Dog Explained

The dog (Canis lupus familiaris,[1]) 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. As a result of the domestication process, the dog developed a sophisticated intelligence that includes unparalleled social cognition and a simple theory of mind 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.[2]

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. Humans did not take an active, intentional role in this process until the last few hundred years. 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.[3] 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.[4] It is common for most breeds to shed this coat, but non-shedding breeds are also popular.

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".[5] 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".[6] The term may derive from Proto-Germanic *dukkōn, represented in Old English finger-docce ("finger-muscle").[7] 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.[8]

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-.[9]

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.[10]

Taxonomy and evolution

See main article: Origin of the domestic dog. The domestic dog was originally classified as Canis familiaris and Canis familiarus domesticus by Linnaeus in 1758,[11] [12] 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,[13] however the timeframe and mechanisms by which dogs diverged are controversial.

The current consensus among biologists and archaeologists is that no one can be sure when dogs were domesticated. There is conclusive evidence that dogs genetically diverged from their wolf ancestors at least 15,000 years ago[14] [15] [16] but most believe domestication to have occurred much earlier. The evidence cited for an earlier divergence comes from archaeological findings and mitochondrial DNA studies, both of which are inconclusive. The archaeological evidence demonstrates that the domestication of dogs occurred prior to 15,000 years ago. 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.[17] The earliest dog fossils, two large skulls from Russia and a mandible from Germany, date from roughly 14,000 years ago.[16] Their likely ancestor is the large Eurasian wolf (Canis lupus lupus). Remains of smaller dogs from Natufian cave deposits in the Middle East have been dated to around 10,000 to 12,000 years ago.[16] 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.

DNA studies have provided a wider range of possible divergence dates, from 15,000 to 40,000 years ago[16], to as much as 100,000 to 140,000 years ago.[18] This evidence depends on a number of assumptions that others claim are violated. Genetic studies are based in comparisons of genetic diversity between species, and depend on a calibration date, such as the wolf-coyote divergence date, which is estimated to be roughly 1 million years ago. If this divergence date is closer to 750,000 or 2 million years ago, then genetic analyses 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, which could bias DNA analyses to support an earlier divergence. 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, 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.

Genetic analyses indicate all dogs are likely descended from a handful of domestication events with a small number of founding females,[17] although there is evidence that domesticated dogs interbred with local populations of wild wolves on several occasions.[16] 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.[16] 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, Saluki, Afghan Hound, Tibetan Terrier, Lhasa Apso, Chow Chow, Pekingese, Shar-Pei, Shi Tzu, Akita, Shiba Inu, Alaskan Malamute, Siberian Husky, and Samoyed.[19] 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 recreated more recently.[19]

There is a great deal of controversy surrounding the evolutionary framework for the domestication of dogs.[20] 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 these 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.[20]

Biology

See main article: Dog anatomy.

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. Nevertheless, their morphology is based on that of their wild ancestors, gray wolves. 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.[21] The tallest dog is a Great Dane that stands 106.7 cm (42.2 in) at the shoulder.[22]

Senses

Sight

The dog's visual system is engineered to serve the purposes of a hunter.[23] 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[23]), 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.[23] 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.[23] The tapetum is a reflective surface behind the retina that reflects light back to give the photoreceptors a second chance to catch the photons. Like most mammals, dogs are dichromats and have color vision equivalent to red-green color blindness in humans.[24] [25] [26] [23] The eyes of different breeds of dogs have different shapes, dimensions, and retina configurations.[27] 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.[24] [25] 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.[23]

Hearing

The frequency range of dog hearing is approximately 40 Hz to 60,000 Hz,[28] which means that dogs can detect sounds outside both ends of the human auditory spectrum.[29] [28] [25] Additionally, dogs have ear mobility which allows them to rapidly pinpoint the exact location of a sound. 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.[30]

Smell

While the human brain is dominated by a large visual cortex, the dog brain is largely dominated by an olfactory cortex.[23] 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.[23] The bloodhound exceeds this standard with nearly 300 million receptors.[23] Dogs can discriminate odors at concentrations nearly 100 million times lower than humans can.[31]

Physical characteristics

Coat

See main article: Coat (dog).

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.[32] [33] 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,[32] which reduces its general visibility. Thus many breeds will have an occasional "blaze", stripe, or "star" of white fur on their chest or underside.[33]

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).[34] In some breeds, puppies can be born with a short tail or no tail at all.[35] This occurs more frequently in those breeds that are frequently docked and thus have no breed standard regarding the tail.

