The dog (Canis lupus familiaris)[2] is a domesticated subspecies of the gray wolf, a mammal of the Canidae family of the order Carnivora. The term encompasses both feral and pet varieties and is also sometimes used to describe wild canids of other subspecies or species. The domestic dog has been one of the most widely kept working and companion animals in human history, as well as being a food source in some cultures. There are estimated to be 400 million dogs in the world.[3]
The dog has developed into hundreds of varied breeds. Height measured to the withers ranges from a few inches in the Chihuahua to a few feet 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; and, coats can be very short to many centimeters long, from coarse hair to something akin to wool, straight or curly, or smooth.[4] It is common for most breeds to shed this coat, however some non-shedding breeds are also popular.
| Domestic dog Fossil range: Late Pleistocene – Recent |
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Domesticated
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| Canis lupus familiaris (Linnaeus, 1758) |
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| These are INVALID scientific names for historical interest only: aegyptius (Linnaeus, 1758), alco (C. E. H. Smith, 1839), americanus (Gmelin, 1792), anglicus (Gmelin, 1792), antarcticus (Gmelin, 1792), aprinus (Gmelin, 1792), aquaticus (Linnaeus, 1758), aquatilis (Gmelin, 1792), avicularis (Gmelin, 1792), borealis (C. E. H. Smith, 1839), brevipilis (Gmelin, 1792), cursorius (Gmelin, 1792), domesticus (Linnaeus, 1758), extrarius (Gmelin, 1792), ferus (C. E. H. Smith, 1839), fricator (Gmelin, 1792), fricatrix (Linnaeus, 1758), fuillus (Gmelin, 1792), gallicus (Gmelin, 1792), glaucus (C. E. H. Smith, 1839), graius (Linnaeus, 1758), grajus (Gmelin, 1792), hagenbecki (Krumbiegel, 1950), haitensis (C. E. H. Smith, 1839), hibernicus (Gmelin, 1792), hirsutus (Gmelin, 1792), hybridus (Gmelin, 1792), islandicus (Gmelin, 1792), italicus (Gmelin, 1792), laniarius (Gmelin, 1792), leoninus (Gmelin, 1792), leporarius (C. E. H. Smith, 1839), major (Gmelin, 1792),mastinus (Linnaeus, 1758), melitacus (Gmelin, 1792), melitaeus (Linnaeus, 1758), minor (Gmelin, 1792), molossus (Gmelin, 1792), mustelinus (Linnaeus, 1758), obesus (Gmelin, 1792), orientalis (Gmelin, 1792), pacificus (C. E. H. Smith, 1839), plancus (Gmelin, 1792), pomeranus (Gmelin, 1792), sagaces (C. E. H. Smith, 1839), sanguinarius (C. E. H. Smith, 1839), sagax (Linnaeus, 1758), scoticus (Gmelin, 1792), sibiricus (Gmelin, 1792), suillus( C. E. H. Smith, 1839), terraenovae (C. E. H. Smith, 1839), terrarius (C. E. H. Smith, 1839), turcicus (Gmelin, 1792), urcani (C. E. H. Smith, 1839), variegatus (Gmelin, 1792), venaticus Gmelin, 1792), vertegus (Gmelin, 1792)[1] |
Etymology and related terminology
The English word dog can be traced back to the Old English docga, a "powerful breed of canine".[5] The term may derive from Proto-Germanic *dukkōn, represented in Old English finger-docce ("finger-muscle").[6] Due to the linguistically 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.[7]
The English word hound is cognate to other Germanic terms, including German Hund, Dutch hond, common Scandinavian hund, Icelandic hundur which, though referring to a specific breed group in English, means "dog" in general in the other Germanic languages. Hound itself is derived from the Proto-Indo-European *kwon-, which is also the direct root of the Greek κυων (kuōn) and the indirect root of the Latin canis through the variant form *kani-.[8]
In breeding circles, a male canine is referred to as a dog, while a female canine is called a bitch. The father of a litter is called the sire, and the mother of a litter is called the dam. Offspring are generally called pups or puppies until they are about a year old. A group of offspring is a litter. The process of birth is whelping. Many terms are used for dogs that are not purebred.[9]
Taxonomy
The English word dog, in common usage, refers to the domestic pet dog, Canis lupus familiaris. The species was originally classified as Canis familiaris and Canis familiarus domesticus by Linnaeus in 1758.[10][11] In 1993, dogs were reclassified as a subspecies of the gray wolf, Canis lupus, by the Smithsonian Institution and the American Society of Mammalogists. "Dog" is sometimes used to refer collectively to any mammal belonging to the family Canidae (as in "the dog family"), such as wolves, foxes, and coyotes. 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 and the dog fish.
