For other members of the dog family, see Canidae.

The dog is a canine omnivorous mammal that has been domesticated for somewhere between 14,000 and 150,000 years. In this time, the dog has developed into hundreds of breeds with a great degree of variation. For example, heights ranging from just a few inches (such as the Chihuahua) to nearly three feet (such as the Irish Wolfhound), and colors ranging from white to black with reds, grays, and browns also occurring in a tremendous variation of patterns. Dogs, being highly social animals, are known for trainability, playfulness, and for ability to fit into human households and social situations. See dog training for details.

Dogs fill a variety of roles in human society. Working dogs of all kinds do traditional jobs such as herding and new jobs such as detecting contraband. For dogs that do not do their 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 they have earned the sobriquet Man's best friend.

Terminology for dogs

Dog, in common usage, refers to the domestic dog, Canis lupus familiaris (originally classified as Canis familiaris by Linnaeus in 1758, but reclassified as a subspecies of the wolf, Canis lupus, by the Smithsonian Institution and the American Society of Mammalogists in 1993). The word 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.

Dog is also a term used by breeders to specifically denote a male domestic dog. The female is known as a bitch. A young dog is called a puppy. The words pooch and poochie are generic, generally affectionate terms for a dog. Many additional terms are used for dogs that are not purebred; see Terms for mixed-breed dogs.

Attributes

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.

Their legs are designed to propel them forward rapidly, leaping as necessary, to chase and overcome prey. Consequently, they have small, tight feet, walking on their front toes; their rear legs are fairly rigid and sturdy; the front legs are loose and flexible, with only muscle attaching them to the torso.

Dogs have a form of colorblindness that affects how they see red (same as yellow), green, and blue (both appear white)^{1, 2}. Because the lenses of dogs' eyes are flatter than humans', they cannot see as much detail; on the other hand, their eyes are more sensitive to light and motion than humans' eyes. Some breeds, particularly the best sighthounds, have a field of vision up to 270° (compared to 100° to 120° for humans), although broad-headed breeds with their eyes set forward have a much narrower field of vision, as low as 180°.^{1, 2}

Dogs detect sounds as low as the 20 to 70 Hz frequency range (compared to 16 to 20 Hz for humans) and as high as 70,000 to 100,000 Hz (compared to 20,000 Hz for humans)², and in addition have a degree of ear mobility that helps them to rapidly pinpoint the exact location of a sound. They can identify a sound's location much faster than can a human, and they can hear sounds up to four times the distance that humans can.

Dogs have about 220 million smell-sensitive cells (compared to 5 million for humans). Some breeds have been selectively bred for excellence in detecting scents, even compared to their canine brethren.

All dogs have a tremendous capacity to learn complex social behavior and to interpret varied body language and sounds, and, like many predators, can react to and learn from novel situations.

Dog coats, colors, and markings

Dogs exhibit a diverse array of coat textures, colors, and markings, and a specialized vocabulary has evolved to describe them.

Originally, dogs all had dense fur with an undercoat and long muzzles and heads, although both of these features have been altered in some of the more extremely modified breeds, such as the Mexican Hairless and the English Bulldog.

One often refers to a specific dog first by coat color rather than by breed; for example, "a blue merle Aussie" or "a chocolate Lab". Coat colors include:

• Blenheim: A combination of chestnut and white; for example, the Cavalier King Charles Spaniel.
• Black: Usually pure black but sometimes grizzled, particularly as dogs age and develop white hairs, usually around the muzzle.
• Black and tan: Coat has both colors but in clearly defined and separated areas; usually the top and sides are black and lower legs and underside are tan, reddish, or chestnut.
• Blue: A dark metallic gray, often as a blue merle or speckled (with black). Kerry Blue Terriers, Australian Silky Terriers, Bearded Collies, and Australian Shepherds are among many breeds that come in blue.
• Brown: Includes dark mahogany, midtone brown, gray-brown, and very dark brown.
• Cream: Depending on the breed and individual, ranges from white through ivory and blond, often occurring with or beneath lemon, yellow, and sable.
• Gold: Rich reddish-yellow, as in a Golden Retriever; often includes colors such as yellow-gold, lion-colored, fawn, apricot, wheaten, tawny, yellow-red, straw, mustard, and sandy.
• Gray: Pale to dark gray, including silver; can be mixed with other colors or various shades to create sandy pepper, pepper, grizzle, blue-black gray, or silver-fawn.
• Lemon: A very pale yellow or wheaten color which is not present at birth (the puppies are born white) but gradually becomes apparent, usually during the first six months of life.
• Liver: A reddish brown somewhat the color of cinnamon or bronze; the breed often determines whether "liver", "chocolate", "brown", or "red" is used to describe the color, as in a liver German Shorthaired Pointer or a chocolate Labrador Retriever.
• Red: Reminiscent of reddish woods such as cherry or mahogany; also tawny, chestnut, orange, rusty, and red-gold.
• Sable: Black-tipped hairs; the background color can be gold, silver, gray, or tan.
• Tricolor: Consisting of three colors; usually black, tan, and white or liver, tan, and white; for example, the Smooth Collie or the Sheltie.
• Wheaten: Pale yellow or fawn, like the color of ripe wheat
• White: Distinct from albino dogs.
• Yellow: Yellowish-gold tan, as in a yellow Labrador Retriever.

