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From Wikipedia, the free encyclopedia

Domestic dog Fossil range: Late Pleistocene – Recent
A Labrador Retriever
Conservation status
Domesticated
Scientific classification
Kingdom: Animalia Subkingdom: Eumetazoa Phylum: Chordata Subphylum: Vertebrata Class: Mammalia Subclass: Theria Order: Carnivora Suborder: Caniformia Family: Canidae Subfamily: Caninae Tribe: Canini[1] Genus: Canis Species: C. lupus Subspecies: C. l. familiaris
Trinomial name
Canis lupus familiaris
Synonyms
Canis familiaris Canis familiaris domesticus

The dog (Canis lupus familiaris,^[2] pronounced /ˈkeɪ.nis ˈluːpəs fʌˈmɪliɛəris/) is a domesticated subspecies of the gray wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The domestic dog has been one of the most widely kept working and companion animals in human history.

The domestication of the gray wolf took place in a handful of events roughly 15,000 years ago in central Asia. The dog quickly became ubiquitous across culture in all parts of the world, and was extremely valuable to early human settlements. For instance, it is believed that the successful emigration across the Bering Strait might not have been possible without sled dogs.^[3] As a result of the domestication process, the dog developed a sophisticated intelligence that includes unparalleled social cognition and a simple theory of mind^{[citation needed]} that is important to their interaction with humans. These social skills have helped the dog to perform in myriad roles, such as hunting, herding, protection, and, more recently, assisting handicapped individuals. Currently, there are estimated to be 400 million dogs in the world.^[4]

Over the 15,000 year span that the dog had been domesticated, it diverged into only a handful of landraces, groups of similar animals whose morphology and behavior have been shaped by environmental factors and functional roles. As the modern understanding of genetics developed, humans began to intentionally breed dogs for a wide range of specific traits. Through this process, the dog has developed into hundreds of varied breeds, and shows more behavioral and morphological variation than any other land mammal.^[5] For example, height measured to the withers ranges from a few inches in the Chihuahua to a few feet 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.^[6] It is common for most breeds to shed this coat, but non-shedding breeds are also popular.

Contents 1 Etymology and related terminology 2 Taxonomy and evolution 3 Biology 3.1 Senses 3.1.1 Sight 3.1.1.1 Acuity 3.1.1.2 Color Perception 3.1.1.3 Field of Vision 3.1.2 Hearing 3.1.3 Smell 3.2 Physical characteristics 3.2.1 Coat 3.2.2 Tail 3.3 Types and breeds 3.4 Health 3.4.1 Mortality 3.4.2 Predation 3.5 Diet 3.6 Reproduction 3.7 Neutering 4 Intelligence and behavior 4.1 Intelligence 4.2 Behavior 4.2.1 Interactions with humans 4.2.2 Health risks to humans 4.2.3 Work 4.2.4 Sports and shows 5 Differences from wolves 5.1 Physical characteristics 5.2 Behavior 5.3 Trainability 6 See also 7 References 8 Further reading 9 External links

Etymology and related terminology

Dog is the common use term that refers to members of the subspecies Canis lupus familiaris. The term is sometimes used to refer to a wider range of species: it can be used to refer to any mammal belonging to the family Canidae, which includes wolves, foxes, jackals, and coyotes; it can be used to refer to the subfamily of Caninae, or the genus Canis, also often called the "true dogs".^[7] Some members of the family have "dog" in their common names, such as the raccoon dog and the African wild dog. A few animals have "dog" in their common names but are not canids, such as the prairie dog and the dog fish.