Origin and evolution
Origins
Based on DNA evidence, the wolf ancestors of modern dogs diverged from other wolves about 100,000 years ago,[12][13] and dogs were domesticated from those wolf ancestors about 15,000 years ago.[14] This date would make dogs the first species to be domesticated by humans.
Evidence suggests that dogs were first domesticated in East Asia,[15] and some of the peoples who entered North America took dogs with them from Asia.[15]
As humans migrated around the planet, a variety of dog forms migrated with them. The agricultural revolution and subsequent urban revolution led to an increase in the dog population and a demand for specialization. These circumstances would provide the opportunity for selective breeding to create specialized working dogs and pets.
Ancestry and history of domestication
Molecular systematics indicate that the domestic dog (Canis lupus familiaris) descends from one or more populations of wild wolves (Canis lupus). As reflected in the nomenclature, dogs are descended from the wolf and are able to interbreed with wolves.
The relationship between human and canine has deep roots. Converging archaeological and genetic evidence indicate a time of domestication in the late Upper Paleolithic close to the Pleistocene/Holocene boundary, between 17,000 and 14,000 years ago. Fossil bone morphologies and genetic analysis of current and ancient dog and wolf populations have not yet been able to conclusively determine whether all dogs descend from a single domestication event, or whether dogs were domesticated independently in more than one location. Domesticated dogs may have interbred with local populations of wild wolves on several occasions (a process known in genetics as introgression).
The earliest dog fossils, two crania from Russia and a mandible from Germany, date from 13,000 to 17,000 years ago. Their likely ancestor is the large northern Holarctic wolf, Canis lupus lupus. Remains of smaller dogs from Mesolithic (Natufian) cave deposits in the Middle East, dated to around 12,000 years ago, have been interpreted as descendants of a lighter Southwest Asian wolf, Canis lupus Arabs. Rock art and skeletal remains indicate that by 14,000 years ago, dogs were present from North Africa across Eurasia to North America. Dog burials at the Mesolithic cemetery of Svaerdborg in Denmark suggest that in ancient Europe dogs were valued companions.
Genetic analyses have so far yielded divergent results. Vilà, Savolainen, and colleagues (1997) concluded that the ancestors of dogs split off from other wolves between 75,000 and 135,000 years ago, while a subsequent analysis by Savolainen et al. (2002) indicated a "common origin from a single gene pool for all dog populations" between 40,000 and 15,000 years ago in East Asia. Verginelli et al. (2005),[16] however, suggest both sets of dates must be reevaluated in light of recent findings showing that poorly calibrated molecular clocks have systematically overestimated the age of geologically recent events. On balance, and in agreement with the archaeological evidence, 15,000 years ago is the most likely time for the wolf-dog divergence.[17]
The Soviets have attempted to domesticate the fox, mentioned in the article Tame Silver Fox, and were able to do so in just nine generations, or less than a human lifetime. This also resulted in other changes, including color, which became black, white, or black and white. They also developed year-round breeding ability, curled-up tails, and droopy ears.
The rapidity of this change has suggested to researchers a scenario of the origin of the domestic dog. Primitive people lived on the edge of survival which involved occasional food shortages, and would not have taken wolf pups and made pets of them. However, wolves would raid garbage dumps near human habitations. Wolves have a flight distance which they keep between themselves and a threatening creature. When a dump was approached by humans, some wolves would run a greater distance from the dump than others. Those that ran the shortest distance would return first, and obtain the greatest amount of food.
This set up a selective breeding situation that resulted in a strain of wolves having shorter and shorter flight distances, until they were eventually comfortable near humans, having domesticated themselves, so to speak. At that point, they were tolerated by humans, so long as they were also useful, in such ways as catching rats or driving away other predators. In time, other uses, such as hunting, were found for them. The Farm Fox Experiment Evolution of Dogs
Development of dog breeds
There are numerous dog breeds, with over 800 being recognized by various kennel clubs worldwide. Many dogs, especially outside the United States of America and Western Europe, belong to no recognized breed. A few basic og_types" title="Category og types">breed types have evolved gradually during the domesticated dog's relationship with humans over the last 10,000 or more years, but all modern breeds are of relatively recent derivation. Many of these are the product of a deliberate process of artificial selection. Because of this, some breeds are highly specialized, and there is extraordinary morphological diversity across different breeds. Despite these differences, dogs are able to distinguish dogs from other kinds of animal.
