The dog ( Canis familiaris or Canis lupus familiaris) is a domesticated descendant of the gray wolf. Also called the domestic dog, it was selectively bred from a population of wolves during the Late Pleistocene by . The dog was the first species to be domesticated by , over 14,000 years ago and before the development of agriculture. Due to their long association with humans, dogs have gained the ability to thrive on a starch-rich diet that would be inadequate for other Canidae.
Dogs have been bred for desired behaviors, sensory capabilities, and physical attributes. vary widely in shape, size, and color. They have the same number of bones (with the exception of the tail), powerful jaws that house around 42 teeth, and well-developed senses of smell, hearing, and sight. Compared to humans, dogs possess a superior sense of smell and hearing, but inferior visual acuity. Dogs perform many roles for humans, such as Hunting dog, Herding dog, Sled dog, Guard dog, Pet, Therapy dog, Service dog, and Police dog and the military.
Communication in dogs includes eye gaze, facial expression, vocalization, body posture (including movements of bodies and limbs), and gustatory communication (scents, pheromones, and taste). They mark their territories by urinating on them, which is more likely when entering a new environment. Over the millennia, dogs have uniquely adapted to human behavior; this adaptation includes being able to understand and communicate with humans. As such, the human–canine bond has been a topic of frequent study, and dogs' influence on human society has given them the sobriquet of "man's best friend".
The global dog population is estimated at 700 million to 1 billion, distributed around the world. The dog is the most popular pet in the United States, present in 34–40% of households. Developed countries make up approximately 20% of the global dog population, while around 75% of dogs are estimated to be from developing countries, mainly in the form of feral and community dogs.
Taxonomy
Dogs are domesticated members of the family
Canidae. They are classified as a subspecies of
Canis lupus, along with
wolves and
dingoes.
Dogs were domesticated from wolves over 14,000 years ago by
, before the development of agriculture.
The remains of the Bonn–Oberkassel dog, buried alongside humans between 14,000 and 15,000 years ago, are the earliest to be conclusively identified as a domesticated dog.
[ Genetic studies show that dogs likely diverged from wolves between 27,000 and 40,000 years ago.]
Dogs, wolves, and have sometimes been classified as separate species.[ In 1758, the Swedish botanist and zoologist Carl Linnaeus assigned the genus name Canis (which is the Latin word for "dog") to the domestic dog, the wolf, and the golden jackal in his book, Systema Naturae. He classified the domestic dog as Canis familiaris and, on the next page, classified the grey wolf as Canis lupus.][ Linnaeus considered the dog to be a separate species from the wolf because of its upturning tail ( cauda recurvata in Latin term), which is not found in any other canid.][ In the 2005 edition of Mammal Species of the World, mammalogist W. Christopher Wozencraft listed the wolf as a wild subspecies of Canis lupus and proposed two additional subspecies: familiaris, as named by Linnaeus in 1758, and dingo, named by Meyer in 1793. Wozencraft included hallstromi (the New Guinea singing dog) as another name (junior synonym) for the dingo. This classification was informed by a 1999 mitochondrial DNA study.][
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The classification of dingoes is disputed and a political issue in Australia. Classifying dingoes as wild dogs simplifies reducing or controlling dingo populations that threaten livestock. Treating dingoes as a separate species allows conservation programs to protect the dingo population.[
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Domestication
The earliest remains generally accepted to be those of a domesticated dog were discovered in Bonn-Oberkassel, Germany. Contextualism, Isotope analysis, Genetics, and morphological evidence shows that this dog was not a local wolf.[ The dog was dated to 14,223 years ago and was found buried along with a man and a woman, all three having been sprayed with red hematite powder and buried under large, thick basalt blocks. The dog had died of canine distemper.][ This timing indicates that the dog was the first species to be domesticated][ in the time of ,][ which predates agriculture.][ Earlier remains dating back to 30,000 years ago have been described as , but their status as dogs or wolves remains debated][ because considerable morphological diversity existed among wolves during the Late Pleistocene.][
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DNA sequences show that all ancient and modern dogs share a common ancestry and descended from an ancient, extinct wolf population that was distinct from any Wolf lineage. Some studies have posited that all living wolves are more closely related to each other than to dogs,[ while others have suggested that dogs are more closely related to modern Eurasian wolves than to American wolves.]
