The term "domestic dog" is generally used for both domesticated and feral varieties. The English word dog comes from Middle English dogge, from Old English docga, a "powerful dog breed". The term may possibly derive from Proto-Germanic *dukkōn, represented in Old English finger-docce ("finger-muscle"). The word also shows the familiar petname diminutive -ga also seen in frogga "frog", picga "pig", stagga "stag", wicga "beetle, worm", among others. Piotr Gąsiorowski has suggested that Old English *docga is actually derived from Old English colour adjective dox.
In 14th-century England, hound (from Old English: hund) was the general word for all domestic canines, and dog referred to a subtype of hound, a group including the mastiff. It is believed this "dog" type was so common, it eventually became the prototype of the category "hound". By the 16th century, dog had become the general word, and hound had begun to refer only to types used for hunting. The word "hound" is ultimately derived from the Proto-Indo-European word *kwon-, "dog". This semantic shift may be compared with in German, where the corresponding words Dogge and Hund kept their original meanings. The term *ḱwon- may ultimately derive from the earliest layer of Proto-Indo-European vocabulary.
A male canine is referred to as a "dog", while a female is traditionally called a "bitch" (derived from Middle English bicche, from Old English bicce, ultimately from Old Norse bikkja. Since the word "bitch" has taken on derogatory connotations, nowadays it is less commonly used to refer to dogs). The father of a litter is called the sire, and the mother is called the dam. The process of birth is "whelping", from the Old English word hwelp; the modern English word "whelp" is an alternative term for puppy. A litter refers to the multiple offspring at one birth which are called puppies or pups from the French poupée, "doll", which has mostly replaced the older term "whelp".
The term dog typically is applied both to the species (or subspecies) as a whole, and any adult male member of the same.
An adult female is a bitch.
An adult male capable of reproduction is a stud.
An adult female capable of reproduction is a brood bitch, or brood mother.
Immature males or females (that is, animals that are incapable of reproduction) are pups or puppies.
A group of pups from the same gestation period is a litter.
The father of a litter is a sire. It is possible for one litter to have multiple sires.
The mother of a litter is a dam.
A group of any three or more adults is a pack.
In 1758, the taxonomist Linnaeus published in his Systema Naturae the classification of species. Canis is a Latin word meaning dog, and under this genus he listed the dog-like carnivores including domestic dogs, wolves, and jackals. He classified the domestic dog as Canis familiaris (Linnaeus, 1758) and on the next page as a separate species he classified the wolf as Canis lupus (Linnaeus, 1758). In 1926, the International Commission on Zoological Nomenclature (ICZN) ruled in Opinion 91 that the domestic dog Canis familiaris (Linnaeus, 1758) be placed on its official list. In 1957, the ICZN ruled in Opinion 451 that Canis dingo (Meyer, 1793) was the name to be used for the dingo and that this be placed on its official list. These are the scientific names for the dog and dingo that appear on the Official Lists and Indexes of Names in Zoology of the ICZN.
In 1978, a review to minimize the number species listed under genus Canis proposed that "Canis dingo is now generally regarded as a distinctive feral domestic dog. Canis familiaris is used for domestic dogs, although taxonomically it should probably be synonymous with Canis lupus." In 1982, the first edition of Mammal Species of the World included a note under Canis lupus with the comment: "Probably ancestor of and conspecific with the domestic dog, familiaris. Canis familiaris has page priority over Canis lupus, but both were published simultaneously in Linnaeus (1758), and Canis lupus has been universally used for this species". In the same year, an application was made to the ICZN to reclassify the dingo to Canis lupus dingo because it was proposed that the wolf (Canis lupus) was the ancestor of dogs and dingoes, however the application was rejected.
In 2003, the ICZN ruled in its Opinion 2027 that the "name of a wild species...is not invalid by virtue of being predated by the name based on a domestic form." Additionally, the ICZN placed the taxon Canis lupus as a conserved name on the official list under this opinion. In the third edition of Mammal Species of the World published in 2005, the mammalogist W. Christopher Wozencraft listed under the wolf Canis lupus what he proposed to be two subspecies: "familiaris Linneaus, 1758 [domestic dog]" and "dingo Meyer, 1793 [domestic dog]",[a] with the comment "Includes the domestic dog as a subspecies, with the dingo provisionally separate – artificial variants created by domestication and selective breeding. Although this may stretch the subspecies concept, it retains the correct allocation of synonyms." Although the earliest use of the name "dingo" was Canis familiaris dingo (Blumenbach, 1780), Wozencraft attributed it to Meyer from 1793 without comment.
This classification by Wozencraft is hotly debated by zoologists. Mathew Crowther, Stephen Jackson and Colin Groves disagree with Wozencraft and argue that based on ICZN Opinion 2027, the implication is that a domestic animal cannot be a subspecies. Crowther, Juliet Clutton-Brock and others argue that because the dingo differs from wolves by behavior, morphology, and that the dingo and dog do not fall genetically within any extant wolf clade, that the dingo should be considered the distinct taxon Canis dingo. Jackson and Groves regard the dog Canis familiaris as a taxonomic synonym for the wolf Canis lupus with them both equally ranked at the species level. They also disagree with Crowther, based on the overlap between dogs and dingoes in their morphology, in their ability to easily hybridize with each other, and that they show the signs of domestication by both having a cranium of smaller capacity than their progenitor, the wolf. Given that Canis familiaris (Linnaeus, 1758) has date priority over Canis dingo (Meyer, 1793), they regard the dingo as a junior taxonomic synonym for the dog Canis familiaris. Gheorghe Benga and others support the dingo as a subspecies of the dog from the earlier Canis familiaris dingo (Blumenbach, 1780). Xiaoming Wang and Richard H. Tedford proposed that the dog should be classified as Canis lupus familiaris under the Biological Species Concept and Canis familiaris under the Evolutionary Species Concept.