Types and breeds

See main article: Dog breeds. While all dogs are genetically very similar,[16] 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.[36] 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,[19] 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.[19] 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).[19] [37]

Health

See main article: Dog health.

See also: CVBD.

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.

Mortality

See main article: Aging in dogs.

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.[38] [39] [40] [41] 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, Bulldogs, Nova Scotia Duck-Tolling Retrievers, Bloodhounds, Irish Wolfhounds, Greater Swiss Mountain Dogs, Great Danes, and Mastiffs, are nearly as short-lived, with median longevities of 6 to 7 years.[41]

The longest-lived breeds, including Toy Poodles, Border Terriers, Miniature Dachshunds, Miniature Poodles, and Tibetan Spaniels, have median longevities of 14 to 15 years.[41] 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.[40] [39] [41] [42] 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.[43] The longest verified records are of dogs living for 24 years.[43]

Predation

Although wild dogs, like wolves, are apex predators, they can be killed in territory disputes with wild animals. 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.[44] 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.[45] 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.[46] 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.[47] Tigers in Manchuria, Indochina, Indonesia, and Malaysia, are reputed to kill dogs with the same vigor as leopards.[48] Striped Hyenas are major predators of village dogs in Turkmenistan, India, and the Caucasus.[49]

Diet

See also: Dog food. Despite its descent from wolves, the domestic dog is an omnivore, 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.

Reproduction

See main article: Canine reproduction. In domestic dogs, sexual maturity begins to happen around age six to twelve months for both males and females,[50] 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. 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.

Adolescence for most domestic dogs is around 12 to 15 months, beyond which they are for the most part more adult than puppy. 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.

Dogs bear their litters roughly 56 to 72 days after fertilization,[51] with an average of 63 days, although the length of gestation can vary. An average litter consists of about six puppies,[52] 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.[53]

Spaying and neutering

See main article: Spaying and 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.[54]

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.[55] 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. Several notable public figures have spoken out against animal overpopulation, including Bob Barker. On his game show, The Price Is Right, Barker stressed the problem at the end of every episode, saying: "Help control the pet population. Have your pets spayed or neutered." The current host, Drew Carey, makes a similar plea at the conclusion of each episode.

Neutering reduces problems caused by hypersexuality, especially in male dogs.[56] Spayed female dogs are less likely to develop some forms of cancer, affecting mammary glands, ovaries, and other reproductive organs.[57]

However, neutering increases the risk of urinary incontinence in female dogs,[58] and prostate cancer in males,[59] as well as osteosarcoma, hemangiosarcoma, cruciate ligament rupture, obesity, and diabetes mellitus in either gender.[60] The hormonal changes involved with sterilization can change the animal's personality and metabolism. Recent studies proved that spayed and neutered dogs in general are more aggressive towards people and other dogs, and more fearful and sensitive to touch than dogs than had not been sterilized.[61]

Spaying or neutering very young animals (early-age spay), can result in increased health concerns later on in life for both sexes.[62] Incontinence in female dogs is made worse by spaying too early.[62] In both males and females, alteration causes changes in hormones during development. This inhibits the natural signals needed for proper body development, leading to larger animals with greater risk for hip dysplasia, osteoporosis, and other joint disorders.[63] Other studies have shown, however, that early-age neutering of male dogs is associated with no major risks compared to neutering at the more traditional age of six months.[64]

Behavior and intelligence

See main article: Dog 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".[23] Rather, dog behavior is affected by genetic factors as well as environmental factors.[23] Domestic dogs exhibit a number of behaviors and predispositions that were inherited from wolves.[23] 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.

Intelligence

See main article: Dog intelligence.

Intelligence is an umbrella term that encompasses the faculties involved in a wide range of mental tasks, such as learning, problem-solving, and communication. The domestic dog has a predisposition to exhibit a social intelligence that is uncommon in the animal world.[23] Dogs are capable of learning in a number of ways, such as through simple reinforcement learning (e.g.,classical or operant conditioning) and by observation.[23]

Dogs go through a series of stages of cognitive development. They are not born with an understanding of object permanence; the understanding that objects which are not being actively perceived still remain in existence. The understanding of object permanence occurs during as the infant is learning the coordination of secondary circular reactions, as described by Jean Piaget. That is, as the infants learn to interact intentionally with objects around it. For dogs, this occurs at roughly 8 weeks of age.[23]