The dog is a domestic animal that likely travelled a Commensalism pathway into domestication (i.e. humans initially neither benefitted nor were harmed by wild dogs eating refuse from their camps).[ The questions of when and where dogs were first domesticated remains uncertain.][ Genetic studies suggest a domestication process commencing over 25,000 years ago, in one or several wolf populations in either Europe, the high Arctic, or eastern Asia.][ In 2021, a literature review of the current evidence Inference that the dog was domesticated in Siberia 23,000 years ago by ancient North Siberians, then later dispersed eastward into the Americas and westward across Eurasia,][ with dogs likely accompanying the first humans to inhabit the Americas.][ Some studies have suggested that the extinct Japanese wolf is closely related to the ancestor of domestic dogs.][
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In 2018, a study identified 429 genes that differed between modern dogs and modern wolves. As the differences in these genes could also be found in ancient dog fossils, these were regarded as being the result of the initial domestication and not from recent breed formation. These genes are linked to neural crest and central nervous system development. These genes affect embryogenesis and can confer tameness, smaller jaws, floppy ears, and diminished craniofacial development, which distinguish domesticated dogs from wolves and are considered to reflect domestication syndrome. The study concluded that during early dog domestication, the initial selection was for behavior. This trait is influenced by those genes which act in the neural crest, which led to the phenotypes observed in modern dogs.
Breeds
There are around 450 official [[dog breeds]], the most of any mammal.[ Most breeds were derived from small numbers of founders within the last 200 years.][ Since then, dogs have undergone rapid phenotypic change and have been subjected to artificial selection by humans. The skull, body, and limb proportions between breeds display more phenotypic diversity than can be found within the entire order of [[carnivore]]s. These breeds possess distinct traits related to morphology, which include body size, skull shape, tail phenotype, fur type, and colour.][ As such, humans have long used dogs for their desirable traits to complete or fulfill a certain work or role. Their behavioural traits include guarding, herding, hunting,][ retrieving, and scent detection. Their personality traits include hypersocial behavior, boldness, and aggression.][ Present-day dogs are dispersed around the world.][ An example of this dispersal is the numerous modern breeds of European lineage during the Victorian era.][
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File:Dog morphological variation.png|Morphological variation in six dogs
File:Dog coat variation.png|Phenotype in four dogs
Anatomy and physiology
Size and skeleton
Dogs are extremely variable in size, ranging from one of the largest breeds, the Great Dane, at and , to one of the smallest, the Chihuahua, at and .
Compared to the dog's wolf-like ancestors, selective breeding since domestication has seen the dog's skeleton increase in size for larger types such as and miniaturised for smaller types such as ; dwarfism has been selectively bred for some types where short legs are preferred, such as and . Most dogs naturally have 26 vertebrae in their tails, but some with Natural bobtail have as few as three.
The dog's skull has identical components regardless of breed type, but there is significant Cephalic index between types. The three basic skull shapes are the elongated dolichocephalic type as seen in , the intermediate mesocephalic or mesaticephalic type, and the very short and broad brachycephalic type exemplified by mastiff type skulls. The jaw contains around 42 teeth, and it has evolved for the consumption of flesh. Dogs use their carnassial teeth to cut food into bite-sized chunks, more especially meat.
Senses
Dogs' senses include vision, hearing, smell, taste, touch, and magnetoreception. One study suggests that dogs can feel small variations in Earth's magnetic field.
Dogs' vision is Dichromacy; their visual world consists of yellows, blues, and grays.
