Dog
thumb|300px|Dogs show great morphological variation

The domestic dog (Canis lupus familiaris when considered a subspecies of the wolf or Canis familiaris when considered a distinct species) is a member of the genus Canis (canines), which forms part of the wolf-like canids, and is the most widely abundant terrestrial carnivore. The dog and the extant gray wolf are sister taxa as modern wolves are not closely related to the wolves that were first domesticated, which implies that the direct ancestor of the dog is extinct. The dog was the first species to be domesticated and has been selectively bred over millennia for various behaviors, sensory capabilities, and physical attributes.

Their long association with humans has led dogs to be uniquely attuned to human behavior and they are able to thrive on a starch-rich diet that would be inadequate for other canid species. Dogs vary widely in shape, size and colors.Why are different breeds of dogs all considered the same species? – Scientific American .  Nikhil Swaminathan. Accessed on 28 August 2016. They perform many roles for humans, such as hunting, herding, pulling loads, protection, assisting police and military, companionship and, more recently, aiding disabled people and therapeutic roles. This influence on human society has given them the sobriquet of "man's best friend".

Terminology
 The term dog typically is applied both to the species (or subspecies) as a whole, and any adult male member of the same.
 An adult female is a bitch.
 An adult male capable of reproduction is a stud.
 An adult female capable of reproduction is a brood bitch, or brood mother.
 Immature males or females (that is, animals that are incapable of reproduction) are pups or puppies.
 A group of pups from the same gestation period is called a litter.
 The father of a litter is a sire. It is possible for one litter to have multiple sires.
 The mother of a litter is a dam.
 A group of any three or more adults is a pack.

Taxonomy

In 1758, the Swedish botanist and zoologist Carl Linnaeus published in his Systema Naturae the binomial nomenclature – or the two-word naming – of species. Canis is the Latin word meaning "dog", and under this genus he listed the dog-like carnivores including domestic dogs, wolves, and jackals. He classified the domestic dog as Canis familiaris, and on the next page he classified the wolf as Canis lupus. Linnaeus considered the dog to be a separate species from the wolf because of its cauda recurvata - its upturning tail which is not found in any other canid.

In 1999, a study of mitochondrial DNA indicated that the domestic dog may have originated from multiple grey wolf populations, with the dingo and New Guinea singing dog "breeds" having developed at a time when human populations were more isolated from each other. In the third edition of Mammal Species of the World published in 2005, the mammalogist W. Christopher Wozencraft listed under the wolf Canis lupus its wild subspecies, and proposed two additional subspecies: "familiaris Linneaus, 1758 [domestic dog]" and "dingo Meyer, 1793 [domestic dog]". Wozencraft included hallstromi – the New Guinea singing dog – as a taxonomic synonym for the dingo. Wozencraft referred to the mDNA study as one of the guides in forming his decision. The inclusion of familiaris and dingo under a "domestic dog" clade has been noted by other mammalogists. This classification by Wozencraft is debated among zoologists.

Origin

The origin of the domestic dog includes the dog's evolutionary divergence from the wolf, its domestication, and its development into dog types and dog breeds. The dog is a member of the genus Canis, which forms part of the wolf-like canids, and was the first species and the only large carnivore to have been domesticated. The dog and the extant gray wolf are sister taxa, as modern wolves are not closely related to the population of wolves that was first domesticated.

The genetic divergence between dogs and wolves occurred between 40,000–20,000 years ago, just before or during the Last Glacial Maximum. This timespan represents the upper time-limit for the commencement of domestication because it is the time of divergence and not the time of domestication, which occurred later. The domestication of animals commenced over 15,000 years ago, beginning with the grey wolf (Canis lupus) by nomadic hunter-gatherers. The archaeological record and genetic analysis show the remains of the Bonn–Oberkassel dog buried beside humans 14,200 years ago to be the first undisputed dog, with disputed remains occurring 36,000 years ago. It was not until 11,000 years ago that people living in the Near East entered into relationships with wild populations of aurochs, boar, sheep, and goats.

Where the domestication of the dog took place remains debated, with the most plausible proposals spanning Western Europe, Central Asia and East Asia. This has been made more complicated by the recent proposal that an initial wolf population split into East and West Eurasian groups. These two groups, before going extinct, were domesticated independently into two distinct dog populations between 14,000 and 6,400 years ago. The Western Eurasian dog population was gradually and partially replaced by East Asian dogs introduced by humans at least 6,400 years ago. This proposal is also debated.

Biology
thumb|250px|Lateral view of skeleton

Anatomy

thumb|Skull of a dog
Domestic dogs have been selectively bred for millennia for various behaviors, sensory capabilities, and physical attributes. Modern dog breeds show more variation in size, appearance, and behavior than any other domestic animal. Dogs are predators and scavengers, and like many other predatory mammals, the dog has powerful muscles, fused wrist bones, a cardiovascular system that supports both sprinting and endurance, and teeth for catching and tearing.

Size and weight
Dogs are highly variable in height and weight. The smallest known adult dog was a Yorkshire Terrier, that stood only  at the shoulder,  in length along the head-and-body, and weighed only . The largest known dog was an English Mastiff which weighed  and was  from the snout to the tail. The tallest dog is a Great Dane that stands  at the shoulder.

