The dog (Canis familiaris when considered a distinct species or Canis lupus familiaris when considered a subspecies of the wolf)^[5] is a domesticated carnivore of the family Canidae. It is part of the wolf-like canids,^[6] and is the most widely abundant terrestrial carnivore.^{[7][8][9][10][11]} The dog and the extant gray wolf are sister taxa as modern wolves are not closely related to the wolves that were first domesticated,^[12][13][14] which implies that the direct ancestor of the dog is extinct.^[15] The dog was the first species to be domesticated,^[14][16] and has been selectively bred over millennia for various behaviors, sensory capabilities, and physical attributes.^[17]

Their long association with humans has led dogs to be uniquely attuned to human behavior,^[18] and they can thrive on a starch-rich diet that would be inadequate for other canids.^[19] Dogs vary widely in shape, size, and colors.^[20] 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."

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",^[21] 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.^[2] 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.^[22]

In 1999, a study of mitochondrial DNA indicated that the domestic dog might have originated from multiple grey wolf populations, with the dingo and New Guinea singing dog "breeds" having developed at a time when human communities were more isolated from each other.^[23] 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 informing his decision.^[4] Other mammalogists have noted the inclusion of familiaris and dingo under a "domestic dog" clade.^[24] This classification by Wozencraft is debated among zoologists.^[25]

In 2019, a workshop hosted by the IUCN/Species Survival Commission's Canid Specialist Group considered the New Guinea singing dog and the dingo to be feral dogs Canis familiaris, and therefore should not be assessed for the IUCN Red List.^[26]

Origin

The domestic dog's origin includes the dog's genetic 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.^[14][27] Genetic studies comparing dogs with modern wolves show reciprocal monophyly (separate groups), which implies that dogs are not genetically close to any living wolf and that their wild ancestor is extinct.^[28][14] An extinct Late Pleistocene wolf may have been the dog's ancestor,^[27][1] with the dog's similarity to the extant grey wolf being the result of genetic admixture between the two.^[1] In 2020, a literature review of canid domestication stated that modern dogs were not descended from the same Canis lineage as modern wolves, and proposes that dogs may be descended from a Pleistocene wolf closer in size to a village dog.^[29]

The genetic divergence between dogs and wolves occurred between 20,000 and 40,000 years ago, just before or during the Last Glacial Maximum^[30][1] (20,000-27,000 years ago). This period represents the upper time-limit for domestication commencement because it is the time of divergence and not the time of domestication, which occurred later.^[30][31] One of the most critical transitions in human history was the domestication of animals, which began with the long-term association between wolves and hunter-gatherers more than 15,000 years ago.^[28] 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.^[1] By 11,000 years ago, there were five distinct dog lineages all sharing a common ancestry distinct from present-day wolves.^[32]

Biology

Anatomy

Domestic dogs have been selectively bred for millennia for various behaviors, sensory capabilities, and physical attributes.^[17] Modern dog breeds show more variation in size, appearance, and behavior than any other domestic animal.^[17] Dogs are predators and scavengers; like many other predatory mammals, the dog has powerful muscles, large and sharp claws and teeth, 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 6.3 centimetres ( inches) at the shoulder, 9.5 cm ( in) in length along the head-and-body, and weighed only 113 grams (4 ounces). The most massive known dog was a Saint Bernard, which weighed 167.6 kg ( lb) and was 250 cm (8 ft 2 in) from the snout to the tail.^[33] The tallest dog is a Great Dane that stands 106.7 cm (3 ft 6 in) at the shoulder.^[34]

Senses

The dog's senses include vision, hearing, smell, taste, touch and sensitivity to the earth's magnetic field. Another study suggested that dogs can see the earth's magnetic field.^[35][36][37]

Coat

The coats of domestic dogs are of two varieties: "double" being familiar 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.^[38]

The coat can be maintained or affected by multiple nutrients present in the diet; see Coat (dog) for more information.

