Dog

Domestic dog Fossil range: Late Pleistocene - Recent
other images of dogs
Conservation status
Conservation status: Domesticated
Scientific classification
Domain: Eukaryota Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Carnivora Family: Canidae Genus: Canis Species: C. lupus Subspecies: C. l. familiaris
Trinomial name
Canis lupus familiaris

File:Dog.jpg

The dog (Canis lupus familiaris or Canis familiaris) is humankind's first, and perhaps most important, domestic animal. It is usually considered to be a subspecies of the gray wolf (Canis lupus), a mammal of the Canidae family of the order Carnivora.

The word "dog" is also sometimes used to refer to other members of the Canidae family, for instance the bush dog (Speothos venaticus) of South America and the raccoon dog (Nyctereutes procyonoides) of Asia.

Overview

Origins

According to recent genetic research the lineage of dogs separated from that of wolves about 100,000 years ago (Villa 1997).

Some research appears to show that dogs were domesticated from wolves as recently as 15,000 years ago, or perhaps as early as 100,000 years ago based upon recent genetic, fossil and DNA evidence. Other research suggests that dogs have only been domesticated for a much shorter amount of time and were domesticated from populations of wild dogs, which had previously diverged from wolves.

New evidence suggests that dogs were first domesticated in East Asia, possibly China, and the first peoples to enter North America took dogs with them from Asia. Genetic research has identified 14 ancient dog breeds, with the oldest being the Chow Chow, Shar Pei, Akita Inu, Shiba Inu and Basenji. Because many of the 14 breeds are associated with China and Japan, the theory that the dog originated in Asia seems to be likely.

As humans migrated around the planet a variety of dog forms migrated with them. The agricultural revolution and subsequent urban revolution led to an increase in the dog population and a demand for specialization. These circumstances would provide the opportunity for selective breeding to create specialized working dogs and pets.

Human relationships

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Shetland Sheepdogs are well known for their loyal companionship and intelligence.

Dogs are highly social animals due to selective breeding. This can account for their trainability, playfulness, and ability to fit into human households and social situations. This similarity has earned dogs a unique position in the realm of interspecies relationships.

The loyalty and devotion that dogs demonstrate as part of their natural instincts as pack animals closely mimics the human idea of love and friendship, leading many dog owners to view their pets as full-fledged family members. Conversely, dogs seem to view their human companions as members of their pack, and make few, if any, distinctions between their owners and fellow dogs. Dogs fill a variety of roles in human society and are often trained as working dogs. For dogs that do not have traditional jobs, a wide range of dog sports provide the opportunity to exhibit their natural skills. In many countries, the most common and perhaps most important role of dogs is as companions.

Dogs have lived and worked with humans in so many roles that their loyalty has earned them the unique sobriquet "man's best friend". However, some cultures consider dogs to be unclean. In some parts of the world, dogs are raised as livestock to produce dog meat for human consumption. In many places, consumption of dog meat is discouraged by social convention or cultural taboo.

Terminology

The English word dog, in common usage, refers to the domestic pet dog, Canis lupus familiaris. The species was originally classified as Canis familiaris by Linnaeus in 1758. In 1993, dogs were reclassified as a subspecies of the gray wolf, Canis lupus, by the Smithsonian Institution and the American Society of Mammalogists. "Dog" is sometimes used to refer collectively to any mammal belonging to the family Canidae (as in "the dog family"), such as wolves, foxes, and coyotes. Some members of the family have "dog" in their common names, such as the African Wild Dog. The constellations Canes Venatici, Canis Major and Canis Minor are named from the Latin word for "dog," for their perceived resemblance to dogs.

The English word dog might derive from the Old English docga, a "powerful breed of canine". The French dogue and Spanish dogo as in dogo Argentino are borrowings from English. The English word hound is a cognate of German Hund, Dutch hond, common Scandinavian hund, Icelandic hundur which, though referring to a specific breed in English, means "dog" in general in the other Germanic languages. Hound itself derives from the Proto-Indo-European *kwon-, which is the direct root of the Greek κυων (kuōn) and the indirect root of the Latin canis through the variant form *kani-.

In breeding circles, a male canine is referred to as a dog, while a female canine is called a bitch. The father of a litter is called the sire, and the mother of a litter is called the dam. Offspring are generally called pups or puppies until they are about a year old. A group of offspring is a litter. The process of birth is whelping. Many terms are used for dogs that are not purebred.

