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Dog

2007 Schools Wikipedia Selection. Related subjects: Mammals

                  iDomestic dog
   Labrador Retrievera breed of domestic dog
   Labrador Retriever
   a breed of domestic dog

                             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

   The dog is a mammal in the order Carnivora. 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. 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. Over time, the dog has developed into hundreds of breeds with a
   great degree of variation. For example, heights at the withers range
   from just a few inches (such as the Chihuahua) to roughly three feet
   (such as the Irish Wolfhound), and colors range from white to black,
   with reds, grays (usually called blue), and browns occurring in a
   tremendous variation of patterns.

   Dogs, like humans, are highly social animals and this similarity in
   their overall behavioural pattern accounts 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 with and worked with humans in
   so many roles that their loyalty has earned them the unique sobriquet
   "man's best friend" Conversely, 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 the German Hund and Dutch hond which, though referring to a
   specific breed in English, means "dog" in general in German and Dutch.
   Hound itself derives from the Proto-Indo-European *kwn,to-, an extended
   zero-grade form of the root *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. 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

   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. Dogs are descended from wolves, and are also pack animals,
   making them easier than other animals to train because dogs' instincts
   are to obey. But 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.

Physical characteristics

   Shiba Inus have a unique appearance that resembles foxes.
   Enlarge
   Shiba Inus have a unique appearance that resembles foxes.
   Some dogs, like this Weimaraner, have their predatory instincts
   suppressed in order to better assist human hunters.
   Enlarge
   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
   behaviour 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

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

   Dogs were thought to be dichromats and thus, by human standards, colour
   blind. It is now known that dogs can't see the colour red very well.

   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 Collie/Saluki angles her ears to find the source of a sound.
   Enlarge
   This Collie/ Saluki 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 behaviour 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.

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
   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 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 avidly 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. Dogs do vomit more readily than humans, as part of their
   typical feeding behaviour of gulping down food then regurgitating
   indigestible bones, fur, etc. This behaviour 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.

Dangerous substances

   Some foods commonly enjoyed by humans are dangerous to dogs, including
   chocolate ( Theobromine poisoning), onions, grapes and raisins , some
   types of gum, certain sweeteners and Macadamia nuts. Now that it is
   thought that the only dangerous substance in chocolate is the cocoa,
   this means that white chocolate can be used as a rare treat.

   The acute danger from grapes and raisins has been uncovered only since
   about 2000, and made public slowly since then. At present the cause is
   not known, but one veterinarian believes it may be an acute auto-immune
   response to plant-borne viruses in the same manner as FIP in cats.
   Whatever the reason, since only small quantities are necessary to
   induce acute renal failure, dogs should not be fed grapes or raisins,
   and sultanas and currants should likely be withheld as well.

   Cooked bones should never be given to dogs, as the heat changes the
   chemical and physical properties so that they cannot be chewed
   properly, splintering into jagged shards, and resist digestion.

   Human medications should not be given to a dog as a substitute for
   their regular medication as some can be especially toxic, especially
   paracetamol/acetaminophen (Tylenol). Alcoholic beverages pose much of
   the same hazards to dogs as they do to humans.

   Dogs may also find some poisons attractive, including antifreeze, snail
   bait, insect bait, and rodent poisons. Antifreeze may be one of the
   most insidious of poisons to dogs because of its sweet taste and
   because a dog may walk upon or lie down upon a spill of it or its
   residue and then lick it off. Dogs must be kept strictly away from
   antifreeze and not allowed access to any place that has had a spill of
   it that has not been completely removed.

   Plants such as caladium, dieffenbachia and philodendron will cause
   throat irritations that will burn the throat going down as well as
   coming up. Hops are particularly dangerous and even small quantities
   can lead to malignant hyperthermia.

   Amaryllis, daffodil, english ivy, iris, and tulip (especially the
   bulbs) cause gastric irritation and sometimes central nervous system
   excitement followed by coma, and, in severe cases, even death.

   Ingesting foxglove, lily of the valley, larkspur and oleander can be
   life threatening because the cardiovascular system is affected. Equally
   life threatening is the yew which affects the nervous system. If any of
   these plants are ingested, get the dog to a veterinarian immediately.

   Many household cleaners such as ammonia, bleach, disinfectants, drain
   cleaner, soaps, detergents, and other cleaners, mothballs and matches
   are dangerous to dogs, as are cosmetics such as deodorants, hair
   coloring, nail polish and remover, home permanent lotion, and suntan
   lotion.