Senses

The dog's senses include vision, hearing, sense of smell, sense of taste, touch and sensitivity to the earth's magnetic field. Another study suggested that dogs can see the earth's magnetic field.Magnetoreception molecule found in the eyes of dogs and primates  MPI Brain Research, 22 February 2016

Coat

thumb|Dogs display a wide variation on coat type, density, length, color, and composition

The coats of domestic dogs are of two varieties: "double" being common with dogs (as well as wolves) originating from colder climates, made up of a coarse guard hair and a soft down hair, or "single", with the topcoat only. Breeds may have an occasional "blaze", stripe, or "star" of white fur on their chest or underside.

Regarding coat appearance or health, the coat can be maintained or affected by multiple nutrients present in the diet, see Coat (dog) for more information.

Tail

There are many different shapes for dog tails: straight, straight up, sickle, curled, or cork-screw. As with many canids, one of the primary functions of a dog's tail is to communicate their emotional state, which can be important in getting along with others. In some hunting dogs, however, the tail is traditionally docked to avoid injuries. In some breeds, such as the Braque du Bourbonnais, puppies can be born with a short tail or no tail at all.

Differences from wolves
thumb|150px|The Saarloos wolfdog carries more gray wolf DNA than any other dog breed

Despite their close genetic relationship and the ability to inter-breed, there are a number of diagnostic features to distinguish the gray wolves from domestic dogs. Domesticated dogs are clearly distinguishable from wolves by starch gel electrophoresis of red blood cell acid phosphatase.Elliot, D.G., and M. Wong. 1972. Acid phosphatase, handy enzyme that separates the dog from the wolf. Acta Biologica et Medica Germanica 28:957–962 The tympanic bullae are large, convex and almost spherical in gray wolves, while the bullae of dogs are smaller, compressed and slightly crumpled. Compared with equally sized wolves, dogs tend to have 20% smaller skulls and 30% smaller brains. The teeth of gray wolves are also proportionately larger than those of dogs.Clutton-Brock, Juliet (1987). A Natural History of Domesticated Mammals. British Museum (Natural History), p. 24,  Dogs have a more domed forehead and a distinctive "stop" between forehead and nose. The temporalis muscle that closes the jaws is more robust in wolves. Wolves do not have dewclaws on their back legs, unless there has been admixture with dogs that had them.  Most dogs lack a functioning pre-caudal gland and enter estrus twice yearly, unlike gray wolves which only do so once a year. So-called primitive dogs such as dingoes and Basenjis retain the yearly estrus cycle.

Dogs generally have brown eyes and wolves almost always have amber or light colored eyes. The skin of domestic dogs tends to be thicker than that of wolves, with some Inuit tribes favoring the former for use as clothing due to its greater resistance to wear and tear in harsh weather. The paws of a dog are half the size of those of a wolf, and their tails tend to curl upwards, another trait not found in wolves. The dog has developed into hundreds of varied breeds, and shows more behavioral and morphological variation than any other land mammal. For example, height measured to the withers ranges from a  in the chihuahua to  in the Irish wolfhound; color varies from white through grays (usually called "blue") to black, and browns from light (tan) to dark ("red" or "chocolate") in a wide variation of patterns; coats can be short or long, coarse-haired to wool-like, straight, curly, or smooth. It is common for most breeds to shed their coat.

Health

There are many household plants that are poisonous to dogs (and other mammals) including begonia, Poinsettia and aloe vera.

Some breeds of dogs are prone to certain genetic ailments such as elbow and hip dysplasia, blindness, deafness, pulmonic stenosis, cleft palate, and trick knees. Two serious medical conditions particularly affecting dogs are pyometra, affecting unspayed females of all types and ages, and gastric dilatation volvulus (bloat), which affects the larger breeds or deep-chested dogs. Both of these are acute conditions, and can kill rapidly. Dogs are also susceptible to parasites such as fleas, ticks, mites, hookworms, tapeworms, roundworms, and heartworms (roundworm species that lives in the heart of dogs).

A number of common human foods and household ingestibles are toxic to dogs, including chocolate solids (theobromine poisoning), onion and garlic (thiosulphate, sulfoxide or disulfide poisoning),Sources vary on which of these are considered the most significant toxic item. grapes and raisins, macadamia nuts, xylitol, as well as various plants and other potentially ingested materials. The nicotine in tobacco can also be dangerous. Dogs can be exposed to the substance by scavenging through garbage bins or ashtrays and eating cigars and cigarettes. Signs can be vomiting of large amounts (e.g., from eating cigar butts) or diarrhea. Some other signs are abdominal pain, loss of coordination, collapse, or death. Dogs are susceptible to theobromine poisoning, typically from ingestion of chocolate. Theobromine is toxic to dogs because, although the dog's metabolism is capable of breaking down the chemical, the process is so slow that for some dogs even small amounts of chocolate can be fatal, especially dark chocolate.

Dogs are also vulnerable to some of the same health conditions as humans, including diabetes, dental and heart disease, epilepsy, cancer, hypothyroidism, and arthritis.

Lifespan

thumb|left|Mixed-breed dogs such as this terrier have been found to run faster and live longer than their pure-bred parents (see Heterosis).

In 2013, a study found that mixed breeds live on average 1.2 years longer than pure breeds, and that increasing body-weight was negatively correlated with longevity (i.e. the heavier the dog the shorter its lifespan).

The typical lifespan of dogs varies widely among breeds, but for most the median longevity, the age at which half the dogs in a population have died and half are still alive, ranges from 10 to 13 years. Individual dogs may live well beyond the median of their breed.