Intelligence

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Many dogs can easily be trained to retrieve.

Among dog lovers, dogs are generally valued for their intelligence, and both anecdotal evidence and scientific research suggest that dogs have a reasonably high intelligence. This intelligence is expressed differently with different breeds and individuals, however. For example, Border Collies are noted for their ability to learn commands, while other breeds may not be so motivated towards obedience, but instead show their cleverness in devising ways to steal food or escape from a yard. Being highly adaptable animals themselves, dogs have learned to do many jobs as required by humans over the generations. Dogs are employed in various roles across the globe, proving invaluable assets in areas such as search-and-rescue; law enforcement (including attack dogs, sniffer dogs and tracking dogs); guards for livestock, people or property; herding; Arctic exploration sled-pullers; guiding the blind and acting as a pair of ears for the deaf; assisting with hunting, and a great many other roles which they may be trained to assume. Most dogs rarely have to deal with complex tasks and are unlikely to learn relatively complicated activities (such as opening doors) unaided. Some dogs (such as guide dogs for the visually impaired) are specially trained to recognize and avoid dangerous situations.

Evaluation of a dog's intelligence

The meaning of "intelligence" in general, not only in reference to dogs, is hard to define. Some tests measure problem-solving abilities and others test the ability to learn in comparison to others of the same age. Defining it for dogs is just as difficult. It is likely that dogs do not have the ability to premeditate an action to solve a problem. Some dogs may, however, have more drive to keep trying various things until they accidentally reach a solution and still others might have more ability to make the association between the "accident" and the result.^{[citation needed]}

For example, the ability to learn quickly could be a sign of intelligence. Conversely it could be interpreted as a sign of blind subservience and a desire to please. In contrast, some dogs who do not learn very quickly may have other talents. An example is breeds that are not particularly interested in pleasing their owners, such as Siberian Huskies. Huskies are often fascinated with the myriad of possibilities for escaping from yards, catching small animals, and often figuring out on their own numerous inventive ways of doing both.

Assistance dogs are also required to be obedient at all times. This means they must learn a tremendous number of commands, understand how to act in a large variety of situations, and recognize threats to their human companion, some of which they might never before have encountered.

Many owners of livestock guardian breeds believe that breeds like the Great Pyrenees or the Kuvasz are not easily trained because their stubborn nature prevents them from seeing the point of such commands as “sit” or “down”. Hounds may also suffer from this type of ranking. In fact several rank in the bottom tier of "The Intelligence of Dogs" list (such as Beagles, Bloodhounds, and Basset Hounds).^{[citation needed]} These dogs are bred to have more of a "pack" mentality with other dogs and less reliance on a master's direct commands. While they may not have the same kind of intelligence as a Border Collie, they were not bred to learn and obey commands quickly, but to think for themselves while trailing game.

Physical characteristics

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Some dogs, like this Weimaraner, have their predatory instincts suppressed in order to better assist human hunters.

Modern dog breeds show more variation in size, appearance, and behavior than any other domestic animal. Within the range of extremes, dogs generally share attributes with their wild ancestors, the wolves. Dogs are predators and scavengers, possessing sharp teeth and strong jaws for attacking, holding, and tearing their food. Although selective breeding has changed the appearance of many breeds, all dogs retain basic traits from their distant ancestors. Like many other predatory mammals, the dog has powerful muscles, fused wristbones, a cardiovascular system that supports both sprinting and endurance, and teeth for catching and tearing. Compared to the bone structure of the human foot, dogs technically walk on their toes.

Sight

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Amazonian dogs, such as this one from Alto Amazonas, Peru are critical for indigenous peoples' hunting strategies, particularly in the rain forest.

Like most mammals, dogs are dichromats and have color vision equivalent to red-green color blindness in humans.

Different breeds of dogs have different eye shapes and dimensions, and they also have different retina configurations. Dogs with long noses have a "visual streak" which runs across the width of the retina and gives them a very wide field of excellent vision, while those with short noses 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 breeds, particularly the best sighthounds, have a field of vision up to 270° (compared to 180° for humans), although broad-headed breeds with short noses have a much narrower field of vision, as low as 180°.

Hearing

This mixed-breed dog angles her ears to find the source of a sound.