Premature graying can occur in dogs from as early as one year of age; this is shown to be associated with impulsive behaviors, anxiety behaviors, fear of noise, and fear of unfamiliar people or animals.^[39]

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 crucial in getting along with others. In some hunting dogs, however, the tail is traditionally docked to avoid injuries.^[40] In some breeds, such as the Braque du Bourbonnais, puppies can be born with a short tail or no tail at all.^[41]

Differences from wolves

Despite their close genetic relationship and interbreedability, there are several diagnostic features to distinguish the gray wolves from domestic dogs. Domesticated dogs are distinguishable from wolves by starch gel electrophoresis of red blood cell acid phosphatase.^[42] The tympanic bullae are large, convex, and almost spherical in gray wolves, while the bullae of dogs are smaller, compressed, and slightly crumpled.^[43] Compared with equally sized wolves, dogs tend to have 20% smaller skulls and 30% smaller brains.^[44]:35 The teeth of gray wolves are also proportionately larger than those of dogs.^[45] Dogs have a more domed forehead and a distinctive "stop" between the forehead and nose.^[46] The temporalis muscle that closes the jaws is more robust in wolves.^[5]:158 Wolves do not have dewclaws on their back legs unless there has been admixture with dogs that had them.^[47] Most dogs lack a functioning pre-caudal gland and enter estrus twice yearly, unlike gray wolves, which only do so once a year.^[48] So-called primitive dogs such as dingoes and Basenjis retain the yearly estrus cycle.^[49]

Dogs generally have brown eyes, and wolves almost always have amber or light-colored eyes.^[50] Domestic dogs' skin 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.^[51] The paws of a dog are half the size of a wolf, and their tails tend to curl upwards, another trait not found in wolves.^[52] The dog has developed into hundreds of varied breeds and shows more behavioral and morphological variation than any other land mammal.^[53]

Health

Many household plants are poisonous to dogs (and other mammals), including Begonia, Poinsettia, and Aloe vera.^[54]

Some breeds of dogs are prone to specific genetic ailments such as elbow and hip dysplasia, blindness, deafness, pulmonic stenosis, cleft palate, and trick knees. Two severe medical conditions significantly 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).

Several human foods and household ingestibles are toxic to dogs, including chocolate solids (theobromine poisoning), onion and garlic (thiosulphate, sulfoxide or disulfide poisoning),^[55]grapes and raisins, macadamia nuts, xylitol,^[56] as well as various plants and other potentially ingested materials.^[57][58] 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 symptoms are abdominal pain, loss of coordination, collapse, or death.^[59] Dogs are susceptible to theobromine poisoning, typically from the 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, mostly 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.^[60]

Lifespan

In 2013, a study found that mixed breed dogs live on average 1.2 years longer than purebred dogs. Increasing body-weight was negatively correlated with longevity (i.e., the heavier the dog, the shorter its lifespan).^[61]

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.^{[62][63][64][65]} 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 reasonable sample size) is the Dogue de Bordeaux, with a median longevity of about 5.2 years. Still, several breeds, including miniature bull terriers, bloodhounds, and Irish wolfhounds are nearly as short-lived, with median longevities of 6 to 7 years.^[65]

The longest-lived breeds, including toy poodles, Japanese spitz, Border terriers, and Tibetan spaniels, have median longevities of 14 to 15 years.^[65] 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.^{[63][64][65][66]} The longest-lived dog was "Bluey," an Australian Cattle Dog who died in 1939 at 29.5 years of age.^[67][68]

Reproduction

In domestic dogs, sexual maturity happens around six to twelve months of age for both males and females,^[17][69] although this can be delayed until up to two years old for some large breeds, and 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 become estrus, mentally, and physically receptive to copulation.^[17] Because the ova survive and can be fertilized for a week after ovulation, more than one male can sire the same litter.^[17]

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 heartbeat is detectable.^[70][71]

Dogs bear their litters roughly 58 to 68 days after fertilization,^[17][72] with an average of 63 days, although the length of gestation can vary. An average litter consists of about six puppies,^[73] though this number may vary widely based on dog breed. 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 to reproduce.^[74]

Neutering

Neutering refers to the sterilization of animals, usually by removing the male's testicles or the female's ovaries and uterus, to eliminate the ability to procreate and reduce sex drive. Because of dogs' overpopulation 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. That way, they do not have undesired puppies that may later be euthanized.^[75]

According to the Humane Society of the United States, 3-4 million dogs and cats are euthanized each year. 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.^[76] Local humane societies, SPCAs, and other animal protection organizations urge people to neuter their pets and adopt animals from shelters instead of purchasing them.