Handlers of working dogs such as herding dogs and sled dogs know that pups learn behaviors quickly by following examples set by experienced dogs.[23] Many of these behaviors are allelomimetic in that they depend on a genetic predisposition to learn and imitate behaviors of other dogs.[23] This form of intelligence is not peculiar to those tasks dogs have been bred to perform, but can be generalized to myriad abstract problems. Adler & Alder demonstrated this by giving Dachshund puppies the task of learning to pull a cart by tugging on an attached piece of ribbon in order to get a reward in the cart. Puppies that watched an experienced dog successfully retrieve the reward in this way learned the task fifteen times faster than those who were left to solve the problem on their own.[65] [23] In addition to learning by example from other dogs, dogs have also been shown to learn by mimicking human behaviors. In another 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.[66]

Furthermore, the ability for dogs to learn by example has been shown to be as effective as operant conditioning. McKinley and Young have demonstrated that dogs show equivalent accuracy and learning times when taught to identify an object by operant conditioning as they do when taught by human example. Their study found that handing an object between experimenters who then use its name in a sentence successfully taught an observing dog each object's name, allowing the dog to subsequently retrieve the item.[67]

Dogs also demonstrate sophisticated social cognition by associating behavioral cues with abstract meanings.[23] One such class of social cognition involves the understanding that others are conscious agents. This is called a theory of mind, and is an area in which dogs excel. 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.[68] 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.[23] 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.[23] Studies have also investigated whether dogs engaged in partnered play change their behavior depending on the attention-state of their partner.[69] 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.[69]

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.[23] 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.[23] [69]

Interactions with humans

Domestic dogs inherited a complex social hierarchy and behaviors from their ancestor, the wolf. 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. 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.[20]

Although experts largely disagree over the details of dog domestication, it is agreed that human interaction played a significant role in shaping the subspecies.[20] 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.[70]

Work

Dogs have lived and worked with humans in so many roles that they have earned the unique nickname, "man's best friend",[71] a phrase which is used in other languages as well. They have been bred for herding livestock,[72] hunting (e.g.,pointers, hounds),[73] keeping living spaces clear of rats,[74] guarding, helping fishermen with nets, and pulling loads, in addition to their roles as companions.[74]

More recently, dogs have taken on a number of roles under the general classification of service dogs, which provide assistance to individuals with physical or mental disabilities.[75] [76] Service dogs include guide dogs, utility dogs, assistance dogs, hearing dogs, and psychological therapy dogs. Some dogs owned by epileptics have even 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] whether show (breed conformation shows) or sports, including dog racing and dog sledding.

Conformation shows, also referred to as breed shows, are a type of dog show in which a judge familiar with a specific dog breed evaluates individual purebred dogs for how well the dogs conform to their established breed type as described in their breed standard. As the breed standard only deals with the externally observable qualities of the dog (such as appearance, movement, and temperament), separately tested-for qualities are not part of the judging in conformation shows (such as tests for ability, health, or any other specific tests for characteristics that cannot be directly observed).

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. Unlike tame wolves, dogs tend to respond more to voice than hand signals.[85] Although they are less difficult to control than wolves, they can be comparatively more difficult to teach than a motivated wolf.[86]

See also

Further reading

External links

Notes and References

  1. Web site: ADW: Canis lupus familiaris: Information. Animaldiversity.ummz.umich.edu. 2008-11-05.
  2. Book: Coppinger, Ray. Dogs: a Startling New Understanding of Canine Origin, Behavior and Evolution. 2001. 0684855305. Scribner. New York. 352.
  3. Am J Hum Genet.. 2008. 82. 10.1016/j.ajhg.2007.12.001.. Canine Behavioral Genetics: Pointing Out the Phenotypes and Herding up the Genes. Tyrone C. Spady1 and Elaine A. Ostrander1[low asterisk].
  4. The Complete dog book: the photograph, history, and official standard of every breed admitted to AKC registration, and the selection, training, breeding, care, and feeding of pure-bred dogs. New York: Howell Book House, 1992. ISBN 0876054645
  5. Rasmussen. G. S. A.. April 1999. Livestock predation by the painted hunting dog Lycaon pictus in a cattle ranching region of Zimbabwe: a case study. Biological Conservation. 88. 1. 133–139.
  6. Web site: Domestic PetDog Classified By Linnaeus In 1758 As Canis Familiaris And Canis Familiarus Domesticus. www.encyclocentral.com. 2008-06-18.
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