Reproduction

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
   stressed the issue every episode by stating: "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.

Parasites

   Common external parasites are various species of fleas, ticks, and
   mites. Internal parasites include hookworms, tapeworms, roundworms, and
   heartworms.

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

   The typical lifespan of dogs varies considerably by breed. For example,
   many giant dog breeds average only 7 or 8 years, while some small
   terrier breeds might live as long as 20 years. 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 in 1939. 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 exercise, treating his diseases, and caring for its
   special needs.

Behaviour

   Dogs are very social animals, but their personality and behaviour 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. 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.

Ancestry and history of domestication

   This ancient mosaic, likely Roman, shows a large dog with a collar
   hunting a lion.
   Enlarge
   This ancient mosaic, likely Roman, shows a large dog with a collar
   hunting a lion.

   Molecular systematics indicate that the domestic dog (Canis lupus
   familiaris) descends from one or more populations of wild wolves (Canis
   lupus). As reflected in the nomenclature, dogs are descended from the
   wolf and are able to interbreed with wolves.

   The relationship between human and canine has deep roots. Wolf remains
   have been found in association with hominid remains dating from 400,000
   years ago. Converging archaeological and genetic evidence indicate a
   time of domestication in the late Upper Paleolithic close to the
   Pleistocene/ Holocene boundary, between 17,000 and 14,000 years ago.
   Fossil bone morphologies and genetic analysis of current and ancient
   dog and wolf populations have not yet been able to conclusively
   determine whether all dogs descend from a single domestication event,
   or whether dogs were domesticated independently in more than one
   location. Domesticated dogs may have interbred with local populations
   of wild wolves on several occasions (so-called introgression).

   The earliest dog fossils, two crania from Russia and a mandible from
   Germany, date from 13,000 to 17,000 years ago. Their likely ancestor is
   the large northern Holarctic wolf, Canis lupus lupus. Remains of
   smaller dogs from Mesolithic ( Natufian) cave deposits in the Middle
   East, dated to around 12,000 years ago, have been interpreted as
   descendants of a lighter Southwest Asian wolf, Canis lupus arabs. Rock
   art and skeletal remains indicate that by 14,000 years ago, dogs were
   present from North Africa across Eurasia to North America. Dog burials
   at the Mesolithic cemetery of Svaerdborg in Denmark suggest that in
   ancient Europe dogs were valued companions.

   Genetic analyses have so far yielded divergent results. Vilà,
   Savolainen, and colleagues (1997) concluded that dogs split off from
   wolves between 75,000 and 135,000 years ago, while a subsequent
   analysis by Savolainen et al. (2002) indicated a "common origin from a
   single gene pool for all dog populations" between 40,000 and 15,000
   years ago in East Asia. Verginelli et al. (2005), however, suggest both
   sets of dates must be reevaluated in light of recent findings showing
   that poorly calibrated molecular clocks have systematically
   overestimated the age of geologically recent events. On balance, and in
   agreement with the archaeological evidence, 15,000 years ago is the
   most likely time for the wolf-dog divergence.

   Verginelli examined ancient DNA evidence from five prehistoric Italian
   canids carbon-dated to between 15,000 and 3,000 years old, 341 wolves
   from several populations worldwide, and 547 purebred dogs. Their
   results indicate multiple independent origins of dogs and/or of
   frequent interbreeding between early proto-dogs and wolves throughout a
   vast geographic range. The detailed history remains unexplored and
   until further evidence is available, the following section on wolf
   ancestors must be considered purely speculative.

Wolf ancestors

   Although all wolves belong to the species Canis lupus, there are (or
   were) many subspecies that had developed a distinctive appearance,
   social structure, and other traits. For example, the Japanese Wolf and
   the Eastern Timber Wolf possess different distinctive coloration,
   hunting and social structures. The origin of the dog is so ancient and
   so worldwide that many varieties of wolf played a part in it. It is
   wrong to say that dogs descended from modern wolves. They descended
   from ancestral wolves, and this difference must always be kept in mind.
   Ancestral wolves of many varieties existed all over the world, as they
   do today. Humans are of a tropical origin, and it was there that the
   domestication of dogs from wolves first took place. It follows then,
   that the first wolves to be domesticated were the warm-climate,
   short-haired varieties that gave rise to many of our dog breeds, with
   the long-haired, northern wolves giving rise to our northern breeds
   when humans reached these lattitudes.

