CHIEN PURE RACE
Le chien est la sous-espèce domestique de Canis lupus, un mammifère de la famille des Canidés (Canidae), laquelle comprend également le loup gris, ancêtre sauvage du chien, et le dingo, chien domestique redevenu sauvage. Le chien est la première espèce animale à avoir été domestiquée par l'Homme pour l'usage de la chasse dans une société humaine paléolithique qui ne maitrise alors ni l'agriculture ni l'élevage. La lignée du chien s'est différenciée génétiquement de celle du loup gris il y a environ 100 000 ans, et les plus anciens restes confirmés de chien domestique sont vieux, selon les sources, de 33 000 ans ou de 12 000 ans, donc antérieurs de plusieurs dizaines de milliers d'années à ceux de toute autre espèce domestique connue. Depuis la Préhistoire, le chien a accompagné l'homme durant toute sa phase de sédentarisation, marquée par l'apparition des premières civilisations agricoles. C'est à ce moment qu'il a acquis la capacité de digérer l'amidon, et que ses fonctions d'auxiliaire de l'homme se sont étendues. Ces nouvelles fonctions ont entrainé une différenciation accrue de la sous-espèce et l'apparition progressive de races canines identifiables. Le chien est aujourd'hui utilisé à la fois comme animal de travail et comme animal de compagnie. Son instinct de meute, sa domestication précoce et les caractéristiques comportementales qui en découlent lui valent familièrement le surnom de «meilleur ami de l'Homme». Cette place particulière dans la société humaine a conduit à l'élaboration d'une règlementation spécifique. Ainsi, là où les critères de la Fédération cynologique internationale ont une reconnaissance légale, l'appellation chien de race est conditionnée à l'enregistrement du chien dans les livres des origines de son pays de naissance. Selon le pays, des vaccins peuvent être obligatoires et certains types de chien, jugés dangereux, sont soumis à des restrictions. Le chien est généralement soumis aux différentes législations sur les carnivores domestiques. C'est notamment le cas en Europe, où sa circulation est facilitée grâce à l'instauration du passeport européen pour animal de compagnie.
Dénominations
Le terme chien est issu du latin canis, de même sens. La femelle du chien s'appelle la chienne, et le jeune chien le chiot. Selon le cas, le chien glapit, jappe, grogne ou aboie. Alors qu'on estimait autrefois que le chien constituait une espèce à part entière (Canis canis ou encore Canis familiaris), les recherches génétiques contemporaines ont permis d'établir qu'il n'est que le résultat de la domestication du loup gris commun. C'est pourquoi, malgré les différences morphologiques majeures qu'on constate entre les deux animaux, les scientifiques regroupent aujourd'hui la totalité des races canines en un ensemble nommé Canis lupus familiaris, sous-espèce de Canis lupus.
Caractéristiques physiques
Le squelette du chien compte environ trois cents os (soit environ quatre-vingts de plus qu'un squelette humain adulte), le nombre étant variable d'une race à l'autre. Malgré sa domestication et la dépendance à l'homme qui en découle, le chien a gardé sa musculature athlétique qui en fait un animal sportif et actif. Il possède un thorax large et descendu, et des pattes qui ne reposent au sol que par leur troisième phalange. Le chien est donc un digitigrade. Les membres antérieurs comportent cinq doigts, dont l'un, le pouce, nommé ergot, est atrophié et ne touche pas le sol. Les postérieurs en comptent généralement quatre, l'ergot n'existant que chez certaines races mais pouvant être double chez quelques bergers (beauceron, briard). Les cinq orteils se terminent par des griffes et sont soutenus par des coussinets plantaires. La tête du chien comporte une mâchoire puissante. La morsure d'un rottweiler a été mesurée à 149 kg/cm2, celle d'un berger allemand a une pression de 108 kg/cm2, et celle d'un pitbull 106 kg/cm2. La denture définitive, constituée de quarante-deux dents, est en place vers 6 mois. Chez le chien, la taille et la masse sont très variables d'une race à l'autre : dans les extrêmes, la masse du chihuahua peut être de 900 g et celui du mastiff peut atteindre 140 kg. L'espérance de vie de cet animal est en moyenne de onze ans, sachant que la durée de vie peut habituellement aller de huit à vingt et un ans. Son sens de l'orientation est beaucoup plus précis que celui de l'homme. De même, son sens de l'équilibre serait légèrement plus aiguisé. La température corporelle normale du chien va de 38,5 à 38,7 °C. Sa respiration normale va de seize à dix-huit mouvements à la minute (le jeune 18 à 20, le vieux 14 à 16). Sa fréquence cardiaque au repos est généralement comprise entre 70 et 130 battements par minute (les valeurs hautes s'observant plutôt chez les petites races, et inversement). Le pouls peut se prendre en palpant l'artère fémorale, sur la face interne de la cuisse. L'existence de huit groupes sanguins dans l'espèce canine a été mise en évidence à partir des années 1960, mais le chien ne possédant pas initialement d'anticorps anti-globules rouges, une première transfusion sanguine est possible sans détermination des groupes du donneur et du receveur. Cette détermination est fortement conseillée à partir de la seconde transfusion du fait que le receveur a pu s'immuniser contre les antigènes du donneur lors de la première transfusion.
