Thedomestic dog(Canis lupus familiarisorCanis familiaris) is a usually furrycanid. The global dog population is estimated to between 700 million[2]to over one billion, making the dog the most abundant member of orderCarnivora.[3]The dog wasthe first domesticated animal[4][5]and although it is said that the"dog is man's best friend"[6]regarding 17-24% of dogs in the developed countries, in the developing world they are feral, village or community dogs, with pet dogs uncommon.[7]These live their lives as scavengers and have never been owned by humans, with one study showing their most common response when approached by strangers was to run away (52%) or respond with aggression (11%).[8]Contents[hide] 1Etymology and related terminology 2Taxonomy 3Origin 4Biology 4.1Senses 4.1.1Vision 4.1.2Hearing 4.1.3Smell 4.1.4Magnetic sensitivity 4.2Physical characteristics 4.2.1Coat 4.2.2Tail 4.3Types and breeds 4.4Health 4.4.1Lifespan 4.4.2Predation 4.5Diet 4.6Reproduction 4.6.1Neutering 5Intelligence, behavior and communication 5.1Intelligence 5.2Behavior 5.3Communication 5.3.1Dog growl 6Differences from wolves 6.1Physical characteristics 6.2Behavioral differences 7Roles with humans 7.1Early roles 7.2As pets 7.3Work 7.4Sports and shows 7.5As a food source 7.6Health risks to humans 7.7Health benefits for humans 7.8Medical detection dogs 7.9Shelters 8Cultural depictions 8.1Mythology 8.2Religion and culture 8.3Gallery of dogs in art 9See also 10References 11Bibliography 12Further reading 13External linksEtymology and related terminologyThe term "domestic dog" is generally used for both of thedomesticatedandferalvarieties. The English worddogcomes fromMiddle Englishdogge, fromOld Englishdocga, a "powerful dog breed".[9]The term may possibly derive from Proto-Germanic*dukkn, represented in Old Englishfinger-docce("finger-muscle").[10]The word also shows the familiar petnamediminutive-gaalso seen infrogga"frog",picga"pig",stagga"stag",wicga"beetle, worm", among others.[11]The termdogmay ultimately derive from the earliest layer of Proto-Indo-European vocabulary, reflecting the role of the dog as the earliestdomesticated animal.[12]In 14th-century England,hound(fromOld English:hund) was the general word for all domestic canines, anddogreferred 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".[13]By the 16th century,doghad become the general word, andhoundhad begun to refer only to types used for hunting.[14]Hound,cognateto GermanHund, Dutchhond, common Scandinavianhund, and Icelandichundur, is ultimately derived from the Proto-Indo-European*kwon-"dog", found inSanskritkukuur (),[15]Welshci(pluralcwn),Latincanis, Greekkn, andLithuanianu.[16]In breeding circles, a male canine is referred to as a dog, while a female is called a bitch[17](Middle Englishbicche, from Old Englishbicce, ultimately from Old Norsebikkja). A group of offspring is alitter. The father of a litter is called the sire, and the mother is called the dam. Offspring are, in general, called pups orpuppies, from Frenchpoupe, until they are about a year old. The process of birth is whelping, from the Old English wordhwelp(cf. GermanWelpe, Dutchwelp, Swedishvalpa, Icelandichvelpur).[18]The term "whelp" can also be used to refer to the young of any canid, or as a (somewhat archaic) alternative to "puppy".TaxonomyIn 1753,Carl Linnaeuslisted among the types ofquadrupedsfamiliar to him the Latin word for dog,canis. Among the species within this genus, Linnaeus listed thered fox(asCanis vulpes),wolves(Canis lupus), and the domestic dog (Canis canis). In later editions, Linnaeus droppedCanis canisand greatly expanded his list of theCanisgenus of quadrupeds, and by 1758 included alongside thefoxes, wolves, andjackalsand many more terms that are now listed as synonyms for domestic dog, includingaegyptius(hairless dog),aquaticus, (water dog), andmustelinus(literally "badger dog"). Among these were two that later experts have been widely used for domestic dogs as a species:Canis domesticusand, most predominantly,Canis familiaris, the "common" or "familiar" dog.[19]By 1993 with advancements inmolecular biology, the mitochondrial DNAmtDNAanalysis of extant (i.e. living today) Canidea 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."[20]In the same year, the domestic dogCanis familiariswas reclassified asCanis lupus familiaris, a subspecies of the gray wolfCanis lupusinMammal Species of the World.[21]By 1999, further genetic analysis indicated that the domestic dog may have emerged from multiple wolf populations.[22][23]Based on these latest two pieces of research and the reference reclassification,canis lupus familiarisis the name