   The Indian Wolf is thought to have contributed to the development of
   more breeds of dogs than other subspecies. Many of today's wild dogs,
   such as the dingo and the pariah dogs, are descended from this wolf.
   The Indian Wolf is also thought to have bred with descendants of the
   European wolf to create the Mastiffs and eventually leading to the
   development of such diverse breeds as the Pug, the Saint Bernard, and
   the Bloodhound. The Tibetan Mastiff is an example of an ancient breed.

   The European wolf, in turn, may have contributed many of its attributes
   to the Spitz dog types, most terriers, and many of today's sheepdogs.
   The Chinese wolf is probably ancestor to the Pekingese and toy
   spaniels, although it is also probable that descendants of the Chinese
   and European wolves encountered each other over the millennia,
   contributing to many of the oriental toy breeds.

   The Eastern Timber Wolf is a direct ancestor to most, if not all, of
   the North American northern sled dog types. This interbreeding still
   occurs with dogs living in the Arctic region, where the attributes of
   the wolf that enable survival in a hostile environment are valued by
   humans. Additionally, unintentional crossbreeding occurs simply because
   dogs and wolves live in the same environment. The general reproductive
   isolation which is required to define dogs and wolves as separate
   species is purely a result of lack of opportunity, stemming from a
   general mutual unfamiliarity, suspicion, mistrust, and fear.

   The phenotypic characteristics that distinguish a wolf from a dog are
   tenuous. Wolves typically have a "brush tail" and erect ears. While
   some dog breeds possess one of these characteristics, they rarely
   possess both.

Speed of domestication

   Current research indicates that domestication, or the attributes of a
   domesticated animal, can occur much more quickly than previously
   believed. Domestication of a wild dog may occur within one or two human
   generations with deliberate selective breeding. It is also now
   generally believed that initial domestication was through mutual
   desire. Wild canines who scavenged around human habitations received
   more food than their more skittish or fearful counterparts. Canines who
   attacked people or their children were likely killed or driven away,
   while those more friendly animals survived. Canines would have been
   beneficial by chasing away other vermin or scavengers. With their sharp
   senses, they would also be valuable as an alarm against marauding
   predators. The relationship is theorized to have developed in this way.

Dog meat for human consumption

   In a number of countries around the world, apart from being kept as
   pets, certain breeds of dogs are slaughtered as a source of meat and
   specifically raised on farms for that purpose. In countries where dogs
   are particularly popular as household pets, the use of dogs as a source
   of food is often considered a taboo and abhorrent cultural practice,
   although there are exceptions such as Vietnam where dogs are popular as
   pets and as meat.

Dog abuse

   Cruelty to dogs refers to treatment which causes unacceptable suffering
   or harm. What qualifies as unacceptable suffering varies depending on
   the country and its culture.

Famous dogs

   The long shared history of dogs and humans has resulted in many
   individual dogs achieving fame or notoriety, and many fictional dogs
   have been created for literature, cinema, and elsewhere.

Dog breeds

   A Jack Russell Terrier playing with his toy.
   Enlarge
   A Jack Russell Terrier playing with his toy.
   The dog has developed into hundreds of breeds with a great degree of
   variation, such as this Miniature Pinscher and Boxer.
   Enlarge
   The dog has developed into hundreds of breeds with a great degree of
   variation, such as this Miniature Pinscher and Boxer.
   A Maltese lying in the fall leaves.
   Enlarge
   A Maltese lying in the fall leaves.

   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 and Western Europe, belong to no recognized
   breed.

   A few basic breed types have evolved gradually during the domesticated
   dog's relationship with man 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 behavioural
   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
   behaviour.
   A 10-year-old Staffordshire Bull Terrier/Labrador.
   Enlarge
   A 10-year-old Staffordshire Bull Terrier/ Labrador.

   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 colour 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.

