurasia and into South-West Asia and Europe.
In August 2009, a study looked at 680 base pairs on the mitochondrial D-loop, 300 SNPs and 89 microsatellite markers of 318 African village dogs. The village dogs were found to be more genetically distinct when compared to non-native dogs, and with a similar haplotype diversity as had been found in East Asian village dogs. This finding called to question an East Asian origin of the domestic dog in an earlier 2002 study which appeared to have included many East Asian village dogs but few from other regions.
In September 2009, a study looked of 16,159 base pairs on the mitochondrial genomes of 169 dogs and 582 base-pairs of the mtDNA control regions of 1,543 dogs and eight wolves to reveal three haplogroups composed of ten sub-haplogroups. All ten sub-haplogroups could be found only in south-eastern Asia south of the Yangtze River and with diversity decreasing across Eurasia, with seven in Central China, five in North China and south-western Asia, until only four sub-haplogroups could be found in Europe. Therefore, this study concluded that dogs originated in a single domestication event from this region less than 16,300 YBP.
In 2010, a study looked at 48,000 SNPs from 912 dogs from 85 breeds and 225 grey wolves from 11 populations. The dog breeds shared a higher proportion of multi-locus haplotypes unique to grey wolves from the Middle East. Therefore, this study concluded that Middle Eastern grey wolves were the dominant source of dog diversity, European wolves to some European breeds, and Asian wolves to some Asian breeds, rather than wolves from Asia for all breeds as was suggested by an earlier 2009 mDNA study. Alternatively, there may have been significant admixture between some regional breeds and regional wolves.
In 2011, a study looked at 14,437 base pairs of Y-chromosome DNA sequences from 151 dogs sampled world-wide and eight wolves to reveal that the dogs exhibited five haplogroups composed of 28 haplotypes. Two of the haplogroups could be found world-wide. One could be found primarily in East Asia (including Siberia), North America, but at low frequencies in south-western Asia, Scandinavia, and Britain but not in continental Europe. One haplogroup could be found East Asia and in low frequencies in south-western Asia. One haplogroup consisted of only four individuals, with one in eastern Siberia and 3 in Africa. The south-western part of south-eastern Asia that is south of the Yangtze River (comprising South-East Asia and the Chinese provinces of Yunnan and Guangxi) provided 16 dogs representing 11 haplotypes which showed the highest diversity. Therefore, based on both mDNA markers from the 2009 study and Y-chromosome markers from this study that are in agreement, 50% of the dog gene pool is shared universally, but based on the wider diversity found in the south-western part of South-eastern Asia dogs have originated from this region.
Genetic studies comparing the dog with extant gray wolves did not result in agreement among researchers. In 1868, Charles Darwin wrote that some authors at the time proposed an unknown or extinct species was the ancestor of the dog. In 1934, an eminent paleontologist indicated that the ancestor of the dog lineage may have been the extinct Canis lupus variabilis.
In November 2013, a study analysed the complete and partial mitochondrial genome sequences of 18 fossil canids dating from 1,000 to 36,000 YBP from the Old and New Worlds, and compared these with the complete mitochondrial genome sequences from modern wolves and dogs. The data indicate that 22% 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 that 78% are sister to one or more ancient canids from Europe. Some 64% of the dogs are sister to a 14,500 YBP wolf sequence with a most recent common ancestor 32,100 YBP. This group of dogs matches three fossil pre-Columbian New World dogs between 1,000 and 8,500 YBP, which supports the hypothesis that pre-Columbian dogs in the New World share ancestry with modern dogs and that they likely arrived with the first humans to the New World. The data from this study indicates a European origin of dogs 18,800–32,100 years ago which supports the hypothesis that dog domestication preceded the emergence of agriculture and was initiated close to the Last Glacial Maximum when hunter-gatherers preyed on megafauna.