Sens
Le cerveau du chien figure parmi les plus performants du règne animal, démontrant de très bonnes capacités cognitives avec des sens très développés.
Le sens de l'odorat est un sens extrêmement développé chez le chien. La taille de ses cavités nasales est environ trente fois plus grande que chez l'homme et la surface de la muqueuse olfactive, qui varie beaucoup en fonction de la race, est de huit à vingt fois supérieure à celle de l'homme (85 à 200 cm2 contre 10 cm2). Il possède dix fois plus de cellules olfactives et quarante fois plus de neurones consacrés à l'odorat que l'homme. À noter que ce sens est discriminant (le chien est capable de déceler et de suivre une odeur précise parmi une multitude d'autres odeurs, même si celle-ci est en proportion infime), capacité largement utilisée par l'homme pour les recherches de drogues, explosifs, personnes disparues, chasse, etc.
L'ouïe est aussi un sens très précis : le chien peut entendre des sons jusqu'à quatre fois plus loin que l'homme et capte également des sons inaudibles pour l'homme (ultrasons). En effet, la plage de fréquences que perçoivent les chiens s'étend de 40 Hz à 60 000 Hz (contre 20 Hz à 20 000 Hz pour l'homme). De plus, les oreilles du chien peuvent s'orienter vers une source sonore en pivotant grâce à de nombreux muscles, ce qui leur permet une grande précision dans la localisation sonore.
La vision du chien est plutôt modeste comparée à ses deux premiers sens. Toutefois, la gamme de couleurs qu'il perçoit, même si elle n'est pas aussi importante que chez l'homme, est tout de même assez ample. Le chien perçoit facilement les objets en mouvement mais il a du mal à faire le point sur des objets immobiles ainsi que sur les distances et sur les détails. Cependant le champ de vision du chien est plus vaste (environ 250 degrés) que chez l'homme (180 degrés maximum) avec une vision périphérique dix fois plus sensible. Le chien a également une vision optimisée dans le noir, possédant une surface réfléchissante derrière la rétine (le tapetum lucidum), qui renvoie la lumière et donne un effet d'yeux brillants dans l'obscurité.
Le toucher est particulier chez le chien car les organes sensibles au toucher sont des poils, plus particulièrement les sourcils, les vibrisses et les poils situés sous la mâchoire avec plus ou moins le même niveau de développement que le toucher de la peau chez l'homme. Hormis ces organes sensoriels, le toucher reste assez peu développé sur la peau, mais le chien est capable de faire aisément la différence entre une caresse et une correction ou bien la chaleur et le froid.
Le goût. Bien que le chien perçoive des différences de saveurs, ce sens est assez peu développé car contrairement à l'homme, c'est d'abord l'odeur d'une nourriture qui entre en premier en ligne de compte.
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The domestic dog is a domesticated canid which has been selectively bred over millennia for various behaviours, sensory capabilities, and physical attributes. Although initially thought to have originated as an artificial 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 an extinct wolf-like canid in Eurasia 40,000 years ago. Their long association with humans has led to dogs being uniquely attuned to human behavior and are able to thrive on a starch-rich diet which would be inadequate for other canid species. Dogs are also the oldest domesticated animal. Dogs vary widely in shape, size and colours. 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 influence on human society has given them the sobriquet, "man's best friend".