Dogs detect sounds as low as the 16 to 20 Hz frequency range (compared to 20 to 70 Hz for humans) and above 45 kHz (compared to 13 to 20 kHz for humans), and in addition have a degree of ear mobility that helps them to rapidly pinpoint the exact location of a sound. Eighteen or more muscles can tilt, rotate and raise or lower a dog's ear. Additionally, a dog can identify a sound's location much faster than a human can, as well as hear sounds up to four times the distance that humans are able to. Those with more natural ear shapes, like those of wild canids like the fox, generally hear better than those with the floppier ears of many domesticated species.

Smell

Dogs have nearly 220 million smell-sensitive cells over an area about the size of a pocket handkerchief (compared to 5 million over an area the size of a postage stamp for humans). Some breeds have been selectively bred for excellence in detecting scents, even compared to their canine brethren. What information a dog actually detects when he is scenting is not perfectly understood; although once a matter of debate, it now seems to be well established that dogs can distinguish two different types of scents when trailing, an air scent from some person or thing that has recently passed by, as well as a ground scent that remains detectable for a much longer period. The characteristics and behavior of these two types of scent trail would seem, after some thought, to be quite different, the air scent being intermittent but perhaps less obscured by competing scents, whereas the ground scent would be relatively permanent with respect to careful and repetitive search by the dog, but would seem to be much more contaminated with other scents. In any event, it is established by those who train tracking dogs that it is impossible to teach the dog how to track any better than it does naturally; the object instead is to motivate it properly, and teach it to maintain focus on a single track and ignore any others that might otherwise seem of greater interest to an untrained dog. An intensive search for a scent, for instance searching a ship for contraband, can actually be very fatiguing for a dog, and the dog must be motivated to continue this hard work for a long period of time.

Coat color

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. 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. This reduces the general visibility of the animal. One reminder of this pattern is that many breeds will have the occasional "blaze", stripe, or "star" of white fur on their chest or undersides.

Sprint metabolism

Dogs can generate large amounts of energy for a short period of time. This setup is useful for hunting and combat. An example of this is that almost any dog, even one that is usually slow and lazy, can outsprint any human. However, almost any human can catch up with any dog in a marathon run, or other activity where endurance is needed.

A dog's heart and lungs are oversized relative to its body and its normal everyday needs. A dog also has relatively more red blood cells than a human. Most of the time the dog will keep the extra red blood cells stored in its spleen. When the animal enters into a situation where its full metabolism is required, such as play, catching game, or fighting other dogs, the extra cells are released into the bloodstream. The "oversized" heart and lungs will now be running at full capacity, and the animal will have an enhanced ability to engage in aerobic activity. This activity will produce internal heating. Dogs, being covered in fur, are limited in their ability to cool down. After a short time the animal must either cease its athletic activity or risk harming itself from overheating. One can easily observe this pattern of intense activity followed by rest periods in puppies. During the rest phase the spleen collects red blood cells and the animal may pant to cool down.

Working, utility and assistance dogs

Labrador Retrievers are often used as assistance dogs.

There are several types of working dogs:

• Assistance dogs which help the seeing and hearing-impaired. Others are trained to help those with epilepsy and psychiatric disorders, by detecting the onset of the condition so they can seek help. The typical assistance dog is a sociable breed such as a Labrador Retriever.
• The detection dog, which is a dog trained to and works at using its senses (almost always the sense of smell) to detect substances such as explosives or illegal drugs.
• Guard dogs trained to protect property. These are commonly Doberman Pinschers, German Shepherds and Rottweilers or mixes of these breeds.
• Herding dogs trained to protect livestock in the range against predators. Sheepdogs are a common breed.
• Hunting dogs that search for and retrieve game. Pointers and retrievers are typical hunting breeds.
• Police dogs, typically German Shepherds, are trained to assist law enforcement officers.
• Rescue dogs that search for missing humans. The archetypal breeds are the St. Bernard and the Bloodhound, although any dog with a good sense of smell can be trained to perform this task.
• Therapy dogs, with friendly and gentle temperaments, trained to provide comfort and affection to hospitalized and institutionalized patients.
• The war dog, used by the military to detect mines and enemy soldiers.

Show and sport (competition) dogs

An English Springer Spaniel during a show in a country where docking is illegal

Owners of dogs often enter them in competitions, whether show (breed conformation shows) or sports, including dog racing & dog sledding. The winners garner much prestige and prize money. These dogs are often bred specifically for competition, which may not be entirely beneficial for the breeds due to the magnification of hereditary defects.