While the human brain is dominated by a large visual cortex, the dog brain is dominated by a large olfactory system. Dogs have roughly forty times more smell-sensitive receptors than humans, ranging from about 125million to nearly 300million in some dog breeds, such as .
This sense of smell is the most prominent sense of the species; it detects chemical changes in the environment, allowing dogs to pinpoint the location of mating partners, potential stressors, resources, etc.
Dogs have stiff, deeply embedded hairs known as that sense atmospheric changes, vibrations, and objects not visible in low light conditions. The lower most part of whiskers hold more receptor cells than other hair types, which help in alerting dogs of objects that could collide with the nose, ears, and jaw. Whiskers likely also facilitate the movement of food towards the mouth.
Coat
The Pelage of domestic dogs are of two varieties: "double" being common in 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. Premature graying can occur in dogs as early as one year of age; this is associated with Impulsivity, anxiety behaviors, and fear of unfamiliar noise, people, or animals.[
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Dewclaw
A dog's dewclaw is the fifth digit in its forelimb and hind legs. Dewclaws on the forelimbs are attached by bone and ligament, while the dewclaws on the hind legs are attached only by skin. Most dogs are not born with dewclaws in their hind legs, and some are without them in their forelimbs. Dogs' dewclaws consist of the Phalanx bone. Some publications theorize that dewclaws in wolves, who usually do not have dewclaws, were a sign of hybridization with dogs.
Tail
A dog's tail is the terminal appendage of the vertebral column, which is made up of a string of 5 to 23 enclosed in muscles and skin that support the dog's back extensor muscles. One of the primary functions of a dog's tail is to communicate their emotional state.
A study suggests that dogs show asymmetric tail-wagging responses to different emotive stimuli. "Stimuli that could be expected to elicit approach tendencies seem to be associated with a higher amplitude of tail-wagging movements to the right side".
Health
Numerous disorders have been known to affect dogs. Some are congenital and others are acquired. Dogs can acquire upper respiratory tract diseases including diseases that affect the nasal cavity, the larynx, and the trachea; lower respiratory tract diseases which includes pulmonary disease and acute respiratory diseases; heart diseases which includes any cardiovascular inflammation or dysfunction of the heart; hematopoiesis including anaemia and clotting disorders; gastrointestinal disease such as diarrhoea and gastric dilatation volvulus; hepatic disease such as portosystemic shunts and liver failure; pancreatic disease such as pancreatitis; renal disease; lower urinary tract disease such as cystitis and urolithiasis; endocrine disorders such as diabetes mellitus, Cushing's syndrome, hypoadrenocorticism, and hypothyroidism; nervous system diseases such as seizures and spinal injury; musculoskeletal disease such as arthritis and myopathies; dermatological disorders such as alopecia and pyoderma; ophthalmological diseases such as conjunctivitis, glaucoma, entropion, and progressive retinal atrophy; and neoplasia.
Common dog parasites are lice, , fly larvae, , , , , and coccidia. Taenia is a notable genus with 5 species in which dogs are the definitive host.[ Common infections in dogs include canine adenovirus, canine distemper virus, canine parvovirus, leptospirosis, canine influenza, and canine coronavirus. All of these conditions have vaccines available.][
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Dogs are the companion animal most frequently reported for exposure to . Most poisonings are accidental and over 80% of reports of exposure to the ASPCA animal poisoning hotline are due to oral exposure. The most common substances people report exposure to are: pharmaceuticals, toxic foods, and rodenticides.
Data from the Pet Poison Helpline shows that human drugs are the most frequent cause of toxicosis death. The most common household products ingested are cleaning products. Most food related poisonings involved theobromine poisoning (chocolate). Other common food poisonings include xylitol, Vitis (grapes, raisins, etc.), and Allium (garlic, onions, etc.). Pyrethrin insecticides were the most common cause of pesticide poisoning. Metaldehyde, a common pesticide for snails and slugs, typically causes severe outcomes when ingested by dogs.