The English word "dog" can be traced back to the Old English docga, a "powerful breed of canine".^[8] The term may derive from Proto-Germanic *dukkōn, represented in Old English finger-docce ("finger-muscle").^[9] Due to the linguistically archaic structure of the word, the term dog may ultimately derive from the earliest layer of Proto-Indo-European vocabulary, reflecting the role of the dog as the earliest domesticated animal.^[10]

The English word hound, which refers to a specific breed group in English, means "dog" in general in other Germanic languages - it is cognate to German hund, Dutch hond, common Scandinavian hund, and Icelandic hundur. Hound itself is derived from the Proto-Indo-European *kwon-, which is also the direct root of the Greek κυων (kuōn) and the indirect root of the Latin canis through the variant form *kani-.^[11]

In breeding circles, a male canine is referred to as a dog, while a female is called a bitch. A group of offspring is a litter. The father of a litter is called the sire, and the mother is called the dam. Offspring are generally called pups or puppies until they are about a year old. The process of birth is whelping.^[12]

Taxonomy and evolution

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The domestic dog was originally classified as Canis familiaris and Canis familiarus domesticus by Linnaeus in 1758,^[13][14] and is currently classified as Canis lupus familiaris, a subspecies of the gray wolf Canis lupus, by the Smithsonian Institution and the American Society of Mammalogists. Overwhelming evidence from behavior, vocalizations, morphology, and molecular biology led to the contemporary scientific understanding that a single species, the gray wolf, is the common ancestor for all breeds of domestic dogs,^[15][3] however the timeframe and mechanisms by which dogs diverged are controversial.^[3]

The current consensus among biologists and archaeologists is that no one can be sure when dogs were domesticated.^[3][16] There is conclusive evidence that dogs genetically diverged from their wolf ancestors at least 15,000 years ago^[17][18][19] but some believe domestication to have occurred earlier.^[3] The bulk of the scientific evidence for the evolution of the domestic dog stems from archealogical findings and mitochondrial DNA studies. The divergence date of roughly 15000 years ago is based in part on archaeological evidence that demonstrates that the domestication of dogs occurred prior to 15,000 years ago.^{[3] [16]}, and some genetic evidence indicates that the domestication of dogs from their wolf ancestors began in the late Upper Paleolithic close to the Pleistocene/Holocene boundary, between 17,000 and 14,000 years ago.^[20] But there is a wide range of other, contradictory findings that make this issue contraversial.

Archaeological evidence plays a large role in this debate. In 2008, a team of international scientists released findings from an excavation at Goyet Cave in Belgium declaring that a large, toothy canine existed 31,700 years ago and ate a diet of horse, musk ox and reindeer.^[21] The morphology of the skeleton led researchers and the context in which it was found led researchers to hypothesize that this canine was an ancient domesticated dog. Prior to this Belgium discovery, the earliest dog fossils were two large skulls from Russia and a mandible from Germany, that dated from roughly 14,000 years ago.^[19][3] Remains of smaller dogs from Natufian cave deposits in the Middle East have been dated to around 10,000 to 12,000 years ago.^[19] There is a great deal of archealogical evidence for dogs throughout Europe and Asia around this period and through the next two thousand years (roughly 8,000 to 10,000 years ago), with fossils uncovered in Germany, the French Alps, and Iraq, and cave paintings in Turkey.^[3]

Thus, the archaeological evidence suggests that the latest dogs could have diverged from wolves was roughly 15000 years ago, although it is possible that they diverged much earlier.^[3]

DNA studies have provided a wider range of possible divergence dates, from 15,000 to 40,000 years ago^[19], to as much as 100,000 to 140,000 years ago.^[22] This evidence depends on a number of assumptions that may be violated.^[3] Genetic studies are based in comparisons of genetic diversity between species, and depend on a calibration date. Many estimates of divergence dates from DNA evidence use an estimated wolf-coyote divergence date (roughly 1 million years ago) as a calibration. If this estimate is incorrect, and the actual wolf-coyote divergence is closer to 750,000 or 2 million years ago, then the DNA evidence that supports specific dog-wolf divergence dates would be interpreted very differently. Furthermore, it is believed that the genetic diversity of wolves has been in decline for the last 200 years, and that the genetic diversity of dogs has been reduced by selective breeding. This could significantly bias DNA analyses to support an earlier divergence date. The genetic evidence for the domestication event occurring in East Asia is also subject to violations of assumptions. These conclusions are based on the location of maximal genetic divergence, and assumes that hybridization does not occur, and that breeds remain geographically localized. Although these assumptions hold for many species, there is good reason to believe that they do not hold for canines.^[3]

