Dogs are carnivorous mammals presumed to be wolf descendants. Since prehistoric
times, dogs were domesticated as guardians and companions; they were valued for their intelligence,
docility and ability to bond. The Bible references them as flock guardians and home watchers. Then,
semi-wild canines wandered about devouring dead bodies and street remains. Specific characteristics
bred for specific functions created pure, mixed and partially domesticated varieties: sporting,
companionship, guarding, tracking or herding.
The dog (Canis lupus familiaris) is a domesticated subspecies of the wolf, a mammal of the Canidae
family of the order Carnivora. The term encompasses both feral and pet varieties and is also sometimes
used to describe wild canids of other subspecies or species. The domestic dog has been (and continues
to be) one of the most widely-kept working and companion animals in human history, as well as being a
food source in some cultures. There are estimated to be 400 million dogs in the world.
The dog has developed into hundreds of varied breeds. Height measured to the withers ranges from a
few inches in the Chihuahua to a few feet in the Great Dane; color varies from white through grays
(usually called blue) to black, and browns from light (tan) to dark ("red" or "chocolate") in a wide variation
of patterns; and, coats can be very short to many centimeters long, from coarse hair to something akin to
wool, straight or curly, or smooth.
Origin and Evolution
Based on DNA evidence, the wolf ancestors of modern dogs diverged from other wolves about 100,000 years ago, and dogs were domesticated from those wolf ancestors about 15,000 years ago. This date would make dogs the first species to be domesticated by humans. Evidence suggests that dogs were first domesticated in East Asia possibly China and some of the peoples who entered North America took dogs with them from Asia.
Ancestry and History of Domestication
Molecular systematics indicate that the domestic dog (Canis lupus familiaris) descends from one or more populations of wild wolves (Canis lupis).
The relationship with humans and canines has deep roots. Converging archaeology and genetic evidence indicates a time of domestication between 17,000 and 14,000 years ago. Fossil bones and genetic analysis of current and ancient dogs and wolf populations have not yet been able to conclusively determine whether all dogs descended from a single domestication event or whether dogs where domesticated independently in more than one location.
Development of Dog Breeds
There are numerous dog breeds with over 800 being recognized by various kennel clubs worldwide. 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 dogs relationship with humans over the last 10,000 or more years, but all modern breed are of relatively recent deviation. Many of these are the product of a deliberate process of artificial election. Because of this some breed are highly specialized, and there is extraordinary morphological diversity across different breeds. Despite these diversities, dogs are able to distinguish dogs from other kinds of animals.
Mixed-breed dogs or Mongrels (also called "mutts") are dogs that do not belong to specific breeds, being mixtures more than two in variant percentages. Mixed breed dogs and purebred dogs are both suitable as companions, pets, working dogs, or competitors in dog sports. Sometimes different breed dogs are deliberately bred to create crossbreeds such as the Cockapoo, a mixture of Cocker Spaniel and Miniature Poodle. Such deliberate crosses may display some degrees of hybrid vigor and other desirable traits, but may or may not inherit any of the desired traits of their parents, such as temperament or a particular coat color.
Physical Characteristics
Modern dog breed 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 attaching, holding, and tearing their food. Although selective breeding has changed the appearance of many breeds, all dogs retain basic traits from the distant ancestors. Like many other predatory mammals, the dog has powerful muscles, fused with bones, a cardiovascular system that supports both sprinting and endurance. Compared to the bone structure of the human foot, technically, dogs walk on their toes.
Like most mammals, dogs are dichromats and have color vision equivalent to red-green color blindness in humans.
Dogs detect sounds as low as the 16 - 20 Hz frequency range (compared to 20 - 70 Hz range for humans) and above 45 kHz (compared to 13 - 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 hear.
What information a dog actually detects when he is scenting is not perfectly understood. It now seems to be well established that dogs can distinguish two different types of scents: an air scent from some person or thing that has recently passed by, and a ground scent that remains detectable for a much longer period of time.
Behavior and Intelligence
Dogs are very social animals, but their personality and behavior vary with breed as well as with how they are treated by their owners and others who come in contact with them. It is not uncommon for dogs to attack humans and other animals, however, this is usually because of lack of care of improper upbringing by its owner. Dogs are valued for their intelligence. This intelligence is expressed differently with different breeds and individual however.
Human Relationship
Dogs are highly social animals. This can account for their trainability, playfulness, and ability to fit into human households and social situations. These attributes have earned dogs a unique position in the realm of interspecies relationships despite being one of the most effective, voracious, and potentially dangerous predators. Dogs and humans at times co-operate in some of the most effective hunting in the animal world, in that context, dogs are super predators.
The loyalty and devotion that dogs demonstrate as part of their natural instincts as pack animals closely mimic 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 owner 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 provides the opportunity to exhibit their natural skills. In many countries the most common and perhaps most important role of dogs is as companions.
Overpopulation - United States
According to the Humane Society of the United States, 3-4 million dogs and cats are euthanized each year in the United States and many more confined to cages in shelters because there are many more animals than there are homes. Spaying or castrating dogs helps keep overpopulation down. Local humane societies, SPCAs and other animal protection organizations urge people to neuter their pets and to adopt animals from shelters instead of purchasing them.
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Health
Dogs are susceptible to various diseases, aliments, and poisons, some of which affect humans in the same way, other of which are unique to dogs. Dogs, like all mammals, are also susceptible to heat exhaustion when dealing with high levels of humidity and/or extreme temperatures.
Infectious diseases commonly associated with dogs include rabies (hydrphobia), canine parvovirus, and canine distemper. Inherited diseases of dogs can include a wide range from elbow or hip dysplasia and medical patellar luxation to epilepsy and pulmonic stenosis. Canines can get just about anything a human can get (excluding many infections which are species specific) like hypothyroidism, cancer, dental disease, heart disease, etc.
