The dog (Canis familiaris or Canis lupus familiaris) is a domesticated descendant of the gray wolf. Also called the domestic dog, it was selectively bred from an extinct population of wolves during the Late Pleistocene by hunter-gatherers. The dog was the first species to be domesticated by humans, over 14,000 years ago and before the development of agriculture. Due to their long association with humans, dogs have gained the ability to thrive on a starch-rich diet that would be inadequate for other canids.
Anatomy and physiology
Size and skeleton
Dogs are extremely variable in size, ranging from one of the largest breeds, the Great Dane, at 50 to 79 kg (110 to 174 lb) and 71 to 81 cm (28 to 32 in), to one of the smallest, the Chihuahua, at 0.5 to 3 kg (1.1 to 6.6 lb) and 13 to 20 cm (5.1 to 7.9 in).[30][31] All healthy dogs, regardless of their size and type, have the same amount of bones (with the exception of the tail), although there is significant skeletal variation between dogs of different types.[32][33] The dog's skeleton is well adapted for running; the vertebrae on the neck and back have extensions for back muscles, consisting of epaxial muscles and hypaxial muscles, to connect to; the long ribs provide room for the heart and lungs; and the shoulders are unattached to the skeleton, allowing for flexibility.[32][33][34]
Coat
The coats of domestic dogs are of two varieties: "double" being common in 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.[49] Premature graying can occur in dogs as early as one year of age; this is associated with impulsive behaviors, anxiety behaviors, and fear of unfamiliar noise, people, or animals.[50] Some dog breeds are hairless, while others have a very thick corded coat. The coats of certain breeds are often groomed to a characteristic style, for example, the Yorkshire Terrier's "show cut".[36]
Ecology
Population
The dog is the most widely abundant large carnivoran living in the human environment.[150][151] In 2020, the estimated global dog population was between 700 million and 1 billion.[152] In the same year, a study found the dog to be the most popular pet in the United States, as they were present in 34 out of every 100 homes.[5] About 20% of the dog population live in developed countries.[153] In the developing world, it is estimated that three-quarters of the world's dog population lives in the developing world as feral, village, or community dogs.[154] Most of these dogs live as scavengers and have never been owned by humans, with one study showing that village dogs' most common response when approached by strangers is to run away (52%) or respond aggressively (11%).[155]
Range
As a domesticated or semi-domesticated animal, the dog has notable exceptions of presence in:
The Aboriginal Tasmanians, who were separated from Australia before the arrival of dingos on that continent[175]
The Andamanese peoples, who were isolated when rising sea levels covered the land bridge to Myanmar[176][177]
The Fuegians, who instead domesticated the Fuegian dog, an already extinct different canid species[178]
Individual Pacific islands whose maritime settlers did not bring dogs or where the dogs died out after original settlement, notably the Mariana Islands,[179] Palau[180] and most of the Caroline Islands with exceptions such as Fais Island and Nukuoro,[181] the Marshall Islands,[182] the Gilbert Islands,[182] New Caledonia,[183] Vanuatu,[183][184] Tonga,[184] Marquesas,[184] Mangaia in the Cook Islands, Rapa Iti in French Polynesia, Easter Island,[184] the Chatham Islands,[185] and Pitcairn Island (settled by the Bounty mutineers, who killed off their dogs to escape discovery by passing ships).[186]
Dogs were introduced to Antarctica as sled dogs. Starting practice in December 1993, dogs were later outlawed by the Protocol on Environmental Protection to the Antarctic Treaty international agreement due to the possible risk of spreading infections.[187]
References
Thalmann O, Perri AR (2018). "Paleogenomic Inferences of Dog Domestication". In Lindqvist C, Rajora O (eds.). Paleogenomics. Population Genomics. Springer, Cham. pp. 273–306. doi:10.1007/13836_2018_27. ISBN 978-3-030-04752-8.
Linnæus C (1758). Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I (in Latin) (10 ed.). Holmiæ (Stockholm): Laurentius Salvius. pp. 38–40. Archived from the original on 8 November 2012. Retrieved 11 February 2017.
Wozencraft WC (2005). "Order Carnivora". In Wilson DE, Reeder DM (eds.). Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Johns Hopkins University Press. pp. 575–577. ISBN 978-0-8018-8221-0. OCLC 62265494. (via Google Books) Archived 14 March 2024 at the Wayback Machine