Etymology
The term "domestic dog" is generally used for both 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. 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". This semantic shift may be compared to in German, where the corresponding words Dogge and Hund kept their original meanings. A male canine is referred to as a dog, while a female is called a bitch. The father of a litter is called the sire, and the mother is called the dam. (Middle English bicche, from Old English bicce, ultimately from Old Norse bikkja) The process of birth is whelping, from the Old English word hwelp; the modern English word "whelp" is an alternate term for puppy. A litter refers to the multiple offspring at one birth which are called puppies or pups from the French poupée, "doll", which has mostly replaced the older term "whelp".
Taxonomy
The dog is classified as Canis lupus familiaris under the Biological Species Concept and Canis familiaris under the Evolutionary Species Concept. In 1758, the taxonomist Linnaeus published in Systema Naturae a categorization of species which included the Canis species. Canis is a Latin word meaning dog, and the list included the dog-like carnivores: the domestic dog, wolves, foxes and jackals. The dog was classified as Canis familiaris, which means "Dog-family" or the family dog. On the next page he recorded the wolf as Canis lupus, which means "Dog-wolf". In 1978, a review aimed at reducing the number of recognized Canis species proposed that "Canis dingo is now generally regarded as a distinctive feral domestic dog. Canis familiaris is used for domestic dogs, although taxonomically it should probably be synonymous with Canis lupus." In 1982, the first edition of Mammal Species of the World listed Canis familiaris under Canis lupus with the comment: "Probably ancestor of and conspecific with the domestic dog, familiaris. Canis familiaris has page priority over Canis lupus, but both were published simultaneously in Linnaeus (1758), and Canis lupus has been universally used for this species", which avoided classifying the wolf as the family dog. The dog is now listed among the many other Latin-named subspecies of Canis lupus as Canis lupus familiaris. In 2003, the ICZN ruled in its Opinion 2027 that if wild animals and their domesticated derivatives are regarded as one species, then the scientific name of that species is the scientific name of the wild animal. In 2005, the third edition of Mammal Species of the World upheld Opinion 2027 with the name Lupus and the note: "Includes the domestic dog as a subspecies, with the dingo provisionally separate - artificial variants created by domestication and selective breeding". However, Canis familiaris is sometimes used due to an ongoing nomenclature debate because wild and domestic animals are separately recognizable entities and that the ICZN allowed users a choice as to which name they could use, and a number of internationally recognized researchers prefer to use Canis familiaris. Later genetic studies strongly supported dogs and gray wolves forming two sister monophyletic clades within the one species, and that the common ancestor of dogs and extant wolves is extinct.
Origin
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 more 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
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.
Health
There are many household plants that are poisonous to dogs including begonia, Poinsettia and aloe vera. 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 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, and mites, as well as hookworms, tapeworms, roundworms, and heartworms. 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), grapes and raisins, macadamia nuts, xylitol, as well as various plants and other potentially ingested materials. The nicotine in tobacco can also be dangerous. Dogs can be exposed to the substance by scavenging garbage or ashtrays; 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. Dogs are highly 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 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.
Intelligence
Dog intelligence is the ability of the dog to perceive information and retain it as knowledge for applying to solve problems. Dogs have been shown to learn by inference. A study with Rico showed that he knew the labels of over 200 different items. He inferred the names of novel items by exclusion learning and correctly retrieved those novel items immediately and also 4 weeks after the initial exposure. Dogs have advanced memory skills. A study documented the learning and memory capabilities of a border collie, "Chaser", who had learned the names and could associate by verbal command over 1,000 words. Dogs are able to read and react appropriately to human body language such as gesturing and pointing, and to understand human voice commands. Dogs demonstrate a theory of mind by engaging in deception. An experimental study showed compelling evidence that Australian dingos can outperform domestic dogs in non-social problem-solving, indicating that domestic dogs may have lost much of their original problem-solving abilities once they joined humans. Another study indicated that after undergoing training to solve a simple manipulation task, dogs that are faced with an insoluble version of the same problem look at the human, while socialized wolves do not. Modern domestic dogs use humans to solve their problems for them.