Neutering reduces problems caused by hypersexuality, especially in male dogs.^[77] Spayed female dogs are less likely to develop cancer, affecting mammary glands, ovaries, and other reproductive organs.^[78] However, neutering increases the risk of urinary incontinence in female dogs,^[79] and prostate cancer in males,^[80] and osteosarcoma, hemangiosarcoma, cruciate ligament rupture, obesity, and diabetes mellitus in either sex.^[81]

Inbreeding depression

A common breeding practice for pet dogs is mating between close relatives (e.g., between half- and full siblings).^[82]Inbreeding depression is considered to be due mainly to the expression of homozygous deleterious recessive mutations.^[83] Outcrossing between unrelated individuals, including dogs of different breeds, results in the beneficial masking of deleterious recessive mutations in progeny.^[84]

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.^[85] 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.^[86] In a study of boxer litters, 22% of puppies died before reaching seven weeks of age.^[87] Stillbirth was the most frequent cause of death, followed by infection. Mortality due to infection increased significantly with increases in inbreeding.^[87]

Intelligence, behavior, and communication

Intelligence

Dog intelligence is the dog's ability to perceive information and retain it as knowledge for applying to solve problems. Studies of two dogs suggest that dogs can learn by inference and have advanced memory skills. A study with Rico, a border collie, showed that he knew the labels of over 200 different items. He inferred the names of novel things by exclusion learning and correctly retrieved those new items immediately and four weeks after the initial exposure. A study of another border collie, "Chaser," documented his learning and memory capabilities. He had learned the names and could associate by verbal command over 1,000 words.^[88] Dogs can read and react appropriately to human body language such as gesturing and pointing and human voice commands.

A 2018 study on canine cognitive abilities found that dogs' capabilities are no more exceptional than those of other animals, such as horses, chimpanzees, or cats.^[89] Various animals, including pigs, pigeons, and chimpanzees, can remember the "what, where, and when" of an event, which dogs cannot do.^[90]

Dogs demonstrate a theory of mind by engaging in deception.^[91] 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.^[92] Another study revealed that after undergoing training to solve a simple manipulation task, dogs faced with an insoluble version of the same problem look at the human, while socialized wolves do not.^[93]

Behavior

Dog behavior is the internally coordinated responses (actions or inactions) of the domestic dog (individuals or groups) to internal and external stimuli.^[94] As the oldest domesticated species, with estimates ranging from 9,000-30,000 years BCE, dogs' minds inevitably have been shaped by millennia of contact with humans. As a result of this physical and social evolution, dogs have acquired the ability to understand and communicate with humans more than any other species, and they are uniquely attuned to human behaviors.^[18] 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 or other highly intelligent mammals such as great apes but rather parallel to children's social-cognitive skills.^[95]

Unlike other domestic species selected for production-related traits, dogs were initially selected for their behaviors.^[96][97] In 2016, a study found that only 11 fixed genes 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 response^[97][98] (i.e., selection for tameness), and emotional processing.^[97] Dogs generally show reduced fear and aggression compared with wolves.^[97][99] Some of these genes have been associated with aggression in some dog breeds, indicating their importance in both the initial domestication and later in breed formation.^[97] Traits of high sociability and lack of fear in dogs may include genetic modifications related to Williams-Beuren syndrome in humans, which cause hyper sociability at the expense of problem-solving ability.^{[100][101][102]}

Communication

Dog communication is how dogs convey information to other dogs, understand messages from humans, and translate the information that dogs are transmitting.^[103]:xii 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 estimated global dog population was between 700 million^[104] and 987 million.^[105] Although it is said that the "dog is man's best friend,"^[106] this refers mainly 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.^[51] 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%).^[107] 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.^[108]

