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The origin of the domestic dog (Canis lupus familiaris or Canis familiaris) began from a single domestication of a now-extinct wolf-like canid in Western Europe 11 to 16 thousand years ago. This period predates the rise of agriculture and implies that the earliest dogs arose along with hunter-gatherers and not agriculturists. 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. This era towards the end of the last ice age is known as the Magdalenian period dating from around 17,000 to 12,000 years ago, and refers to one of the later cultures of the Upper Paleolithic in western Europe at that time.
See under Wolf ancestry
There are three schools of thought on the origin of the dog.
Within the Canidae, three distinct phylogenetic groupings are apparent:
Additionally, there are several canids that have no close living relatives and define distinct evolutionary lineages; such as the gray fox (genus Urocyon), the bat-eared fox (genus Otocyon), and the raccoon dog (genus Nyctereutes).
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. 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 - until DNA analysis indicated otherwise.
It has been thought for some time that "...the wolf is the most probable ancestor and closest relative of the domestic dog." In 1995, DNA analysis of extant (i.e. living today) Canidea species indicated that the wolf and the domestic dog were so genetically similar that the wolf may have been the ancestor of the dog. By 1999, further genetic evidence supported this view and indicated that the domestic dog may have emerged from multiple wolf populations. In 2002, this amount of populations was narrowed down to a possibility of at least five separate female lines when different dog haplotypes were split into five differing clades.
In 1997, a study determined that domestic dogs could have originated as much as 135,000 years ago. 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. These hypervariable sites are mutational hotspots where somatic mitochondrial DNA and germline mutations usually take place. 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.
In 2002, a study examined the mitochondrial DNA mtDNA 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. 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.
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. 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.
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. 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.
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.
During the Late Pleistocene megafaunal extinctions, a number of wolves disappeared that were genetically unique and morphologically distinct. In 2007, a study found that none of the 16 mtDNA haplotypes recovered from a sample of 20 Pleistocene East Beringian wolves was shared with any modern wolf.
Between March 2013 and January 2014, three studies were released that undertook similar investigation using the same or similar samples and each had Robert K Wayne as a senior author.
In March 2013, a study isolated, sequenced and analysed 413 nucleotides of the mitochondrial control region of ancient DNA from the 33,000-year old skull of a dog-like canid that was excavated from Razboinichya Cave in the Altai Mountains of southern Siberia in 1975. The sample was deposited in GenBank with accession number JX173682. The sample was compared with those of 72 extant dogs and 30 wolves, 35 prehistoric New World canids, and 4 coyotes. "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". One of the team members had conducted an earlier study, which suggests the Altai dog did not give rise to later lineages and probably represents wolf domestication disrupted by the climatic and cultural changes associated with the Last Glacial Maximum. This dog and the one from the Goyet cave in Belguim, separated by thousands of kilometers, show that dog domestication was multiregional, and thus had no single place of origin.
In November 2013, a study analysed the complete and partial mitochondrial genomes of 18 fossil canids dating from 1,000 to 36,000 years ago from the Old and New Worlds, and compared these with the complete mitochondrial genome sequences from 49 wolves and 77 dogs - including divergent dog breeds such as the Basenji and Dingo - 3 recently published Chinese indigenous dogs, and 4 coyotes totaling 148 mitochondrial genomes. 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, 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. 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 (the phylogenetic equivalent to a great-great-grand-aunt). 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 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 18,000-32,000 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-gatherrers 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. Furthermore, several ancient dogs may represent failed domestication events, such as the 33,000 year old Altai Mountain specimen of Russia, and the 36,000 year old Goyet specimen of Belgium (cataloged as Canis species KF661079) that appears to be in a sister group to all modern dogs and wolves. Further discussion by the study's senior authors can be found online.
In January 2014, a study analysed 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) from Croatia, Israel, and China; 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; and a golden jackal (Canis aureus). For some analyses, data was leveraged from a companion study of 12 additional dog breeds.
