Man's Best Friend
The dog is a canine carnivorous mammal that has been domesticated for at least 14,000 years and perhaps for as long as 150,000 years based on recent 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, and browns also 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. Working dogs of all kinds do traditional jobs such as herding and new jobs such as detecting contraband and helping the blind or disabled. 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 their loyalty has earned them the sobriquet "man's best friend".
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 are dichromats and thus, by human standards, color blind. 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-°.
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), 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 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 it must be motivated to continue this hard work for a long period of time.
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.
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 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 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. 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 single phenotypic characteristic that seems to separate dogs from wolves is the sickle tail-dogs who have tails tend to have an upward curve in the tail, whereas wolves' tails hang straight-the "brush tail"-similar to that of a fox. There are a few exceptions, such as the Great Pyrenees, which has a brush tail. However, wolves also have erect ears, and the Pyrenees has floppy ears.
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). 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. 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.
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.
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.
As evidenced by their attacks on other creatures, both wild and domestic, dogs are superpredators. Their sharp teeth and powerful jaws can inflict serious injuries; their sharp claws have powerful muscles behind them. Scratches from dogs are easily infected. Even without aggressive intent, by just acting boisterously, a dog of adequate size can knock down a person, possibly causing serious injury. All that protects man from an animal with such abilities to kill large prey is its temperament, without which large dogs singly or medium-sized dogs in groups would be nearly as dangerous as the big cats, animals with obvious similarities in behavior. Dogs are near-equals of Man in the food chain, and where the usual respect that two similarly-predatory animals have for each other breaks down, tragedy ensues for one or the other, as is true for wolves.
Formal and informal training, selective breeding, and society's response to dogs that prove dangerous combine to reduce the overall physical threat from dogs to a very low level with most confrontations between man and dog ending without injury. However, improperly managed confrontations can lead to severe injury from the most well-tempered dog, much as almost any human can be incited to violence given sufficiently serious provocation.
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