Origin of the domestic dog
Encyclopedia
The origin of the domestic dog
(Canis lupus familiaris) began with the domestication
of the gray wolf
(Canis lupus) several tens of thousands of years ago. Domesticated dogs provided early humans with a guard animal, a source of food, fur, and a beast of burden
. The process continues to this day, as the intentional cross-breeding of dogs continues, to create the so called "designer dogs."
carnivore
s that can be linked with some certainty to canids (wolves, foxes and dogs), are the Eocene
Miacids
some 56 to 38 million years ago. From the miacids evolved the cat
-like (Feloidea) and dog-like (Canoidea) carnivores. The canoid line led from the coyote
-sized Mesocyon
of the Oligocene
(38 to 24 million years ago) to the fox
-like Leptocyon
and the wolf-like Tomarctus
that wandered North America
some 10 million years ago. Canis lepophagus
, a small, narrow skulled North American canid of the Miocene
era, led to the first true wolves at the end of the Blancan North American Stage
such as Canis priscolatrans which evolved into Canis etruscus, then Canis mosbachensis,' and in turn C. mosbachensis which evolved to become Canis lupus, the Gray Wolf
—immediate precursor to the domestic dogs
has placed the earliest known domestication
at potentially 30,000 BC, and with certainty at 7,000 BC
. Other evidence suggests that dogs were first domesticated in East Asia
.
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 Palestine.
In 2008 re-examination of fossil 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 dogwolf was part of the Aurignacian culture that had produced the art in Chauvet Cave
.
In 2010, the remains of a 33,000-year-old "incipient dog" were found in the Altai Mountains of southern Siberia. In 2011 the skeleton of a 26,000- to 27,000-year-old dog were found in the Czech Republic. It had been interred with a bone in its mouth—perhaps to assist its journey in the afterlife.
Domestication of the wolf over time has produced a number of physical changes typical of all domesticated
mammals. 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.
Before DNA
was used, researchers were divided into two schools of thought:
Carles Vilà, who has conducted the most extensive study to date, has shown that DNA evidence has ruled out any ancestor canine species except the wolf. Vilà's team analyzed 162 different examples of wolf DNA from 27 populations in Europe, Asia, and North America. These results were compared with DNA from 140 individual dogs from 67 breeds gathered from around the world. Using blood or hair samples, DNA was extracted and genetic distance
for mitochondrial DNA
was estimated between individuals.
Based on this DNA evidence, most of the domesticated dogs were found to be members of one of four groups. The largest and most diverse group contains sequences found in the most ancient dog breeds, including the dingo
of Australia
, the New Guinea Singing Dog
, and many modern breeds, like the collie
and retriever
. Other groups such as the German Shepherd Dog
showed a closer relation to wolf sequences than to those of the main dog group, suggesting that such breeds had been produced by crossing dogs with wild wolves. It is also possible that this is evidence that dogs may have been domesticated from wolves on different occasions and at different places. Vilà is still uncertain whether domestication happened once–after which domesticated dogs bred with wolves from time to time–or whether it happened more than once.
A 2002 study by Peter Savolainen et al. identified mitochondrial DNA evidence suggesting a common origin from a single East Asia
n gene pool for all dog populations. In 2010, a study by Bridgett vonHoldt et al., using a larger data set of nuclear markers, pointed to the Middle East
as the source of most of the genetic diversity in the domestic dog and a more likely origin of domestication events. Z-L Ding et al. (2011) presented new Y-chromosome data from 151 dogs sampled worldwide, again pointing to a single domestication region south of the Yangtze river. The convergence of mtDNA and Y-chromosome variability in this region, the authors propose, indicate that a large number of wolves were domesticated, probably several hundred, as part of a sustained cultural practice.