Coat patterns include:

• Brindle: A mixture of black with brown, tan, or gold; usually in a "tiger stripe" pattern
• Harlequin: "Torn" patches of black on white; only the Great Dane exhibits this pattern
• Merle: Marbled coat with darker patches and spots of the specified color; for example, a blue merle is marbled gray and blue with black and sometimes white patches; a red (or liver) merle has deep red or brown on lighter red, often with white or black mixed in.
• Particolor: Two-colored coat with the colors appearing in patches in roughly equal quantiles (in breeds where this is an allowed coat color; in breeds where patches of white are considered undesirable, a dog showing even a small patch of white might be classified as a particolor).

Coat textures vary tremendously, so that some coats make the dogs more cuddly and others make them impervious to cold water. Densely furred breeds such as most sled dogs and Spitz types can have up to 600 hairs per inch, while fine-haired breeds such as the Yorkshire Terrier can have as few as 100, and the "hairless" breeds such as the Mexican Hairless have none on parts of their bodies. The texture of the coat often depends on the distribution and the length of the two parts of a dog's coat, its thick, warm undercoat (or down) and its, rougher somewhat weather-resistant outer coat (topcoat), also referred to as guard hairs. Breeds with soft coats often have more or longer undercoat hairs than guard hairs; rough-textured coats often have more or longer guard hairs. Textures include:

• Double-coated: Having a thick, warm, short undercoat (or down) that is usually dense enough to resist penetration by water and a stronger, rougher weather-resistant outer coat (topcoat), also referred to as guard hairs. Most other coat types are also double coated.
• Single-coated: Lacking an undercoat.

• Smooth-coated: "Smooth" to the eye and touch.
• Wire-haired: Also called broken-coated. The harsh outer guard hairs are prominent, providing excellent weather protection for hunting dogs such as the Border Terrier or Wirehaired Pointing Griffon.

• Long-haired: Hair longer than an inch or so.
• Short-haired: Hair around an inch or so long.

• Corded coat: for example, see Puli

Ears

Dogs ears come in a variety of sizes, shapes, lengths, position on the head, and amount and type of droop. Every variation has a term, including:

• Bat ear: Erect, broad next to the head and rounded at the tip.
• Button ear: A smaller ear where the tip folds forward nearly to the skull, forming a V, such as the Jack Russell Terrier.
• Cropped ear: Shaped by cutting; see docking.
• Drop ear: An ear that folds and droops close to the head, such as most scent hounds'. Also called a pendant ear.
• Natural: Like a wolf's.
• Prick ear: Erect and pointed; also called pricked or erect.
• Rose ear: A very small drop ear that folds back; typical of many sight hounds and the English Bulldog.
• Semiprick ear: A prick ear where the tip just begins to fold forward, such as with the Rough Collie.

Tails

As with ears, tails come in a tremendous variety of shapes, lengths, amount of fur, and tailset (positions). Among them:

• Corkscrew: Short and twisted, such as a Pug
• Docked: Shortened by surgery or other method, usually two or three days after birth; see docking
• Odd: Twisted, but not short. Uncommon. Tibetan Terriers have odd tails.
• Saber: Carried in a slight curve like that of a saber
• Sickle: Carried out and up in a semicircle like a sickle
• Squirrel: Carried high and towards the head, often with the tip curving even further towards the head.
• Wheel: Carried up and over the back in a broad curve, resembling a wheel.