Behavior
Dog behavior is the internally coordinated responses (actions or inactions) of the domestic dog (individuals or groups) to internal and/or external stimuli. As the oldest domesticated species, with estimates ranging from 9,000–30,000 years BCE, the minds of dogs inevitably have been shaped by millennia of contact with humans. As a result of this physical and social evolution, dogs, more than any other species, have acquired the ability to understand and communicate with humans and they are uniquely attuned to our behaviors. Behavioral scientists have uncovered a surprising set of social-cognitive abilities in the otherwise humble domestic dog. These abilities are not possessed by the dog's closest canine relatives nor by other highly intelligent mammals such as great apes. Rather, these skills parallel some of the social-cognitive skills of human children.
Communication
Dog communication is about how dogs "speak" to each other, how they understand messages that humans send to them, and how humans can translate the ideas that dogs are trying to transmit. These communication behaviors include eye gaze, facial expression, vocalization, body posture (including movements of bodies and limbs) and gustatory communication (scents, pheromones and taste). Humans communicate with dogs by using vocalization, hand signals and body posture.
Dénominations
Le terme chien est issu du latin canis, de même sens. La femelle du chien s'appelle la chienne, et le jeune chien le chiot. Selon le cas, le chien glapit, jappe, grogne ou aboie. Alors qu'on estimait autrefois que le chien constituait une espèce à part entière (Canis canis ou encore Canis familiaris), les recherches génétiques contemporaines ont permis d'établir qu'il n'est que le résultat de la domestication du loup gris commun. C'est pourquoi, malgré les différences morphologiques majeures qu'on constate entre les deux animaux, les scientifiques regroupent aujourd'hui la totalité des races canines en un ensemble nommé Canis lupus familiaris, sous-espèce de Canis lupus.
Caractéristiques physiques
Le squelette du chien compte environ trois cents os (soit environ quatre-vingts de plus qu'un squelette humain adulte), le nombre étant variable d'une race à l'autre. Malgré sa domestication et la dépendance à l'homme qui en découle, le chien a gardé sa musculature athlétique qui en fait un animal sportif et actif. Il possède un thorax large et descendu, et des pattes qui ne reposent au sol que par leur troisième phalange. Le chien est donc un digitigrade. Les membres antérieurs comportent cinq doigts, dont l'un, le pouce, nommé ergot, est atrophié et ne touche pas le sol. Les postérieurs en comptent généralement quatre, l'ergot n'existant que chez certaines races mais pouvant être double chez quelques bergers (beauceron, briard). Les cinq orteils se terminent par des griffes et sont soutenus par des coussinets plantaires. La tête du chien comporte une mâchoire puissante. La morsure d'un rottweiler a été mesurée à 149 kg/cm2, celle d'un berger allemand a une pression de 108 kg/cm2, et celle d'un pitbull 106 kg/cm2. La denture définitive, constituée de quarante-deux dents, est en place vers 6 mois. Chez le chien, la taille et la masse sont très variables d'une race à l'autre : dans les extrêmes, la masse du chihuahua peut être de 900 g et celui du mastiff peut atteindre 140 kg. L'espérance de vie de cet animal est en moyenne de onze ans, sachant que la durée de vie peut habituellement aller de huit à vingt et un ans. Son sens de l'orientation est beaucoup plus précis que celui de l'homme. De même, son sens de l'équilibre serait légèrement plus aiguisé. La température corporelle normale du chien va de 38,5 à 38,7 °C. Sa respiration normale va de seize à dix-huit mouvements à la minute (le jeune 18 à 20, le vieux 14 à 16). Sa fréquence cardiaque au repos est généralement comprise entre 70 et 130 battements par minute (les valeurs hautes s'observant plutôt chez les petites races, et inversement). Le pouls peut se prendre en palpant l'artère fémorale, sur la face interne de la cuisse. L'existence de huit groupes sanguins dans l'espèce canine a été mise en évidence à partir des années 1960, mais le chien ne possédant pas initialement d'anticorps anti-globules rouges, une première transfusion sanguine est possible sans détermination des groupes du donneur et du receveur. Cette détermination est fortement conseillée à partir de la seconde transfusion du fait que le receveur a pu s'immuniser contre les antigènes du donneur lors de la première transfusion.