Competitors and predators

Although dogs are the most abundant and widely distributed terrestrial carnivores, feral, and free-ranging dogs' potential to compete with other large carnivores is limited by their strong association with humans.^[7] For example, a review of the studies in dogs' competitive effects on sympatric carnivores did not mention any research on competition between dogs and wolves.^[109][110] 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.^[109][111]

Wolves kill dogs wherever they are found together.^[112] 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 they are in the wolf's territory.^[112] A strategy has been reported in Russia where one wolf lures a dog into a heavy brush where another wolf waits in ambush.^[113] 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.^[114] 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 have led to demands for more liberal wolf hunting regulations.^[109]

Coyotes and big cats have also been known to attack dogs. In particular, leopards are known to have a preference for dogs and have been recorded to kill and consume them no matter their size.^[115]Tigers in Manchuria, Indochina, Indonesia, and Malaysia are also reported to kill dogs.^[116]Striped hyenas are known to kill dogs in Turkmenistan, India, and the Caucasus.^[117]

Diet

Dogs have been described as carnivores^[118][119] or omnivores.^{[17][120][121][122]} Compared to wolves, dogs from agricultural societies have extra copies of amylase and other genes involved in starch digestion that contribute to an increased ability to thrive on a starch-rich diet.^[19] Also, like humans, some dog breeds produce amylase in their saliva. Based on metabolism and nutrition, many consider the dog to be an omnivore.^[123]

However, dogs are not merely omnivores. More like cats and less like other omnivores, dogs can only produce bile acid with taurine, and it cannot produce vitamin D, which it obtains from animal flesh. Also, more like cats, the dog requires arginine to maintain its nitrogen balance. These nutritional requirements place the dog part-way between carnivores and omnivores.^[124]

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 Fuegians, who instead domesticated the Fuegian dog, a different canid species
• Individual Pacific islands whose maritime settlers did not bring dogs, or where dogs died out after original settlement, notably: the Mariana Islands,^[125]Palau,^[126]Marshall Islands,^[127]Gilbert Islands,^[127]New Caledonia,^[128]Vanuatu,^[128][129]Tonga,^[129]Marquesas,^[129]Mangaia in the Cook Islands, Rapa Iti in French Polynesia, Easter Island,^[129]Chatham Islands,^[130] and Pitcairn Island (settled by the Bounty mutineers, who killed off their dogs to escape discovery by passing ships^[131]).

Dogs were introduced to Antarctica as sled dogs but were later outlawed by international agreement due to the possible risk of spreading infections.^[132]

Breeds

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 0.46 kg (1 lb) teacup poodle to a 90 kg (200 lb) giant mastiff. Phenotypic variation can include height measured to the withers ranging from 15.2 cm (6 in) in the Chihuahua to 76 cm (30 in) 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 variety of patterns; coats can be short or long, coarse-haired to wool-like, straight, curly, or smooth.^[133] The skull, body, and limb proportions vary significantly between breeds, with dogs displaying more phenotypic diversity than can be found within carnivores' entire order. Some breeds demonstrate outstanding skills in herding, retrieving, scent detection, and guarding, demonstrating 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 unknown.^[27]

Roles with humans

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. These attributes have given dogs a relationship with humans that has enabled them to become one of the most successful species today.^{[134]:pages95–136}

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 disabled 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.^[135][136]

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.^[137] They would have benefited from humans' upright gait that gives them a more extensive range over which to see potential predators and prey, and better color vision that, at least by day, gives humans better visual discrimination.^[137] Camp dogs would also have benefited from human tool use, bringing down larger prey and controlling fire for various purposes.^[137]

Humans would also have derived enormous benefit from the dogs associated with their camps.^[138] For instance, dogs would have improved sanitation by cleaning up food scraps.^[138] Dogs may have provided warmth, as referred to in the Australian Aboriginal expression "three dog night" (a frigidly cold night). They would have alerted the camp to predators or strangers, using their acute hearing to provide an early warning.^[138]

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.^[138] The relationship between a dog's presence 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 were an essential factor in wolf domestication.^[139]