Reference

• The New Encyclopedia of the Dog, Bruce Fogle DVM, 2000

Anatomy

Like most predatory mammals, the dog has powerful muscles, a cardiovascular system that supports both sprinting and endurance, and teeth for catching, holding, and tearing.

The dog's ancestral skeleton provided the ability to run and leap. Although selective breeding has changed the appearance of many breeds, all dogs retain the basic ingredients from their distant ancestors. Dogs have disconnected shoulder bones (absent the collar bone of the human skeleton) that allow a greater stride length for running and leaping. They walk on four toes, front and back, and most have vestigial dewclaws on their front legs.

The dog's ancestor was about the size of a Dingo, and its skeleton took about 10 months to mature. Today's toy breeds have skeletons that mature in only a few months, while giant breeds such as the Mastiffs take 16 to 18 months for the skeleton to mature. Dwarfism has affected the proportions of some breeds' skeleton, as in the Basset Hound.

Ancestry and history of domestication

Molecular systematics indicate that the domestic dog is descended from a wolf-like ancestor, and dogs and wolves can still interbreed. The domestication of the dog probably occurred at least 14,000 years ago, and perhaps long before that. There is archaeological evidence of dog remains, showing the characteristic morphological differences from wolves, from at least 14,000 years ago, while wolf remains have been found in association with hominid remains that are at least 400,000 years old. The molecular genetic data suggest that the domestic lineage separated from modern wolves around 150,000 years ago (Vilà et al, 1997). In the early 2000s, some research (http://www.amonline.net.au/archive.cfm?id=716) indicated that domestication in fact had already begun to occur as early as 100,000 years ago.

Dogs were, and are, valued for their aid in hunting. Dog burials at the Mesolithic cemetery of Svaerdborg in Denmark indicate that in ancient Europe, dogs were valued companions.

Some evidence suggests that several varieties of ancient wolves contributed to the domestic dog, with deliberate or unintentional interbreeding taking traits from one or more of the ancestral wolf lines. Although all wolves belong to the species Canis lupus, there are (or were) many subspecies that had evolved somewhat distinctive appearance, social structure, and other traits. For example, the Japanese wolf, which became extinct in the early 20th century, was much smaller than most wolves, generally had a gray coat with reddish underbelly, and possibly had a more solitary hunting habit; the North American wolf, which still exists in limited ranges, is much larger than many wolf subspecies, displays many coat colors from nearly white through solid black, and exhibits a complex social structure involving highly formulaic dominance and submission rituals.

The Indian or Asian wolf probably led to the development of more breeds of dogs than other subspecies. Many of today's wild dogs, such as the dingo, the dhole and pariah dogs, are descended from this wolf, along with sighthounds such as the Greyhound. Recent genetic evidence (http://www.abc.net.au/rn/science/ss/stories/s728909.htm) shows that most modern dog breeds are related to Asian canines, contradicting earlier hypotheses that the dog, like humans, had evolved originally in Africa. The Asian wolf also likely interbred with descendants of the European wolf to create the Mastiffs—the Tibetan Mastiff being an example of a very ancient breed—leading eventually to the development of such diverse breeds as the Pug, the Saint Bernard, and the Bloodhound.

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 a 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 North American wolf is a direct ancestor to most, if not all, of the North American northern sled dog types; this mixing and crossing still goes on today with dogs living in the Arctic where the attributes of the wolf that enable it to survive in a hostile environment are still valued. Additionally, accidental crossbreeding occurs simply because dogs and wolves live in the same environment.

Current research indicates that domestication, or the attributes of a domesticated animal, can occur much more quickly (http://www.amsci.org/amsci/articles/99articles/Trut.html#26879) than previously believed, even within a human generation or two with determined selective breeding. It is also now generally believed that initial domestication was not attained deliberately by human intervention but through natural selection: wild canines who scavenged around human habitation received more food than their more skittish counterparts; those who attacked people or their children were probably killed or driven away, while those more tolerant animals survived, and so on.

Dog society

Dogs thrive in small social groups or packs which, from their viewpoint, includes humans. Dog packs are characterized by companionate hierarchy, in which each individual has a rank, and in which there is intense loyalty within the group. Dogs thrive in human society because their relationships with humans mimic their natural social patterns. The dog is always aware of its rank relative to other individuals in the group. An assertive dog may consider itself the alpha animal, considering its human master to be subordinate.

