The dog or domestic dog (Canis familiaris) is a domesticated descendant of the grey wolf, characterized by an upturning tail. The dog derived from an ancient, extinct wolf, and the modern grey wolf is the dog's nearest living relative. The dog was the first species to be domesticated, by hunter-gatherers over 15,000 years ago, before the development of agriculture. Their long association with humans has led dogs to be uniquely adapted to human behavior, leading to a large number of domestic individuals and the ability to thrive on a starch-rich diet that would be inadequate for other canids.
In 1758, the Swedish botanist and zoologist Carl Linnaeus published in his Systema Naturae the two-word naming of species (binomial nomenclature). Canis is the Latin word meaning "dog," and under this genus, he listed the domestic dog, the grey wolf, and the golden jackal. 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), which is not found in any other canid.
In 1999, a study of mitochondrial DNA (mtDNA) indicated that the domestic dog may have originated from the grey wolf, with the dingo and New Guinea singing dog breeds having developed at a time when human communities were more isolated from each other. In the third edition of Mammal Species of the World published in 2005, the mammalogistW. Christopher Wozencraft listed under the wolf Canis lupus its wild subspecies and proposed two additional subspecies which formed the domestic dog clade: familiaris as named by Linneaus 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. Wozencraft referred to the mtDNA study as one of the guides informing his decision. Mammalogists have debated the inclusion of familiaris and dingo together under the "domestic dog" clade.
In 2019, a workshop hosted by the IUCN/Species Survival Commission's Canid Specialist Group considered the dingo and the New Guinea singing dog to be feral Canis familiaris and therefore did not assess them for the IUCN Red List.
Location of a dog's carnassials; the inside of the 4th upper premolar aligns with the outside of the 1st lower molar, working like scissor blades
The Cretaceous-Paleogene extinction event occurred 65 million years ago and brought an end to the dinosaurs and the appearance of the first carnivorans. The name carnivoran is given to a member of the order Carnivora. Carnivorans possess a common arrangement of teeth called carnassials, in which the first lower molar and the last upper premolar possess blade-like enamel crowns that act similar to a pair of shears for cutting meat. This dental arrangement has been modified by adaptation over the past 60 million years for diets composed of meat, for crushing vegetation, or for the loss of the carnassial function altogether as in seals, sea lions, and walruses. Today, not all carnivorans are carnivores, such as the insect-eating Aardwolf.
The carnivoran ancestors of the dog-like caniforms and the cat-like feliforms began their separate evolutionary paths just after the end of the dinosaurs. The first members of the dog family Canidae appeared 40 million years ago, of which only its subfamily the Caninae survives today in the form of the wolf-like and fox-like canines. Within the Caninae, the first members of genus Canis appeared six million years ago, the ancestors of modern domestic dogs, wolves, coyotes, and golden jackals.
The generally accepted earliest dog remains were discovered in Bonn-Oberkassel, Germany. Contextual, isotopic, genetic, 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. Earlier remains dating back to 30,000 years ago have been described as Paleolithic dogs but their status as dogs or wolves remains debated because considerable morphological diversity existed among wolves during the Late Pleistocene.
The dog is a classic example of a domestic animal that likely travelled a commensal pathway into domestication. The questions of when and where dogs were first domesticated have taxed geneticists and archaeologists for decades. 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 infers 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.
Dogs are the most variable mammal on earth with around 450 globally recognized dog breeds. In the Victorian era, directed human selection developed the modern dog breeds, which resulted in a vast range of phenotypes. Most breeds were derived from small numbers of founders within the last 200 years, and since then dogs have undergone rapid phenotypic change and were formed into today's modern breeds due to artificial selection imposed by humans. The skull, body, and limb proportions vary significantly between breeds, with dogs displaying more phenotypic diversity than can be found within the entire order of carnivores. These breeds possess distinct traits related to morphology, which include body size, skull shape, tail phenotype, fur type and colour. Their behavioural traits include guarding, herding, and hunting, retrieving, and scent detection. Their personality traits include hypersocial behavior, boldness, and aggression, which demonstrates the functional and behavioral diversity of dogs. As a result, today dogs are the most abundant carnivore species and are dispersed around the world. The most striking example of this dispersal is that of the numerous modern breeds of European lineage during the Victorian era.
A lateral view of a dog skeleton
All healthy dogs, regardless of their size and type, have an identical skeletal structure with the exception of the number of bones in the tail, although there is significant skeletal variation between dogs of different types. The dog's skeleton is well adapted for running; the vertebrae on the neck and back have extensions for powerful back muscles to connect to, the long ribs provide plenty of room for the heart and lungs, and the shoulders are unattached to the skeleton allowing great flexibility.