Main article: Origin of the domestic dog
The origin of the domestic dog is not clear. It is known that the dog was the first domesticated species. The domestic dog is a member of the genus Canis (canines), which forms part of the wolf-like canids, and is the most widely abundant terrestrial carnivore. The closest living relative of the dog is the gray wolf and there is no evidence of any other canine contributing to its genetic lineage. The dog and the extant gray wolf form two sister clades, with modern wolves not closely related to the wolves that were first domesticated. The archaeological record shows the first undisputed dog remains buried beside humans 14,700 years ago, with disputed remains occurring 36,000 years ago. These dates imply that the earliest dogs arose in the time of human hunter-gatherers and not agriculturists.
Where the genetic divergence of dog and wolf took place remains controversial, with the most plausible proposals spanning Western Europe, Central Asia, and East Asia. This has been made more complicated by the most recent proposal that fits the available evidence, which is that an initial wolf population split into East and West Eurasian wolves, these were then domesticated independently before going extinct into two distinct dog populations between 14,000-6,400 years ago, and then the Western Eurasian dog population was partially and gradually replaced by East Asian dogs that were brought by humans at least 6,400 years ago.
Lateral view of skeleton.
"Five different types of dogs," c. 1547.
Main article: Dog anatomy
Domestic dogs have been selectively bred for millennia for various behaviors, sensory capabilities, and physical attributes. Modern dog breeds show more variation in size, appearance, and behavior than any other domestic animal. Dogs are predators and scavengers, and like many other predatory mammals, the dog has powerful muscles, fused wrist bones, a cardiovascular system that supports both sprinting and endurance, and teeth for catching and tearing.
Size and weight
Dogs are highly variable in height and weight. The smallest known adult dog was a Yorkshire Terrier, that stood only 6.3 cm (2.5 in) at the shoulder, 9.5 cm (3.7 in) in length along the head-and-body, and weighed only 113 grams (4.0 oz). The largest known dog was an English Mastiff which weighed 155.6 kg (343 lb) and was 250 cm (98 in) from the snout to the tail. The tallest dog is a Great Dane that stands 106.7 cm (42.0 in) at the shoulder.
The dog's senses include vision, hearing, sense of smell, sense of taste, touch and sensitivity to the earth's magnetic field. Another study suggested that dogs can see the earth's magnetic field.
See further: Dog anatomy-senses
Main article: Coat (dog)
Montage showing the coat variation of the dog.
A Golden Retriever with a golden shade of coat. Shades of coat colors can vary within breeds of dogs. For example, some Golden Retrievers have light, almost cream colored coats, and others may have dark, brownish shades of coat. 
The coats of domestic dogs are of two varieties: "double" being common with dogs (as well as wolves) originating from colder climates, made up of a coarse guard hair and a soft down hair, or "single", with the topcoat only.
Domestic dogs often display the remnants of countershading, a common natural camouflage pattern. A countershaded animal will have dark coloring on its upper surfaces and light coloring below, which reduces its general visibility. Thus, many breeds will have an occasional "blaze", stripe, or "star" of white fur on their chest or underside.
Regarding coat appearance or health, the coat can be maintained or affected by multiple nutrients present in the diet, see Coat (dog) for more information.
See also: Docking
There are many different shapes for dog tails: straight, straight up, sickle, curled, or cork-screw. As with many canids, one of the primary functions of a dog's tail is to communicate their emotional state, which can be important in getting along with others. In some hunting dogs, however, the tail is traditionally docked to avoid injuries. In some breeds, such as the Braque du Bourbonnais, puppies can be born with a short tail or no tail at all.
Main article: Dog health
There are many household plants that are poisonous to dogs including begonia, Poinsettia and aloe vera.
Some breeds of dogs are prone to certain genetic ailments such as elbow and hip dysplasia, blindness, deafness, pulmonic stenosis, cleft palate, and trick knees. Two serious medical conditions particularly affecting dogs are pyometra, affecting unspayed females of all types and ages, and gastric dilatation volvulus (bloat), which affects the larger breeds or deep-chested dogs. Both of these are acute conditions, and can kill rapidly. Dogs are also susceptible to parasites such as fleas, ticks, and mites, as well as hookworms, tapeworms, roundworms, and heartworms.
A number of common human foods and household ingestibles are toxic to dogs, including chocolate solids (theobromine poisoning), onion and garlic (thiosulphate, sulfoxide or disulfide poisoning), grapes and raisins, macadamia nuts, xylitol, as well as various plants and other potentially ingested materials. The nicotine in tobacco can also be dangerous. Dogs can be exposed to the substance by scavenging garbage or ashtrays; eating cigars and cigarettes. Signs can be vomiting of large amounts (e.g., from eating cigar butts) or diarrhea. Some other signs are abdominal pain, loss of coordination, collapse, or death. Dogs are highly susceptible to theobromine poisoning, typically from ingestion of chocolate. Theobromine is toxic to dogs because, although the dog's metabolism is capable of breaking down the chemical, the process is so slow that even small amounts of chocolate can be fatal, especially dark chocolate.
Dogs are also vulnerable to some of the same health conditions as humans, including diabetes, dental and heart disease, epilepsy, cancer, hypothyroidism, and arthritis.
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