Dominance and submission

Dogs, like wolves, establish a hierarchy through aggressive play and roughhousing along a continuum of dominance and submission. When kept as pets, dogs include humans in this hierarchy. It is important for successful socialization that puppies participate with their littermates in learning to relate to other dogs. Dogs learn to successfully relate to other dogs by keeping the peace rather than constantly fighting to reestablish this hierarchy.

Dominance behavior

Dominant dogs generally take the initiative and are more active than less dominant dogs. Displays of dominance include standing above or over other dogs, placing a paw on other dogs, holding the tail and ears erect, looking directly at other dogs, circling and sniffing other dogs, growling if the other dog moves, and aggressive marking of territory with urine. Submissive displays mirror dominant displays and include adopting a posture that is lower than other dogs, such as crouching, rolling over on the back and exposing the abdomen, lowering the tail—even tucking it beneath the legs, flattening of the ears, averting the gaze, nervously licking or swallowing, dribbling of urine, and freezing or fleeing when other dogs are encountered.

Ideally, the dominant/submissive social structure of dogs avoids conflict and enforces social stability. Poorly socialized dogs who are inept at establishing dominance hierarchy may become involved in excess conflicts, especially from a human viewpoint. People who misunderstand dog behavior or who have inadvertently placed themselves in a disadvantageous position within the dominance submissive hierarchy can find themselves participants in similar conflicts with the animal(s).

It is problematic to anthropomorphize the dominance/submission behavior of a pet or to mistake it for characteristics more appropriately applied to humans. It can be dangerous for a dog to be dominant relative to its master or mistress. By rewarding "bravery" or "boldness", there is a risk that in fulfilling a dog's wants it begins to feel it is the dominant pack member. Likewise, it can be dangerous for a dog to consider itself "the equal of any dog", because unnecessary and destructive conflict can result; rewarding a dog's aggressive behavior may eventually backfire. Likewise, submission in a dog is not necessarily an indication of a problem dog. Continuing to discipline a dog after it has adopted a submissive posture is contrary to a goal of obedience. From the dog's viewpoint, it has conceded the point and is communicating its acceptance of the owner's dominance.

Behavior when isolated

Dogs value the companionship of the others in their "pack" and are sometimes distressed if they are separated from it. Typical reactions when a dog is separated from the pack are barking, howling, digging, and chewing. These activities may distress humans when they need to leave dogs alone for a period of time. However, this behavior, called separation anxiety, can be overcome with training, or at least decreased to the point where it becomes manageable. If young puppies are habituated to periods alone from an early age, this can normally be prevented entirely.

Favorite activities

Dogs enjoy spending time with and interacting with other dogs. Roughhousing and chasing one another are favorite activities. Off-leash dog parks can be good places for dogs to exercise and interact with other dogs. When seeking relaxation, dogs enjoy lying about with their companions, favoring spots with a good view of their surroundings.

Dog breeds

There are numerous dog breeds, 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. Moreover, 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. Some groups use a definition that ultimately requires extreme in-breeding to qualify. Dogs that are bred in this manner often end up with severe health problems. Other reorganizations define a breed more loosely, such that an individual may be considered of one breed as long as, say, three of its grandparents were of that breed. These considerations come into play among breeders who enter their dogs in dog shows. Purebred dogs frequently suffer from serious inherited health and/or behavioral problems. This is by no means true of the majority of purebred dogs, and the same problems can occur in populations of mixed breed dogs. Even prize-winning purebred dogs are sometimes possessed of crippling genetic defects due to inbreeding.

In February 2004, the Canine Studies Institute in Aurora, Ohio, managed to arrange all breeds of dog into ten categories, according to Darwinian Evolutionary principles. [1] (http://news.independent.co.uk/world/science_medical/story.jsp?story=491197)

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.

Mixed-breed dogs are dogs that do not belong to specific breeds, being mixtures of two or more. 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.

Interactions between dogs and humans

The relationship between dogs and humans is ancient. Dogs serve humans in many ways.

Dogs as working partners

There are guard dogs, hunting dogs, and herding dogs. Dogs have served as guides for the blind, as commandos, and have flown into outer space (see Laika). Most modern working dogs are put in positions which capitalize on their sensory or strength and endurance advantages over normal humans.