• Dog agility is a sport in which dogs complete a timed obstacle course.
• Dogsled racing is a winter sport where a team of dogs, usually high performance mixed breed dogs called Alaskan Huskies or Eurohounds, pull a sled and driver (called a musher). The Iditarod Trail Sled Dog Race is perhaps the most famous of these races. Dog sledding is an ancient form of transportation and still a very effective way of moving freight across this type of terrain.
• Dog racing, almost always Greyhounds, involves dogs racing at betting tracks in a sport not unlike horseracing, reaching speeds of 40 miles per hour. Elsewhere, Dachshunds are often raced, as a humorous sidelight in charity events.
• Dog fighting and dog baiting are blood sports involving dogs. They are illegal in most jurisdictions, but are still occasionally performed underground.
• The show dog, purebreds entered in conformation dog shows and evaluated by how closely they match the ideal characteristics of the breed. The Westminster Kennel Club Dog Show is one of the most famous of this type of competition.

Diet

At present, there is some debate as to whether domestic dogs should be classified as omnivores or carnivores, by diet. The classification in the Order Carnivora does not necessarily mean that a dog's diet must be restricted to meat; unlike an obligate carnivore, such as the cat family with its shorter small intestine, a dog is dependent on neither 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 in fact dogs can consume a large proportion of these in their diet. Wild canines not only eat available plants to obtain essential amino acids, but also obtain nutrients from vegetable matter from the stomach and intestinal contents of their herbivorous prey, which they usually consume. Domestic dogs can survive healthily on a reasonable and carefully designed vegetarian diet, particularly if eggs and milk products are included. Some sources suggest that a dog fed on a strict vegetarian diet may develop dilated cardiomyopathy since it lacks L-carnitine, however, maintaining a balanced diet is also a factor since L-carnitine is found naturally in many nuts, seeds, beans, vegetables, fruits and whole grains. In the wild, dogs can survive on a vegetarian diet when animal prey is not available. However it has been noted, both by observation of extremely stressful conditions such as the Iditarod Trail Sled Dog Race and by scientific studies of similar conditions, that high-protein (approximately 40%) diets including meat help prevent damage to muscle tissue. (This research is also true for some other mammals.) This level of protein corresponds to the percentage of protein found in the wild dog's diet when prey is abundant; higher levels of protein seem to confer no added benefit.

Dogs frequently eat grass, which is a harmless activity. Explanations abound, but rationales such as that it neutralizes acid, or that eating grass might make the dog vomit, so dogs eat grass to remove unwanted substances from their stomachs, are at best educated guesses. Indeed, dogs may eat grass when they have an upset stomach in order to cause vomiting. The grass binds with the offending material. Then the grass acts as an irritant and causes the dog to vomit, bringing up the poisonous material at the same time.. Dogs do vomit more readily than humans, as part of their typical feeding behavior of gulping down food then regurgitating indigestible bones, fur, etc. This behavior is typical of pack feeding in the wild, where the most important thing is to get as much of the kill as possible before others consume it all. Individual domestic dogs, however, may be very "picky" eaters, in the absence of this evolutionary pressure.

Also, dogs eat grass, because it's a normal part of their diet. Wild canine relatives of dogs — wolves and foxes — eat all of an animal when they catch it. They end up, therefore, eating grasses and plants in the intestines of these animals. Domestic dogs, eating prepared dog food, lack this part of their diet and so they eat grass. Moreover, they just like it. A veterinarian remembers a beagle that picks raspberries faster than his owner. Finally, dogs may appear to eat grass, when they are just running the blades through their mouth to gather information. Their sense of smell and taste may act together to detect if other animals have walked through their area or urinated on the grass.

Reproduction

General

In domestic dogs, sexual maturity (puberty) begins to happen around age 6 to 12 months for both males and females, although this can be delayed until up to two years old for some large breeds. Adolescence for most domestic dogs is around 12 to 15 months, beyond which they are for the most part more adult than puppy. As with other domesticated species, domestication has selectively bred for higher libido and earlier and more frequent breeding cycles in dogs, than in their wild ancestors.

Females

Females have a twice-yearly fertile period (technically every 7 months in most breeds), known as 'seasons', during which her body prepares for pregnancy, and at the peak she will come "into heat", her fertile period, during which time she will be mentally and physically receptive to copulation. A female is able to become pregnant on her first heat; this is not normally considered advisable as she is mentally and physically still young in other ways.