The data indicates that dogs and wolves diverged through a dynamic process involving population bottlenecks in both lineages and post-divergence gene flow, which confounds previous inferences of dog origins. Dogs arose from a single domestication 11 to 16 thousand years ago. This period predates the rise of agriculture and, along with new evidence from variation in amylase copy number, implies that the earliest dogs arose alongside hunter-gathers rather than agriculturists. The amylase copy number variation is also present in wolf populations, suggesting that the initial duplication was likely a standing variant when the domestication process began.
There was evidence of wolf-dog admixture in two dog lineages that have been isolated from wolves geographically in the recent past. This suggests wolf-dog admixture was occurring ancestrally and has impacted multiple, if not most, dog lineages. Admixture has likely complicated previous inferences of dog origins. For instance, the presence of long shared haplotypes in Middle East wolves with several dog breeds may reflect historic admixture rather than recent divergence.
No one wolf lineage of those sampled was more closely related to dogs than any other, suggesting that the nearest wild relative to dogs was a more basal wolf than sampled in this study. This basal wolf lineage has gone extinct and the current wolf diversity from each region represents novel younger wolf lineages, as suggested by their recent divergence.
Investigation of outlier regions of the genome with respect to selection signatures showed evidence for enrichment in gene categories involved in skeletal and dental morphology. Genes in these categories may have played roles in the evolution to early dogs having shortened, broader skulls, more extreme tooth crowding, smaller carnassials, and reduced body size. Evidence was found for selection on genes involved in neural development. Notably, four of the top eight selection candidate regions each contain a gene known to impact memory and behavior in mice and humans.
The co-senior author of the studies, Robert K Wayne, has stated that:
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Archaeology has placed the earliest known domestication approximately 30,000 BC, and with certainty at 7,000 BC. While evidence for fossil dogs lessens considerably beyond 14,000 years ago and ending 33,000 years ago, there are fossils of wolf bones in association with early humans from well beyond 100,000 years ago.
Due to the difficulty in assessing the structural differences in bones, the identification of a domestic dog based on cultural evidence is of special value. Perhaps the earliest clear evidence for this domestication is the first dog found buried together with human from 12,000 years ago in Israel and a burial site in Germany called Bonn-Oberkassel with joint human and dog interments dating to 14,000 years ago.
In 2008, re-examination of material excavated from Goyet Cave in Belgium in the late 19th century resulted in the identification of a 31,700 year old dog, a large and powerful animal who ate reindeer, musk oxen and horses. This dog was part of the Aurignacian culture that had produced the art in Chauvet Cave.
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 colouration 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.
A study of fossil dogs and wolves in Belgium, Ukraine, and Russia tentatively dates domestication from 14,000 years ago to more than 31,700 years ago. Another recent study has found support for claims of dog domestication between 14,000 and 16,000 years ago, with a range between 9,000 and 34,000 years ago, depending on mutation rate assumptions.
Although experts largely disagree over the details of dog domestication, it is agreed that human interaction played a significant role in shaping the subspecies.:pages95-136 Domestication may have occurred initially in separate areas, particularly Siberia and Europe. It is thought that the current lineage of dogs were domesticated between 15,000 years and 8,500 years ago. Shortly after the latest domestication, dogs became ubiquitous in human populations, and spread throughout the world.
There is evidence the present lineage of dogs genetically diverged from their wolf ancestors at least 15,000 years ago, but some believe domestication to have occurred earlier. Evidence is accruing that there were previous domestication events, but that those lineages died out.
In 2008, a team of international scientists released findings from an excavation at Goyet Cave in Belgium declaring a large, toothy canine existed 31,700 years ago and ate a diet of horse, musk ox and reindeer.
Prior to this Belgian discovery, the earliest dog bones found were two large skulls from Russia and a mandible from Germany dated from roughly 14,000 years ago. Remains of smaller dogs from Natufian cave deposits in the Middle East, including the earliest burial of a human being with a domestic dog, have been dated to around 10,000 to 12,000 years ago. There is a great deal of archaeological evidence for dogs throughout Europe and Asia around this period and through the next two thousand years (roughly 8,000 to 10,000 years ago), with specimens uncovered in Germany, the French Alps, and Iraq, and cave paintings in Turkey. The oldest remains of a domesticated dog in the Americas were found in Texas and have been dated to about 9,400 years ago.