For example, a new and particularly effective role of working dogs is that of the drug- or bomb-sniffing dog. All canines have olfactory sensitivity thousands or millions of times more sensitive than humans. This allows them to pick up on the subtle smells of distinctive chemicals, such as cannabis or plastic explosive. Airport security frequently tours concourses and baggage areas with a dog trained to respond to such chemicals.

K-9 police units typically feature a long-term human-canine team, in which the dog is trained to home in on the scents of particular people, and to facilitate their arrest once located. Most criminals find being wrestled to the ground by an aggressive dog much more frightening than being tackled by a human. Such dogs are also frequently used to find missing persons, especially in the wilderness.

Several cities in Italy are experimenting with working dogs as rescue swimmers. In this situation, a strong and well-trained dog is equipped with flotation devices and dropped in the water near a floundering swimmer. The swimmer then grabs onto the dog, and the animal tows the swimmer to shore. The Newfoundland has long been used for water rescue, not only on shore, but from fishing boats as well.

Dogs are commonly used as search and rescue workers in cases of disasters. The St. Bernard has been historically used for such purposes in Europe in the case of avalanche. In the aftermath of the 9-11 attacks in New York, rescue dogs were brought in to search for survivors in the rubble. Some of the dogs became so disturbed at being unable to find any survivors that people had to be "planted" for the dogs to find so that they did not become depressed at their failure.

Dogs as hunting/sporting partners

Many people compete with their dogs in a variety of dog sports, including agility, flyball, and many others. This often strengthens the bond between human and dog, since they must trust one another in a variety of environments and must learn how the other works and thinks.

Setters in particular have a long history as upland gun dogs. They have a native ability to discover and "hold" upland game birds; to freeze them momentarily on the ground with their silent, elongated pointing stance. Once the hunter approaches, at his command they will flush the birds to fly and for the hunter to shoot at.

As water dogs, the retrievers are unsurpassed. They can spend long hours in a duck blind and, after the hunter has fired at multiple ducks or geese, they can visually spot and remember the location of downed birds. At command, they dive into the icy water, swim out and retrieve the birds one by one. They can follow hand, verbal, and whistle commands at great distance as the hunter directs them to the downed bird. They typically have large, gentle muzzles to mitigate any potential damage to the game.

When trained, beagles are particularly adept at chasing through thick briars and brush to chase rabbits. Many hound breeds are excellent at treeing raccoons during hunting season.

Hunters with dogs report the satisfaction that the dogs seem to exhibit. Excitement is evident as they see the hunters load weapons, take to the field, and begin the hunt.

Dogs as pets

Relationships between humans and dogs are often characterized by strong emotional bonds. Consequently, dogs are popular as pets and companions, independent of any utilitarian considerations. Many dog owners consider having unconditional acceptance from a friend who is always happy to see them to be quite utilitarian, particularly if the dog also leads them to regular exercise. Dogs are quite dependent on human companionship and may suffer poor health without it.

Some research has shown that dogs are able to convey a depth of emotion not seen to the same extent in any other animal; this is purportedly due to their closely-knit development with modern man, and the survival-benefits of such communication as dogs became more dependent on humans for sustenance.

Nevertheless, it is often unwise to anthropomorphize the responses of dogs. Despite understandably positive interpretations by dog owners, it is questionable whether these animals are truly capable of feeling emotions on a human level. More research is needed to determine the intelligence level of dogs, and the motivations behind their responses to their masters.

Dogs as food

Main article: Taboo meat

In some places (such as parts of East Asia) dogs are raised for their meat, causing friction with people who keep dogs as pets. In times of great stress, such as when the Vikings of Greenland starved to death in the "little iceage", humans have been known to eat their pets.

Dog reproduction

Unlike undomesticated canine species, where the females typically come into estrus (also called in season or in heat) once a year, usually in late winter, and bear one litter of young, the female of the domestic dog can come into season at any time of the year and usually twice a year. Most bitches 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 rather than age, with the different maturation rates of the various sizes of dogs accounting for this variation in age of first season. The amount of time between cycles varies greatly among different dogs, but a given dog's cycle tends to be consistent through her life.

Dogs bear their litters roughly 9 weeks after insemination.

An average litter consists of about six puppies, especially for breeds that have not strayed too far from their wild ancestors. However, litters of many more or only one or two puppies are also common. Some breeds have a tendency to produce very large litters. Since a mother can provide milk for only a few of those puppies, humans must assist in the care and feeding when the litter exceeds eight or so.