Genetic analyses indicate all dogs are likely descended from a handful of domestication events with a small number of founding females,^[20][3] although there is evidence that domesticated dogs interbred with local populations of wild wolves on several occasions.^[19] Data suggests that dogs first diverged from wolves in East Asia, and that these domesticated dogs then quickly migrated throughout the world, reaching the North American continent around 8000 B.C.^[19] The oldest groups of dogs, which show the greatest genetic variability and are the most similar to their wolf ancestors, are primarily Asian and African breeds, including the Basenji, Lhasa Apso, and Siberian Husky.^[23] Some breeds that were thought to be very old, such as the Pharaoh Hound, Ibizan Hound, and Norwegian Elkhound, are now known to have been created more recently.^[23]

There is a great deal of controversy surrounding the evolutionary framework for the domestication of dogs.^[3] Although it is widely claimed that "man domesticated the wolf,"^[24] man may not have taken so proactive a role in the process^[3]. The nature of the interaction between man and wolf that led to domestication is unknown and contraversial. At least three early species of the Homo genus began spreading out of Africa roughly 400,000 years ago, and thus lived for a considerable period in contact with canine species. Despite this, there is no evidence of any adaptation of canine species to the presence of the close relatives of modern man. If dogs were domesticated, as believed, roughly 15,000 years ago, the event (or events) would have coincided with a large expansion in human territory and the development of agriculture. This has led some biologists to suggest that one of the forces that led to the domestication of dogs was a shift in human lifestyle in the form of established human settlements. Permanent settlements would have coincided with a greater amount of disposable food and would have created a barrier between wild and anthropogenic canine populations.^[3]

Biology

Domestic dogs have been selectively bred for millennia for various behaviors, sensory capabilities, and physical attributes.^[25] Modern dog breeds show more variation in size, appearance, and behavior than any other domestic animal. Nevertheless, their morphology is based on that of their wild ancestors, gray wolves.^[25] 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. Dogs are highly variable in height and weight. The smallest known dog was a Yorkshire Terrier, who stood only 6.3 cm (2.5 in) at the shoulder, 9.5 cm (3.75 in) in length along the head-and-body, and weighed only 113 grams (4 ounces). The largest known dog was an English Mastiff which weighed 155.6 kg (343 lbs) and was 250 cm (8.2 feet) from the snout to the tail.^[26] The tallest dog is a Great Dane that stands 106.7 cm (42.2 in) at the shoulder.^[27]

Senses

Sight

Acuity

The dog's visual system is engineered to serve the purposes of a hunter.^[28] While a dog's visual acuity is poor (that of a poodle's has been estimated to translate to a Snellen rating of 20/75^[28]), their visual discrimination for moving objects is very high; dogs have been shown to be able to discriminate between humans (i.e., identifying their owner) from distances up to a mile.^[28] As crepuscular hunters, dogs often rely on their vision in low light situations: they have very large pupils, a high density of rods in the fovea, an increased flicker rate, and a tapetum lucidum.^[28] The tapetum is a reflective surface behind the retina that reflects light back to give the photoreceptors a second chance to catch the photons.