The breed with the shortest lifespan (among breeds for which there is a questionnaire survey with a reasonable sample size) is the Dogue de Bordeaux, with a median longevity of about 5.2 years, but several breeds, including miniature bull terriers, bloodhounds, and Irish wolfhounds are nearly as short-lived, with median longevities of 6 to 7 years.

The longest-lived breeds, including toy poodles, Japanese spitz, Border terriers, and Tibetan spaniels, have median longevities of 14 to 15 years. The median longevity of mixed-breed dogs, taken as an average of all sizes, is one or more years longer than that of purebred dogs when all breeds are averaged. The longest-lived dog was "Bluey", an Australian Cattle Dog who died in 1939 at age 29.5 years of age.Edition included both Bluey and Taffy.

Reproduction

thumb|Female dog nursing newborn puppies
In domestic dogs, sexual maturity happens around six to twelve months of age for both males and females, although this can be delayed until up to two years old for some large breeds. This is the time at which female dogs will have their first estrous cycle. They will experience subsequent estrous cycles semiannually, during which the body prepares for pregnancy. At the peak of the cycle, females will come into estrus, being mentally and physically receptive to copulation. Because the ova survive and are capable of being fertilized for a week after ovulation, it is possible for more than one male to sire the same litter.

Fertilization typically occurs 2–5 days after ovulation; 14–16 days after ovulation, the embryo attaches to the uterus, and after 7-8 more days the heart beat is detectable.

Dogs bear their litters roughly 58 to 68 days after fertilization, with an average of 63 days, although the length of gestation can vary. An average litter consists of about six puppies, though this number may vary widely based on the breed of dog. In general, toy dogs produce from one to four puppies in each litter, while much larger breeds may average as many as twelve.

Some dog breeds have acquired traits through selective breeding that interfere with reproduction. Male French Bulldogs, for instance, are incapable of mounting the female. For many dogs of this breed, the female must be artificially inseminated in order to reproduce.

Neutering
right|thumb|A feral dog from Sri Lanka nursing very well-developed puppies

Neutering refers to the sterilization of animals, usually by removal of the male's testicles or the female's ovaries and uterus, in order to eliminate the ability to procreate and reduce sex drive. Because of the overpopulation of dogs in some countries, many animal control agencies, such as the American Society for the Prevention of Cruelty to Animals (ASPCA), advise that dogs not intended for further breeding should be neutered, so that they do not have undesired puppies that may later be euthanized.

According to the Humane Society of the United States, 3–4 million dogs and cats are euthanized each year in the United States and many more are confined to cages in shelters because there are many more animals than there are homes. Spaying or castrating dogs helps keep overpopulation down. Local humane societies, SPCAs, and other animal protection organizations urge people to neuter their pets and to adopt animals from shelters instead of purchasing them.

Neutering reduces problems caused by hypersexuality, especially in male dogs. Spayed female dogs are less likely to develop some forms of cancer, affecting mammary glands, ovaries, and other reproductive organs. However, neutering increases the risk of urinary incontinence in female dogs, and prostate cancer in males, as well as osteosarcoma, hemangiosarcoma, cruciate ligament rupture, obesity, and diabetes mellitus in either sex.

Inbreeding depression

A common breeding practice for pet dogs is mating between close relatives (e.g. between half- and full siblings). Inbreeding depression is considered to be due largely to the expression of homozygous deleterious recessive mutations. Outcrossing between unrelated individuals, including dogs of different breeds, results in the beneficial masking of deleterious recessive mutations in progeny.

In a study of seven breeds of dogs (Bernese mountain dog, basset hound, Cairn terrier, Epagneul Breton, German Shepherd dog, Leonberger, and West Highland white terrier) it was found that inbreeding decreases litter size and survival. Another analysis of data on 42,855 dachshund litters found that as the inbreeding coefficient increased, litter size decreased and the percentage of stillborn puppies increased, thus indicating inbreeding depression. In a study of boxer litters, 22% of puppies died before reaching 7 weeks of age. Stillbirth was the most frequent cause of death, followed by infection. Mortality due to infection increased significantly with increases in inbreeding.

Intelligence, behavior, and communication

Intelligence

Dog intelligence is the ability of the dog to perceive information and retain it as knowledge for applying to solve problems. Dogs have been shown to learn by inference. A study with Rico showed that he knew the labels of over 200 different items. He inferred the names of novel items by exclusion learning and correctly retrieved those novel items immediately and also 4 weeks after the initial exposure. Dogs have advanced memory skills. A study documented the learning and memory capabilities of a border collie, "Chaser", who had learned the names and could associate by verbal command over 1,000 words. Dogs are able to read and react appropriately to human body language such as gesturing and pointing, and to understand human voice commands, although a 2018 study on canine cognitive abilities found that dogs' capabilities are not more exceptional than those of other animals, such as horses, chimpanzees or cats.

Dogs demonstrate a theory of mind by engaging in deception. An experimental study showed compelling evidence that Australian dingos can outperform domestic dogs in non-social problem-solving, indicating that domestic dogs may have lost much of their original problem-solving abilities once they joined humans. Another study indicated that after undergoing training to solve a simple manipulation task, dogs that are faced with an insoluble version of the same problem look at the human, while socialized wolves do not. Modern domestic dogs use humans to solve their problems for them.