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.

Puppies often have characteristics that do not last beyond early puppyhood. For example, eyes are often blue when they first open but change to other colors as the puppy matures. As another example, Kerry Blue Terrier puppies have black coats when they are born and their distinctive "blue" color appears gradually as the puppy nears maturity. The ears of erect-eared breeds such as the German Shepherd Dog are softly folded at birth but straighten as the puppy grows.

Dog experts advise that dogs not intended for further breeding should be spayed or neutered so that they do not have undesired puppies, which are often abandoned or are euthanized due to lack of space and resources in shelters. Abandoned dogs often go feral and form predatory packs that attack livestock and occasionally also prove dangerous to humans. Spaying and neutering can also help prevent diseases such as breast cancer and prostate cancer that occur as the unneutered animal ages (due to hormonal changes). Also, it is not required for a female dog to either experience a heat cycle or have puppies before spaying; likewise, a male dog does not need the experience of mating before neutering. These myths account for numerous health problems and unwanted puppies.

Dangers

As evidenced by their attacks on other creatures, both wild and domestic, dogs can be voracious, aggressive, predators. Their sharp teeth and powerful jaws can inflict serious injuries; their sharp claws have powerful muscles behind them. Scratches from dogs are easily infected. Although confrontations between man and dog ordinarily stop well short of harm, human ignorance or stupidity can lead to severe injury from even the most well-tempered dog. Contrary to myth, barking dogs can bite a person who fails to recognize the warning. Likewise, a wagging tail indicates an excited state, which is not always a result of "happy" excitation; a wagging dog is not equivalent to a purring cat.

Some behaviors that people (especially people unfamiliar with dogs) might display could potentially evoke a predatory or aggressive response from a dog. These include (but are not limited to):

• Attacking a dog
• Attempting to take food away from a dog
• Threatening a puppy in the presence of an adult dog, especially its mother
• Looking a dog directly in the eyes, especially when on the same level of the dog (such as small children)
• Approaching a sick or injured dog
• Running away from a dog: the chase-and-catch instinct in wolves is not fully lost, and most dogs can outrun and overtake the average human
• Ignoring "Beware of Dog" signs: trained attack dogs, unlike most dogs, may attack an intruder without warning

Although most dogs are not inherently aggressive (unless they are feral, trained to attack intruders, threatened or provoked), it is important to remember that they are predatory by nature and instinct is something that never disappears. This is not to say that all of the above behaviors will always result in injury. In fact, some dog experts advocate acclimating a puppy to a removal of its food in order that its handler can, later in life, do so if needed (the dog is eating something dangerous, for example) without as high a degree of danger.

Small children are especially prone to provoking dogs, in part because their pre-ambulatory movements suggest similarities to prey that dogs instinctively attack. Also, young children may well unintentionally provoke the dog (pulling on ears or tails is common) because they do not know any better. Because of a dog's pack instincts, they may also attempt to establish a dominant position over a child, this should not be allowed. To avoid potential conflicts, children should be kept separate from any dog in the absence of adult supervision until the dog has shown its acceptance of the child in its midst and the child has shown an understanding of appropriate behavior.

Miscellaneous facts

Treats

Many dogs consider anything given them directly by hand to be a treat, even the food they are accustomed to at meal time. Special dog treats are not necessary for such animals. Care should also be taken to avoid dropping small but inedible objects (such as marbles, coins, engagement rings, etc.) around such dogs.

Dogs and the Zodiac

The Dog is one of the 12-year cycle of animals which appear in the Chinese zodiac related to the Chinese calendar. It is thought that each animal is associated with certain personality traits. See: Dog (Zodiac).

Sirius, the Dog Star, is the brightest star in the night sky.

Dogs and perspiration

A common misconception is that dogs do not sweat. Primarily, dogs regulate their body temperature in a completely different way, through their tongue. That is why after a dog has been running or on a hot day you will see its mouth wide open and tongue hanging out. In addition, dogs effectively sweat through the pads of their feet. Again, on a warm day and after exercise, a dog's naturally wet footprints might be visible on a smooth floor.

A fine sense of direction

It has been observed that a lost dog can often find its way home, sometimes traveling over long distances. It is believed that dogs and cats know the correct position of the sun at their homes. When lost, the animal notes the angle of the sun as it travels, and moves in the direction that indicates that the angle is becoming correct.