The most puzzling fact of the DNA evidence is that the variability in molecular distance between dogs and wolves seems greater than the 10,000–20,000 years assigned to domestication. Yet the process and economics of domestication by humans only emerged later in this period in any case. Based upon the molecular clock
studies conducted, it would seem that dogs separated from the wolf lineage approximately 100,000 years ago. Although clear evidence for fossil
dogs becomes obscure beyond about 14,000 years ago, there are fossils of wolf bones in association with early humans from well beyond 100,000 years ago.
Tamed wolves might have taken up with hunter-gatherer
s without changing in ways that the fossil record could clearly capture. The influx of new genes from those crossings could very well explain the extraordinarily high number of dog breeds that exist today, the researchers suggest. Dogs have much greater genetic variability than other domesticated animals, such as cats, asserts Vilà.
Once agriculture
took hold, dogs would have been selected for different tasks, their wolf-like natures becoming a handicap as they became herders and guards. Molecular biologist Elaine Ostrander is of the view that "When we became an agricultural society, what we needed dogs for changed enormously, and a further and irrevocable division occurred at that point." This may be the point that stands out in the fossil record, when dogs and wolves began to develop noticeably different morphologies.
A recent study of African dogs found a high level of mtDNA diversity. The authors suggest that a new view of the domestication of the dog may be needed. A study by the Kunming Institute of Zoology
found that the domestic dog is descended from wolves tamed less than 16,300 years ago south of the Yangtse river in China. An older report said that all dog mitochondrial DNA
came from three wild Asian female wolves.
" experiment of Russia
n 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."
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 dog
s and pet
s.
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 mammal
s, 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".
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 their "pack leaders"—again, 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 whippet
s to guard flocks of sheep.
Dog
The domestic dog is a domesticated form of the gray wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and companion animal in...
(Canis lupus familiaris) began with the domestication
Domestication
Domestication or taming is the process whereby a population of animals or plants, through a process of selection, becomes accustomed to human provision and control. In the Convention on Biological Diversity a domesticated species is defined as a 'species in which the evolutionary process has been...
of the gray wolf
Gray Wolf
The gray wolf , also known as the wolf, is the largest extant wild member of the Canidae family...
(Canis lupus) several tens of thousands of years ago. Domesticated dogs provided early humans with a guard animal, a source of food, fur, and a beast of burden
Working animal
A working animal is an animal, usually domesticated, that is kept by humans and trained to perform tasks. They may be close members of the family, such as guide or service dogs, or they may be animals trained strictly to perform a job, such as logging elephants. They may also be used for milk, a...
. The process continues to this day, as the intentional cross-breeding of dogs continues, to create the so called "designer dogs."
Lineage
The earliest fossilFossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
carnivore
Carnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...
s that can be linked with some certainty to canids (wolves, foxes and dogs), are the Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
Miacids
Miacids
Miacids were primitive carnivores which lived during the late Paleocene and Eocene epochs about 62—33 million years ago. Miacids existed for approximately ....
some 56 to 38 million years ago. From the miacids evolved the cat
Cat
The cat , also known as the domestic cat or housecat to distinguish it from other felids and felines, is a small, usually furry, domesticated, carnivorous mammal that is valued by humans for its companionship and for its ability to hunt vermin and household pests...
-like (Feloidea) and dog-like (Canoidea) carnivores. The canoid line led from the coyote
Coyote
The coyote , also known as the American jackal or the prairie wolf, is a species of canine found throughout North and Central America, ranging from Panama in the south, north through Mexico, the United States and Canada...
-sized Mesocyon
Mesocyon
Mesocyon is an extinct genus of terrestrial carnivore within the family Canidae, subfamily Hesperocyoninae, which inhabited North America from the Early Oligocene 33.9—20.6 Ma, existing for approximately ....
of the Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
(38 to 24 million years ago) to the fox
Fox
Fox is a common name for many species of omnivorous mammals belonging to the Canidae family. Foxes are small to medium-sized canids , characterized by possessing a long narrow snout, and a bushy tail .Members of about 37 species are referred to as foxes, of which only 12 species actually belong to...