The definition of a dog breed is a matter of some controversy. Depending on the size of the original founding population, closed gene pool breeds can have problems with inbreeding, specifically due to the founder effect. Dog breeders are increasingly aware of the importance of population genetics and of maintaining diverse gene pools. Health testing and new DNA tests can help avoid problems, by providing a replacement for natural selection. Without selection, inbreeding and closed gene pools can increase the risk of severe health or behavioral problems. Some organizations define a breed more loosely, such that an individual may be considered of one breed as long as 75% of its parentage is of that breed. These considerations affect both pets and the show dogs entered in dog shows. Even prize-winning purebred dogs sometimes possess crippling genetic defects due to founder effect or inbreeding.[18] These problems are not limited to purebred dogs and can affect cross-breed populations.[19] The behavior and appearance of a dog of a particular breed can be predicted to a degree, while mixed-breed dogs show a broader range of innovative appearance and behavior.
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Mixed-breed dogs or Mongrels (also called "mutts") are dogs that do not belong to specific breeds, being mixtures more than two in variant percentages. Mixed breed dogs and purebred dogs are both suitable as companions, pets, working dogs, or competitors in dog sports. Sometimes different breed dogs are deliberately bred, to create cross-breeds such as the Cockapoo, a mixture of Cocker Spaniel and Miniature Poodle. Such deliberate crosses may display some degree of hybrid vigor and other desirable traits, but may or may not inherit any of the desired traits of their parents, such as temperament or a particular color or coat. Without genetic testing of the parents, the crosses can end up inheriting genetic defects that occur in both parental breeds.
A breed is a group of animals that possesses a set of inherited characteristics that distinguishes it from other animals within the same species. Deliberately crossing two or more breeds is also a manner of establishing new breeds, but it is only a breed when offspring will reliably demonstrate that particular set of characteristics and qualities.
Breed popularity
Breed popularity varies widely over time[20] and in different parts of the world and different segments of the population. Counting by American Kennel Club (AKC) registration (not by licensing registration or by United Kennel Club (UKC) registration, which could present different statistics), the Labrador Retriever has been the United States's most commonly registered breed of dog since 1991.[21] However, even within parts of the United States, popularity varies; for example, in 2005 the most-registered breed in New York City was the Poodle while the Yorkshire Terrier was the second-most-registered breed in Houston.[22] However, animal shelters in many parts of the United States report that the most-commonly available dog for adoption is the American Pit Bull Terrier or pit bull-type mixes, making up as much as 20% of dogs available for adoption, none of which would be registered with the AKC.[23] Two decades ago, in 1983, the AKC's top two registered breeds were the American Cocker Spaniel and the Poodle.[24]
In the United Kingdom, The Kennel Club reports that the most-registered breed from at least 1999 to 2005 was the Labrador Retriever. It rounds out the top three for 1999 to 2005 with the German Shepherd Dog, also popular in the US, and the English Cocker Spaniel[25] , which is no longer in the top ten in the US. In the UK, a national dog adoption and rescue service indicates that the most common breed appearing in shelters is the Greyhound followed by the Staffordshire Bull Terrier.[26]
Differences from wolves
Physical characteristics
Compared to equally sized wolves, dogs tend to have 20% smaller skulls and 10% smaller brains, as well as proportionately smaller teeth than other canid species.[3] Dogs require fewer calories to function than wolves. Their diet of human refuse in antiquity made the large brains and jaw muscles needed for hunting unnecessary. It is thought by certain experts that the dog's limp ears are a result of atrophy of the jaw muscles.[3] The skin of domestic dogs tends to be thicker than that of wolves, with some Inuit tribes favouring the former for use as clothing due to its greater resistance to wear and tear in harsh weather.[3] Unlike wolves, but like coyotes, domestic dogs have sweat glands on their paw pads.[3] 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.[27]
Behaviour