Neoplasia is the most common cause of death for dogs.[ Their pathology is similar to that of humans, as is their Immune response to treatment and their outcomes. Genes found in humans to be responsible for disorders are investigated in dogs as being the cause and vice versa.]
Lifespan
The typical lifespan of dogs varies widely among breeds, but the median longevity (the age at which half the dogs in a population have died and half are still alive) is approximately 12.7 years.[
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In a 2024 UK study analyzing 584,734 dogs, it was concluded that purebred dogs lived longer than crossbred dogs, challenging the previous notion of the latter having the higher life expectancies. The authors noted that their study included "" as crossbred and that purebred dogs were typically given better care than their crossbred counterparts, which likely influenced the outcome of the study.
Reproduction
In domestic dogs, sexual maturity happens around six months to one year for both males and females, although this can be delayed until up to two years of age for some large breeds. This is the time at which female dogs will have their first estrous cycle, characterized by their swelling and producing discharges, usually lasting between 4 and 20 days.[Dewey, T. and S. Bhagat. 2002. " Canis lupus familiaris". , Animal Diversity Web.] Fertilization typically occurs two to five days after ovulation. After ejaculation, the dogs are coitally tied for around 5–30 minutes because of the male's bulbus glandis swelling and the female's constrictor vestibuli contracting; the male will continue ejaculating until they untie naturally due to muscle relaxation.
Neutering
Neutering is the sterilization of animals via gonadectomy, which is an orchidectomy (castration) in dogs and ovariohysterectomy (spay) in bitches. Neutering reduces problems caused by hypersexuality, especially in male dogs.
Neutering is the most common surgical procedure in dogs less than a year old in the US and is seen as a control method for overpopulation. Neutering often occurs as early as 6–14 weeks in shelters in the US.
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Neutering is less common in most European countries, especially in Nordic countries—except for the UK, where it is common. In Norway, neutering is illegal unless for the benefit of the animal's health (e.g., ovariohysterectomy in case of ovarian or uterine neoplasia). Some European countries have similar laws to Norway, but their wording either explicitly allows for neutering for controlling reproduction or it is allowed in practice or by contradiction through other laws. Italy and Portugal have passed recent laws that promote it. Germany forbids early age neutering, but neutering is still allowed at the usual age. In Romania, neutering is mandatory except for when a pedigree to select breeds can be shown.
Inbreeding depression
A common breeding practice for pet dogs is to Inbreeding (e.g., between half- and full-siblings).
Behavior
Dog behavior has been shaped by millennia of contact with humans. They have acquired the ability to understand and communicate with humans and are uniquely attuned to human behaviors.[ Behavioral scientists suggest that a set of social-cognitive abilities in domestic dogs that are not possessed by the dog's canine relatives or other highly intelligent mammals, such as , are parallel to children's social-cognitive skills.][ Dogs have about twice the number of neurons in their cerebral cortexes than what cats have, which suggests they could be about twice as intelligent.][
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Most domestic animals were initially bred for the production of goods. Dogs, on the other hand, were selectively bred for desirable behavioral traits.
[ In 2016, a study found that only 11 fixed genes showed variation between wolves and dogs.][ Compared to their wolf counterparts, dogs tend to be less timid and less aggressive, though some of these genes have been associated with aggression in certain dog breeds.]
Dogs have a natural instinct called prey drive (the term is chiefly used to describe Dog training' habits) which can be influenced by breeding. These instincts can drive dogs to consider objects or other animals to be prey or drive possessive behavior. These traits have been enhanced in some breeds so that they may be used to hunt and kill vermin or other pests.
Nursing
The female dog (bitch) may produce colostrum, a type of milk high in nutrients and antibodies, 1–7 days before giving birth. Milk production lasts for around three months,[ The dog can sometimes vomit and refuse food during Birth.]
Intelligence
Researchers have tested dogs' ability to perceive information, retain it as knowledge, and apply it to solve problems. Studies of two dogs suggest that dogs can learn by inference. 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 after four weeks of the initial exposure. A study of another Border Collie, Chaser, documented that he had learned the names and could associate them by verbal command with over 1,000 words.