-like Leptocyon
Leptocyon
Leptocyon is a small extinct genus of canidae endemic to North America during the Oligocene through Miocene living from 24.8—10.3 mya, existing for approximately .Leptocyon was a small bodied, fox-like animal with a slender jaw.-Taxonomy:...
and the wolf-like Tomarctus
Tomarctus
Tomarctus is a canine of the extinct subfamily Borophaginae which inhabited most of North America during the late Early Miocene to the Early Barstovian age of the Middle Miocene . Tomarctus existed for approximately ....
that wandered North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
some 10 million years ago. Canis lepophagus
Canis lepophagus
Canis lepophagus or Hare-eating Wolf is an extinct species of canidae which was endemic to much of North America and lived from the Miocene epoch through Early Pleistocene, 10.3—1.8 Mya. The species existed for approximately . It is one of the more basal species of Canis, having existed before most...
, a small, narrow skulled North American canid of the Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
era, led to the first true wolves at the end of the Blancan North American Stage
Blancan
The Blancan North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology , typically set from 4,750,000 to 1,808,000 years BP, a period of .. It is usually considered to start in the early-mid Pliocene epoch and end...
such as Canis priscolatrans which evolved into Canis etruscus, then Canis mosbachensis,' and in turn C. mosbachensis which evolved to become Canis lupus, the Gray Wolf
Gray Wolf
The gray wolf , also known as the wolf, is the largest extant wild member of the Canidae family...
—immediate precursor to the domestic dogs
Domestication
How exactly the domestication of the Grey Wolf happened is unclear, but theories include the following:- Orphaned wolf-cubs: 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 nursedBreastfeedingBreastfeeding is the feeding of an infant or young child with breast milk directly from female human breasts rather than from a baby bottle or other container. Babies have a sucking reflex that enables them to suck and swallow milk. It is recommended that mothers breastfeed for six months or...
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. - The Promise of Food/Self Domestication: Early wolves would, as scavengers, be attracted to the refuse left at human campsites. Dr. Raymond Coppinger of Hampshire CollegeHampshire CollegeHampshire College is a private liberal arts college in Amherst, Massachusetts. It was founded in 1965 as an experiment in alternative education, in association with four other colleges in the Pioneer Valley: Amherst College, Smith College, Mount Holyoke College, and the University of Massachusetts...
(MassachusettsMassachusettsThe Commonwealth of Massachusetts is a state in the New England region of the northeastern United States of America. It is bordered by Rhode Island and Connecticut to the south, New York to the west, and Vermont and New Hampshire to the north; at its east lies the Atlantic Ocean. As of the 2010...
) argues that those wolves that were more successful at interacting with humans would pass these traits onto their offspring, eventually creating wolves with a greater propensity to be domesticated. The "most social and least fearful" dogs 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.
Archaeology
ArchaeologyArchaeology
Archaeology, or archeology , is the study of human society, primarily through the recovery and analysis of the material culture and environmental data that they have left behind, which includes artifacts, architecture, biofacts and cultural landscapes...
has placed the earliest known domestication
Domestication
Domestication or taming is the process whereby a population of animals or plants, through a process of selection, becomes accustomed to human provision and control. In the Convention on Biological Diversity a domesticated species is defined as a 'species in which the evolutionary process has been...
at potentially 30,000 BC, and with certainty at 7,000 BC
7th millennium BC
During the 7th millennium BC, agriculture spreads from Anatolia to the Balkans.World population was essentially stable at around 5 million people, living mostly scattered across the globe in small hunting-gathering tribes...
. Other evidence suggests that dogs were first domesticated in East Asia
East Asia
East Asia or Eastern Asia is a subregion of Asia that can be defined in either geographical or cultural terms...
.
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 Palestine.