Behavior

Dog behavior is the internally coordinated responses (actions or inactions) of the domestic dog (individuals or groups) to internal and/or external stimuli. As the oldest domesticated species, with estimates ranging from 9,000–30,000 years BCE, the minds of dogs inevitably have been shaped by millennia of contact with humans. As a result of this physical and social evolution, dogs, more than any other species, have acquired the ability to understand and communicate with humans, and they are uniquely attuned to human behaviors. Behavioral scientists have uncovered a surprising set of social-cognitive abilities in the domestic dog. These abilities are not possessed by the dog's closest canine
relatives nor by other highly intelligent mammals such as great apes but rather parallel some of the social-cognitive skills of human children.

Unlike other domestic species which were primarily selected for production-related traits, dogs were initially selected for their behaviors.Serpell J, Duffy D. Dog Breeds and Their Behavior. In: Domestic Dog Cognition and Behavior. Berlin, Heidelberg: Springer; 2014 In 2016, a study found that there were only 11 fixed genes that showed variation between wolves and dogs. These gene variations were unlikely to have been the result of natural evolution, and indicate selection on both morphology and behavior during dog domestication. These genes have been shown to affect the catecholamine synthesis pathway, with the majority of the genes affecting the fight-or-flight responseAlmada RC, Coimbra NC. Recruitment of striatonigral disinhibitory and nigrotectal inhibitory GABAergic pathways during the organization of defensive behavior by mice in a dangerous environment with the venomous snake Bothrops alternatus [ Reptilia, Viperidae ] Synapse 2015:n/a–n/a (i.e. selection for tameness), and emotional processing. Dogs generally show reduced fear and aggression compared with wolves.Coppinger R, Schneider R: Evolution of working dogs. The domestic dog: Its evolution, behaviour and interactions with people. Cambridge: Cambridge University press, 1995. Some of these genes have been associated with aggression in some dog breeds, indicating their importance in both the initial domestication and then later in breed formation. Traits of high sociability and lack of fear in dogs may include genetic modifications related to Williams-Beuren syndrome in humans, which cause hypersociability at the expense of problem solving ability.

Communication

Dog communication is how dogs convey information to other dogs, how they understand messages from humans, and how humans translate the information that dogs are transmitting.Coren, Stanley "How To Speak Dog: Mastering the Art of Dog-Human Communication" 2000 Simon & Schuster, New York. Communication behaviors of dogs include eye gaze, facial expression, vocalization, body posture (including movements of bodies and limbs) and gustatory communication (scents, pheromones and taste). Humans communicate to dogs by using vocalization, hand signals and body posture.

Ecology

Population
In 2013, an estimate of the global dog population was 987 million. Although it is said that the "dog is man's best friend", this refers largely to the ~20% of dogs that live in developed countries. In the developing world, dogs are more commonly feral or communally owned, with pet dogs uncommon. Most of these dogs live their lives as scavengers and have never been owned by humans, with one study showing their most common response when approached by strangers is to run away (52%) or respond aggressively (11%). Little is known about these dogs, or the dogs in developed countries that are feral, stray or are in shelters, because the great majority of modern research on dog cognition has focused on pet dogs living in human homes.

Competitors and predators
Although dogs are the most abundant and widely distributed terrestrial carnivores, the potential of feral and free-ranging dogs to compete with other large carnivores is limited by their strong association with humans. For example, a review of the studies in the competitive effects of dogs on sympatric carnivores did not mention any research on competition between dogs and wolves. Although wolves are known to kill dogs, they tend to live in pairs or in small packs in areas where they are highly persecuted, giving them a disadvantage facing large dog groups.

Wolves kill dogs wherever they are found together. One study reported that in Wisconsin in 1999 more compensation had been paid for losses due to wolves taking dogs than for wolves taking livestock. In Wisconsin wolves will often kill hunting dogs, possibly because the dogs are in the wolf's territory. A strategy has been reported in Russia where one wolf lures a dog into heavy brush where another wolf waits in ambush. In some instances, wolves have displayed an uncharacteristic fearlessness of humans and buildings when attacking dogs, to the extent that they have to be beaten off or killed. Although the numbers of dogs killed each year are relatively low, it induces a fear of wolves entering villages and farmyards to take dogs, and losses of dogs to wolves has led to demands for more liberal wolf hunting regulations.

Coyotes and big cats have also been known to attack dogs. Leopards in particular are known to have a predilection for dogs, and have been recorded to kill and consume them regardless of their size. Tigers in Manchuria, Indochina, Indonesia, and Malaysia are also reported to kill dogs. Striped hyenas are known to kill dogs in Turkmenistan, India, and the Caucasus.

Diet

thumb|left|upright|Golden Retriever gnawing on a pig's foot

Dogs have been described as carnivores or omnivores. Compared to wolves, dogs have genes involved in starch digestion that contribute to an increased ability to thrive on a starch-rich diet. Based on metabolism and nutrition, many consider the dog to be an omnivore. However, the dog is not simply an omnivore. More like the cat and less like other omnivores, the dog can only produce bile acid with taurine, and it cannot produce vitamin D, which it obtains from animal flesh. Also more like the cat, the dog requires arginine to maintain its nitrogen balance. These nutritional requirements place the dog part-way between carnivores and omnivores.