Color Perception

Like most mammals, dogs are dichromats and have color vision equivalent to red-green color blindness in humans (deuteranopia).^{[29][30][31][28]}

Field of Vision

The eyes of different breeds of dogs have different shapes, dimensions, and retina configurations.^[32] Many long-nosed breeds have a "visual streak" — a wide foveal region that runs across the width of the retina and gives them a very wide field of excellent vision. Some long-muzzled breeds, particularly the sighthounds, have a field of vision up to 270° (compared to 180° for humans). Short-nosed breeds, on the other hand, have an "area centralis": a central patch with up to three times the density of nerve endings as the visual streak, giving them detailed sight much more like a human's. Some broad-headed breeds with short noses have a field of vision similar to that of humans.^[29][30] Most breeds have good vision, but some show a genetic predisposition for myopia — such as Rottweilers, where one out of every two has been found to be myopic.^[28]

Hearing

The frequency range of dog hearing is approximately 40 Hz to 60,000 Hz,^[33] which means that dogs can detect sounds outside both ends of the human auditory spectrum.^[34][33][30] Additionally, dogs have ear mobility which allows them to rapidly pinpoint the exact location of a sound.^[35] Eighteen or more muscles can tilt, rotate, raise, or lower a dog's ear. A dog can identify a sound's location much faster than a human can, as well as hear sounds at four times the distance.^[35]

Smell

While the human brain is dominated by a large visual cortex, the dog brain is largely dominated by an olfactory cortex.^[28] The olfactory bulb in dogs is roughly forty times bigger than the olfactory bulb in humans, relative to total brain size, with 125 to 220 million smell-sensitive receptors.^[28] The bloodhound exceeds this standard with nearly 300 million receptors.^[28] Dogs can discriminate odors at concentrations nearly 100 million times lower than humans can.^[36]

Physical characteristics

Coat

The coats of domestic dogs are either "double", made up of a coarse topcoat and a soft undercoat, like a wolf, or "single", with the topcoat only. Dogs with double coats tend to originate in colder climates.

Domestic dogs often display the remnants of countershading, a common natural camouflage pattern. The general theory of countershading is that an animal that is lit from above will appear lighter on its upper half and darker on its lower half, where it will usually be in its own shade.^[37][38] This is a pattern that predators can learn to watch for. A countershaded animal will have dark coloring on its upper surfaces and light coloring below,^[37] which reduces its general visibility. Thus many breeds will have an occasional "blaze", stripe, or "star" of white fur on their chest or underside.^[38]

Tail

There are many different shapes for dog tails: straight, straight up, sickle, curled, or cork-screw. In some breeds, the tail is traditionally docked to avoid injuries (especially for hunting dogs).^[39] In some breeds, puppies can be born with a short tail or no tail at all.^[40] This occurs more frequently in those breeds that are frequently docked and thus have no breed standard regarding the tail.

Types and breeds

While all dogs are genetically very similar,^[19] natural selection and selective breeding have reinforced certain characteristics in certain populations of dogs, giving rise to dog types and dog breeds. Dog types are broad categories based on function, genetics, or characteristics.^[41] Dog breeds are groups of animals that possess a set of inherited characteristics that distinguishes them from other animals within the same species. Modern dog breeds are non-scientific classifications of dogs kept by modern kennel clubs. Purebred dogs of one breed are genetically distinguishable from purebred dogs of other breeds,^[23] but the means by which kennel clubs classify dogs is unsystematic. Systematic analyses of the dog genome has revealed only four major types of dogs that can be said to be statistically distinct.^[23] These include the "old world dogs" (e.g., Malamute and Shar-Pei), "Mastiff"-type (e.g., Labrador Retriever), "herding"-type (e.g., St. Bernard), and "all others" (also called "modern"- or "hunting"-type).^[23][42]

Health

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Dogs are susceptible to various diseases, ailments, and poisons, some of which can affect humans. To defend against many common diseases, dogs are often vaccinated.

Some breeds of dogs are prone to certain genetic ailments such as elbow or 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 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, and mites, as well as hookworms, tapeworms, roundworms, and heartworms.