In 2008 re-examination of fossil 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 dogwolf was part of the Aurignacian culture that had produced the art in Chauvet Cave
Chauvet Cave
The Chauvet-Pont-d'Arc Cave is a cave in the Ardèche department of southern France that contains the earliest known cave paintings, as well as other evidence of Upper Paleolithic life. It is located near the commune of Vallon-Pont-d'Arc on a limestone cliff above the former bed of the Ardèche River...
.
In 2010, the remains of a 33,000-year-old "incipient dog" were found in the Altai Mountains of southern Siberia. In 2011 the skeleton of a 26,000- to 27,000-year-old dog were found in the Czech Republic. It had been interred with a bone in its mouth—perhaps to assist its journey in the afterlife.
Domestication of the wolf over time has produced a number of physical changes typical of all domesticated
Domestication
Domestication or taming is the process whereby a population of animals or plants, through a process of selection, becomes accustomed to human provision and control. In the Convention on Biological Diversity a domesticated species is defined as a 'species in which the evolutionary process has been...
mammals. 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
Brachycephaly
Brachycephaly, also known as flat head syndrome, is a type of cephalic disorder. This can result from premature fusion of the coronal sutures or from external deformation . The coronal suture is the fibrous joint that unites the frontal bone with the two parietal bones of the skull. The parietal...
). Certain wolf-like behaviors, such as the regurgitation of partially digested food for the young, have also disappeared.
DNA evidence
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
was used, researchers were divided into two schools of thought:
- Most supposed that these early dogs were descendants of tamed wolves, which interbred and evolved into a domesticated species.
- Other scientists, while believing wolves were the chief contributor, suspected that jackals or coyotes contributed to the dog's ancestry.
Carles Vilà, who has conducted the most extensive study to date, has shown that DNA evidence has ruled out any ancestor canine species except the wolf. Vilà's team analyzed 162 different examples of wolf DNA from 27 populations in Europe, Asia, and North America. These results were compared with DNA from 140 individual dogs from 67 breeds gathered from around the world. Using blood or hair samples, DNA was extracted and genetic distance
Genetic distance
Genetic distance refers to the genetic divergence between species or between populations within a species. It is measured by a variety of parameters. Smaller genetic distances indicate a close genetic relationship whereas large genetic distances indicate a more distant genetic relationship...
for mitochondrial DNA
Mitochondrial DNA
Mitochondrial DNA is the DNA located in organelles called mitochondria, structures within eukaryotic cells that convert the chemical energy from food into a form that cells can use, adenosine triphosphate...
was estimated between individuals.
Based on this DNA evidence, most of the domesticated dogs were found to be members of one of four groups. The largest and most diverse group contains sequences found in the most ancient dog breeds, including the dingo
Dingo
The Australian Dingo or Warrigal is a free-roaming wild dog unique to the continent of Australia, mainly found in the outback. Its original ancestors are thought to have arrived with humans from southeast Asia thousands of years ago, when dogs were still relatively undomesticated and closer to...
of Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, the New Guinea Singing Dog
New Guinea Singing Dog
The New Guinea Singing Dog is a wild dog once found throughout New Guinea. New Guinea Singing Dogs are named for their unique howl....
, and many modern breeds, like the collie
Collie
The collie is a distinctive type of herding dog, including many related landraces and formal breeds. It originates in Scotland and Northern England. It is a medium-sized, fairly lightly built dog with a pointed snout, and many types have a distinctive white pattern over the shoulders. Collies...
and retriever
Retriever
A retriever is a type of gun dog that retrieves game for a hunter. Generally gun-dogs are divided into three major classifications: retrievers, flushing spaniels, and pointing breeds. Retrievers were bred primarily to retrieve birds or other prey and return them to the hunter without damage...