Range
As a domesticated or semi-domesticated animal, the dog is nearly universal among human societies. Notable exceptions once included:
 Aboriginal Tasmanians, who were separated from Australia before the arrival of dingos on that continent
 The Andamanese, who were isolated when rising sea levels covered the land bridge to Myanmar
 The natives of Tierra del Fuego, who instead domesticated the Fuegian dog, a different canid species
 Certain Pacific islands whose maritime settlers did not bring dogs, or where dogs died out after original settlement, notably: the Mariana Islands, Palau, Marshall Islands, Gilbert Islands, New Caledonia, Vanuatu, Tonga, Marquesas, Mangaia in the Cook Islands, Rapa Iti in French Polynesia, Easter Island, Chatham Islands, and Pitcairn Island (settled by the Bounty mutineers, who killed off their dogs in order to escape discovery by passing ships).

Breeds

thumb|Different dog breeds show a range of phenotypic variation

The domestic dog is the first species, and the only large carnivore, known to have been domesticated. Especially over the past 200 years, dogs have undergone rapid phenotypic change and were formed into today's modern dog breeds due to artificial selection by humans. These breeds can vary in size and weight from a  teacup poodle to a  giant mastiff. Phenotypic variation can include height measured to the withers ranging from  in the Chihuahua to  in the Irish Wolfhound; color varies from white through grays (usually called "blue") to black, and browns from light (tan) to dark ("red" or "chocolate") in a wide variation of patterns; coats can be short or long, coarse-haired to wool-like, straight, curly, or smooth. The skull, body, and limb proportions vary significantly between breeds, with dogs displaying more phenotypic diversity than can be found within the entire order of carnivores. Some breeds demonstrate outstanding skills in herding, retrieving, scent detection, and guarding, which demonstrates the functional and behavioral diversity of dogs. The first dogs were domesticated from shared ancestors of modern wolves, however the phenotypic changes that coincided with the dog–wolf genetic divergence are not known.

Roles with humans
thumb|upright|Gunnar Kaasen and Balto, the lead dog on the last relay team of the 1925 serum run to Nome

Domestic dogs inherited complex behaviors, such as bite inhibition, from their wolf ancestors, which would have been pack hunters with complex body language. These sophisticated forms of social cognition and communication may account for their trainability, playfulness, and ability to fit into human households and social situations, and these attributes have given dogs a relationship with humans that has enabled them to become one of the most successful species on the planet today.

The dogs' value to early human hunter-gatherers led to them quickly becoming ubiquitous across world cultures. Dogs perform many roles for people, such as hunting, herding, pulling loads, protection, assisting police and military, companionship, and, more recently, aiding handicapped individuals. This influence on human society has given them the nickname "man's best friend" in the Western world. In some cultures, however, dogs are also a source of meat.

Early roles
Wolves, and their dog descendants, likely derived significant benefits from living in human camps – more safety, more reliable food, lesser caloric needs, and more chance to breed. They would have benefited from humans' upright gait that gives them larger range over which to see potential predators and prey, as well as better color vision that, at least by day, gives humans better visual discrimination. Camp dogs would also have benefited from human tool use, as in bringing down larger prey and controlling fire for a range of purposes.

Humans would also have derived enormous benefit from the dogs associated with their camps. For instance, dogs would have improved sanitation by cleaning up food scraps. Dogs may have provided warmth, as referred to in the Australian Aboriginal expression "three dog night" (an exceptionally cold night), and they would have alerted the camp to the presence of predators or strangers, using their acute hearing to provide an early warning.

It has been suggested that the most significant benefit would have been the use of dogs' robust sense of smell to assist with the hunt. The relationship between the presence of a dog and success in the hunt is often mentioned as a primary reason for the domestication of the wolf, and a 2004 study of hunter groups with and without a dog gives quantitative support to the hypothesis that the benefits of cooperative hunting was an important factor in wolf domestication.

The cohabitation of dogs and humans likely improved the chances of survival for early human groups, and the domestication of dogs may have been one of the key forces that led to human success.

Human emigrants from Siberia that came across the Bering land bridge into North America likely had dogs in their company. Although one writerA History of Dogs in the Early Americas, Marion Schwartz, 1998, 260 p., , Yale University Press even suggests that the use of sled dogs may have been critical to the success of the waves that entered North America roughly 12,000 years ago, the earliest archaeological evidence of dog-like canids in North America dates from about 9,400 years ago. Dogs were an important part of life for the Athabascan population in North America, and were their only domesticated animal. Dogs as pack animals  may have contributed migration of the Apache and Navajo tribes 1,400 years ago. This use of dogs in these cultures often persisted after the introduction of the horse to North America. p. 12

As pets
thumb|Green velvet dog collar, dating from 1670 to 1690
thumb|Siberian Huskies are pack animals that still enjoy some human companionship
thumb|alt=Couple sitting on the lawn with a pet British Bulldog| A British Bulldog relaxes at a park

It is estimated that three-quarters of the world's dog population lives in the developing world as feral, village, or community dogs, with pet dogs uncommon.

"The most widespread form of interspecies bonding occurs between humans and dogs" and the keeping of dogs as companions, particularly by elites, has a long history. (As a possible example, at the Natufian culture site of Ain Mallaha in Israel, dated to 12,000 BC, the remains of an elderly human and a four-to-five-month-old puppy were found buried together). However, pet dog populations grew significantly after World War II as suburbanization increased. In the 1950s and 1960s, dogs were kept outside more often than they tend to be today (using the expression "in the doghouse" to describe exclusion from the group signifies the distance between the doghouse and the home) and were still primarily functional, acting as a guard, children's playmate, or walking companion. From the 1980s, there have been changes in the role of the pet dog, such as the increased role of dogs in the emotional support of their human guardians. People and dogs have become increasingly integrated and implicated in each other's lives, to the point where pet dogs actively shape the way a family and home are experienced.