Neoteny in the rapid evolution of diverse dog breeds

   This rapid evolution of dogs from wolves is an example of neoteny or
   paedomorphism. As with many species, the young wolves are more social
   and less dominant than adults; therefore, the selection for these
   characteristics, whether deliberate or inadvertent, is more likely to
   result in a simple retention of juvenile characteristics into adulthood
   than to generate a complex of independent new changes in behaviour.
   (This is true of many domesticated animals, including human beings
   themselves, who have many characteristics similar to young bonobo.)
   This paedomorphic selection naturally results in a retention of
   juvenile physical characteristics as well. Compared to wolves, many
   adult dog breeds retain such juvenile characteristics as soft fuzzy
   fur, round torsos, large heads and eyes, ears that hang down rather
   than stand erect, etc.; characteristics which are shared by most
   juvenile mammals, and therefore generally elicit some degree of
   protective and nurturing behaviour cross-species from most adult
   mammals, including humans, who term such characteristics "cute" or
   "appealing".

   The example of canine neoteny goes even further, in that the various
   breeds are differently neotenized according to the type of behaviour
   that was selected. Stephen Jay Gould; Eight Little Piggies: Reflections
   in Natural History; W. W. Norton & Company, 1993; pp. 394
     * Livestock guardian dogs exhibit the controlled characteristics of
       hunting dogs. Members of this group, such as Border Collies,
       Belgian Malinois and German Shepherds use tactics of hunter and
       prey to intimidate and keep control of herds and flocks. Their
       natural instinct to bring down an animal under their charge is
       muted by training. Other members of the group, including Welsh
       Corgis, Canaan dogs, and Cattle dogs herd with a more aggressive
       demeanor and make use of body design to elude the defences of their
       charges.
     * Gun dog breeds used in hunting—that is, pointers, setters,
       spaniels, and retrievers—have an intermediate degree of
       paedomorphism; they are at the point where they share in the pack's
       hunting behavior, but are still in a junior role, not participating
       in the actual attack. They identify potential prey and freeze into
       immobility, for instance, but refrain from then stalking the prey
       as an adult predator would do next; this results in the "pointing"
       behavior for which such dogs are bred. Similarly, they seize dead
       or wounded prey and bring it back to the "pack", even though they
       did not attack it themselves, that is, "retrieving" behaviour.
       Their physical characteristics are closer to that of the mature
       wild canine than the sheepdog breeds, but they typically do not
       have erect ears, etc.
     * Scenthounds maintain an intermediate body type and behavior pattern
       that causes them to actually pursue prey by tracking their scent,
       but tend to refrain from actual individual attacks in favour of
       vocally summoning the pack leaders (in this case, humans) to do the
       job. They often have a characteristic vocalization called a bay.
       Some examples are the Beagle, Bloodhound, Basset Hound, Coonhound,
       Dachshund, Fox Hound, Otter Hound, and Harrier.
     * Sighthounds, who pursue and attack perceived prey on sight,
       maintain the mature canine size and some features, such as narrow
       chest and lean bodies, but have largely lost the erect ears of the
       wolf and thick double layered coats. Some examples are the Afghan,
       Borzoi, Saluki, Sloughi, Pharaoh Hound, Azawakh, Whippet, and
       Greyhound.
     * Mastiff-types are large dogs, both tall and massive with
       barrel-like chests, large bones, and thick skulls. They have
       traditionally been bred for war, protection, and guardian work.
     * Bulldog-types are medium sized dogs bred for combat against both
       wild and domesticated animals. These dogs have a massive, square
       skull and large bones with an extremely muscular build and broad
       shoulders.
     * Terriers similarly have adult aggressive behaviour, famously
       coupled with a lack of juvenile submission, and display
       correspondingly adult physical features such as erect ears,
       although many breeds have also been selected for size and sometimes
       dwarfed legs to enable them to pursue prey in their burrows.

   The least paedomorphic behaviour pattern may be that of the basenji,
   bred in Africa to hunt alongside humans almost on a peer basis; this
   breed is often described as highly independent, neither needing nor
   appreciating a great deal of human attention or nurturing, often
   described as "catlike" in its behavior. It too has the body plan of an
   adult canine predator. Of course, dogs in general possess a significant
   ability to modify their behavior according to experience, including
   adapting to the behaviour of their "pack leaders"—again, humans. This
   allows them to be trained to behave in a way that is not specifically
   the most natural to their breed; nevertheless, the accumulated
   experience of thousands of years shows that some combinations of nature
   and nurture are quite daunting, for instance, training whippets to
   guard flocks of sheep.

Breed popularity

   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; the Yorkshire
   Terrier was the second-most-registered breed in Houston but didn't even
   make the top ten in Honolulu. 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 Britain, 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.

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