. Other groups such as the German Shepherd Dog
German Shepherd Dog
The German Shepherd Dog , also known as an Alsatian or just the German Shepherd, is a breed of large-sized dog that originated in Germany. The German Shepherd is a relatively new breed of dog, with its origin dating to 1899. As part of the Herding Group, the German Shepherd is a working dog...
showed a closer relation to wolf sequences than to those of the main dog group, suggesting that such breeds had been produced by crossing dogs with wild wolves. It is also possible that this is evidence that dogs may have been domesticated from wolves on different occasions and at different places. Vilà is still uncertain whether domestication happened once–after which domesticated dogs bred with wolves from time to time–or whether it happened more than once.
A 2002 study by Peter Savolainen et al. identified mitochondrial DNA evidence suggesting a common origin from a single East Asia
East Asia
East Asia or Eastern Asia is a subregion of Asia that can be defined in either geographical or cultural terms...
n gene pool for all dog populations. In 2010, a study by Bridgett vonHoldt et al., using a larger data set of nuclear markers, pointed to the Middle East
Middle East
The Middle East is a region that encompasses Western Asia and Northern Africa. It is often used as a synonym for Near East, in opposition to Far East...
as the source of most of the genetic diversity in the domestic dog and a more likely origin of domestication events. Z-L Ding et al. (2011) presented new Y-chromosome data from 151 dogs sampled worldwide, again pointing to a single domestication region south of the Yangtze river. The convergence of mtDNA and Y-chromosome variability in this region, the authors propose, indicate that a large number of wolves were domesticated, probably several hundred, as part of a sustained cultural practice.
The most puzzling fact of the DNA evidence is that the variability in molecular distance between dogs and wolves seems greater than the 10,000–20,000 years assigned to domestication. Yet the process and economics of domestication by humans only emerged later in this period in any case. Based upon the molecular clock
Molecular clock
The molecular clock is a technique in molecular evolution that uses fossil constraints and rates of molecular change to deduce the time in geologic history when two species or other taxa diverged. It is used to estimate the time of occurrence of events called speciation or radiation...
studies conducted, it would seem that dogs separated from the wolf lineage approximately 100,000 years ago. Although clear evidence for fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
dogs becomes obscure beyond about 14,000 years ago, there are fossils of wolf bones in association with early humans from well beyond 100,000 years ago.
Tamed wolves might have taken up with hunter-gatherer
Hunter-gatherer
A hunter-gatherer or forage society is one in which most or all food is obtained from wild plants and animals, in contrast to agricultural societies which rely mainly on domesticated species. Hunting and gathering was the ancestral subsistence mode of Homo, and all modern humans were...
s without changing in ways that the fossil record could clearly capture. The influx of new genes from those crossings could very well explain the extraordinarily high number of dog breeds that exist today, the researchers suggest. Dogs have much greater genetic variability than other domesticated animals, such as cats, asserts Vilà.
Once agriculture
Agriculture
Agriculture is the cultivation of animals, plants, fungi and other life forms for food, fiber, and other products used to sustain life. Agriculture was the key implement in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that nurtured the...
took hold, dogs would have been selected for different tasks, their wolf-like natures becoming a handicap as they became herders and guards. Molecular biologist Elaine Ostrander is of the view that "When we became an agricultural society, what we needed dogs for changed enormously, and a further and irrevocable division occurred at that point." This may be the point that stands out in the fossil record, when dogs and wolves began to develop noticeably different morphologies.
A recent study of African dogs found a high level of mtDNA diversity. The authors suggest that a new view of the domestication of the dog may be needed. A study by the Kunming Institute of Zoology
Kunming Institute of Zoology
Kunming Institute of Zoology , one of the 20 biological institutes under the Chinese Academy of Sciences , is one of China's first class zoological research institutes...
found that the domestic dog is descended from wolves tamed less than 16,300 years ago south of the Yangtse river in China. An older report said that all dog mitochondrial DNA
Mitochondrial DNA
Mitochondrial DNA is the DNA located in organelles called mitochondria, structures within eukaryotic cells that convert the chemical energy from food into a form that cells can use, adenosine triphosphate...
came from three wild Asian female wolves.