Compared to the dog's wolf-like ancestors, selective breeding since domestication has seen the dog's skeleton greatly enhanced in size for larger types as mastiffs and miniaturised for smaller types such as terriers; dwarfism has been selectively utilised for some types where short legs are advantageous such as dachshunds and corgis. Most dogs naturally have 26 vertebrae in their tails, but some with naturally short tails have as few as three.
The dog's skull has identical components regardless of breed type, but there is significant divergence in terms of skull shape between types. The three basic skull shapes are the elongated dolichocephalic type as seen in sighthounds, the intermediate mesocephalic or mesaticephalic type, and the very short and broad brachycephalic type exemplified by mastiff type skulls.
A dog's senses include vision, hearing, smell, taste, touch, and sensitivity to Earth's magnetic field. Another study has suggested that dogs can see Earth's magnetic field.
Dogs display wide variation in coat type, density, length, color, and composition
The coats of domestic dogs are of two varieties: "double" being familiar with dogs (as well as wolves) originating from colder climates, made up of a coarse guard hair and a soft down hair, or "single," with the topcoat only. Breeds may have an occasional "blaze," stripe, or "star" of white fur on their chest or underside. Premature graying can occur in dogs from as early as one year of age; this is associated with impulsive behaviors, anxiety behaviors, fear of noise, and fear of unfamiliar people or animals.
There are many different shapes for dog tails: straight, straight up, sickle, curled, or corkscrew. As with many canids, one of the primary functions of a dog's tail is to communicate their emotional state, which can be crucial in getting along with others. In some hunting dogs the tail is traditionally docked to avoid injuries.
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. 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. For dogs in England, increased body weight has been found to be negatively correlated with longevity (i.e., the heavier the dog, the shorter its lifespan), and mixed-breed dogs live on average 1.2 years longer than purebred dogs.
A female dog nursing newborn puppies
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, and is the time at which female dogs will have their first estrous cycle. They will experience subsequent estrous cycles semiannually, during which the body prepares for pregnancy. At the peak of the cycle, females will become estrous, mentally and physically receptive to copulation. Because the ova survive and can be fertilized for a week after ovulation, more than one male can sire the same litter.
Fertilization typically occurs two to five days after ovulation; 14-16 days after ovulation, the embryo attaches to the uterus and after seven to eight more days, a heartbeat is detectable.
Dogs bear their litters roughly 58 to 68 days after fertilization, with an average of 63 days, although the length of gestation can vary. An average litter consists of about six puppies.
According to the Humane Society of the United States, three to four million dogs and cats are euthanized each year. Many more are confined to cages in shelters because there are many more animals than there are homes. Spaying or castrating dogs helps keep overpopulation down.
A common breeding practice for pet dogs is mating between close relatives (e.g., between half and full siblings).Inbreeding depression is considered to be due mainly to the expression of homozygous deleterious recessive mutations. Outcrossing between unrelated individuals, including dogs of different breeds, results in the beneficial masking of deleterious recessive mutations in progeny.
Dog intelligence is the dog's ability to perceive information and retain it as knowledge for applying to solve problems. Studies of two dogs suggest that dogs can learn by inference and have advanced memory skills. A study with Rico, a Border Collie, showed that he knew the labels of over 200 different items. He inferred the names of novel things by exclusion learning and correctly retrieved those new items immediately and four weeks after the initial exposure. A study of another Border Collie, "Chaser," documented his learning and memory capabilities. He had learned the names and could associate by verbal command over 1,000 words. Dogs can read and react appropriately to human body language such as gesturing and pointing and human voice commands.
One study of canine cognitive abilities found that dogs' capabilities are no more exceptional than those of other animals, such as horses, chimpanzees, or cats. One limited study of 18 household dogs found that they lacked spatial memory, and were more focussed on the "what" of a task rather than the "where".
Dogs demonstrate a theory of mind by engaging in deception. An experimental study showed compelling evidence that Australian dingos can outperform domestic dogs in non-social problem-solving, indicating that domestic dogs may have lost much of their original problem-solving abilities once they joined up with humans. Another study revealed that after undergoing training to solve a simple manipulation task, dogs faced with an insoluble version of the same problem look at the human, while socialized wolves do not.
Dog behavior is the internally coordinated responses (actions or inactions) of the domestic dog (individuals or groups) to internal and external stimuli. As the oldest domesticated species, dogs' minds inevitably have been shaped by millennia of contact with humans. As a result of this physical and social evolution, dogs have acquired the ability to understand and communicate with humans more than any other species and they are uniquely attuned to human behaviors. Behavioral scientists have uncovered a surprising set of social-cognitive abilities in domestic dogs. These abilities are not possessed by the dog's closest canine relatives or other highly intelligent mammals, such as great apes, but rather parallel to children's social-cognitive skills.