Dogs tend to be poorer than wolves and coyotes at observational learning, being more responsive to instrumental conditioning.[3] Feral dogs show little of the complex social structure or dominance hierarchy present in wolf packs. For dogs, other members of their kind are of no help in locating food items, and are more like competitors.[3] Feral dogs are primarily scavengers, with studies showing that unlike their wild cousins, they are poor ungulate hunters, having little impact on wildlife populations where they are sympatric. Free ranging pet dogs however are more prone to predatory behaviour toward wild animals. Feral dogs have been reported to be effective hunters of reptiles in the Galapagos islands.[28] Despite common belief, domestic dogs can be monogamous.[29] Breeding in feral packs can be, but does not have to be restricted to a dominant alpha pair (despite common belief, such things also occur in wolf packs).[30] Male dogs are unusual among canids by the fact that they mostly seem to play no role in raising their puppies, and do not kill the young of other females to increase their own reproductive success.[28] Some sources say that dogs differ from wolves and most other large canid species by the fact that they do not regurgitate food for their young, nor the young of other dogs in the same territory.[3] However, this difference was not observed in all domestic dogs. Regurgitating of food by the females for the young as well as care for the young by the males has been observed in domestic dogs, dingos as well as in other feral or semi-feral dogs. Regurgitating of food by the females and direct choosing of only one mate has been observed even in those semi-feral dogs of direct domestic dog ancestry. Also regurgitating of food by males has been observed in free-ranging domestic dogs.[29][31]
Trainibility
Dogs display much greater tractability than tame wolves, and are generally much more responsive to coercive techniques involving fear, aversive stimuli and force than wolves, which are most responsive toward positive conditioning and rewards.[32] Unlike tame wolves, dogs tend to respond more to voice than hand signals.[33] Although they are less difficult to control than wolves, they can be comparatively more difficult to teach than a motivated wolf.[32]
Physical characteristics
- See also: Dog health
Modern dog breeds show more variation in size, appearance, and behavior than any other domestic animal. Within the range of extremes, dogs generally share attributes with their wild ancestors, the wolves. Dogs are predators and scavengers, possessing sharp teeth and strong jaws for attacking, holding, and tearing their food. Although selective breeding has changed the appearance of many breeds, all dogs retain basic traits from their distant ancestors. Like many other predatory mammals, the dog has powerful muscles, fused wristbones, a cardiovascular system that supports both sprinting and endurance, and teeth for catching and tearing. Dogs are more variable in size than any other domesticated animal. The smallest known dog was a Yorkshire Terrier, who stood only 6.3 cm (2.5 in) at the shoulder, 9.5 cm (3.75 in) along the head-and-body length and weighed only 113 grams (4 ounces). The largest known dog was an English Mastiff which weighed 155.6 kg (343 lbs) and was 250 cm (8.2 feet) from the snout to the tail. The tallest dog is a Great Dane that stands 106.7 cm (42.2 in) at the shoulder.[34]
Sight
Like most mammals, dogs are dichromats and have color vision equivalent to red-green color blindness in humans.[35][36][37] Different breeds of dogs have different eye shapes and dimensions, and they also have different retina configurations.[38] Dogs with long noses have a "visual streak" which runs across the width of the retina and gives them a very wide field of excellent vision, while those with short noses have an "area centralis" — a central patch with up to three times the density of nerve endings as the visual streak — giving them detailed sight much more like a human's.
Some breeds, particularly the sighthounds, have a field of vision up to 270° (compared to 180° for humans), although broad-headed breeds with short noses have a much narrower field of vision, as low as 180°.[35][36]
Hearing
According to hypertextbook.com, the frequency range of dog hearing is approximately 40 Hz to 60,000 Hz.[39] Dogs detect sounds as low as the 16 to 20 Hz frequency range (compared to 20 to 70 Hz for humans) and above 45 kHz[40] (compared to 13 to 20 kHz for humans),[39][36] and in addition have a degree of ear mobility that helps them to rapidly pinpoint the exact location of a sound.[41] Eighteen or more muscles can tilt, rotate and raise or lower a dog's ear. Additionally, a dog can identify a sound's location much faster than a human can, as well as hear sounds up to four times the distance that humans are able to.[41] Those with more natural ear shapes, like those of wild canids like the fox, generally hear better than those with the floppier ears of many domesticated species.
Smell
Dogs have nearly 220 million smell-sensitive cells over an area about the size of a pocket handkerchief (compared to 5 million over an area the size of a postage stamp for humans).[43][44] According to nhm.org, dogs can sense odors at concentrations nearly 100 million times lower than humans can.[45] According to Dummies.com, the percentage of the dog's brain that is devoted to analyzing smells is actually 40 times larger than that of a human.[43] Some dog breeds have been selectively bred for excellence in detecting scents, even compared to their canine brethren.
Coat color
Domestic dogs often display the remnants of counter-shading, a common natural camouflage pattern. The general theory of countershading is that an animal that is lit from above will appear lighter on its upper half and darker on its lower half where it will usually be in its own shade.[46][47] This is a pattern that predators can learn to watch for. A countershaded animal will have dark coloring on its upper surfaces and light coloring below.[46] This reduces the general visibility of the animal. One reminder of this pattern is that many breeds will have the occasional "blaze", stripe, or "star" of white fur on their chest or undersides.[47]
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