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Two serious medical conditions affecting dogs are pyometra, affecting unspayed females of all types and ages, and bloat, which affects the larger breed or deep chested dogs. Both of these are acute conditions and can kill rapidly; owners of dogs which may be at risk should learn about such conditions as part of good animal care.
Common external parasites are various species of fleas, ticks, and mites. Internal parasites include hookworms, tapeworms, roundworms, and heartworms.
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 ailments that humans are, including diabetes, epilepsy, cancer, and arthritis.
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Diet
There is some debate as to whether domestic dogs should be classified as omnivores or carnivores by diet. The classification in the Order Carnivora does not necessarily mean that a dog’s diet must be restricted to meat unlike an obligate carnivore, such as the cat family with its shorter small intestine, a dog is neither dependent on meat-specific protein nor a very high level of protein in order to fulfill it basic dietary requirements. Dogs are able to healthily digest a variety of foods including vegetables and grains, and in fact dogs can consume a large portion of these in their diet.
Wild canines not only eat available plants to obtain essential amino acids, but also obtain nutrients from vegetable matter form the stomach and intestinal contents of the herbivorous prey, which they usually consume. Domestic dogs can survive healthily on a reasonable and carefully designed vegetarian diet, particularly if eggs and milk products are included. Some sources suggest that a dog fed on a strict vegetarian diet without L-carnitine may develop dilated cardiomyopathy, however, L-carnitine is found in many nuts, seeds, beans, vegetables, fruits, and whole grains. In the wild, dogs can survive on a vegetarian diet when animal prey is not available. Observation of extremely stressful conditions such as the Iditarod Trail Sled Dog Race and scientific studies of similar conditions has shown that high protein (approximately 40%) diets including meat help prevent damage to muscle tissue in dogs and some other mammals. This level of protein corresponds to the percentage of protein found in the wild dog’s diet when prey is abundant, higher level or protein seem to confer no added benefit.
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Dogs frequently eat grass, which is a harmless activity. Explanations abound but rationales such as that it neutralizes acid or that dog eat grass to induce vomiting to remove unwanted substances from their stomachs, are the best educated guesses. Dogs do vomit more readily than humans, as part of their typical feeding behavior of gulping down food then regurgitating indigestible matter such as bones or fur. This behavior is typical of pack feeding in the wild, where the most important thing is to get as much of the kill as possible before others consume it all. Individual domestic dogs, however, may be very “picky” eaters, in the absence of this social pressure. Dogs may also appear to eat grass when they are running the blades through their mouths to gather information. Their sense of small and taste may act together to detect if other animals have walked through there are or urinated on the grass.
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Dangerous Substances
Human food. Some foods commonly enjoyed by humans are dangerous to dogs, including chocolate (Theobromine poisoning), onions, grapes and raisins, some types of gum, certain sweeteners and Macadamia nuts. The only known dangerous substance in chocolate is cocoa, so the danger of white chocolate is uncertain. The acute danger from grapes and raisins was discovered around 2000, and has slowly been publicized since then. The cause is not known. Small quantities will induce acute renal failure. Sultanas and currants may also be dangerous. Cooked bones are dangerous for dogs, because the heat of cooking changes their chemical and physical properties so that they cannot be chewed properly. As a result they may splinter into jagged shards that resist digestion. Alcoholic beverages pose comparable hazards to dogs as they do to humans, but due to low body weight and lack of alcohol tolerance they are toxic in much smaller portions.
Plants. Plants such as caladium, dieffenbachia and philodendron will cause throat irritations that will burn the throat going down as well as coming up. Hops are particularly dangerous and even small quantities can lead to malignant hyperthermia. Amaryllis, daffodil, english ivy, iris, and tulip (especially the bulbs) cause gastric irritation and sometimes central nervous system excitement followed by coma, and, in severe cases, even death. Ingesting foxglove, lily of the valley, larkspur and oleander can be life threatening because the cardiovascular system is affected. Yew is very dangerous because it affects the nervous system. Immediate veterinary treatment is required for dogs that ingest these.
Household poisons. Many household cleaners such as ammonia, bleach, disinfectants, drain cleaner, soaps, detergents, and other cleaners, mothballs and matches are dangerous to dogs, as are cosmetics such as deodorants, hair coloring, nail polish and remover, home permanent lotion, and suntan lotion. Dogs find some poisons attractive, such as antifreeze (automotive coolant), slug and snail bait, insect bait, and rodent poisons. Antifreeze is insidious to dogs, either puddled or even partly cleaned residue, because of its sweet taste. A dog may pick up antifreeze on its fur and then lick it off.
Animal feces. Dogs occasionally eat their own feces, or the feces of other dogs and other species if available, such as cats, deer, cows, or horses. This is known as coprophagia. Some dogs develop preferences for one type over another. There is no definitive reason known, although boredom, hunger, and nutritional needs have been suggested. Eating cat feces is common, possibly because of the high protein content of cat food. Dogs eating cat feces from a litter box may lead to Toxoplasmosis. Dogs seem to have different preferences in relation to eating feces. Some are attracted to the stools of deer, cows, or horses.
Other risks. Human medications may be toxic to dogs, for example paracetamol/acetaminophen (Tylenol). Zinc toxicity, mostly in the form of the ingestion of US cents minted after 1982, is commonly fatal in dogs where it causes a severe hemolytic anemia. Some wet dog and cat food was recalled by Menu Foods in 2007 because it contained a dangerous substance.
(source: wikipedia.org)
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