Sens
Le cerveau du chien figure parmi les plus performants du règne animal, démontrant de très bonnes capacités cognitives avec des sens très développés.
Le sens de l'odorat est un sens extrêmement développé chez le chien. La taille de ses cavités nasales est environ trente fois plus grande que chez l'homme et la surface de la muqueuse olfactive, qui varie beaucoup en fonction de la race, est de huit à vingt fois supérieure à celle de l'homme (85 à 200 cm2 contre 10 cm2). Il possède dix fois plus de cellules olfactives et quarante fois plus de neurones consacrés à l'odorat que l'homme. À noter que ce sens est discriminant (le chien est capable de déceler et de suivre une odeur précise parmi une multitude d'autres odeurs, même si celle-ci est en proportion infime), capacité largement utilisée par l'homme pour les recherches de drogues, explosifs, personnes disparues, chasse, etc.
L'ouïe est aussi un sens très précis : le chien peut entendre des sons jusqu'à quatre fois plus loin que l'homme et capte également des sons inaudibles pour l'homme (ultrasons). En effet, la plage de fréquences que perçoivent les chiens s'étend de 40 Hz à 60 000 Hz (contre 20 Hz à 20 000 Hz pour l'homme). De plus, les oreilles du chien peuvent s'orienter vers une source sonore en pivotant grâce à de nombreux muscles, ce qui leur permet une grande précision dans la localisation sonore.
La vision du chien est plutôt modeste comparée à ses deux premiers sens. Toutefois, la gamme de couleurs qu'il perçoit, même si elle n'est pas aussi importante que chez l'homme, est tout de même assez ample. Le chien perçoit facilement les objets en mouvement mais il a du mal à faire le point sur des objets immobiles ainsi que sur les distances et sur les détails. Cependant le champ de vision du chien est plus vaste (environ 250 degrés) que chez l'homme (180 degrés maximum) avec une vision périphérique dix fois plus sensible. Le chien a également une vision optimisée dans le noir, possédant une surface réfléchissante derrière la rétine (le tapetum lucidum), qui renvoie la lumière et donne un effet d'yeux brillants dans l'obscurité.
Le toucher est particulier chez le chien car les organes sensibles au toucher sont des poils, plus particulièrement les sourcils, les vibrisses et les poils situés sous la mâchoire avec plus ou moins le même niveau de développement que le toucher de la peau chez l'homme. Hormis ces organes sensoriels, le toucher reste assez peu développé sur la peau, mais le chien est capable de faire aisément la différence entre une caresse et une correction ou bien la chaleur et le froid.
Le goût. Bien que le chien perçoive des différences de saveurs, ce sens est assez peu développé car contrairement à l'homme, c'est d'abord l'odeur d'une nourriture qui entre en premier en ligne de compte.
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The domestic dog is a domesticated canid which has been selectively bred over millennia for various behaviours, sensory capabilities, and physical attributes. Although initially thought to have originated as an artificial 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 an extinct wolf-like canid in Eurasia 40,000 years ago. Their long association with humans has led to dogs being uniquely attuned to human behavior and are able to thrive on a starch-rich diet which would be inadequate for other canid species. Dogs are also the oldest domesticated animal. Dogs vary widely in shape, size and colours. 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 influence on human society has given them the sobriquet, "man's best friend".
Etymology
The term "domestic dog" is generally used for both 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. 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". This semantic shift may be compared to in German, where the corresponding words Dogge and Hund kept their original meanings. A male canine is referred to as a dog, while a female is called a bitch. The father of a litter is called the sire, and the mother is called the dam. (Middle English bicche, from Old English bicce, ultimately from Old Norse bikkja) The process of birth is whelping, from the Old English word hwelp; the modern English word "whelp" is an alternate term for puppy. A litter refers to the multiple offspring at one birth which are called puppies or pups from the French poupée, "doll", which has mostly replaced the older term "whelp".