Diseases and ailments

Some diseases, ailments, and poisons are common to both humans and dogs; others are different.

Transferable diseases

Most diseases that affect dogs or humans are not transferable between the two species. There are some exceptions:

• Rabies, or Hydrophobia, is an often fatal disease that can be transmitted to humans by the bite of certain animals, including dogs. Areas that do not have the disease, such as Australia or the U.S. state of Hawaii, have strict quarantine laws to keep their territories rabies-free. Areas that do have the disease usually require that dogs be vaccinated against rabies. A bite from an unknown dog should always be treated, given the potentially fatal consequences if the dog was rabid.
• Parasites, particularly worms such as tapeworms and roundworms, can be transmitted in a dog's saliva or feces.
• Leptospirosis is a bacterial disease that affects humans and animals. It is caused by bacteria of the genus Leptospira. Humans and dogs become infected through contact with water, food, or soil containing urine from infected animals. This may happen by swallowing contaminated food or water or through skin contact, especially with mucosal surfaces, such as the eyes or nose, or with broken skin.

Genetic ailments

Genetic conditions are a problem in some dogs, particularly purebreeds:

• Hip dysplasia primarily affects larger breeds.
• Luxating patellas can be a problem for smaller breeds.
• Genes for blindness or deafness seem to be carried by some breeds.

Parasites

Several types of parasites are commonly associated with dogs:

• Intestinal worms cause varying degrees of discomfort.
• Heartworm is a dog parasitoid. It is hard to eliminate and can be fatal; prevention, however, is easily achieved using medication.
• Fleas and ticks are common parasites for which there are many effective preventive measures.
• Various mites cause skin problems such as mange.

Dangerous foods

Some foods commonly enjoyed by humans are dangerous to dogs:

• Dogs like the flavor of chocolate, but chocolate in sufficient doses is lethally toxic to dogs (and horses and possibly cats). Chocolate contains theobromine, a chemical stimulant that, together with caffeine and theophylline, belongs to the group of methylxanthine alkaloids. Dogs are unable to metabolize theobromine effectively. If they eat chocolate, the theobromine can remain in their bloodstreams for up to 20 hours, and these animals may experience racing heartbeats, hallucinations, severe diarrhea, epileptic seizures, heart attacks, internal bleeding, and eventually death. A chocolate candy bar can be sufficient to make a small dog extremely ill or even kill it. In case of accidental intake of chocolate by a dog, contact a veterinarian or animal poison control immediately; it is commonly recommended to induce vomiting within two hours of ingestion.

Note:Carob treats are often available as dog treats; these are unrelated to chocolate and are safe.

• Grapes and raisins can cause acute renal failure in dogs. The exact mechanism is not known. As little as one raisin can be fatal to a ten pound dog and other dogs have eaten as much as a pound of grapes or raisins without ill effects. The dog usually vomits a few hours after consumption and begins showing signs of renal failure three to five days later.
• Onions and to a significantly lesser extent garlic contain thiosulfate which causes hemolytic anemia in dogs (and cats). Thiosulfate levels are not affected by cooking or processing. Small puppies have died of hemolytic anemia after being fed baby food containing onion powder. Occasional exposure to small amounts is usually not a problem, but continuous exposure to even small amounts can be a serious threat.
• Macadamia nuts can cause stiffness, tremors, hyperthermia, and abdominal pain. The exact mechanism is not known. Most dogs recover with supportive care when the source of exposure is removed.
• Alcoholic beverages pose much the same temptation and hazard to dogs as to humans.

Contact your veterinarian or the ASPCA Animal Poison Control Center (http://www.aspca.org/site/PageServer?pagename=apcc) in case of possible exposure.

Common unsafe consumption

Some dogs have a fondness for feline feces, and will raid a kitty litter box for "treats". This can be unsafe for the dog's health.

Feeding table scraps to a dog is sometimes not recommended. Dogs get ample correct nutrition from prepared dogfood. Otherwise, just as in humans, their diet must consist of the appropriate mix of vegetables, carbohydrates, and proteins, with the appropriate mix to provide all of the minerals and vitamins that they need. A human diet is not ideal for a dog; in addition, table scraps often consist of fatty scraps rather than meat, which is no better for dogs than it is for humans. Lastly, many people overfeed their dogs by giving them all the table scraps that the dogs will eat—which is usually all the table scraps they are fed, which is often too much food.