The cohabitation of dogs and humans likely improved the chances of survival for early human groups. The domestication of dogs may have been one of the key forces that led to human success.^[140]

Human emigrants from Siberia that came across the Bering land bridge into North America likely had dogs in their company. Although one writer^[141] even suggests that sled dogs' use may have been critical to the success of the waves that entered North America roughly 12,000 years ago,^[141] the earliest archaeological evidence of dog-like canids in North America dates from about 9,400 years ago.^{[134]:104[142]} 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 to the Apache and Navajo tribes' migration 1,400 years ago. This use of dogs in these cultures often persisted after the introduction of the horse to North America.^[143]

As pets

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.^[51]

"The most widespread form of interspecies bonding occurs between humans and dogs"^[138] and the keeping of dogs as companions, particularly by elites, has a long history^[144] (see the Bonn-Oberkassel dog). Pet-dog populations grew significantly after World War II as suburbanization increased.^[144] In the 1950s and 1960s, dogs were kept outside more often than they tend to be today^[145] (the expression "in the doghouse" - recorded since 1932^[146] - to describe exclusion from the group implies a 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 pet dog's role, such as the increased role of dogs in the emotional support of their human guardians.^[147] People and their dogs have become increasingly integrated and implicated in each other's lives,^[148] to the point where pet dogs actively shape how a family and home are experienced.^[149]

There have been two significant trends occurring within the second half of the 20th century in pet dogs' changing status. The first has been the "commodification," shaping it to conform to social expectations of personality and behavior.^[149] The second has been the broadening of the family's concept and the home to include dogs-as-dogs within everyday routines and practices.^[149]

A vast range of commodity forms aims to transform a pet dog into an ideal companion.^[150] 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.^[150] While dog training as an organized activity has operated since the 18th century, it became a high-profile issue in the last decades of the 20th century. 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 a pet dog's new role.^[151] Dog training books, classes, and television programs proliferated as the process of commodifying the pet dog continued.^[152]

The majority of contemporary dog owners describe their pet as part of the family,^[149] although some ambivalence about the relationship is evident in the popular reconceptualization of the dog-human family as a pack.^[149] Some dog-trainers, such as on the television program Dog Whisperer, have promoted a dominance-model of dog-human relationships. However, it has been disputed that "trying to achieve status" is characteristic of dog-human interactions.^[153] 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.^[154]

Increasingly, human family-members engage in activities centered on the dog's perceived needs and interests, or in which the dog is an integral partner, such as dog dancing and dog yoga.^[150]

According to statistics published by the American Pet Products Manufacturers Association in the National Pet Owner Survey in 2009-2010, an estimated 77.5 million people in the United States have pet dogs.^[155] The same source shows that 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. Although several programs promote pet adoption, less than a fifth of the owned dogs come from shelters.

Some research suggests that a pet dog produces a considerable carbon footprint.^[156][157]

A study using magnetic resonance imaging (MRI) to compare 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 human emotional sounds, making them friendly social pets to humans.^[158]

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),^[159][17] hunting (hounds, pointers),^[44] and rodent control (terriers).^[17] Other types of working dogs include search and rescue dogs,^[160]detection dogs trained to detect illicit drugs^[161] or chemical weapons;^[162] guard dogs; dogs who assist fishermen with the use of nets; and dogs that pull loads.^[17] 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.^[163][164]

Various kinds of service dogs and assistance dogs, including guide dogs, hearing dogs, mobility assistance dogs, and psychiatric service dogs, assist individuals with disabilities.^[165][166] Some dogs owned by people with epilepsy 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.^[167]

