Dogs

? Domestic Dog Conservation status: Domesticated
Labrador Retriever a breed of domestic dog
Scientific classification
Kingdom: Animalia Phylum: Chordata Subphylum: Vertabrata Class: Mammalia Order: Carnivora Family: Canidae Genus: Canis Species: C. lupus Subspecies: C. l. familiaris
Trinomial name
Canis lupus familiaris (Linnaeus, 1758)

The dog is a canine mammal of the Order Carnivora. It has been argued the dog has been domesticated for 12,000 years, but perhaps for as long as 150,000 years based on recent genetic evidence. In this time, the dog has developed into hundreds of breeds with a great degree of variation. For example, heights range from just a few inches (such as the Chihuahua) to nearly 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 pack hunters; this similarity in their overall behavioral design accounts for their trainability, playfulness, and ability to fit into human households and social situations. 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 sobriquet "man's best friend." Conversely, some cultures consider dogs to be unclean. In other cultures, some dogs are used as food.

Terminology

Puppies engage in teething on almost anything.

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.
• Bitch is a female dog who is capable of breeding or has bred.
• Pack is used to denote a group of dogs.
• Puppy is a juvenile dog.
• Pooch, Poochie, Dogay, Pup, Pupsie, Doggy or Doggie are all informal and affectionate terms for a dog often used by children.

Many additional terms are used for dogs that are not purebred; see Terms for mixed-breed dogs.

Physical characteristics

Although selective breeding has changed the appearance of many breeds, all dogs retain the basic ingredients from their distant ancestors. 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. Its skeleton provides the ability to run and leap. They have small, tight feet, walking on their toes.

For details about dog appearance and physical attributes, see dog anatomy.

Intelligence

Among dog lovers, 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.

Diet

This English Springer Spaniel is enjoying a bone.

Presently, there is academic discussion as to whether domestic dogs are omnivores or carnivores. 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 a cat, a dog is not dependent on meat protein in order to fulfill its 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 its diet. Wild canines not only eat available plants to obtain key amino acids, but may also obtain nutrients from vegetable matter from the stomach contents of their herbivorous prey. Domestic dogs can survive healthily on a reasonable and carefully designed vegetarian diet, particularly if eggs and milk products are included. In the wild these diets are typically pursued in the absence of available meat. It has also been noted that extremely stressful conditions, such as the Iditarod race and scientific studies of similar conditions, suggest that high-protein diets including meat help prevent damage to muscle tissue. This research is also true of other mammals.

Dangerous substances

Some foods commonly enjoyed by humans are dangerous to dogs, including chocolate (Theobromine poisoning), onions, grapes and raisins, Macadamia nuts, and hops. Also, human medications, such as acetaminophen/paracetamol (Tylenol), can be highly toxic.

Dogs also may find some poisons attractive, including antifreeze and snail bait.

Reproduction

Among professional breeders, dogs are only allowed to mate for a specific purpose. Sometimes dogs are bred to create puppies to sell, or sometimes to carry on an award-winning purebred line. Breeders who do this are usually experienced in this process. Dog breeders have access to records which allow them to accurately guess which characteristics will "breed true" in a particular dog. Dog breeders also have accurate information on the complexities of the reproductive process for the breed of dog that they are accustomed to handling. Dog owners may accidently allow their pets to breed without regard to bloodlines.

Fertility

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 behaviours 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 also called in season or in heat. Conversely, undomesticated canine species experience estrus once a year, typically in late winter.

Menarche

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. The different rates of maturation are responsible for the menarche, not the chronological age.

Pregnancy and litters

Catahoula Leopard Dog nursing litter of puppies

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 favoured for economic reasons. Dogs bear their litters roughly 9 weeks after fertilization. An average litter consists of about six puppies, though this number may vary wildly based on the breed of dog. Since a mother can only provide nutrients and care to a limited number of offspring, humans must assist in the care and feeding when the litter exceeds approximately eight puppies. 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.

Spaying and neutering

Dog experts advise that dogs not intended for further breeding should be spayed or neutered so that they do not have undesired puppies. Unwanted puppies are abandoned, eaten, or sometimes disposed of in an inhumane fashion. It is also common for adult stray dogs who are placed in animal shelters to be euthanized due to lack of space and resources. Spaying and neutering can also help prevent hormone-driven diseases such as breast cancer and prostate cancer, as well as undesired hormone-driven behaviors.

Contrary to myth, it is not required for a female dog to either experience a heat cycle or have puppies before spaying, and likewise, a male dog does not need the experience of mating before neutering; these myths are responsible for numerous unnecessary health problems and unwanted puppies. It should also be noted that a female dog may become pregnant prior to her first cycle and should be kept away from other male dogs, including littermates over the age of 4 months. Many veterinarians recommend that owners neuter/spay their pets around the age of 5 months.

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.

Sight

Dogs were thought to be dichromats and thus, by human standards, color blind.^{1, 2} New research is now being explored that suggests that dogs may actually see some colour, but not to the extent that humans do. 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}

Hearing

Dogs detect sounds as low as the 16 to 20 Hz frequency range (compared to 20 to 70 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 a human can, and they can hear sounds up to four times the distance that humans can.

Scenting

Dogs are predators suited to chasing after, leaping at, and killing prey. (pictured: Weimaraner)

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. Other than the oversimplified obvious, i.e. chemical compounds that affect chemical sensors in the nose, what a dog actually detects when he is scenting is not really 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.

Direction and spatial sense

It has been observed that a lost dog can often find its way home, sometimes traveling over long distances.