There have been two major trends in the changing status of pet dogs. The first has been the 'commodification' of the dog, shaping it to conform to human expectations of personality and behaviour. The second has been the broadening of the concept of the family and the home to include dogs-as-dogs within everyday routines and practices.

There are a vast range of commodity forms available to transform a pet dog into an ideal companion. The list of goods, services and places available is enormous: from dog perfumes, couture, furniture and housing, to dog groomers, therapists, trainers and caretakers, dog cafes, spas, parks and beaches, and dog hotels, airlines and cemeteries. While dog training as an organized activity can be traced back to the 18th century, in the last decades of the 20th century it became a high-profile issue as many normal dog behaviors such as barking, jumping up, digging, rolling in dung, fighting, and urine marking (which dogs do to establish territory through scent), became increasingly incompatible with the new role of a pet dog. Dog training books, classes and television programs proliferated as the process of commodifying the pet dog continued.

The majority of contemporary dog owners describe their pet as part of the family, although some ambivalence about the relationship is evident in the popular reconceptualization of the dog–human family as a pack. A dominance model of dog–human relationships has been promoted by some dog trainers, such as on the television program Dog Whisperer. However it has been disputed that "trying to achieve status" is characteristic of dog–human interactions. Pet dogs play an active role in family life; for example, a study of conversations in dog–human families showed how family members use the dog as a resource, talking to the dog, or talking through the dog, to mediate their interactions with each other.

Increasingly, human family members are engaging in activities centered on the perceived needs and interests of the dog, or in which the dog is an integral partner, such as dog dancing and dog yoga.

According to statistics published by the American Pet Products Manufacturers Association in the National Pet Owner Survey in 2009–2010, it is estimated there are 77.5 million people with pet dogs in the United States. The same survey shows nearly 40% of American households own at least one dog, of which 67% own just one dog, 25% two dogs and nearly 9% more than two dogs. There does not seem to be any gender preference among dogs as pets, as the statistical data reveal an equal number of female and male dog pets. Yet, although several programs are ongoing to promote pet adoption, less than a fifth of the owned dogs come from a shelter.

The latest study using magnetic resonance imaging (MRI) comparing humans and dogs showed that dogs have the same response to voices and use the same parts of the brain as humans do. This gives dogs the ability to recognize emotional human sounds, making them friendly social pets to humans.

Work
Dogs have lived and worked with humans in many roles. In addition to dogs' role as companion animals, dogs have been bred for herding livestock (collies, sheepdogs),Dewey, T. and S. Bhagat. 2002. "Canis lupus familiaris, Animal Diversity Web.  hunting (hounds, pointers), and rodent control (terriers). Other types of working dogs include search and rescue dogs,Vikki Fenton, The use of dogs in search, rescue and recovery, Journal of Wilderness Medicine, Vol. 3, Issue 3, August 1992, pp. 292–300. detection dogs trained to detect illicit drugsJohn J. Ensminger, Police and Military Dogs: Criminal Detection, Forensic Evidence, and Judicial Admissibility (CRC Press, 2012). or chemical weapons;Philip Shernomay, Dogs Take Their Place in Arsenal Against Chemical Attack, New York Times (13 May 2003). guard dogs; dogs who assist fishermen with the use of nets; and dogs that pull loads. In 1957, the dog Laika became the first animal to be launched into Earth orbit, aboard the Soviets' Sputnik 2; she died during the flight.

Various kinds of service dogs and assistance dogs, including guide dogs, hearing dogs, mobility assistance dogs, and psychiatric service dogs provide assistance to individuals with disabilities. Some dogs owned by epileptics have been shown to alert their handler when the handler shows signs of an impending seizure, sometimes well in advance of onset, allowing the guardian to seek safety, medication, or medical care.

Sports and shows

People often enter their dogs in competitions such as breed-conformation shows or sports, including racing, sledding and agility competitions.

In conformation shows, also referred to as breed shows, a judge familiar with the specific dog breed evaluates individual purebred dogs for conformity with their established breed type as described in the breed standard. As the breed standard only deals with the externally observable qualities of the dog (such as appearance, movement, and temperament), separately tested qualities (such as ability or health) are not part of the judging in conformation shows.

As food

Dog meat is consumed in some East Asian countries, including Korea, China and Vietnam, a practice that dates back to antiquity. It is estimated that 13–16 million dogs are killed and consumed in Asia every year. In China, debates have ensued over banning the consumption of dog meat.  Following the Sui and Tang dynasties of the first millennium, however, people living on the plains of northern China began to eschew eating dogs. This is likely due to the spread of Buddhism and Islam, two religions that forbade the consumption of certain animals, including dogs. As members of the upper classes shunned dog meat, it gradually became a social taboo to eat it, despite the fact that the general population continued to consume it for centuries afterward. Other cultures, such as Polynesia and pre-Columbian Mexico, also consumed dog meat in their history. However, Western, South Asian, African, and Middle Eastern cultures, in general, regard consumption of dog meat as taboo. In some places, however, such as in rural areas of Poland, dog fat is believed to have medicinal properties – being good for the lungs for instance. Dog meat is also consumed in some parts of Switzerland.  Proponents of eating dog meat have argued that placing a distinction between livestock and dogs is western hypocrisy, and that there is no difference with eating the meat of different animals.

