Sight

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

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 *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.

Dog

The dog (Canis lupus familiaris) is a subspecies of the wolf, a mammal of the Canidae family of the order Carnivora. The term encompasses both feral and domestic variants. It is also sometimes used to describe wild canids of other subspecies or species.

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); colors vary from white through grays (usually called blue) to black, and browns from light (tan) to dark ("red" or "chocolate") in a tremendous variation of patterns; and coats can be anything from very short to several centimeters long, from coarse hair to something akin to wool, straight or curly, or smooth.

Origins

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

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

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

Human relationships

Dogs, like humans, are highly social animals and this similarity in their overall behavioral 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". However, some cultures consider dogs to be unclean. In some parts of the world, dogs are raised as livestock to produce dog meat for human consumption. In many places, consumption of dog meat is discouraged by social convention or cultural taboo.

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. Being highly adaptable animals themselves, dogs have learned to do a great number of very eclectic jobs as man has required over the generations. Dogs are employed in various roles across the globe, proving invaluable assets in areas such as search-and-rescue; law enforcement (including attack dogs, sniffer dogs and tracking dogs); guards for livestock, people or property; herding; Arctic exploration sled-pullers; guiding the blind and acting as a pair of ears for the deaf; assisting with hunting, and a great many other roles which they may be trained to assume. Dogs are descended from wolves, and are also pack animals, making them easier than other animals to train because dogs' instincts are to obey. 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

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

Evaluation of a dog's intelligence

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

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

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

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

DOG HISTORY

The dog is part of a family of similar animals that include wolves, coyotes, foxes, jackals and wild hunting dogs such as the Dingo and African Wild Hunting Dog, who all share common characteristics. Many of these wild dogs have been claimed to be the domsetic dog's wild ancestor but the exact origins of the dog and domestication history of the dog are uncertain.

Paleontologists and archaeologists have determined that Miacis, a weasel-like animal, is the ancestor of the canids as well as other families such as bears, racoons, civets, hyaenas and cats. From Miacis evolved Cynodictis, a dog-like animal from which later evolved the dog family.

All canids share common characteristics - they bear live young, have similar dental structures, walk on their toes rather than the soles of their feet, and are homeothermic (able to maintain their body temperature at a constant level).

The domestic dog has been represented in art for many years with the earliest being sculptures of dogs found in Iraq and dating back to 6500 BC. Dog bones have been discovered dated at around 8300 BC in the USA, 7500 BC in the UK with similar finds in Czechoslovakia. One thing is certain, the domestic dog spread rapidly all over the world.

The dog's natural hunting instincts have been used by humans over the years to hunt a variety of prey in different environments and this led to the development of different groups of dogs, and ultimately to different dog breeds.

"Sight Hounds" or "Gaze Hounds" were an early group of dogs developed whose characteristics included a deep chest, long legs and a keen sense of sight. These dogs were used to spot prey from a distance and then to sprint swiftly and silently to run down prey in open, treeless countries. From this group dog breeds such as the Afghan, Saluki and Greyhound emerged.

"Scent Hounds" with an exceptional sense of smell provided by large noses with well opened nostrils were later developed in Europe. These dogs were not bred for speed but stamina, and were used to track and hunt prey over long periods of time. From this group of hounds dog breeds such as the Otterhound, Elkhound, Basset Hound and Dachshund emerged.

Hunting dogs were also developed, mostly in Britain, to hunt burrowing prey such as badgers, foxes and rabbits, and to control many types of vermin. These dogs needed to be feisty and energetic and so the group of dogs known as Terriers were developed. Most breeds of Terrier are descended from the Old English Black and Tan Terrier and the White English Terrier, both now extinct. Over the years two distinct types of terrier developed: smaller earth terriers with short legs who would go to ground after badgers, foxes and rabbits and larger terriers for hunting otters, water rats and wildlife that lived near rivers and around farms. Today many breeds of Terrier exist and these include the Fox Terrier, Welsh Terrier, Airedale Terrier and West Highland White Terrier.

Following the invention of the gun, dogs with sensitive noses were developed to locate and indicate the location of prey, to flush out prey or retrive the prey once shot which required a soft mouth. For this purpose Pointers and Retrievers were developed.

Although hunting has been responsible for the development of many dog breeds, dogs were also used to aid humans in protecting and working with other domesticated animals kept by man and so guard dogs and herding dogs were developed. In addition breeds were also developed to aid humans in other activities such as sled dogs, war dogs, dogs of burden, guide and rescue dogs and toy dogs developed as small companion dogs.

As a result of the wide diversity of roles in which the dog has been selectively bred to perform over the years many different breeds of dog emerged throughout the world and exist today.

Smell

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

Hearing

Dogs detect sounds as low as the 16 to 20Hz 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.Dogs respond to the last part of the word.