Arctic North-East Siberia
In 2015, a study looked at the mitogenome contol region sequences of 13 ancient canid remains and one modern wolf from five sites across Arctic north-east Siberia. The 14 canids revealed nine haplotypes, three of which were on record and the others unique. Four of the Siberian canids dated 28,000 YBP, and one Canis c.f. variabilis dated 360,000 YBP, were as divergent as the ancient European specimens found in an earlier study, and the European origin of domestic dogs may not be conclusive. The phylogenetic relationship of the extracted sequences showed that the haplotype from specimen S805 (28,000 YBP) was one step away from another haplotype S902 (8,000 YBP) that represents the domestic dog lineages. Several ancient haplotypes were oriented around S805, including Canis c.f. variabilis (360,000 YBP), Belgium (36,000 YBP - the "Goyet dog") and Belgium (30,000 YBP), and Konsteki, Russia (22,000 YBP). Given the position of the S805 haplotype, it may potentially represent a direct link from the putative progenitor (including Canis c.f. variabilis) to the domestic dog and modern wolf lineages.
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.
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. The DNA sequence of seven of the skulls indicated seven unique haplotypes that represented ancient wolf lineages lost until now. The osteometric analysis of the skulls showed that one large canid fossil from Goyet was clearly different from recent wolves, resembling most closely the Eliseevichi-1 dogs (15,000 years YBP) and so was identified as a Paleolithic dog (see below).
In November 2013, a DNA study sequenced three haplotypes from the ancient Belgium canids (the Goyet dog - Belgium 36,000 YBP cataloged as Canis species, and with Belgium 30,000 YBP and 26,000 years YBP 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, its 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 YBP 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.
Altai dog – 33,000 BP
- Genus Canis, species indeterminate
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 YBP, modern wolves from Europe and North America, and prehistoric Greenland dogs from the Thule period (1,000 YBP or later) to represent 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".
In March 2013, a DNA study of the Altai dog deposited the sequence in GenBank with a classification of Canis lupus familiaris (dog). "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.
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. 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.
Paleolithic dog – 27,000 BP
- Detailed DNA analysis yet to be conducted
In 2002, a study looked at the fossil skulls from two large canids dated at 13,905 YBP 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". In 2013, a study re-calibrated the age of the Eliseevichi-1 specimens to 15,000 YBP and classified them as Canis lupus familiaris(dog). In 2009, a study looked at these two early dog skulls in comparison to other much earlier but morphologically similar fossil skulls that had been found across Europe and concluded that the earlier specimens were "Paleolithic dogs", which were morphologically and genetically distinct from Pleistocene wolves that lived in Europe at that time. The study proposed, 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 showed their diet had been restricted compared to wolves, that the Paleolithic dog was domesticated. The study hypothesized that the Paleolithic dogs may have provided the stock from which early dogs came, or alternatively that they are a type of wolf that is not known to science.
- See also Paleolithic dog.
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 three 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, 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.
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.
One test indicated that dogs and modern wolves form sister clades, meaning that 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.
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 three 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.
There was a three-fold population decline for the three wolf samples since divergence, and it 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, namely changes in climate and prey, including megafaunal extinctions. This indicates that before the divergence of dogs from wolves there was much more wolf diversity. The results support a recent divergence between dogs and wolves followed by a dramatic reduction in population size.
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 two copies of the gene and the Siberian Husky that is associated with hunter-gatherers had just three or four 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.
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 basal to gray wolves from the Middle East, China, Europe and North America but shared 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.: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 Saarloos wolfdog showed more association with the gray wolf, which 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, although 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 four 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 that the ancestry of present-day dog breeds descends from more than one region.:3–4
An attempt to explore admixture between Taimyr-1 and gray wolves produced unreliable results.:23
Dog domestication (from the Latin domesticus: "belonging to the house") is a process by which the dog has become adapted to man and the captive environment by some combination of genetic changes occurring over generations. The process of dog domestication is unknown; the two main theories are self-domestication and human domestication. As a result of this process there is also evidence of convergent evolution having occurred between dogs and humans.
Archaeological evidence locates the earliest dog remains along with human remains 15,000 years ago at the Eliseevich-I Upper Paleolithic site, Russian Plain, Europe. Domesticated dogs are more clearly identified when they are associated with human occupation, and those interred side-by-side with human remains provide the most conclusive evidence.