In Korea, the primary dog breed raised for meat, the nureongi (누렁이), differs from those breeds raised for pets that Koreans may keep in their homes.Pettid, Michael J., Korean Cuisine: An Illustrated History, London: Reaktion Books Ltd., 2008, 25. 

The most popular Korean dog dish is gaejang-guk (also called bosintang), a spicy stew meant to balance the body's heat during the summer months. Followers of the custom claim this is done to ensure good health by balancing one's gi, or vital energy of the body. A 19th century version of gaejang-guk explains that the dish is prepared by boiling dog meat with scallions and chili powder. Variations of the dish contain chicken and bamboo shoots. While the dishes are still popular in Korea with a segment of the population, dog is not as widely consumed as beef, chicken, and pork.

Health risks to humans

In 2005, the WHO reported that 55,000 people died in Asia and Africa from rabies, a disease for which dogs are the most important vector.

Citing a 2008 study, the U.S. Center for Disease Control estimated in 2015 that 4.5 million people in the USA are bitten by dogs each year. citing  A 2015 study estimated that 1.8% of the U.S. population is bitten each year. In the 1980s and 1990s the US averaged 17 fatalities per year, while since 2007 this has increased to an average of 31. 77% of dog bites are from the pet of family or friends, and 50% of attacks occur on the property of the dog's legal owner.

A Colorado study found bites in children were less severe than bites in adults. The incidence of dog bites in the US is 12.9 per 10,000 inhabitants, but for boys aged 5 to 9, the incidence rate is 60.7 per 10,000. Moreover, children have a much higher chance to be bitten in the face or neck. Sharp claws with powerful muscles behind them can lacerate flesh in a scratch that can lead to serious infections.

In the UK between 2003 and 2004, there were 5,868 dog attacks on humans, resulting in 5,770 working days lost in sick leave.

In the United States, cats and dogs are a factor in more than 86,000 falls each year. It has been estimated around 2% of dog-related injuries treated in UK hospitals are domestic accidents. The same study found that while dog involvement in road traffic accidents was difficult to quantify, dog-associated road accidents involving injury more commonly involved two-wheeled vehicles.

Toxocara canis (dog roundworm) eggs in dog feces can cause toxocariasis. In the United States, about 10,000 cases of Toxocara infection are reported in humans each year, and almost 14% of the U.S. population is infected. In Great Britain, 24% of soil samples taken from public parks contained T. canis eggs. Untreated toxocariasis can cause retinal damage and decreased vision. Dog feces can also contain hookworms that cause cutaneous larva migrans in humans.

Health benefits for humans
thumb|alt=Small dog laying between the hands|Doberman puppy being cuddled
The scientific evidence is mixed as to whether companionship of a dog can enhance human physical health and psychological wellbeing. Studies suggesting that there are benefits to physical health and psychological wellbeing have been criticised for being poorly controlled, and finding that "the health of elderly people is related to their health habits and social supports but not to their ownership of, or attachment to, a companion animal." Earlier studies have shown that people who keep pet dogs or cats exhibit better mental and physical health than those who do not, making fewer visits to the doctor and being less likely to be on medication than non-guardians.

A 2005 paper states "recent research has failed to support earlier findings that pet ownership is associated with a reduced risk of cardiovascular disease, a reduced use of general practitioner services, or any psychological or physical benefits on health for community dwelling older people. Research has, however, pointed to significantly less absenteeism from school through sickness among children who live with pets." In one study, new guardians reported a highly significant reduction in minor health problems during the first month following pet acquisition, and this effect was sustained in those with dogs through to the end of the study.

In addition, people with pet dogs took considerably more physical exercise than those with cats and those without pets. The results provide evidence that keeping pets may have positive effects on human health and behaviour, and that for guardians of dogs these effects are relatively long-term. Pet guardianship has also been associated with increased coronary artery disease survival, with human guardians being significantly less likely to die within one year of an acute myocardial infarction than those who did not own dogs.

The health benefits of dogs can result from contact with dogs in general, and not solely from having dogs as pets. For example, when in the presence of a pet dog, people show reductions in cardiovascular, behavioral, and psychological indicators of anxiety. Other health benefits are gained from exposure to immune-stimulating microorganisms, which, according to the hygiene hypothesis, can protect against allergies and autoimmune diseases. The benefits of contact with a dog also include social support, as dogs are able to not only provide companionship and social support themselves, but also to act as facilitators of social interactions between humans. One study indicated that wheelchair users experience more positive social interactions with strangers when they are accompanied by a dog than when they are not. In 2015, a study found that pet owners were significantly more likely to get to know people in their neighborhood than non-pet owners.

The practice of using dogs and other animals as a part of therapy dates back to the late 18th century, when animals were introduced into mental institutions to help socialize patients with mental disorders.Kruger, K.A. & Serpell, J.A. (2006). Animal-assisted interventions in mental health: Definitions and theoretical foundations, In Fine, A.H. (Ed.), Handbook on animal-assisted therapy: Theoretical foundations and guidelines for practice. San Diego, CA, Academic Press: 21–38.  Animal-assisted intervention research has shown that animal-assisted therapy with a dog can increase social behaviors, such as smiling and laughing, among people with Alzheimer's disease. One study demonstrated that children with ADHD and conduct disorders who participated in an education program with dogs and other animals showed increased attendance, increased knowledge and skill objectives, and decreased antisocial and violent behavior compared with those who were not in an animal-assisted program.