Common household chemicals

Some common household chemicals are particularly dangerous to dogs:

• Antifreeze, due to its sweet taste, poses an extreme danger of poisoning to a dog that either drinks from a spill or licks it off its fur. It can cause seizures and death. Dogs should not be allowed access to any place in which an antifreeze leak or spill has happened until the spill is completely cleaned out. Some brands of antifreeze are marketed as being less harmful or less attractive to animals.

Additional health information

For additional information on dog health, see Category:Dog health.

Intelligence

Dogs are generally valued for their intelligence. Anecdotal evidence suggests that dogs have a reasonably high intelligence. For a detailed discussion on what dog intelligence is, see dog intelligence.

References and further reading

• Abrantes, Roger (1999). Dogs Home Alone. Wakan Tanka, 46 pages. ISBN 0966048423 (paperback).
• ¹A&E Television Networks (1998). Big Dogs, Little Dogs: The companion volume to the A&E special presentation", A Lookout Book, GT Publishing. ISBN 1-57719-353-9 (hardcover).
• ²Alderton, David (1984). The Dog, Chartwell Books. ISBN 0-89009-786-0.
• Donaldson, Jean (1997). The Culture Clash. James & Kenneth Publishers. ISBN 1888047054 (paperback).
• Milani, Myrna M. (1986). The Body Language and Emotion of Dogs: A practical guide to the Physical and Behavioral Displays Owners and Dogs Exchange and How to Use Them to Create a Lasting Bond, William Morrow, 283 pages. ISBN 0688128416 (trade paperback).
• Pfaffenberger, Clare (1971). New Knowledge of Dog Behavior. Wiley, ISBN 0876057040 (hardcover); Dogwise Publications, 2001, 208 pages, ISBN 1929242042 (paperback).
• Shook, Larry (1995). "Breeders Can Hazardous to Health",The Puppy Report: How to Select a Healthy, Happy Dog, Chapter Two, pp. 13–34. Ballantine, 130 pages, ISBN 0345384393 (mass market paperback); Globe Pequot, 1992, ISBN 1558211403 (hardcover; this is much cheaper should you buy).
• Shook, Larry (1995). The Puppy Report: How to Select a Healthy, Happy Dog, Chapter Four, "Hereditary Problems in Purebred Dogs", pp. 57–72. Ballantine, 130 pages, ISBN 0345384393 (mass market paperback); Globe Pequot, 1992, ISBN 1558211403 (hardcover; this is much cheaper should you buy).
• Thomas, Elizabeth Marshall (1993). The Hidden Life of Dogs (hardcover), A Peter Davison Book, Houghton Mifflin. ISBN 0395669588.
• Vilà, Caries; Savolainen, Peter; Maldonado, Jesus E.; Amorim, Isabel R.; Rice, John E.; Honeycutt, Rodney L.; Crandall, Keith A.; Lundeberg, Joakim; Wayne, Robert K. (1997). Multiple and ancient origins of the domestic dog. (http://www.mnh.si.edu/GeneticsLab/StaffPage/MaldonadoJ/PublicationsCV/Science_Dog_Paper.pdf) Science 276, pp. 1687–1689.

Related topics

• List of dog topics
• List of historical dogs
• List of fictional dogs

External links

• Wikibooks:How to choose your pet and take care of it
• wikibooks:Dog Care
• Dogpatch (http://www.dogpatch.org/dogs) Considerable info about breeds, training, sports, and all other things dog
• Dog Training (http://www.dogtraininghq.com) Resources for dog owners to train their dogs correctly.
• National Geographic News (http://news.nationalgeographic.com/news/2004/02/0209_040209_dogsdogsdogs.html) Many articles and photos about dogs
• Genetics and origins:
  • "Multiple and Ancient Origins of the Domestic Dog" (http://www.idir.net/~wolf2dog/wayne1.htm)
  • Canid Genetics (http://www.fiu.edu/~milesk/Genetics.htm)
  • "Dog Genome Sequencing" (http://www.nhgri.nih.gov/11008069) - NHGRI
  • "World's dogs are descended from Asian wolves" (http://www.ananova.com/news/story/sm_713600.html)

• Health and medical:
  • Information about the third eyelid of dogs, and the problem of Kertao, or "dry eye". (http://www.petcat.us/questions.