Experimental evidence
As an experiment in the domestication of wolves, the "farm foxTame Silver Fox
The domesticated silver fox is a domesticated form of the silver morph of the red fox. As a result of selective breeding, the new foxes became not only tamer, but more dog-like as well....
" experiment of Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
n scientist Dmitry Belyaev attempted to reenact how domestication may have occurred. Researchers, working with wild silver foxes
Red Fox
The red fox is the largest of the true foxes, as well as being the most geographically spread member of the Carnivora, being distributed across the entire northern hemisphere from the Arctic Circle to North Africa, Central America, and the steppes of Asia...
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
Tame Silver Fox
The domesticated silver fox is a domesticated form of the silver morph of the red fox. As a result of selective breeding, the new foxes became not only tamer, but more dog-like as well....
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."
Specialization
As humans migrated around the planet, a variety of dog forms migrated with them. The agricultural revolutionNeolithic Revolution
The Neolithic Revolution was the first agricultural revolution. It was the transition from hunting and gathering to agriculture and settlement. Archaeological data indicates that various forms of plants and animal domestication evolved independently in 6 separate locations worldwide circa...
and subsequent urban revolution
Urban revolution
In anthropology and archaeology, the Urban Revolution is the process by which small, kin-based, nonliterate agricultural villages were transformed into large, socially complex, urban societies....
led to an increase in the dog population and a demand for specialization
Specialization (functional)
Specialization is the separation of tasks within a system. In a multicellular creature, cells are specialized for functions such as bone construction or oxygen transport. In capitalist societies, individual workers specialize for functions such as building construction or gasoline transport...
. These circumstances would provide the opportunity for selective breeding
Selective breeding
Selective breeding is the process of breeding plants and animals for particular genetic traits. Typically, strains that are selectively bred are domesticated, and the breeding is sometimes done by a professional breeder. Bred animals are known as breeds, while bred plants are known as varieties,...
to create specialized types
Dog type
Dog types are broad categories of dogs based on function, with dogs identified primarily by specific function or style of work rather than by lineage or appearance....
of working dog
Working dog
A working dog refers to a canine working animal, i.e., a type of dog that is not merely a pet but learns and performs tasks to assist and/or entertain its human companions, or a breed of such origin...
s and pet
Pet
A pet is a household animal kept for companionship and a person's enjoyment, as opposed to wild animals or to livestock, laboratory animals, working animals or sport animals, which are kept for economic or productive reasons. The most popular pets are noted for their loyal or playful...
s.
Neoteny in the rapid evolution of diverse dog breeds
Neoteny
Neoteny , also called juvenilization , is one of the two ways by which paedomorphism can arise. Paedomorphism is the retention by adults of traits previously seen only in juveniles, and is a subject studied in the field of developmental biology. In neoteny, the physiological development of an...
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 mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s, 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".
- Herding dogHerding dogA herding dog, also known as a stock dog or working dog, is a type of pastoral dog that either has been trained in herding or belongs to breeds developed for herding...
s exhibit the controlled characteristics of hunting dogs. Members of this group, such as Border CollieBorder CollieThe Border Collie is a herding dog breed developed in the Anglo-Scottish border region for herding livestock, especially sheep. It is the most widespread of the collie breeds....
s, Belgian MalinoisBelgian Shepherd Dog (Malinois)The Belgian Shepherd Dog is a breed of dog, sometimes classified as a variety of the Belgian Shepherd Dog rather than as a separate breed. The Malinois is recognized in the United States under the name Belgian Malinois...
and German Shepherds, use tactics of hunter and prey to intimidate and keep control of herds and flocks. Their natural instinct to bring down an animal under their charge is muted by training. Other members of the group, including Welsh CorgiWelsh CorgiThe Welsh corgi is a small type of herding dog that originated in Wales. Two distinct breeds are recognized: the Pembroke Welsh corgi and the Cardigan Welsh corgi, with the Pembroke being the more common..-Description:...