|400,000||Eurasia||Lower Paleolithic sites including Boxgrove near Kent, England (400,000 years BP), Zhoukoudian in North China (300,000 BP), and Lazeret in southern France (150,000 years BP) have yielded wolf bones in close association with hominid bones. "The sites of occupation and hunting activities of humans and wolves must often have overlapped." We do not know if the co-location was the result of coincidence or a relationship.|
|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".:15 More recent researchers have proposed that Canis lupus variabilis may be an ancestor of the dog lineage.:7 At the site, the small wolf's remains were in close proximity to Peking man (Homo erectus pekinensis). In 2015, a mitochondrial DNA analysis was conducted on 14 ancient canid remains from Arctic Siberia and suggests a genetic contribution from regional sources of wolves, including possibly Canis cf. variabilis, to the modern dog lineage. This was the first study to extract DNA material from Canis variabilis, and it was thought to be widespread across Eurasia until 300,000 years ago.|
|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.|
|15,000||Eliseevich-I site, Russian Plain, Russia||Two fossil dog skulls. In 2002, a study looked at the fossil skulls of two 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". The Eliseevichi-1 skull is very similar in shape to the Goyet skull (36,000 BP), the Mezin dog skull (13,500 BP) and Mezhirich dog skull (13,500 BP). In 2013, the DNA sequence was identified as Canis lupus familiaris i.e. dog. See Paleolithic dog.|
|14,700||Bonn-Oberkassel, Germany||Dog mandible. Directly associated with a human double grave of a 50-year-old man and a 20-25-year-old woman. In 2013, the DNA sequence was identified as Canis lupus familiaris i.e. dog.|
|13,500 approx||Mezin, Ukraine||Ancient dog skull 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), Eliseevichi-1 dog skulls (15,000) and Mezhirich dog skull (13,500 BP). The Epigravettian Mezin site is well known for its round mammoth bone dwelling.|
|13,500 approx||Mezhirich, Ukraine||Ancient dog skull. 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 Eliseevichi-1 dog skulls (15,000) and Mezin dog skull (13,500 BP). The Epigravettian Mazhirich site has four mammoth bone dwellings present.|
|12,500||Karstein cave, Germany||Ancient dog skull. In 2013, the DNA sequence was identified as Canis lupus familiaris i.e. dog.|
|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 the Ust-Yana region. DNA analysis confirmed it as an early dog.|
|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.|
|9,200||Texas, USA||Dog bone fragment. Found in Hinds Cave in southwest Texas. In 2011, the DNA sequence was identified as Canis lupus familiaris i.e. dog, whose ancestry was rooted in Eurasia.|
|8,000||Svaerdborg site, Denmark||Three different dog types recorded at this Maglemosian culture site.|
|7,800||Jiahu site, China||Eleven dog interments. Jaihu is a Neolithic site 22 kilometers north of Wuyang in Henan Province.|
|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). 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 buried lying on their right side and facing towards the east as did their humans. Some were buried with artifacts, e.g., stone blades, birch bark and antler bone.|
|5,250||Skateholm, Sweden||Cemeteries contained dogs among humans. Generally, adults were buried in the central area with children and dogs in the outer area. In some cases adults, children and dogs were buried together as if forming a family. Dogs were buried with the same artifacts as humans - red ochre, flint tools or red deer antler. A dog burial with an antler head-dress and three flint blades was recovered at one of the sites.:36|
|1,500||Dionisio Point, Canada||Dogs buried in association with human burials. Two settlements with plank houses surrounded by midden. Dog remains have been recovered from the house areas and associated with human burials, and others found carefully buried within the midden which may have been a highly-symbolic place.|
Domestication of the dog
Domestication is a process by which a population of animals becomes adapted to man and the captive environment by some combination of genetic changes occurring over generations. Domestication is an evolutionary process in which one population of a species is reproductively isolated from another intentionally by humans. This reproductive isolation leads to 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 shows in morphological changes such as teeth size.
As a result of the archaeological evidence, humans formed a theory to help explain the observations. The current theory of dog domestication is based on comparisons between the dog and the extant (i.e. living today) gray wolf. However, in 2002 a 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. Recently two DNA studies indicated that the ancestor of the dog was not the extant gray wolf and that the fossil remains of their common ancestor have yet to be found. In 1983, a study proposed that the ancestor of Canis familiaris was a wild Canis familiaris. In 2015, a study found that the dog, the gray wolf and the now-extinct Taimyr wolf all triverged from a common ancestor 40,000 years ago i.e. without human intervention.
The process of domestication is unknown, but the two main hypotheses are self-domestication and human domestication.:210
The first of the two main hypotheses of dog domestication is self-domestication by wolves. Some wolves moved into a mutually beneficial 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 primitive dogs emerged from this group.