As with most domesticated species, one of the first and strongest effects seen from selective breeding is selection for cooperation with the breeding process as directed by humans. In domestic dogs, one of the behaviors that is noted is the abolition of the pair bond seen in wild canines. The ability of female domestic dog to come into estrus at any time of the year and usually twice a year is also valued. The amount of time between cycles varies greatly among different dogs, but a particular dog's cycle tends to be consistent through her life. This is also called in season or in heat. Conversely, undomesticated canine species experience estrus once a year, typically in late winter.

Most female dogs come into season for the first time between 6 and 12 months, although some larger breeds delay until as late as 2 years. Like most mammals, the age that a bitch first comes into season is mostly a function of her current body weight as a proportion of her body weight when fully mature. The different rates of maturation are responsible for the menarche, not the chronological age. They then experience fertile seasons biannually until old age. Female dogs do not experience menopause, although their cycles will become irregular and fertility becomes unpredictable as they become older. Dogs over around 7 or 8 years are usually considered no longer appropriate for breeding, but can still remain fertile.

Copulation

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When copulating, a male canine initially mounts the female from behind, as with most tetrapods, a position known informally as doggy style. The female will hold her tail to the side and allow this if receptive. If unreceptive she may sit or lie down, snap, move away, or otherwise be uncooperative or not allow mating. The male will often move about as he tries to get a good purchase upon her, and whilst attempting penetration of his penis to the female's vulva. At the time of penetration, the penis is not truly erect. Rather, it is held rigid by a small bone, known as the baculum.

When the male achieves penetration, he will often hold tighter and thrust faster. At this point the male's penis expands. Canine reproduction is different from human sexual intercourse, because human males acquire an erection prior to penetration. Canine males enter first, then swell and become erect.

The male dog has a bulbus glandis, a spherical area of erectile tissue at the base of the penis, which traps the penis inside the female's vagina during copulation as it becomes engorged with blood. [1]

Once the penis is locked into the vagina by the bulbus glandis, the male will usually lift a leg and swing it over the female's back while turning around. The two stand with their hind ends touching and the penis locked inside the vagina while ejaculation occurs, decreasing leakage of semen from the vagina. After some time, typically 5 - 20 minutes (but sometimes longer), the bulbus glandis disengorges, allowing the mates to separate. Virgin dogs can become quite distressed at finding themselves unable to separate during their first copulation, and may try to pull away or run. Dog breeders' often suggest it is appropriate to help calm and settle the mating dogs once this stage is reached, if they show anxiety.

Note that similar canine mounting behavior (sometimes with pelvic thrusting) is also used by dominant canines of both sexes. Dominance mounting, with or without thrusting, should not be confused with copulatory mounting, in which the thrusting is short term until a "tie" is achieved.

Gestation and litters

A Catahoula Leopard mother nursing her litter of puppies.

Dogs bear their litters roughly 9 weeks after fertilization, although the length of gestation can vary from 56 to 72 days. A general rule of thumb is that a mammal will produce half as many offspring as the number of teats on the mother. This rule is altered in domesticated animals since larger litters are often favored for economic reasons and in dogs, particularly, the great range of sizes and shapes plays a role in how many healthy puppies a female can carry. An average litter consists of about six puppies, 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 12 pups in each litter. The number of puppies also varies with the mother's age and health, the father's sperm count, the timing of the breeding, and many other factors.

Some breeds have been developed to emphasize certain physical traits beyond the point at which they can safely bear litters on their own. For example, the Bulldog often requires artificial insemination and almost always requires cesarean section for giving birth. Since a mother can provide nutrients and care to only a limited number of offspring, humans must assist in the care and feeding when the litter exceeds approximately eight puppies.

Overpopulation

According to the Humane Society of the United States, 3-4 million dogs and cats are euthanized 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 neutering dogs helps keep overpopulation down. Local humane societies, SPCA's and other animal protection organizations urge people to spay or neuter their pets and to adopt animals from shelters instead of purchasing them. Several notable public figures have spoken out against animal over population, including Bob Barker. On his game show, The Price is Right, Barker stresses the issue at the end of every episode, saying: "Help control the pet population. Have your pets spayed or neutered."