Sports and shows

People often enter their dogs in competitions,^[168] 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 dog's externally observable qualities (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,^[169]China,^[135]Vietnam,^[136] and the Philippines,^[170] which dates back to antiquity.^[171] It is estimated that 13-16 million dogs are killed and consumed in Asia every year.^[172] In China, debates have ensued over banning the consumption of dog meat.^[173] Following the Sui and Tang dynasties of the first millennium, however, people living on northern China's plains began to eschew eating dogs, which is likely due to Buddhism and Islam's spread, two religions that forbade the consumption of certain animals, including dog. As members of the upper classes shunned dog meat, it gradually became a social taboo to eat it, even though the general population continued to consume it for centuries afterward.^[174] Dog meat is also consumed in some parts of Switzerland.^[175] Other cultures, such as Polynesia and pre-Columbian Mexico, also consumed dog meat in their history. Dog fat is also reportedly believed to be beneficial for the lungs in some parts of Poland^[176][177] and Central Asia.^[178][179] Proponents of eating dog meat have argued that placing a distinction between livestock and dogs is western hypocrisy and that there is no difference in eating different animals' meat.^{[180][181][182][183]}

In Korea, the primary dog breed raised for meat, the nureongi (), differs from those breeds raised for pets that Koreans may keep in their homes.^[184]

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 the body's vital energy. 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 prevalent in Korea with a segment of the population, dog is not as widely consumed as beef, chicken, and pork.^[184]

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.^[185]

Citing a 2008 study, the U.S. Centers for Disease Control estimated in 2015 that 4.5 million people in the USA are bitten by dogs each year.^[186] A 2015 study estimated that 1.8% of the U.S. population is bitten each year.^[187] In the 1980s and 1990s, the U.S. averaged 17 fatalities per year, while since 2007, this has increased to an average of 31.^[188] 77% of dog bites are from the pet of family or friends, and 50% of attacks occur on the dog's legal owner's property.^[188]

A Colorado study found bites in children were less severe than bites in adults.^[189] The incidence of dog bites in the U.S. 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 of being bitten in the face or neck.^[190] Sharp claws with powerful muscles behind them can lacerate flesh in a scratch that can lead to serious infections.^[191]

In the U.K., between 2003 and 2004, there were 5,868 dog attacks on humans, resulting in 5,770 working days lost in sick leave.^[192]

In the United States, cats and dogs are a factor in more than 86,000 falls each year.^[193] It has been estimated that around 2% of dog-related injuries treated in U.K. 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.^[194]

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.^[195] In Great Britain, 24% of soil samples taken from public parks contained T. canis eggs.^{[196][failed verification]} Untreated toxocariasis can cause retinal damage and decreased vision.^[196] Dog feces can also contain hookworms that cause cutaneous larva migrans in humans.^{[197][198][199][200]}

Health benefits for humans

Dogs suffer from the same common disorders as humans; these include cancer, diabetes, heart disease, and neurologic disorders. The pathology is similar to humans, as is their response to treatment and their outcomes. Researchers are now identifying the genes associated with dog diseases similar to human disorders but lack mouse models to find cures for dogs and humans. The genes involved in canine obsessive-compulsive disorders led to the detection of four genes in humans' related pathways.^[201]

The scientific evidence is mixed as to whether a dog's companionship can enhance human physical health and psychological well-being.^[202] Studies suggesting that there are benefits to physical health and psychological well-being ^[203] have been criticized for being poorly controlled.^[204] It found 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.^[205]

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."^[202] In one study, new guardians reported a highly significant reduction in minor health problems during the first month following pet acquisition. This effect was sustained in those with dogs through to the end of the study.^[206]

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 behavior and that for guardians of dogs, these effects are relatively long-term.^[206] Pet guardianship has also been associated with increased coronary artery disease survival. Human guardians are significantly less likely to die within one year of an acute myocardial infarction than those who did not own dogs.^[207]

The health benefits of dogs can result from contact with dogs in general, not solely from having dogs as pets. For example, when in a pet dog's presence, people show reductions in cardiovascular, behavioral, and psychological indicators of anxiety.^[208] Other health benefits are gained from exposure to immune-stimulating microorganisms, which can protect against allergies and autoimmune diseases according to the hygiene hypothesis. The benefits of contact with a dog also include social support, as dogs cannot only provide companionship and social support themselves but also act as facilitators of social interactions between humans.^[209] One study indicated that wheelchair users experience more positive social interactions with strangers when accompanied by a dog than when they are not.^[210] In 2015, a study found that pet owners were significantly more likely to get to know people in their neighborhood than non-pet owners.^[211]