Cooperation Two recent DNA studies indicate 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.
A leading evolutionary biologist 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."
Natural selection without humans 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.":92
A dog's cranium is 15% smaller than an equally heavy wolf's, and the dog is less aggressive and more playful. Other species pairs show similar differences. Bonobos, like chimpanzees, are a close genetic cousin to humans, but unlike the chimpanzees, bonobos are not aggressive and do not participate in lethal inter-group 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. In other examples, the guinea pig's cranium is 13% smaller than its wild cousin the cavy, 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.:104
In the "farm fox" experiment, humans selectively bred foxes against aggression, causing 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.:114
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. The most docile or interesting animals could have been permitted to reproduce. After several generations of unconscious and later of conscious selection of human-defined behavioral traits, the first dogs emerged.
Orphaned wolf-pups Studies have shown that some wolf pups taken at an early age and reared by humans are easily tamed and socialized,:140 and one study has demonstrated that adult wolves can be socialized.:141 Some researchers propose that humans adopted orphaned wolf pups and breastfed them alongside human babies. 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. These breedings over generations would become more dog-like.:pages55-56
Against this proposition, at the time of domestication near the Last Glacial Maximum humans were already the top predator and had no need for wolves that would grow to eat five 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.:29 Other researchers attempting to socialize wolf pups after they reached 21 days of age found it very time-consuming and seldom practical or reliable in achieving success.
- See further: Socialization - dogs and wolves
Human selection The "farm fox" experiment attempted to reenact how domestication may have occurred. Researchers worked with farmed silver foxes selectively bred over 35 generations for tamability, i.e. becoming less fearful and less aggressive. The "domestic" 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, 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. A further criticism based on information obtained after the experiment's publication was 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. When humans restrict dogs' breeding diversity, another variable also comes into play that may have contributed to the change – inbreeding.:30
- See further: Reproductive isolation
In 2014, a whole genome study of the DNA differences between wolves and dogs found that dogs did not show a reduced fear response but did show greater synaptic plasticity. Synaptic plasticity is widely believed to be the cellular correlate of learning and memory, and this change may have altered the learning and memory abilities of dogs in comparison to wolves.
- See further: Dog learning by inference
In August 2015, a study looked at over 100 pig genome sequences to ascertain their process of domestication. The process of domestication was assumed to have been initiated by humans, involved few individuals and relied on reproductive isolation between wild and domestic forms. The study found that the assumption of reproductive isolation with population bottlenecks were not supported. The study indicated that pigs were domesticated separately in Western Asia and China, with Western Asian pigs introduced into Europe where they crossed with wild boar. The study also found that despite back-crossing with wild pigs, the genomes of domestic pigs have strong signatures of selection at DNA loci that affect behavior and morphology. The study concluded that human selection for domestic traits likely counteracted the homogenizing effect of gene flow from wild boars and created 'islands of domestication' in the genome. The same process may also apply to other domesticated animals, including dogs.
Convergent evolution between dogs and humans
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 a solution to the problem of moving through the water. What has been found between dogs and humans 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.: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.
The pointing gesture is a human-specific signal, is referential in its nature, and is a foundation building-block of human communication. Human infants acquire it weeks before the first spoken word. 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 demonstrating a similar level of performance as 2-year-old children can be explained as a joint outcome of their evolutionary history as well as their socialization in a human environment.
Later studies support coevolution in that dogs can discriminate the emotional expressions of human faces, and that most people can tell from a bark whether a dog is alone, being approached by a stranger, playing, or being aggressive, and can tell from a growl how big the dog is.
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 processes, and cancer, likely as a result of shared selection pressures.
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.
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. One observer has stated, "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....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 they 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. Powerful emotions were in play that many observers today refer to as love – boundless, unquestioning love.":40
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?
In 2002, a study proposed 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.
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, but 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 may have learned to mark their territory after watching wolves and dogs.
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 led 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.
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 exist 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.
In 2003, a study compared the behavior and ethics of chimpanzees, wolves and humans. Humans' genetically closest relative appears to be a frightful caricature of human egoism, and 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 that can be found 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 rivaled 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.
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 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. From a biologist's vantage point, the interwining process of hominization and canization makes sense only if viewed in terms of coevolution.
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