s, Canaan dogCanaan DogThe Canaan dog is a Canaanite breed of dog which may have existed in the eastern Mediterranean seaboard for millennia, as referenced in ancient sculptures.-Appearance:...
s, and Cattle dogs, herd with a more aggressive demeanor (such as biting and nipping at the heels of the animals) and make use of body design to elude the defences of their charges. - Gun dogGun dogthumb|right|A group of Gun dogs as printed in Dogs of All Nations by W.E. Mason in 1915Gun dogs, also gundogs or bird dogs, are types of dogs developed to assist hunters in finding and retrieving game, usually birds. Gun dogs are divided into three primary types: Retrievers, flushing dogs, and...
breeds used in hunting—that is, pointers, setterSetterThe setter is a type of gundog used most often for hunting game such as quail, pheasant, and grouse. A setter silently searches for game by scent. When prey is encountered the dog freezes rather than chasing after the game. Setters get their name from their distinctive stance; a sort of crouch...
s, spanielSpanielA spaniel is a type of gun dog. It is assumed spaniels originated from Spain as the word spaniel may be derived from Hispania or possibly from the French phrase "Chiens de l’Espagnol" . Spaniels were especially bred to flush game out of dense brush. By the late 17th century spaniels had become...
s, and retrieverRetrieverA retriever is a type of gun dog that retrieves game for a hunter. Generally gun-dogs are divided into three major classifications: retrievers, flushing spaniels, and pointing breeds. Retrievers were bred primarily to retrieve birds or other prey and return them to the hunter without damage...
s—have an intermediate degree of paedomorphism; they are at the point where they share in the pack's hunting behavior, but are still in a junior role, not participating in the actual attack. They identify potential prey and freeze into immobility, for instance, but then refrain from stalking the prey as an adult predator would do; this results in the "pointing" behavior for which such dogs are bred. Similarly, they seize dead or wounded prey and bring it back to the "pack", even though they did not attack it themselves, that is, "retrieving" behavior. Their physical characteristics are closer to that of the mature wild canine than the sheepdog breeds, but they typically do not have erect ears, etc.
- ScenthoundScent houndScent hounds are a type of hound that primarily hunts by scent rather than sight. The Scenthound breeds are generally regarded as having some of the most sensitive noses among canines....
s maintain an intermediate body type and behavior pattern that causes them to actually pursue prey by tracking their scent, but tend to refrain from actual individual attacks in favor of vocally summoning the pack leaders (in this case, humans) to do the job. They often have a characteristic vocalization called a bay. Some examples are the Beagle, Bloodhound, Basset Hound, Coonhound, Dachshund, Fox Hound, Otter Hound, and Harrier. - SighthoundSighthoundSighthounds, also called gazehounds, are hounds that primarily hunt by speed and sight, instead of by scent and endurance as scent hounds do.-Appearance:...
s, who pursue and attack perceived prey on sight, maintain the mature canine size and some features, such as narrow chest and lean bodies, but have largely lost the erect ears of the wolf and thick double layered coats. Some examples are the Afghan HoundAfghan HoundThe Afghan Hound is one of the oldest sighthound dog breeds. Distinguished by its thick, fine, silky coat and its tail with a ring curl at the end, the breed acquired its unique features in the cold mountains of Afghanistan, where it was originally used to hunt hares and gazelles by coursing them....
, BorzoiBorzoiThe borzoi is a breed of domestic dog also called the Russian wolfhound and descended from dogs brought to Russia from central Asian countries. It is similar in shape to a greyhound, and is also a member of the sighthound family.The system by which Russians over the ages named their sighthounds...
, SalukiSalukiThe Saluki, also known as the Royal Dog of Egypt and Persian Greyhound is one of the oldest known breeds of domesticated dog. From the period of the Middle Kingdom onwards, Saluki-like animals appear on the ancient Egyptian tombs of 2134 BC. They have connections both to the Bible and Imperial...
