Dog breed
Dogs are the most variable mammal on Earth, with artificial selection producing upward of 360 globally recognized breeds.
[1] These breeds possess distinct traits related to morphology, which include body size and shape, tail phenotype, fur type, etc, but are only one species of dog.
As a result of their adaptability to many environments and breedability for human needs, today dogs are the most abundant carnivore species and are dispersed around the world.
"[9] In 2017, a study showed that 9,000 years ago the domestic dog was present at what is now Zhokhov Island, arctic north-eastern Siberia, which was connected to the mainland at that time.
[2] In the Victorian era, directed human selection developed the modern dog breeds, which resulted in a vast range of phenotypes.
The skull, body, and limb proportions vary significantly between breeds, with dogs displaying more phenotypic diversity than can be found within the entire order of carnivores.
These breeds possess distinct traits related to morphology, which include body size, skull shape, tail phenotype, fur type and colour.
[15] The difference in size has been attributed to a lncRNA variant in the IGF1 region arisen in wolves from northern latitudes c. 53.000 years ago and fixed by natural and subsequently by human selection.
Indicators of recent selection were shown by many of the 51 genomic regions that were associated with traits that define a breed, which include body size, coat characteristics, and ear floppiness.
[12][13] In 2010, a study looked at 48,000 single nucleotide polymorphisms that gave a genome-wide coverage of 912 dogs representing 85 breeds.
[21] The study found distinct genetic clusters within modern dogs that largely corresponded to phenotype or function.
[21] The study found that there were three well-supported groups that were highly divergent and distinct from modern domestic dogs.
The earliest books in the English language to mention numbers of dog types are from the "Cynegetica" (hunting literature), namely, The Art of Venery (1327) by Twiti (Twici), a treatise that describes hunting with the limer (a leashed bloodhound type); the pack of running hounds, which included barcelets and brachetz (both scent hounds); and the sighthound and greyhound.
[22] More significant in recording the use and description of various dog types is The Master of Game (circa 1406) by Edward of York,[23][24] a treatise that describes dogs and their work, such as the alaunt, greyhound, pack scent hounds, spaniel, and mastiff, used by the privileged and wealthy for hunting purposes.
The Master of Game is a combination of the earlier Art of Venery and the French hunting treatise Livre de Chasse by Gaston Phoebus (circa 1387).
The study found a deep genetic split between old-world and new-world wolves, and confirmed the genetic divergence of 13 breeds from a 2010 study (Afghan Hound, Akita, Alaskan Malamute, American Eskimo, Basenji, Canaan dog, Chow Chow, Dingo, New Guinea singing dog, Saluki, Samoyed, Shar-Pei, Siberian Husky), plus another three: the Eurasier, Finnish Spitz and Shiba Inu.
[28] The 2012 study found that modern breeds only emerged in the 19th century and that claims of their antiquity are based on little or no historical or empirical evidence.
A dog breed is represented by a sufficient number of individuals to stably transfer its specific characteristics over generations.
Four varieties of the Belgian Shepherd Dog are recognised as four distinct breeds by the New Zealand Kennel Club.
[33] Further, some groups of dogs which clearly share a persistent set of characteristics and documented descent from a known foundation stock may still not be recognized by some clubs as breeds.
[34] In Canada, the Animal Pedigree Act lays out strict standards for the documenting of what it calls "evolving breeds".
Each of the member and contract partners issue and maintain their own pedigrees and respective breed standards, and train their own judges.
[44][45] Notably, dog breeds with flat faces and short noses have breathing difficulties,[46] eye trouble and other health issues.
[51][52][53][54] Historically, crosses between dogs of different types were more well accepted at a time when modern purebred breeds (based on the eugenics principles) did not yet exist.
This advantage can be progressively diluted when two crossbreeds are bred in the attempt to create a breed, narrowing the gene pool.
Purebred dogs have been, for the most part, artificially created from random-bred populations by human selective breeding with the purpose of enhancing desired physical, behavioral, or temperamental characteristics.