One study of canine cognitive abilities found that dogs' capabilities are similar to those of , chimpanzees, or .[ One study of 18 household dogs found that the dogs could not distinguish food bowls at specific locations without distinguishing cues; the study stated that this indicates a lack of spatial memory.][ A study stated that dogs have a visual sense for number. The dogs showed a ratio-dependent activation both for numerical values from 1–3 to larger than four.]
Dogs demonstrate a theory of mind by engaging in deception.
Communication
Dog communication is the transfer of information between dogs, as well as between dogs and humans.
Humans communicate with dogs by using vocalization, hand signals, and body posture. With their acute sense of hearing, dogs rely on the auditory aspect of communication for understanding and responding to various cues, including the distinctive barking patterns that convey different messages. A study using functional magnetic resonance imaging (fMRI) has shown that dogs respond to both vocal and nonvocal voices using the brain's region towards the temporal pole, similar to that of humans' brains. Most dogs also looked significantly longer at the face whose expression matched the valence of vocalization.
Ecology
Population
The dog is the most widely abundant large living in the human environment.[ About 20% of the dog population live in developed countries.][ In the developing world, it is estimated that three-quarters of the world's dog population lives in the developing world as feral, Free-ranging dog, or community dogs.]
Competitors
Feral and ' potential to compete with other large carnivores is limited by their strong association with humans.[ Although wolves are known to kill dogs, wolves tend to live in pairs in areas where they are highly persecuted, giving them a disadvantage when facing large dog groups.][ 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.][
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and have also been known to attack dogs. In particular, are known to have a preference for dogs and have been recorded to kill and consume them, no matter their size.
in the Amur river region have killed dogs in the middle of villages. They will not tolerate wolves as competitors within their territories, and the tigers could be considering dogs in the same way.[ are known to kill dogs in their range.]
Diet
Dogs are typically described as .[
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Of the twenty-one amino acids common to all life forms (including selenocysteine), dogs cannot synthesize ten: arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
Range
As a domesticated or semi-domesticated animal, the dog has notable exceptions of presence in:
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The Aboriginal Tasmanians, who were separated from Australia before the arrival of on that continent
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The Andamanese peoples, who were isolated when rising sea levels covered the land bridge to Myanmar
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The Fuegians, who instead domesticated the Fuegian dog, an already extinct different canid species
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Individual Pacific islands whose maritime settlers did not bring dogs or where the dogs died out after original settlement, notably the Mariana Islands,
[ New Caledonia,][ Marquesas,][ Mangaia in the Cook Islands, Rapa Iti in French Polynesia, Easter Island,][ the Chatham Islands,]
Dogs were introduced to Antarctica as . Starting practice in December 1993, dogs were later outlawed by the Protocol on Environmental Protection to the Antarctic Treaty international agreement due to the possible risk of spreading infections.
Roles with humans
The domesticated dog originated as a predator and scavenger.
Pets
The keeping of dogs as companions, particularly by elites, has a long history.[ In the 1980s, there have been changes in the pet dog's functions, such as the increased role of dogs in the emotional support of their human guardians.][ The second has been the broadening of the concepts of family and the home to include dogs-as-dogs within everyday routines and practices.][
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Products such as dog-training books, classes, and television programs target dog owners.
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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.
Workers
In addition to dogs' role as companion animals, dogs have been bred for Herding dog (such as and ); for hunting; for Pest control (such as terriers); as search and rescue dogs;[ In 1957, the dog Laika became one of the first animals to be launched into Geocentric orbit aboard the Soviets's Sputnik 2; Laika died during the flight from Hyperthermia.]
Shows and sports
Dogs compete in breed-conformation shows and dog sports (including racing, sledding, and Dog agility). In dog 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 a breed standard.