Dogs are also vulnerable to some of the same health conditions as humans, including diabetes, dental and heart disease, epilepsy, cancer, hypothyroidism, and arthritis.^{[citation needed]}

Mortality

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.^{[43][44][45][46]} 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.^[46]

The longest-lived breeds, including Toy Poodles, Border Terriers, and Tibetan Spaniels, have median longevities of 14 to 15 years.^[46] 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.^{[45][44][46][47]} The dog widely reported to be the longest-lived is "Bluey," who died in 1939 and was claimed to be 29.5 years old at the time of his death; however, the Bluey record is anecdotal and unverified.^[48] The longest verified records are of dogs living for 24 years.^[48]

Predation

Although wild dogs, like wolves, are apex predators, they can be killed in territory disputes with wild animals.^[49] Furthermore, in areas where both dogs and other large predators live, dogs can be a major food source for big cats or canines. Reports from Croatia indicate that dogs are killed more frequently than sheep. Wolves in Russia apparently limit feral dog populations. In Wisconsin, more compensation has been paid for dog losses than livestock.^[49] Some wolf pairs have been reported to prey on dogs by having one wolf lure the dog out into heavy brush where the second animal waits in ambush.^[50] 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.^[51] 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 the dog's size or ferocity.^[52] Tigers in Manchuria, Indochina, Indonesia, and Malaysia, are reputed to kill dogs with the same vigor as leopards.^[53] Striped Hyenas are major predators of village dogs in Turkmenistan, India, and the Caucasus.^[54]

Diet

Despite its descent from wolves, the domestic dog is an omnivore,^[25] though it is classified in the order Carnivora. Unlike an obligate carnivore, such as a member of the cat family with its shorter small intestine, a dog is neither dependent on meat-specific protein nor a very high level of protein in order to fulfill its basic dietary requirements. Dogs are able to healthily digest a variety of foods, including vegetables and grains, and can consume a large proportion of these in their diet. In the wild, canines often eat available plants and fruits.^[25]

Reproduction

In domestic dogs, sexual maturity begins to happen around age six to twelve months for both males and females,^[25][55] 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 biannually, 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.^[25] Because the ova survive and are capable of being fertilized for a week after ovulation, it is possible for a female to mate with more than one male.^[25]

Adolescence for most domestic dogs is around 12 to 15 months, beyond which they are for the most part more adult than puppy.^{[citation needed]} Domestication has selectively bred for higher libido and earlier and more frequent breeding cycles in dogs than in their wild ancestors, and dogs remain reproductively active until old age.^{[citation needed]}

Dogs bear their litters roughly 56 to 72 days after fertilization,^[56][25] with an average of 63 days, although the length of gestation can vary. An average litter consists of about six puppies,^[57] though this number may vary widely based on the breed of dog. Toy dogs generally 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.^[58]

Neutering

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, 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 have to be destroyed later.^[59]

According to the Humane Society of the United States, 3–4 million dogs and cats are put down 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.^[60] 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.^[61] Spayed female dogs are less likely to develop some forms of cancer, affecting mammary glands, ovaries, and other reproductive organs.^[62] However, neutering increases the risk of urinary incontinence in female dogs,^[63] and prostate cancer in males,^[64] as well as osteosarcoma, hemangiosarcoma, cruciate ligament rupture, obesity, and diabetes mellitus in either gender.^[65]

Intelligence and behavior

Intelligence

The domestic dog has a predisposition to exhibit a social intelligence that is uncommon in the animal world.^[28] Dogs are capable of learning in a number of ways, such as through simple reinforcement (e.g. classical or operant conditioning) and by observation.^[28]

Dogs go through a series of stages of cognitive development. They are not born with the understanding that objects which are not being actively perceived still remain in existence, called object permanence. This occurs as the infant learns to interact intentionally with objects around it. For dogs, this occurs at roughly 8 weeks of age.^[28]