Unlike other domestic species selected for production-related traits, dogs were initially selected for their behaviors. In 2016, a study found that only 11 fixed genes showed variation between wolves and dogs. These gene variations were unlikely to have been the result of natural evolution and indicate selection on both morphology and behavior during dog domestication. These genes have been shown to affect the catecholamine synthesis pathway, with the majority of the genes affecting the fight-or-flight response (i.e., selection for tameness) and emotional processing. Dogs generally show reduced fear and aggression compared with wolves. Some of these genes have been associated with aggression in some dog breeds, indicating their importance in both the initial domestication and later in breed formation. Traits of high sociability and lack of fear in dogs may include genetic modifications related to Williams-Beuren syndrome in humans, which cause hypersociability at the expense of problem-solving ability.
Dog communication is how dogs convey information to other dogs, understand messages from humans and translate the information that dogs are transmitting. Communication behaviors of dogs include eye gaze, facial expression, vocalization, body posture (including movements of bodies and limbs), and gustatory communication (scents, pheromones, and taste). Humans communicate to dogs by using vocalization, hand signals, and body posture.
The dog is probably the most widely abundant large carnivoran living in the human environment.
In 2013, an estimated global dog population was between 700 million and 987 million. Although it is said that the "dog is man's best friend," this refers mainly to the ~20% of dogs that live as pets in developed countries. In the developing world, dogs are more commonly feral or communally owned, with pet dogs uncommon. Most of these dogs live their lives as scavengers and have never been owned by humans, with one study showing their most common response when approached by strangers is to run away (52%) or respond aggressively (11%). Little is known about these dogs, or the dogs in developed countries that are feral, strays, or are in shelters because the great majority of modern research on dog cognition has focused on pet dogs living in human homes.
Competitors and predators
Although dogs are the most abundant and widely distributed terrestrial carnivores, feral and free-ranging dogs' potential to compete with other large carnivores is limited by their strong association with humans. For example, a review of the studies in dogs' competitive effects on sympatric carnivores did not mention any research on competition between dogs and wolves. Although wolves are known to kill dogs, they tend to live in pairs or in small packs in areas where they are highly persecuted, giving them a disadvantage facing large dog groups.
Wolves kill dogs wherever they are found together. In some instances, wolves have displayed an uncharacteristic fearlessness of humans and buildings when attacking dogs to the extent that they have to be beaten off or killed. Although the numbers of dogs killed each year are relatively low, it induces a fear of wolves entering villages and farmyards to take dogs and losses of dogs to wolves have led to demands for more liberal wolf hunting regulations.
Coyotes and big cats have also been known to attack dogs. In particular, leopards are known to have a preference for dogs and have been recorded to kill and consume them, no matter what their size.Siberian tigers in the Amur river region have killed dogs in the middle of villages. This indicates that the dogs were targeted. Amur tigers will not tolerate wolves as competitors within their territories, and the tigers could be considering dogs in the same way.Striped hyenas are known to kill dogs in their range.
Dogs have been described as omnivores. Compared to wolves, dogs from agricultural societies have extra copies of amylase and other genes involved in starch digestion that contribute to an increased ability to thrive on a starch-rich diet. Similar to humans, some dog breeds produce amylase in their saliva and are classified as having a high starch diet. However, more like cats and less like other omnivores, dogs can only produce bile acid with taurine and they cannot produce vitamin D, which they obtain from animal flesh. Also, more like cats, dogs require arginine to maintain its nitrogen balance. These nutritional requirements place dogs halfway between carnivores and omnivores.
As a domesticated or semi-domesticated animal, the dog is nearly universal among human societies. Notable exceptions once included:
Dogs were introduced to Antarctica as sled dogs, but were later outlawed by international agreement due to the possible risk of spreading infections.
Roles with humans
Domestic dogs inherited complex behaviors, such as bite inhibition, from their wolf ancestors, which would have been pack hunters with a complex body language. These sophisticated forms of social cognition and communication may account for their trainability, playfulness and ability to fit into human households and social situations. These attributes have given dogs a relationship with humans that has enabled them to become one of the most successful animals today.
