Dog

The domestic dog (Canis lupus familiaris or Canis familiaris) is a domesticated canid which has been selectively bred for millennia for various behaviors, sensory capabilities, and physical attributes.

Although initially thought to have originated as a manmade variant of an extant canid species (variously supposed as being the dhole, golden jackal,or gray wolf), extensive genetic studies undertaken during the 2010s indicate that dogs diverged from other wolf-like canids in Eurasia 40,000 years ago. Being the oldest domesticated animals, their long association with people has allowed dogs to be uniquely attuned to human behavior, as well as thrive on a starch-rich diet which would be inadequate for other canid species.

Dogs perform many roles for people, such as hunting, herding, pulling loads, protection, assisting police and military, companionship, and, more recently, aiding handicapped individuals. This impact on human society has given them the nickname "man's best friend" in the Western world. In some cultures, however, dogs are a source of meat.

>> Etymology
The term "domestic dog" is generally used for both of the 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. The term dog may ultimately derive from the earliest layer of Proto-Indo-European vocabulary, reflecting the role of the dog as the earliest domesticated animal.

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"

In breeding circles, a male canine is referred to as a dog, while a female is called a bitch (Middle English bicche, from Old English bicce, ultimately from Old Norse bikkja). A group of offspring is a litter. The father of a litter is called the sire, and the mother is called the dam. Offspring are, in general, called pups or puppies, from French poupée, until they are about a year old. The process of birth is whelping, from the Old English word hwelp.

>> Taxonomy
In 1753, Carl Linnaeus listed among the types of quadrupeds familiar to him the Latin word for dog, canis. Among the species within this genus, Linnaeus listed the red fox (as Canis vulpes), wolves (Canis lupus), and the domestic dog (Canis canis). In later editions, Linnaeus dropped Canis canis and greatly expanded his list of the Canis genus of quadrupeds and, by 1758, included alongside the foxes, wolves, and jackals and many more terms that are now listed as synonyms for domestic dog, including aegyptius (hairless dog), aquaticus, (water dog), and mustelinus (literally "badger dog"). Among these were two that later experts have been widely used for domestic dogs as a species: Canis domesticus and, most predominantly, Canis familiaris, the "common" or "familiar" dog.

By 1993, with advancements in molecular biology, the mitochondrial DNA mtDNA analysis of extant (i.e. living today) Canidae species indicated that "The domestic dog is an extremely close relative of the gray wolf, differing from it by at most 0.2% of mtDNA sequence.... In comparison, the gray wolf differs from its closest wild relative, the coyote, by about 4% of mitochondrial DNA sequence." In the same year, the domestic dog Canis familiaris was reclassified as Canis lupus familiaris, a subspecies of the gray wolf Canis lupus in Mammal Species of the World. By 1999, further genetic analysis indicated that the domestic dog may have emerged from multiple wolf populations. Based on these latest two pieces of research and the reference reclassification, canis lupus familiaris is the name for the taxon listed by ITIS. However, canis familiaris is also accepted due to a nomenclature debate regarding the naming of wild and domestic sub-species.

In 2014, a mtDNA study of extant and extinct dogs and wolves questioned this classification, the study posited a common ancestor to wolves and dogs, rather than a speciation event. (See Origin and Gray wolf.)

>> Origin
Main article: Origin of the domestic dog
The origin of the domestic dog (Canis lupus familiaris or Canis familiaris) is not clear. Whole genome sequencing indicates that the dog, the gray wolf and the extinct Taymyr wolf diverged at around the same time 27,000–40,000 years ago. These dates imply that the earliest dogs arose in the time of human hunter-gatherers and not agriculturists. Modern dogs are most closely related to ancient wolf fossils that have been found in Europe than they are to modern gray wolves. Nearly all dog breeds' genetic closeness to the gray wolf are due to admixture, except several Arctic dog breeds are close to the Taimyr wolf of North Asia due to admixture.

>> Biology

- Anatomy
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.

- Senses
The dog's senses include vision, hearing, sense of smell, sense of taste, touch and sensitivity to the earth's magnetic field.

- 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.

- Tail
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.