Dog health

Dogs are susceptible to various diseases, ailments, and poisons, some of which affect humans in the same way, others of which are unique to dogs. Dogs, like all mammals, are also susceptible to heat exhaustion when dealing with high levels of humidity and/or extreme temperatures.

Diseases

Infectious diseases commonly associated with dogs include rabies (hydrophobia), canine parvovirus, and canine distemper. Congenital diseases of dogs can include a wide range from hip dysplasia and medial patellar luxation to epilepsy and pulmonic stenosis. Canines can get just about anything a human can get (excluding many infections which are species specific) like hypothyroidism, cancer, dental disease, heart disease, etc.

Two serious medical conditions 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; owners of dogs which may be at risk should learn about such conditions as part of good animal care.

Parasites

Common external parasites are various species of fleas, ticks, and mites. Internal parasites include hookworms, tapeworms, roundworms, and heartworms. See also CVBD (Canine Vector-Borne Diseases).

Common physical disorders

Some breeds of dogs are also prone to certain genetic ailments, such as hip dysplasia, luxating patellas, cleft palate, blindness, or deafness. Dogs are also susceptible to the same ailments that humans are, including diabetes, epilepsy, cancer, and arthritis. Gastric torsion and bloat is a dangerous problem in some large-chested breeds.

Lifespan and old age

The typical lifespan of dogs varies considerably by breed. For example, many giant dog breeds (such as Great Danes) average only 7 or 8 years, while some small terrier breeds, or toy breeds might live as long as 20 or above. The average lifespan for mixed-breed and midsize dogs is about 13 to 14 years. The longest-lived dog with reliable documentation died at 29 years and 27 days, the breed of the dog was an Australian cattle dog and it lived in Virginia, USA, the date of death was in 1939. The oldest currently living dog is from Canberra, Australia and is now 27 years old. Although the lifespans of all living species are mostly uncontrollable, one can significantly extend a dog's life by feeding it the right kinds of foods, giving it regular exercise, treating its diseases, caring for its special needs and giving it love and comfort.

Behavior

Dogs are very social animals, but their personality and behavior vary with breed as well as how they are treated by their owners and others who come in contact with them. Physical abuse and starvation can produce very neurotic, dangerous dogs, and even simply failing to socialize them properly may entail maladaptive behaviors. ^{[citation needed]} It is not uncommon for dogs to attack humans and other animals; however, this is usually because of lack of care or improper upbringing by its owner.

Dog breeds

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The dog has developed into hundreds of breeds with a great degree of variation, such as this Miniature Pinscher and Boxer.

There are numerous dog breeds, with over 800 being recognized by various kennel clubs worldwide. As all dog breeds have been derived from mixed-breed dog populations, the term "purebred" has meaning only with respect to a certain number of generations. Many dogs, especially outside the United States of America and Western Europe, belong to no recognized breed.

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The Papillon is a highly athletic breed of dog

A few basic breed types have evolved gradually during the domesticated dog's relationship with humans over the last 10,000 or more years, but most modern breeds are of relatively recent derivation. Many of these are the product of a deliberate process of artificial selection. Because of this, some breeds are highly specialized, and there is extraordinary morphological diversity across different breeds. Despite these differences, dogs are able to distinguish dogs from other kinds of animal.

The definition of a dog breed is a matter of some controversy. Depending on the size of the original founding population, closed gene pool breeds can have problems with inbreeding, specifically due to founder effect. Dog breeders are increasingly aware of the importance of population genetics and of maintaining diverse gene pools. Health testing and new DNA tests can help avoid problems, by providing a replacement for natural selection. Without selection, inbreeding and closed gene pools can increase the risk of severe health or behavioral problems. Some organizations define a breed more loosely, such that an individual may be considered of one breed as long as 75% of its parentage is of that breed. These considerations affect both pets and the show dogs entered in dog shows. Even prize-winning purebred dogs sometimes possess crippling genetic defects due to founder effect or inbreeding. These problems are not limited to purebred dogs and can affect mixed-breed populations. The behavior and appearance of a dog of a particular breed can be predicted fairly accurately, while mixed-breed dogs show a broader range of innovative appearance and behavior.

In February 2004, the Canine Studies Institute in Aurora, Ohio, arranged recognized breeds of dogs into ten categories.