, SloughiSloughiThe Sloughi is a North African breed of dog, specifically a member of the sighthound family. It is found in Morocco, Algeria, Tunisia and Libya. Sloughis are likely closely related to the Azawakh, but not to the Saluki .-Appearance:...
, Pharaoh HoundPharaoh HoundThe Pharaoh Hound is a breed of dog and the national hound of the Mediterranean nation of Malta. Its native name is Kelb tal-Fenek in Maltese, which means "rabbit hound". The dog is the traditional hunting companion of Maltese outdoorsmen. The breed has no conclusive links with Ancient Egypt and...
, AzawakhAzawakhThe Azawakh is a sighthound dog breed from Africa.-Appearance:Morphology is very similar to that of the Middle Eastern and South Indian sight hounds, all swift, high-bred coursing hounds, although there are several obvious differences. For example, a short, flat back combined with long legs place...
, WhippetWhippetThe Whippet is a breed of dog in the sighthound family. They are active and playful and are physically similar to a small Greyhound.- Description :...
, and GreyhoundGreyhoundThe Greyhound is a breed of sighthound that has been primarily bred for coursing game and racing, and the breed has also recently seen a resurgence in its popularity as a pedigree show dog and family pet. It is a gentle and intelligent breed...
. - MastiffEnglish MastiffThe English Mastiff, referred to by virtually all Kennel Clubs simply as the Mastiff, is a breed of large dog perhaps descended from the ancient Alaunt through the Pugnaces Britanniae. Distinguishable by enormous size, massive head, and a limited range of colors, but always displaying a black mask,...
-types are large dogs, both tall and massive with barrel-like chests, large bones, and thick skulls. They have traditionally been bred for war, protection, and guardian work. - BulldogBulldogBulldog is the name for a breed of dog commonly referred to as the English Bulldog. Other Bulldog breeds include the American Bulldog, Olde English Bulldogge and the French Bulldog. The Bulldog is a muscular heavy dog with a wrinkled face and a distinctive pushed-in nose...
-types are medium sized dogs bred for combat against both wild and domesticated animals. These dogs have a massive, square skull and large bones with an extremely muscular build and broad shoulders. - TerrierTerrierA terrier is a dog of any one of many breeds or landraces of terrier type, which are typically small, wiry, very active and fearless dogs. Terrier breeds vary greatly in size from just a couple of pounds to over 70 pounds and are usually categorized by size or function...
s similarly have adult aggressive behavior, famously coupled with a lack of juvenile submission, and display correspondingly adult physical features such as erect ears, although many breeds have also been selected for size and sometimes dwarfed legsAchondroplasiaAchondroplasia dwarfism occurs as a sporadic mutation in approximately 85% of cases or may be inherited in an autosomal dominant genetic disorder that is a common cause of dwarfism...
to enable them to pursue prey in their burrows.
The least paedomorphic behavior pattern may be that of the basenji
Basenji
The Basenji is a breed of hunting dog that was bred from stock originating in central Africa. Most of the major kennel clubs in the English-speaking world place the breed in the Hound Group; more specifically, it may be classified as belonging to the sighthound type...
, bred in Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
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 their "pack leaders"—again, 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 whippet
Whippet
The Whippet is a breed of dog in the sighthound family. They are active and playful and are physically similar to a small Greyhound.- Description :...
s to guard flocks of sheep.
Further reading
- Klütsch CFC, Seppälä EH, Lohi H, Fall T, Hedhammar Å, Uhlén M, Savolainen P (2010) Regional occurrence, high frequency but low diversity of mitochondrial DNA haplogroup d1 suggests a recent dog-wolf hybridization in Scandinavia. Animal Genetics, online early.
- Morey, Darcy. Dogs: Domestication and the Development of a Social Bond (Cambridge University Press; 2010) 384 pages; uses zooarchaeology to explores ties between humans and canines over the past 15,000 years with a focus on the New World and Arctic regions.