It is estimated that three-quarters of the world's dog population lives in the developing world as feral, village, or community dogs, with pet dogs uncommon.[page needed]
"The most widespread form of interspecies bonding occurs between humans and dogs" and the keeping of dogs as companions, particularly by elites, has a long history. Pet dog populations grew significantly after World War II as suburbanization increased. In the 1950s and 1960s, dogs were kept outside more often than they tend to be today(the expression "in the doghouse" - recorded since 1932 - to describe exclusion from the group implies a distance between the doghouse and the home) and were still primarily functional, acting as a guard, children's playmate, or walking companion. From the 1980s, there have been changes in the pet dog's role, such as the increased role of dogs in the emotional support of their human guardians.[page needed] People and their dogs have become increasingly integrated and implicated in each other's lives[page needed] to the point where pet dogs actively shape how a family and home are experienced.
There have been two significant trends occurring within the second half of the 20th century in pet dogs' changing status. The first has been "commodification," shaping it to conform to social expectations of personality and behavior.The second has been the broadening of the family's concept and the home to include dogs-as-dogs within everyday routines and practices.
A vast range of commodity forms aims to transform a pet dog into an ideal companion. The list of goods, services, and places available is enormous: from dog perfumes, couture, furniture and housing to dog groomers, therapists, trainers and caretakers, dog cafes, spas, parks and beaches and dog hotels, airlines and cemeteries. Dog training books, classes, and television programs proliferated as the process of commodifying the pet dog continued.
The majority of contemporary dog owners describe their pet as part of the family, although some ambivalence about the relationship is evident in the popular reconceptualization of the dog-human family as a pack. Some dog trainers, such as on the television program Dog Whisperer, have promoted a dominance model of dog-human relationships. However, it has been disputed that "trying to achieve status" is characteristic of dog-human interactions. Pet dogs play an active role in family life; for example, a study of conversations in dog-human families showed how family members use the dog as a resource, talking to the dog, or talking through the dog; to mediate their interactions with each other.
Increasingly, human family-members engage in activities centered on the dog's perceived needs and interests, or in which the dog is an integral partner, such as dog dancing and dog yoga.
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. The same source shows that nearly 40% of American households own at least one dog, of which 67% own just one dog, 25% two dogs and nearly 9% more than two dogs. There does not seem to be any gender preference among dogs as pets, as the statistical data reveal an equal number of male and female pet dogs. Although several programs promote pet adoption, less than one-fifth of the owned dogs come from shelters.
A study using magnetic resonance imaging (MRI) to compare humans and dogs showed that dogs have the same response to voices and use the same parts of the brain as humans do. This gives dogs the ability to recognize human emotional sounds, making them friendly social pets to humans.
People often enter their dogs in competitions, such as breed-conformation shows or sports, including racing, sledding and agility competitions. In conformation shows, also referred to as breed shows, a judge familiar with the specific dog breed evaluates individual purebred dogs for conformity with their established breed type as described in the breed standard. As the breed standard only deals with the dog's externally observable qualities (such as appearance, movement and temperament), separately tested qualities (such as ability or health) are not part of the judging in conformation shows.
Dog meat is consumed in some East Asian countries, including Korea,[page needed]ChinaVietnam and the Philippines, which dates back to antiquity. Based on limited data, it is estimated that 13-16 million dogs are killed and consumed in Asia every year. In China, debates have ensued over banning the consumption of dog meat. Following the Sui and Tang dynasties of the first millennium, however, people living on northern China's plains began to eschew eating dogs, which is likely due to Buddhism and Islam's spread, two religions that forbade the consumption of certain animals, including the dog. As members of the upper classes shunned dog meat, it gradually became a social taboo to eat it, even though the general population continued to consume it for centuries afterward. Dog meat is also consumed in some parts of Switzerland. Other cultures, such as Polynesia and pre-Columbian Mexico, also consumed dog meat in their history. Dog fat is also reportedly believed to be beneficial for the lungs in some parts of Poland and Central Asia. Proponents of eating dog meat have argued that placing a distinction between livestock and dogs is Western hypocrisy and that there is no difference in eating different animals' meat.
In Korea, the primary dog breed raised for meat, the Nureongi, differs from those breeds raised for pets that Koreans may keep in their homes.
The most popular Korean dog dish is called bosintang, a spicy stew meant to balance the body's heat during the summer months. Followers of the custom claim this is done to ensure good health by balancing one's gi, or the body's vital energy. A 19th-century version of bosintang explains that the dish is prepared by boiling dog meat with scallions and chili powder. Variations of the dish contain chicken and bamboo shoots. While the dishes are still prevalent in Korea with a segment of the population, dog is not as widely consumed as beef, pork and chicken.