Taxonomy
The dog is classified as Canis lupus familiaris under the Biological Species Concept and Canis familiaris under the Evolutionary Species Concept. In 1758, the taxonomist Linnaeus published in Systema Naturae a categorization of species which included the Canis species. Canis is a Latin word meaning dog, and the list included the dog-like carnivores: the domestic dog, wolves, foxes and jackals. The dog was classified as Canis familiaris, which means "Dog-family" or the family dog. On the next page he recorded the wolf as Canis lupus, which means "Dog-wolf". In 1978, a review aimed at reducing the number of recognized Canis species proposed that "Canis dingo is now generally regarded as a distinctive feral domestic dog. Canis familiaris is used for domestic dogs, although taxonomically it should probably be synonymous with Canis lupus." In 1982, the first edition of Mammal Species of the World listed Canis familiaris under Canis lupus with the comment: "Probably ancestor of and conspecific with the domestic dog, familiaris. Canis familiaris has page priority over Canis lupus, but both were published simultaneously in Linnaeus (1758), and Canis lupus has been universally used for this species", which avoided classifying the wolf as the family dog. The dog is now listed among the many other Latin-named subspecies of Canis lupus as Canis lupus familiaris. In 2003, the ICZN ruled in its Opinion 2027 that if wild animals and their domesticated derivatives are regarded as one species, then the scientific name of that species is the scientific name of the wild animal. In 2005, the third edition of Mammal Species of the World upheld Opinion 2027 with the name Lupus and the note: "Includes the domestic dog as a subspecies, with the dingo provisionally separate - artificial variants created by domestication and selective breeding". However, Canis familiaris is sometimes used due to an ongoing nomenclature debate because wild and domestic animals are separately recognizable entities and that the ICZN allowed users a choice as to which name they could use, and a number of internationally recognized researchers prefer to use Canis familiaris. Later genetic studies strongly supported dogs and gray wolves forming two sister monophyletic clades within the one species, and that the common ancestor of dogs and extant wolves is extinct.
Origin
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 more 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
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.
Health
There are many household plants that are poisonous to dogs including begonia, Poinsettia and aloe vera. 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 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, and mites, as well as hookworms, tapeworms, roundworms, and heartworms. 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), grapes and raisins, macadamia nuts, xylitol, as well as various plants and other potentially ingested materials. The nicotine in tobacco can also be dangerous. Dogs can be exposed to the substance by scavenging garbage or ashtrays; 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. Dogs are highly 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 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.
Intelligence
Dog intelligence is the ability of the dog to perceive information and retain it as knowledge for applying to solve problems. Dogs have been shown to learn by inference. A study with Rico showed that he knew the labels of over 200 different items. He inferred the names of novel items by exclusion learning and correctly retrieved those novel items immediately and also 4 weeks after the initial exposure. Dogs have advanced memory skills. A study documented the learning and memory capabilities of a border collie, "Chaser", who had learned the names and could associate by verbal command over 1,000 words. Dogs are able to read and react appropriately to human body language such as gesturing and pointing, and to understand human voice commands. Dogs demonstrate a theory of mind by engaging in deception. An experimental study showed compelling evidence that Australian dingos can outperform domestic dogs in non-social problem-solving, indicating that domestic dogs may have lost much of their original problem-solving abilities once they joined humans. Another study indicated that after undergoing training to solve a simple manipulation task, dogs that are faced with an insoluble version of the same problem look at the human, while socialized wolves do not. Modern domestic dogs use humans to solve their problems for them.
Behavior
Dog behavior is the internally coordinated responses (actions or inactions) of the domestic dog (individuals or groups) to internal and/or external stimuli. As the oldest domesticated species, with estimates ranging from 9,000–30,000 years BCE, the minds of dogs inevitably have been shaped by millennia of contact with humans. As a result of this physical and social evolution, dogs, more than any other species, have acquired the ability to understand and communicate with humans and they are uniquely attuned to our behaviors. Behavioral scientists have uncovered a surprising set of social-cognitive abilities in the otherwise humble domestic dog. These abilities are not possessed by the dog's closest canine relatives nor by other highly intelligent mammals such as great apes. Rather, these skills parallel some of the social-cognitive skills of human children.
Communication
Dog communication is about how dogs "speak" to each other, how they understand messages that humans send to them, and how humans can translate the ideas that dogs are trying to transmit. These communication behaviors include eye gaze, facial expression, vocalization, body posture (including movements of bodies and limbs) and gustatory communication (scents, pheromones and taste). Humans communicate with dogs by using vocalization, hand signals and body posture.