Mixed-breed dogs or Mongrels are dogs that do not belong to specific breeds, being mixtures of two or more in variant percentages. Mixed breeds, or dogs with no purebred ancestry, are not inherently "better" or "worse" than purebred dogs as companions, pets, working dogs, or competitors in dog sports. Sometimes mixed-breed dogs are deliberately bred, for example, the Cockapoo, a mixture of Cocker Spaniel and Miniature Poodle. Such deliberate crosses may display hybrid vigor and other desirable traits, but can also lack one or more of the desired traits of their parents, such as temperament or a particular color or coat. However, without genetic testing of the parents, the crosses can sometimes end up inheriting genetic defects that occur in both parental breeds. Deliberately crossing two or more breeds is also a manner of establishing new breeds.

Breed popularity

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Breed popularity varies widely over time and in different parts of the world and different segments of the population. Counting by American Kennel Club (AKC) registration (not by licensing registration or by United Kennel Club (UKC) registration, which could present different statistics), the Labrador Retriever has been the United States's most commonly registered breed of dog since 1991. However, even within parts of the United States, popularity varies; for example, in 2005 the most-registered breed in New York City was the Poodle while the Yorkshire Terrier was the second-most-registered breed in Houston. However, animal shelters in many parts of the United States report that the most-commonly available dog for adoption is the American Pit Bull Terrier or pit bull-type mixes, making up as much as 20% of dogs available for adoption, none of which would be registered with the AKC. Two decades ago, in 1983, the AKC's top two registered breeds were the American Cocker Spaniel and the Poodle.

In 2006 a British dog journal published an exhaustive research paper which pooled together quantifiable dog breed facts such as average lifespan, cost of maintenance, insurance claims made, known behavioural faults and various other criteria in order to arrive at the conclusion that the Staffordshire Bull Terrier is the 'highest scoring' dog breed in terms of desirable and established pedigree dog breed traits.

In the United Kingdom, The Kennel Club reports that the most-registered breed from at least 1999 to 2005 was the Labrador Retriever. It rounds out the top three for 1999 to 2005 with the German Shepherd Dog, also popular in the States, and the English Cocker Spaniel , which is no longer even in the top ten in the States. In the United Kindom a national dog adoption and rescue service indicates that the most common breed appearing in shelters is the Greyhound followed by the Staffordshire Bull Terrier.

In religion

Islam

See also Islam and animals

Muhammad, the prophet of Islam expressed that the company of dogs voids a portion of a Muslim’s good deeds.

Islamic law considers dogs to be unclean but this is not derived from the Qur'an. Muhammad is said to have given an order to kill all the dogs in Medina because the angel Gabriel does not enter a house in which there is a dog. This hadith is however the "occasion for revelation" of verse ^[Quran 5:4] which indicates the importance of the hunting dog. David Gordon White states that Islam, like Judaism and Christianity, usually cast the dog in a negative light by emphasizing its impurity and often identify dogs as demons or minions of the Devil. The story of the Seven sleepers of Ephesus in the Qur'an (and also role of the dog in early Christianity) are the striking exceptions.. Muhammad didn't like dogs (and most Muslims do not have dogs as pets). According to one tradition attributed to Muhammad, black dogs are evil, or even devils, in animal form.

Muhammad commanded Muslims not trade or deal in dogs.

Muhammad said that dogs and donkeys - if they pass in front of men in prayer - they will void or nullify that prayer.

Dr. Khaled Abou El Fadl, a professor of law at the UCLA School of Law where he teaches Islamic law, has written on the subject.

References

ISBN links support NWE through referral fees

• American Kennel Club (AKC). 2006. The Complete Dog Book. New York: Ballantine Books. ISBN 0345476263.
• American Veterinary Medical Association (AVMA). 2007. "Market Research Statistics: Cat and Dog Ownership". Accessed July 16, 2007.
• Clutton-Brook, J. 1999. A Natural History of Domesticated Mammals. Cambridge, UK: Cambridge University Press. ISBN 0521634954
• Kruuk, H. 2002. Hunter and Hunted: Relationships between carnivores and people. Cambridge, UK: Cambridge University Press. ISBN 0521814103
• McGourty, C. 2002. "Origin of dogs traced". BBC News. Accessed July 23, 2007
• Nowak, R. M., and J. L. Paradiso. 1983. Walker's Mammals of the World. Baltimore, Maryland: The Johns Hopkins University Press. ISBN 0801825253.
• Voelker, W. 1986. The Natural History of Living Mammals. Medford, New Jersey: Plexus Publishing. ISBN 0937548081.

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