Weather detection

Dogs also have the ability to sense inclement weather (mainly thunderstorms) many miles away. This is due to their keen ability to detect fluctuations in barometric pressure and can explain a dog's anxiety before and during a storm. The evolutionary ability of sensing weather can be traced back to when wolves used it to move the pack into proper shelter before a dangerous storm.

Diseases and ailments

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.

For additional information on these and other related topics, see dog health and Category:Dog health.

Diseases

Diseases commonly associated with dogs include rabies (hydrophobia), canine parvovirus, and canine distemper, although there are many others.

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.

Behaviour

Some dogs can be trained to retrieve

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. The requirements of coordinating complex social behavior requires that canines have the ability to sense and deliver a wide variety of cues via body language, more so than for even humans, who can use language for the same purpose. Physiologically, this correlates with such features as a large number of nerves innervating the facial muscles of dogs, allowing subtle control of a wide variety of facial expressions; in contrast to cats, for instance, who have many fewer nerves governing their facial muscles, resulting in a smaller repertoire or "vocabulary" of expressions. This ability to read and deliver nonverbal cues makes dogs expert at reading human beings, as well, often even more so than other humans are, who rely on language. Most dog owners have a large collection of stories about their dogs recognizing individuals by their footsteps outside the door, and so on.

Interactions between Dogs and Humans

Main article: Dog society

The relationship between dogs and humans is rooted in history and dogs coexist with humans in a variety of ways. Dogs thrive in small social groups or packs which, from their viewpoint, can include humans. Dog society can be thought of as dog packs characterized by a 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.

Treats

Many dogs consider anything given to 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, rings, etc.) around such dogs. Some food considered as treats for humans, such as chocolate and raisins, are poisonous to dogs.

If a dog has something valuable (rings, money, irreplaceable items), a treat should be used to "barter" with the dog to retrieve the stolen item. Chasing a dog will encourage play behavior, which may cause the item to be swallowed or destroyed.

Dogs as working partners

Many breeds of dogs, but not least German Shepherd, Labrador Retriever, and Border Collie are commonly used as working dogs. There are service dogs, 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 and other Russian space dogs). Most modern working dogs are put in positions which capitalize on their sensory or strength and endurance advantages over normal humans. Dogs are also used for searching for or rescuing people and animals, such as in avalanches, at disaster sites, and for missing people or pets.

Dogs as hunting and 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 after 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

A 9 year old English Collie cross. Some say mongrels make the best 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. Empirically, dogs are quite dependent on human companionship and may suffer poor health in its absence. Many dogs are reported to have separation anxiety if its owner is away for an extended period of time.

Some research demonstrates 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 food and drink

In some countries, certain breeds of dogs are raised for their meat. Often times, this causes friction with societies that want a complete ban on consumption of dog meat. In times of great stress, such as when the Vikings of Greenland starved to death at the start of the Little Ice Age (14th century - 19th century), humans have been known to eat their pets.

In some small Chinese provincial towns, there is a special breed of dog (called "Black Dogs" in Chinese language) mainly used for cuisine. Almost any breed of dog is eaten in some parts of China however in major cities like Beijing, Shanghai and Hong Kong, consumption of dog meat is prohibited by law and perpetrators will face heavy fines if caught. While some Western dog lovers may claim that dog is regarded as a "lower source of food," many Asians, in actuality, regard it as a luxury food, costing much more than other types of meat. However if dog meat is served to house guests that can be seen as an insult towards the guest, since dog meat is preferable to be eaten privately or at restaurants.

The people of Korea have been known to eat certain breeds of dogs as well. This led to issues during the 2002 Football World Cup when South Korea was hosting the game with the local government keen to obscure this practice from visiting countries.

Attacks on humans and livestock

Humans have a tendency to anthropomorphize animals, particularly pets such as dogs, which are generally portrayed as being "man's best friend". Animals are often given attributes such as "loyal", "cute", and "guardian", but these all have the potential to lure people into a false sense of security.

After thousands of years of domestication and selective breeding for dogs whose aggression towards humans goes no further than a ferocious bark that strongly indicates dislike of a human behavior, most dogs are unlikely to attack people. However, their sharp teeth and claws can inflict injury in an attack; a large dog can knock a human down. Provocation can range from something as seemingly innocuous as a toddler pulling a dog's tail, in which case the dog might nip to discourage the behavior, to something completely transparent to humans, such as an odor or a movement that sets a dog off, to blatant human aggression or violence towards a dog, causing it to defend itself. There are hundreds of shades of provocation that may or may not lead to an attack upon a human. Canine aggression upon humans is ordinarily not tolerated, but any human aggression against an animal having formidable means of self-defense is foolhardy in the extreme.

With formidable skills and weapons as hunters as well as large and unfussy appetites, dogs often menace livestock and wildlife. In most jurisdictions, dogs are destroyed for killing other creatures, so dogs should be prevented from any encounter with livestock or wildlife that might lead to a predatory response. The same creatures that wolves, coyotes, and foxes, attack as prey, especially sheep and poultry, are similarly attractive prey to dogs.

For more information about attack provocations and attack behavior, see dog attacks.

Abandoned Dogs

Wild dogs are shot by farmers in an effort to protect livestock. Bodies are sometimes tied to fences as warning to other dogs, especially in rural United States and Canada. Abandoned domestic dogs who become feral are particularly dangerous; they lack the survival skills of wild canines, as well as the genetic and learned fear of the humans' world. Feral dogs often form predatory packs that attack livestock and occasionally also prove dangerous to humans.

Ancestry and history of domestication

This ancient mosaic shows a large dog with a collar hunting a lion.

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

The relationship between man 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 appear to 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 indicate 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 results must be reevaluated in light of recent findings showing that molecular clocks must be recalibrated to date geologically recent events, such as 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