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.^[212] 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.^[213] 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 not in an animal-assisted program.^[214]

Shelters

Every year, between 6 and 8 million dogs and cats enter U.S. animal shelters.^[215] 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.^[216] The percentage of dogs in U.S. animal shelters eventually adopted and removed from shelters by their new legal owners has increased since the mid-1990s from around 25% to a 2012 average of 40% among reporting shelters^[217] (with many shelters reporting 60-75%).^[218]

Terminology^[219]

• The term dog typically is applied 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.
• An immature male or female (that is, an animal not yet capable of reproduction) is a puppy or pup.
• A group of puppies from the same gestation period is a litter.
• The father of a litter is a sire.
• The mother of a litter is a dam.
• A group of any three or more adults is a pack.
• A pack leader is an alpha. Typically a pack will have either an individual alpha, or a male-female alpha pair.
• A pack member subservient to alphas is a beta.
• A pack member subservient to all others is an omega.

Cultural depictions

In China, Korea, and Japan, dogs are viewed as kind protectors.^[220]

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,^[221] and her worshippers frequently dedicated small models of seated dogs to her.^[221] In the Neo-Assyrian and Neo-Babylonian periods, dogs were used as emblems of magical protection.^[221]

In mythology, dogs often serve as pets or as watchdogs.^[220] Stories of dogs guarding the gates of the underworld recur throughout Indo-European mythologies^[222][223] and may originate from Proto-Indo-European religion.^[222][223] In Greek mythology, Cerberus is a three-headed watchdog who guards the gates of Hades.^[220] In Norse mythology, a bloody, four-eyed dog called Garmr guards Helheim.^[220] In Persian mythology, two four-eyed dogs guard the Chinvat Bridge.^[220] In Welsh mythology, Annwn is guarded by C?n Annwn.^[220] In Hindu mythology, Yama, the god of death, owns two watchdogs who have four eyes. They are said to watch over the gates of Naraka.^[224]

The hunter god Muthappan from the 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.^[225] In Philippine mythology, Kimat, the pet of Tadaklan, the god of thunder, is responsible for lightning.

The dog's role in Chinese mythology includes a position as one of the twelve animals that 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)
• Canes Venatici (the Hunting Dogs)

In Christianity, dogs represent faithfulness.^[220] 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 after that.^[226] As such, the Dominican Order (Ecclesiastical Latin: Dominicanus) means "dogs of the Lord" or "hounds of the Lord" (Ecclesiastical Latin: domini canis).^[226] In Christian folklore, a church grim often takes the form of a black dog to guard Christian churches and their churchyards from sacrilege.^[227]

Jewish law does not prohibit keeping dogs and other pets.^[228] Jewish law requires Jews to feed dogs (and other animals that they own) before themselves and make arrangements for feeding them before obtaining them.^[228]

The view on dogs in Islam is mixed, with some schools of thought viewing it as unclean,^[220] 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."^[229] Therefore, Sunni Malaki and Hanafi jurists permit the trade of and keeping of dogs as pets.^[230]

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 caves' walls. 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.^[231]

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.^[232] The museum contains ancient artifacts, fine art, and educational opportunities for visitors.^[232]

See also

Lists

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

References

Bibliography

• Miklósi, Adám (2007). Dog Behaviour, Evolution, and Cognition. Oxford University Press. doi:10.1093/acprof:oso/9780199295852.001.0001. ISBN 978-0-19-929585-2.
• Smith, Bradley, ed. (2015). The Dingo Debate: Origins, Behaviour and Conservation. CSIRO Publishing, Melbourne, Australia. ISBN 978-1-4863-0030-3.
• Boitani, Luigi; Mech, L. David (2003). Wolves: Behavior, Ecology, and Conservation. Chicago: University of Chicago Press. p. 482. ISBN 978-0-226-51696-7. OCLC 904338888.

Further reading

• Alexandra Horowitz (2016). Being a Dog: Following the Dog Into a World of Smell. Scribner. ISBN 978-1476795997.

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