Dogs as food
Humans have consumed dog meat going back at least 14,000 years. It is unknown to what extent prehistoric dogs were consumed and bred for meat. For centuries, the practice was prevalent in Southeast Asia, East Asia, Africa, and Oceania before cultural changes triggered by the spread of religions resulted in dog meat consumption declining and becoming more taboo.[ Switzerland, Polynesia, and pre-Columbian Mexico historically consumed dog meat.]
Eating dog meat is a Taboo in most parts of the world,[ Vietnam,][ Korea,][ China is the world's largest consumer of dogs, with an estimated 10 to 20 million dogs killed every year for human consumption.]
There is a long history of dog meat consumption in South Korea, but the practice has fallen out of favor.[ In 2018, the South Korean government passed a bill banning restaurants that sell dog meat from doing so during that year's Winter Olympics.]
Health risks
In 2018, the World Health Organization (WHO) reported that 59,000 people died globally from rabies, with 59.6% of the deaths in Asia and 36.4% in Africa. Rabies is a disease for which dogs are the most significant Disease vector.[ The primary victims of dog bite incidents are children. They are more likely to sustain more serious injuries from bites, which can lead to death.]
Toxocara canis (dog roundworm) eggs in dog feces can cause toxocariasis. It is estimated that nearly 14% of people in the United States are infected with Toxocara; about 10,000 cases are reported each year.
Health benefits
The scientific evidence is mixed as to whether a dog's companionship can enhance human physical and psychological well-being.[ Earlier studies have shown that pet-dog or -cat guardians make fewer hospital visits and are less likely to be on medication for heart problems and sleeping difficulties than non-guardians.]
A 2005 paper by the British Medical Journal 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.
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
One study indicated that wheelchair-users experience more positive social interactions with strangers when accompanied by a dog than when they are not.[
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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 .
One study demonstrated that children with ADHD and who participated in an education program with dogs and other animals showed increased attendance, knowledge, and skill-objectives and decreased antisocial and Violence compared with those not in an animal-assisted program.
Cultural importance
Artworks have depicted dogs as symbols of Guide, protection, loyalty, fidelity, faithfulness, alertness, and love.[ In the Neo-Assyrian and Neo-Babylonian periods, dogs served as emblems of magical protection.][ In China, Korea, and Japan, dogs are viewed as kind protectors.][
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In mythology, dogs often appear as pets or as watchdogs.
Stories of dogs guarding the gates of the underworld recur throughout Indo-European mythologies[ In Greek mythology, Cerberus is a three-headed, dragon-tailed watchdog who guards the gates of Hades.][ Dogs also feature in association with the Greek goddess Hecate.][ In Persian mythology, two four-eyed dogs guard the Chinvat Bridge.][ In Welsh mythology, Cŵn Annwn guards Annwn.][ In Hindu mythology, Yama, the god of death, owns two watchdogs named Shyama and Sharvara, which each have four eyes—they are said to watch over the gates of Naraka.]
In Christianity, dogs represent faithfulness.[ Within the Roman Catholic denomination specifically, the iconography of Saint Dominic includes a dog after the saint's mother dreamt of a dog springing from her womb and became pregnant shortly after that.][ In Christian folklore, a church grim often takes the form of a black dog to guard Christian churches and their from sacrilege.]
Jewish law does not prohibit keeping dogs and other pets but requires Jews to feed dogs (and other animals that they own) before themselves and to make arrangements for feeding them before obtaining them.[ although Khaled Abou El Fadl states that this view is based on "pre-Islamic Arab mythology" and "a tradition ... falsely attributed to the Prophet".]
Terminology
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Dog – the species (or subspecies) as a whole, also any male member of the same.
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Bitch – any female member of the species (or subspecies).
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Puppy or pup – a young member of the species (or subspecies) under 12 months old.
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Sire – the male parent of a litter.
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Dam – the female parent of a litter.
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Litter – all of the puppies resulting from a single whelping.
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Whelping – the act of a bitch giving birth.
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Whelps – puppies still dependent upon their dam.
See also
Bibliography
External links