Puppies learn behaviors quickly by following examples set by experienced dogs.^[28] This form of intelligence is not peculiar to those tasks dogs have been bred to perform, but can be generalized to myriad abstract problems. For example, Dachshund puppies who watched an experienced dog pull a cart by tugging on an attached piece of ribbon in order to get a reward from inside the cart learned the task fifteen times faster than those who were left to solve the problem on their own.^[66][28] Dogs can also learn by mimicking human behaviors. In one study, puppies were presented with a box, and shown that when a handler pressed a lever, a ball would roll out of the box. The handler then allowed the puppy to play with the ball, making it an intrinsic reward. The pups were then allowed to interact with the box. Roughly three-quarters of the puppies subsequently touched the lever, and over half successfully released the ball, compared to only 6 percent in a control group that did not watch the human manipulate the lever.^[67]Another study found that handing an object between experimenters who then used the object's name in a sentence successfully taught an observing dog each object's name, allowing the dog to subsequently retrieve the item.^[68]

Dogs also demonstrate sophisticated social cognition by associating behavioral cues with abstract meanings.^[28] One such class of social cognition involves the understanding that others are conscious agents. Research has shown that dogs are capable of interpreting subtle social cues, and appear to recognize when a human or dog's attention is focused on them. To test this, researchers devised a task in which a reward was hidden underneath one of two buckets. The experimenter then attempted to communicate with the dog to indicate the location of the reward by using a wide range of signals: tapping the bucket, pointing to the bucket, nodding to the bucket, or simply looking at the bucket.^[69] The results showed that domestic dogs were better than chimpanzees, wolves, and human infants at this task, and even young puppies with limited exposure to humans performed well.^[28] Dr. Stanley Coren, an expert on dog psychology, states that these results demonstrated the social cognition of dogs can exceed that of even our closest genetic relatives, and that this capacity is a recent genetic acquisition which distinguishes the dog from its ancestor, the wolf.^[28] Studies have also investigated whether dogs engaged in partnered play change their behavior depending on the attention-state of their partner.^[70] Those studies showed that play signals were only sent when the dog was holding the attention of its partner. If the partner was distracted, the dog instead engaged in attention-getting behavior before sending a play signal.^[70]

Dr. Coren has also argued that dogs demonstrate a sophisticated theory of mind by engaging in deception, which he supports with a number of anecdotes, including one example where a dog hid a stolen treat by sitting on it until the rightful owner of the treat left the room.^[28] Although this could have been accidental, Coren suggests that the thief understood that the treat's owner would be unable to find the treat if it were out of view. Together, the empirical data and anecdotal evidence points to dogs possessing at least a limited form of theory of mind.^[28][70]

Behavior

Although dogs have been the subject of a great deal of behaviorist psychology (e.g. Pavlov's dog), they do not enter the world with a psychological "blank slate".^[28] Rather, dog behavior is affected by genetic factors as well as environmental factors.^[28] Domestic dogs exhibit a number of behaviors and predispositions that were inherited from wolves.^[28] The grey wolf is a social animal that has evolved a sophisticated means of communication and social structure. The domestic dog has inherited some of these predispositions, but many of the salient characteristics in dog behavior have been largely shaped by selective breeding by humans. Thus some of these characteristics, such as the dog's highly developed social cognition, are found only in primitive forms in grey wolves.^[69]

Interactions with humans

Domestic dogs inherited a complex social hierarchy and behaviors from their wolf ancestors. Dogs are pack animals with a complex set of behaviors related to determining each dog's position in the social hierarchy, and they exhibit various postures and other means of nonverbal communication that reveal their states of mind.^[25] 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 earned dogs a unique relationship with humans despite being potentially dangerous apex predators.^[3]

Although experts largely disagree over the details of dog domestication, it is agreed that human interaction played a significant role in shaping the subspecies.^[3] Shortly after domestication, dogs became ubiquitous in human populations, and spread throughout the world. Emigrants from Siberia likely crossed the Bering Strait with dogs in their company, and some experts suggest that use of sled dogs may have been critical to the success of the waves that entered North America roughly 12,000 years ago. Dogs were an important part of life for the Athabascan population in North America, and were their only domesticated animal. Dogs also carried much of the load in the migration of the Apache and Navajo tribes 1,400 years ago. Use of dogs as pack animals in these cultures often persisted after the introduction of the horse to North America.^[16]

Health risks to humans

In the USA, dogs cause 88% of the 86,000 falls caused by pets. Dogs can also cause toxocariasis in humans, which can cause blindness, and can also cause human hookworm.^[71] This is not to say that dogs are dangerous.