Shelters

Every year, between 6 and 8 million dogs and cats enter US animal shelters.Animals abandoned as recession hits home . TheStar.com. 22 December 2008. The Humane Society of the United States (HSUS) estimates that approximately 3 to 4 million of those dogs and cats are euthanized yearly in the United States.HSUS Pet Overpopulation Estimates  The Humane Society of the United States However, the percentage of dogs in US animal shelters that are eventually adopted and removed from the shelters by their new legal owners has increased since the mid-1990s from around 25% to a 2012 average of 40% among reporting shelters (with many shelters reporting 60–75%).

Cultural depictions
thumb|Dogs at Lake Balaton, depicted on the Seuso Treasure

In China, Korea, and Japan, dogs are viewed as kind protectors.

Mythology and religion
In ancient Mesopotamia, from the Old Babylonian period until the Neo-Babylonian, dogs were the symbol of Ninisina, the goddess of healing and medicine, and her worshippers frequently dedicated small models of seated dogs to her. In the Neo-Assyrian and Neo-Babylonian periods, dogs were used as emblems of magical protection.

In mythology, dogs often serve as pets or as watchdogs. Stories of dogs guarding the gates of the underworld recur throughout Indo-European mythologies and may originate from Proto-Indo-European religion. In Greek mythology, Cerberus is a three-headed watchdog who guards the gates of Hades. In Norse mythology, a bloody, four-eyed dog called Garmr guards Helheim. In Persian mythology, two four-eyed dogs guard the Chinvat Bridge. In Welsh mythology, Annwn is guarded by Cŵn Annwn. In Hindu mythology, Yama, the god of death, owns two watch dogs who have four eyes. They are said to watch over the gates of Naraka.

thumb|200px|A painting of Saint Dominic with a dog bearing a torch at his side

The hunter god Muthappan from North Malabar region of Kerala has a hunting dog as his mount. Dogs are found in and out of the Muthappan Temple and offerings at the shrine take the form of bronze dog figurines. In Philippine mythology, Kimat who is the pet of Tadaklan, god of thunder, is responsible for lightning. 

The role of the dog in Chinese mythology includes a position as one of the twelve animals which cyclically represent years (the zodiacal dog). Three of the 88 constellations in western astronomy also represent dogs: Canis Major (the Great Dog, whose brightest star, Sirius, is also called the Dog Star), Canis Minor (the Little Dog), and Canes Venatici (the Hunting Dogs).

In Christianity, dogs represent faithfulness. Within the Roman Catholic denomination specifically, the iconography of Saint Dominic includes a dog, after the hallow's mother dreamt of a dog springing from her womb and becoming pregnant shortly thereafter. As such, the Dominican Order (Ecclesiastical Latin: Dominicanus) means "dogs of the Lord" or "hounds of the Lord" (Ecclesiastical Latin: domini canis). In Christian folklore, a church grim often takes the form of a black dog to guard Christian churches and their churchyards from sacrilege.

Jewish law does not prohibit keeping dogs and other pets. Jewish law requires Jews to feed dogs (and other animals that they own) before themselves, and make arrangements for feeding them before obtaining them.

The view on dogs in Islam is mixed, with some schools of thought viewing it as unclean, although Khaled Abou El Fadl states that this view is based on "pre-Islamic Arab mythology" and "a tradition to be falsely attributed to the Prophet". Therefore, Sunni Malaki and Hanafi jurists permit the trade of and keeping of dogs as pets.

Literature
In Homer's epic poem the Odyssey, when the disguised Odysseus returns home after 20 years he is recognized only by his faithful dog, Argos, who has been waiting for his return.

 Art 

Cultural depictions of dogs in art extend back thousands of years to when dogs were portrayed on the walls of caves. Representations of dogs became more elaborate as individual breeds evolved and the relationships between human and canine developed. Hunting scenes were popular in the Middle Ages and the Renaissance. Dogs were depicted to symbolize guidance, protection, loyalty, fidelity, faithfulness, watchfulness, and love.

 Education and appreciation 
The American Kennel Club reopened a museum called "Museum of the Dog" in Manhattan after moving the attraction from outside of St. Louis. The museum contains ancient artifacts, fine art, and educational opportunities for visitors.
thumb|center|Dog with mastiff features, China, 4th century, Brooklyn Museum

 See also 

 Animal track
 Cynanthropy
 Dog–cat relationship
 Dog odor
 Dognapping
 Ethnocynology
 Hachikō – a notable example of dog loyalty
 Mountain dog
 Pet recovery service
 Toy Group
 Wolfdog

 Lists 
 Lists of dogs
 List of fictional dogs
 List of individual dogs

References

Bibliography
 
 
 

Further reading
 
 

External links

 Biodiversity Heritage Library bibliography for Canis lupus familiaris
 Fédération Cynologique Internationale (FCI) – World Canine Organisation
 Dogs in the Ancient World, an article on the history of dogs
 View the dog genome on Ensembl

Category:Dogs
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Category:Cosmopolitan vertebrates
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Category:Cosmopolitan species
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Category:Mammals described in 1758
Category:Taxa named by Carl Linnaeus