In 2018, the WHO reported that 59,000 people died globally from rabies, with 59.6% in Asia and 36.4% in Africa. Rabies is a disease for which dogs are the most important vector. Significant dog bites affect tens of millions of people globally each year. Children in mid-to-late childhood are the largest percentage bitten by dogs, with a greater risk of injury to the head and neck. They are more likely to need medical treatment and have the highest death rate.  Sharp claws with powerful muscles behind them can lacerate flesh in a scratch that can lead to serious infections.
In the U.S., cats and dogs are a factor in more than 86,000 falls each year. It has been estimated that around 2% of dog-related injuries treated in U.K. hospitals are domestic accidents. The same study found that while dog involvement in road traffic accidents was difficult to quantify, dog-associated road accidents involving injury more commonly involved two-wheeled vehicles.
Dogs suffer from the same common disorders as humans; these include cancer, diabetes, heart disease and neurologic disorders. Their pathology is similar to humans, as is their response to treatment and their outcomes. Researchers are identifying the genes associated with dog diseases similar to human disorders, but lack mouse models to find cures for both dogs and humans. The genes involved in canine obsessive-compulsive disorders led to the detection of four genes in humans' related pathways.
The scientific evidence is mixed as to whether a dog's companionship can enhance human physical health and psychological well-being. Studies suggesting that there are benefits to physical health and psychological well-being have been criticized for being poorly controlled. It found that "the health of elderly people is related to their health habits and social supports but not to their ownership of, or attachment to, a companion animal." Earlier studies have shown that people who keep pet dogs or cats exhibit better mental and physical health than those who do not, making fewer visits to the doctor and being less likely to be on medication than non-guardians.
A 2005 paper states "recent research has failed to support earlier findings that pet ownership is associated with a reduced risk of cardiovascular disease, a reduced use of general practitioner services, or any psychological or physical benefits on health for community dwelling older people. Research has, however, pointed to significantly less absenteeism from school through sickness among children who live with pets." In one study, new guardians reported a highly significant reduction in minor health problems during the first month following pet acquisition. This effect was sustained in those with dogs through to the end of the study.
People with pet dogs took considerably more physical exercise than those with cats and those without pets. The results provide evidence that keeping pets may have positive effects on human health and behavior and that for guardians of dogs, these effects are relatively long-term. Pet guardianship has also been associated with increased coronary artery disease survival. Human guardians are significantly less likely to die within one year of an acute myocardial infarction than those who did not own dogs.
The health benefits of dogs can result from contact with dogs in general, not solely from having dogs as pets. For example, when in a pet dog's presence, people show reductions in cardiovascular, behavioral and psychological indicators of anxiety. Other health benefits are gained from exposure to immune-stimulating microorganisms, which can protect against allergies and autoimmune diseases according to the hygiene hypothesis. The benefits of contact with a dog also include social support, as dogs cannot only provide companionship and social support themselves but also act as facilitators of social interactions between humans. One study indicated that wheelchair users experience more positive social interactions with strangers when accompanied by a dog than when they are not. In 2015, a study found that pet owners were significantly more likely to get to know people in their neighborhood than non-pet owners.
Using dogs and other animals as a part of therapy dates back to the late 18th century, when animals were introduced into mental institutions to help socialize patients with mental disorders. Animal-assisted intervention research has shown that animal-assisted therapy with a dog can increase social behaviors, such as smiling and laughing, among people with Alzheimer's disease. One study demonstrated that children with ADHD and conduct disorders who participated in an education program with dogs and other animals showed increased attendance, increased knowledge and skill objectives and decreased antisocial and violent behavior compared with those not in an animal-assisted program.
In Christianity, dogs represent faithfulness. Within the Roman Catholic denomination specifically, the iconography of Saint Dominic includes a dog, after the hallow's mother dreamt of a dog springing from her womb and becoming pregnant shortly after that. As such, the Dominican Order (Ecclesiastical Latin: Domini canis) means "dog of the Lord" or "hound of the Lord" (Ecclesiastical Latin: Domini canis). In Christian folklore, a church grim often takes the form of a black dog to guard Christian churches and their churchyards from sacrilege.Jewish law does not prohibit keeping dogs and other pets. Jewish law requires Jews to feed dogs (and other animals that they own) before themselves and make arrangements for feeding them before obtaining them. The view on dogs in Islam is mixed, with some schools of thought viewing it as unclean, although Khaled Abou El Fadl states that this view is based on "pre-Islamic Arab mythology" and "a tradition to be falsely attributed to the Prophet." Therefore, Sunni Malaki and Hanafi jurists permit the trade of and keeping of dogs as pets.
Dog - the species (or subspecies) as a whole, also any male member of the same.
Bitch - any female member of the species (or subspecies).
Puppy or pup - a young member of the species (or subspecies) under 12 months old.
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