Work

Dogs have lived and worked with humans in so many roles that they have earned the unique nickname, "man's best friend",^[72] a phrase which is used in other languages as well. They have been bred for herding livestock,^[73] hunting (e.g. pointers and hounds),^[74] rodent control,^[25] guarding, helping fishermen with nets, and pulling loads, in addition to their roles as companions.^[25]

Service dogs such as guide dogs, utility dogs, assistance dogs, hearing dogs, and psychological therapy dogs provide assistance to individuals with physical or mental disabilities.^[75][76] 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 owner to seek safety, medication, or medical care.^[77]

Sports and shows

Owners of dogs often enter them in competitions^[78] such as breed conformation shows or sports, including racing and sledding.

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.

Differences from wolves

Physical characteristics

Compared to equally sized wolves, dogs tend to have 20% smaller skulls, 10% smaller brains, as well as proportionately smaller teeth than other canid species.^[79] Dogs require fewer calories to function than wolves. Their diet of human refuse in antiquity made the large brains and jaw muscles needed for hunting unnecessary. It is thought by certain experts that the dog's limp ears are a result of atrophy of the jaw muscles.^[79] 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.^[79] 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.^[80]

Behavior

Dogs tend to be poorer than wolves at observational learning, being more responsive to instrumental conditioning.^[79] Feral dogs show little of the complex social structure or dominance hierarchy present in wolf packs. For dogs, other members of their kind are of no help in locating food items, and are more like competitors.^[79] Feral dogs are primarily scavengers, with studies showing that unlike their wild cousins, they are poor ungulate hunters, having little impact on wildlife populations where they are sympatric. However, feral dogs have been reported to be effective hunters of reptiles in the Galapagos islands,^[81] and free ranging pet dogs are more prone to predatory behavior toward wild animals.

Despite common belief, domestic dogs can be monogamous.^[82] Breeding in feral packs can be, but does not have to be restricted to a dominant alpha pair (despite common belief, such things also occur in wolf packs).^[83] Male dogs are unusual among canids by the fact that they mostly seem to play no role in raising their puppies, and do not kill the young of other females to increase their own reproductive success.^[81] Some sources say that dogs differ from wolves and most other large canid species by the fact that they do not regurgitate food for their young, nor the young of other dogs in the same territory.^[79] However, this difference was not observed in all domestic dogs. Regurgitating of food by the females for the young as well as care for the young by the males has been observed in domestic dogs, dingos as well as in other feral or semi-feral dogs. Regurgitating of food by the females and direct choosing of only one mate has been observed even in those semi-feral dogs of direct domestic dog ancestry. Also regurgitating of food by males has been observed in free-ranging domestic dogs.^[82][84]

Trainability

Dogs display much greater tractability than tame wolves, and are generally much more responsive to coercive techniques involving fear, aversive stimuli, and force than wolves, which are most responsive toward positive conditioning and rewards.^[85] Unlike tame wolves, dogs tend to respond more to voice than hand signals.^[86] Although they are less difficult to control than wolves, they can be comparatively more difficult to teach than a motivated wolf.^[85]

See also

• Bark (dog)
• Cerberus
• Dingo
• Dog king – Scandinavian tradition
• Dog license
• Dog odor
• Dog paddle – basic swimming stroke
• Dog park
• Dogs in religion
• Fear of dogs
• List of dog breeds
• List of dogs
• List of fictional dogs
• List of most popular dog breeds
• Subspecies of Canis lupus
• Wolf-dog hybrid

