Dog
The domestic dog (Canis familiaris when considered a distinct species or Canis lupus familiaris when considered a subspecies of the wolf)[5] is a member of the genus Canis (canines), which forms part of the wolf-like canids,[6] and is the most widely abundant terrestrial carnivore.[7][8][9][10][11] The dog and the extant gray wolf are sister taxa[12][13][14] as modern wolves are not closely related to the wolves that were first domesticated,[13][14] which implies that the direct ancestor of the dog is extinct.[15] The dog was the first species to be domesticated,[14][16] and has been selectively bred over millennia for various behaviors, sensory capabilities, and physical attributes.[17]
Their long association with humans has led dogs to be uniquely attuned to human behavior[18] and they are able to thrive on a starch-rich diet that would be inadequate for other canids.[19] Dogs vary widely in shape, size and colors.[20] They perform many roles for humans, such as hunting, herding, pulling loads, protection, assisting police and military, companionship and, more recently, aiding disabled people and therapeutic roles. This influence on human society has given them the sobriquet of "man's best friend".
Terminology
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 called 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.
Taxonomy
In 1758, the Swedish botanist and zoologist Carl Linnaeus published in his Systema Naturae the binomial nomenclature – or the two-word naming – of species. Canis is the Latin word meaning "dog",[21] and under this genus he listed the dog-like carnivores including domestic dogs, wolves, and jackals. He classified the domestic dog as Canis familiaris, and on the next page he classified the wolf as Canis lupus.[3] Linnaeus considered the dog to be a separate species from the wolf because of its cauda recurvata - its upturning tail which is not found in any other canid.[22]
In 1999, a study of mitochondrial DNA indicated that the domestic dog may have originated from multiple grey wolf populations, with the dingo and New Guinea singing dog "breeds" having developed at a time when human populations were more isolated from each other.[23] In the third edition of Mammal Species of the World published in 2005, the mammalogist W. Christopher Wozencraft listed under the wolf Canis lupus its wild subspecies, and proposed two additional subspecies: "familiaris Linneaus, 1758 [domestic dog]" and "dingo Meyer, 1793 [domestic dog]". Wozencraft included hallstromi – the New Guinea singing dog – as a taxonomic synonym for the dingo. Wozencraft referred to the mDNA study as one of the guides in forming his decision.[1] The inclusion of familiaris and dingo under a "domestic dog" clade has been noted by other mammalogists.[24] This classification by Wozencraft is debated among zoologists.[25]
In 2019, a workshop hosted by the IUCN/Species Survival Commission's Canid Specialist Group considered the New Guinea Singing Dog and the Dingo to be feral dogs Canis familiaris, and therefore should not be assessed for the IUCN Red List.[26]
Origin
The origin of the domestic dog includes the dog's evolutionary divergence from the wolf, its domestication, and its development into dog types and dog breeds. The dog is a member of the genus Canis, which forms part of the wolf-like canids, and was the first species and the only large carnivore to have been domesticated.[14][27] The dog and the extant gray wolf are sister taxa, as modern wolves are not closely related to the population of wolves that was first domesticated.[14]
The genetic divergence between dogs and wolves occurred between 40,000–20,000 years ago, just before or during the Last Glacial Maximum.[28][2] This timespan represents the upper time-limit for the commencement of domestication because it is the time of divergence and not the time of domestication, which occurred later.[28][29] The domestication of animals commenced over 15,000 years ago, beginning with the grey wolf (Canis lupus) by nomadic hunter-gatherers.[28] The archaeological record and genetic analysis show the remains of the Bonn–Oberkassel dog buried beside humans 14,200 years ago to be the first undisputed dog, with disputed remains occurring 36,000 years ago. The domestication of the dog predates agriculture.[2] It was not until 11,000 years ago that people living in the Near East entered into relationships with wild populations of aurochs, boar, sheep, and goats.[28]
Where the domestication of the dog took place remains debated, with the most plausible proposals spanning Western Europe,[9][29] Central Asia[29][30] and East Asia.[29][31] This has been made more complicated by the recent proposal that an initial wolf population split into East and West Eurasian groups. These two groups, before going extinct, were domesticated independently into two distinct dog populations between 14,000 and 6,400 years ago. The Western Eurasian dog population was gradually and partially replaced by East Asian dogs introduced by humans at least 6,400 years ago.[29][2] This proposal is also debated.[2]
In 2020, a literature review of canid domestication stated that modern dogs were not descended from the same Canis lineage as modern wolves, and proposes that dogs may be descended from a Pleistocene wolf closer in size to a village dog.[32]
Biology
Domestic dogs have been selectively bred for millennia for various behaviors, sensory capabilities, and physical attributes.[17] Modern dog breeds show more variation in size, appearance, and behavior than any other domestic animal.[17] Dogs are predators and scavengers; 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 a Saint Bernard which weighed 167.6 kg (369 lb) and was 250 cm (98 in) from the snout to the tail.[33] The tallest dog is a Great Dane that stands 106.7 cm (42.0 in) at the shoulder.[34]
Senses
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.[35][36][37]
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. Breeds may have an occasional "blaze", stripe, or "star" of white fur on their chest or underside.[38]
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.
Premature graying can occur in dogs from as early as one year of age. This has been shown to be associated with impulsive behaviors, anxiety behaviors, fear of noise, and fear of unfamiliar people or animals.[39]
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.[40] In some breeds, such as the Braque du Bourbonnais, puppies can be born with a short tail or no tail at all.[41]
Differences from wolves
Despite their close genetic relationship and the ability to inter-breed, there are a number of diagnostic features to distinguish the gray wolves from domestic dogs. Domesticated dogs are clearly distinguishable from wolves by starch gel electrophoresis of red blood cell acid phosphatase.[43] The tympanic bullae are large, convex and almost spherical in gray wolves, while the bullae of dogs are smaller, compressed and slightly crumpled.[44] Compared with equally sized wolves, dogs tend to have 20% smaller skulls and 30% smaller brains.[45]:35 The teeth of gray wolves are also proportionately larger than those of dogs.[46] Dogs have a more domed forehead and a distinctive "stop" between forehead and nose.[47] The temporalis muscle that closes the jaws is more robust in wolves.[5]:p158 Wolves do not have dewclaws on their back legs, unless there has been admixture with dogs that had them.[48] Most dogs lack a functioning pre-caudal gland and enter estrus twice yearly, unlike gray wolves which only do so once a year.[49] So-called primitive dogs such as dingoes and Basenjis retain the yearly estrus cycle.[50]
Dogs generally have brown eyes and wolves almost always have amber or light colored eyes.[51] The skin of domestic dogs tends to be thicker than that of wolves, with some Inuit tribes favoring the former for use as clothing due to its greater resistance to wear and tear in harsh weather.[52] The paws of a dog are half the size of those of a wolf, and their tails tend to curl upwards, another trait not found in wolves.[53] The dog has developed into hundreds of varied breeds, and shows more behavioral and morphological variation than any other land mammal.[54]
Health
There are many household plants that are poisonous to dogs (and other mammals) including begonia, Poinsettia and aloe vera.[55]
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, mites, hookworms, tapeworms, roundworms, and heartworms (roundworm species that lives in the heart of dogs).
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),[56] grapes and raisins, macadamia nuts, xylitol,[57] as well as various plants and other potentially ingested materials.[58][59] The nicotine in tobacco can also be dangerous. Dogs can be exposed to the substance by scavenging through garbage bins or ashtrays and 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.[60] Dogs are 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 for some dogs 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.[61]
