The domestic dog (Canis lupus familiaris),[2][3] is a subspecies of the gray wolf (Canis lupus), a member of the Canidae family of the mammalian order Carnivora. The term "domestic dog" is generally used for both domesticated and feral varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and pet animal in human history. The word "dog" may also mean the male of a canine species,[4] as opposed to the word "bitch" for the female of the species. The present lineage of dogs was domesticated from gray wolves probably about 15,000 years ago.[5] Though remains of domesticated dogs have been found in Siberia and Belgium from about 33,000 years ago, none of those lineages seem to have survived the Last Glacial Maximum. Although DNA testing suggests an evolutionary split between dogs and wolves around 100,000 years ago, no fossil specimens prior to 33,000 years ago are clearly morphologically domesticated dog.[6][7][8] Dogs' value to early human hunter-gatherers led to them quickly becoming ubiquitous across world cultures. 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, dogs are also a source of meat.[9][10] In 2001, there were estimated to be 400 million dogs in the world.[11] Most breeds of dogs are at most a few hundred years old, having been artificially selected for particular morphologies and behaviors by people for specific functional roles. Through this selective breeding, the dog has developed into hundreds of varied breeds, and shows more behavioral and morphological variation than any other land mammal.[12] For example, height measured to the withers ranges from 6 inches (150 mm) in the Chihuahua to about 2.5 feet (0.76 m) in the Irish Wolfhound; 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; coats can be short or long, coarse-haired to wool-like, straight, curly, or smooth.[13] It is common for most breeds to shed this coat. Etymology and related terminology "Dog" is the common use term that refers to members of the subspecies Canis lupus familiaris (canis, "dog"; lupus

"wolf"; familiaris, "of a household" or "domestic"). The term can also be used to refer to a wider range of related species, such as the members of the genus Canis, or "true dogs", including the wolf, coyote, and jackals, or it can refer to the members of the tribe Canini, which would also include the African wild dog, or it can be used to refer to any member of the family Canidae, which would also include the foxes, bush dog, raccoon dog, and others.[14] Some members of the family have "dog" in their common names, such as the raccoon dog and the African wild dog. A few animals have "dog" in their common names but are not canids, such as the prairie dog. The English word "dog" comes from Middle English dogge, from Old English docga, a "powerful dog breed".[15] The term may derive from Proto-Germanic *dukkon, represented in Old English finger-docce ("finger-muscle").[16] The word also shows the familiar petname diminutive -ga also seen in frogga "frog", picga "pig", stagga "stag", wicga "beetle, worm", among others.[17] Due to the archaic structure of the word, 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.[18] 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 of "hound" was so common, it eventually became the prototype of the category “hound”.[19] By the 16th century, dog had become the general word, and hound had begun to refer only to types used for hunting.[20] Hound, cognate to German Hund, Dutch hond, common Scandinavian hund, and Icelandic hundur, is ultimately derived from the Proto-Indo-European *kwon- "dog", found in Sanskrit kukuur (?)[21], Welsh ci (plural cwn), Latin canis, Greek kyon, and Lithuanian suo.[22] 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 poupee, until they are about a year old. The process of birth is whelping, from the Old English word hwelp (cf. German Welpe, Dutch welp, Swedish valpa, Icelandic hvelpur).