References

Further reading

• Abrantes, Roger (1999). Dogs Home Alone. Wakan Tanka, 46 pages. ISBN 0-9660484-2-3 (paperback).
• A&E Television Networks (1998). Big Dogs, Little Dogs: The companion volume to the A&E special presentation, A Lookout Book, GT Publishing. ISBN 1-57719-353-9 (hardcover).
• Alderton, David (1984). The Dog, Chartwell Books. ISBN 0-89009-786-0.
• Bloch, Günther. Die Pizza-Hunde (German), 2007, Franckh-Kosmos-Verlags GmbH & Co. KG, Stuttgart, ISBN 9783440109861
• Brewer, Douglas J. (2002) Dogs in Antiquity: Anubis to Cerberus: The Origins of the Domestic Dog, Aris & Phillips ISBN 0-85668-704-9
• Coppinger, Raymond and Lorna Coppinger (2002). Dogs: A New Understanding of Canine Origin, Behavior and Evolution, University of Chicago Press ISBN 0-226-11563-1
• Cunliffe, Juliette (2004). The Encyclopedia of Dog Breeds. Parragon Publishing. ISBN 0-7525-8276-3.
• Derr, Mark (2004). Dog's Best Friend: Annals of the Dog-Human Relationship. University of Chicago Press. ISBN 0-226-14280-9
• Donaldson, Jean (1997). The Culture Clash. James & Kenneth Publishers. ISBN 1-888047-05-4 (paperback).
• Fogle, Bruce, DVM (2000). The New Encyclopedia of the Dog. Doring Kindersley (DK). ISBN 0-7894-6130-7.
• Grenier, Roger (2000). The Difficulty of Being a Dog. University of Chicago Press ISBN 0-226-30828-6
• Milani, Myrna M. (1986). The Body Language and Emotion of Dogs: A practical guide to the Physical and Behavioral Displays Owners and Dogs Exchange and How to Use Them to Create a Lasting Bond, William Morrow, 283 pages. ISBN 0-688-12841-6 (trade paperback).
• Pfaffenberger, Clare (1971). New Knowledge of Dog Behavior. Wiley, ISBN 0-87605-704-0 (hardcover); Dogwise Publications, 2001, 208 pages, ISBN 1-929242-04-2 (paperback).
• Shook, Larry (1995). "Breeders Can Hazardous to Health", The Puppy Report: How to Select a Healthy, Happy Dog, Chapter Two, pp. 13–34. Ballantine, 130 pages, ISBN 0-345-38439-3 (mass market paperback); Globe Pequot, 1992, ISBN 1-55821-140-3 (hardcover; this is much cheaper should you buy).
• Shook, Larry (1995). The Puppy Report: How to Select a Healthy, Happy Dog, Chapter Four, "Hereditary Problems in Purebred Dogs", pp. 57–72. Ballantine, 130 pages, ISBN 0-345-38439-3 (mass market paperback); Globe Pequot, 1992, ISBN 1-55821-140-3 (hardcover; this is much cheaper should you buy).
• Thomas, Elizabeth Marshall (1993). The Hidden Life of Dogs (hardcover), A Peter Davison Book, Houghton Mifflin. ISBN 0-395-66958-8.
• Trumler, Eberhard. Mit dem Hund auf du; Zum Verständnis seines Wesens und Verhaltens (German); 4. Auflage Januar 1996; R. Piper GmbH & Co. KG, München
• Small animal internal medicine, RW Nelson, Couto page 107

External links

Wikispecies has information related to: Dog

• American Kennel Club
• Australian National Kennel Club
• Biodiversity Heritage Library bibliography for Canis lupus familiaris
• Canadian Kennel Club
• Fédération Cynologique Internationale (FCI) - World Canine Organisation
• New Zealand Kennel Club
• The Kennel Club (UK)

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