A great deal of controversy surrounds the evolutionary framework for the domestication of dogs. Although it is widely claimed that "man domesticated the wolf," man might not have taken such a proactive role in the process. The nature of the interaction between man and wolf that led to domestication is unknown and controversial. 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 canine species.
It is not known whether humans domesticated the wolf as such to initiate dog's divergence from its ancestors, or whether dog's evolutionary path had already taken a different course prior to domestication. For example, it is hypothesized that some wolves gathered around the campsites of paleolithic camps to scavenge refuse, and associated evolutionary pressure developed that favored those who were less frightened by, and keener in approaching, humans.
As an experiment in the domestication of wolves, the "farm fox" experiment of Russian scientist Dmitry Belyaev attempted to reenact how domestication may have occurred. 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."
How exactly the domestication of the wolf happened is unclear, but theories include one or more of the following:
"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 withe 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.":40
Studies have shown that some wolf pups taken at an early age and reared by humans are easily tamed and socialized. At least one study has demonstrated that adult wolves can be successfully socialized. However, according to other researchers attempts to socialize wolves after the pups reach 21 days of age are very time-consuming and seldom practical or reliable in achieving success.
Many scientists believe that humans adopted orphaned wolf cubs and nursed them alongside human babies. Once these early adoptees started breeding among themselves, a new generation of tame "wolf-like" domestic animals would result which would, over generations of time, become more dog-like.
Early wolves would, as scavengers, be attracted to human field kills and refuse left at human campsites. Dr. Raymond Coppinger of Hampshire College (Massachusetts) argues 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 "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.
Coppinger believes that a behavioral characteristic called "flight distance" was crucial to the transformation from wild wolf to the ancestors of the modern dog. It 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. "My argument is that what domesticated—or tame—means is to be able to eat in the presence of human beings. That is the thing that wild wolves can't do."
Furthermore, selection for domesticity had the side effect of selecting genetically related physical characteristics, and behavior such as barking. Hypothetically, wolves separated into two populations–the village-oriented scavengers and the packs of hunters. The next steps have not been defined, but selective pressure must have been present to sustain the divergence of these populations.
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As humans migrated around the planet, a variety of dog forms migrated with them. The agricultural revolution and subsequent urban revolution led to an increase in the dog population and a demand for specialization. These circumstances would provide the opportunity for selective breeding to create specialized types of working dogs and pets. These specializations originated simply from human selection for tameness alone.
Domesticated dogs provided early humans with a hunting companion, guard, a source of food and fur, and a beast of burden, while the humans provided the dogs with food and shelter. The process continues to this day, with the intentional artificial selection and cross-breeding of dogs to create new breeds of dogs.
This rapid evolution of dogs from wolves is an example of neoteny or paedomorphism. As with many species, young wolves are more social and less dominant than adults; therefore, the selection for these characteristics, whether deliberate or inadvertent, is more likely to result in a simple retention of juvenile characteristics into adulthood than to generate a complex of independent new changes in behavior. (This is true of many domesticated animals.)
This paedomorphic selection naturally results in a retention of juvenile physical characteristics as well. Compared to wolves, many adult dog breeds retain such juvenile characteristics as soft fuzzy fur, round torsos, large heads and eyes, ears that hang down rather than stand erect, etc.; characteristics which are shared by most juvenile mammals, and therefore generally elicit some degree of protective and nurturing behavior cross-species from most adult mammals, including humans, who term such characteristics "cute" or "appealing". It has been seen that these traits can even prompt an adult female wolf to act more defensively of dog puppies than of wolf puppies. The example of canine neoteny goes even further, in that the various breeds are differently neotenized according to the type of behavior that was selected.
The least paedomorphic behavior pattern may be that of the basenji, bred in Africa to hunt alongside humans almost on a peer basis. This breed is often described as highly independent, neither needing nor appreciating a great deal of human attention or nurturing, often described as "catlike" in its behavior. It too has the body plan of an adult canine predator.
Of course, dogs in general possess a significant ability to modify their behavior according to experience, including adapting to the behavior of humans. This allows them to be trained to behave in a way that is not specifically the most natural to their breed; nevertheless, the accumulated experience of thousands of years shows that some combinations of nature and nurture are quite daunting, for instance, training whippets to guard flocks of sheep.