Origin of the domestic dog that was the most divergent group. The study found that the skulls of the "Goyet dog" and the "Altai dog" had some dog-like characteristics and proposed that the may have represented an aborted domestication episode. If so, there may have been originally more than one ancient domestication event for dogs as there was for domestic pigs. One theory is that domestication occurred during one of the five cold Heinrich events that occurred after the arrival of humans in West Europe 37 000, 29 000, 23 000, 16 500 and 12 000 YBP. The theory is that the extreme cold during
Dog type were described as species by Johann Friedrich Gmelin in 1788, and by Robert Kerr in his English translation of "Systema naturae" ("The Animal Kingdom") in 1792. Today the species Linnaeus named are identifiable as dog types, not species or subspecies. Some, such as "Canis aegyptius", a hairless dog type of Peru, have been documented and registered as breeds (Peruvian Hairless Dog). There are only two categories (subspecies) of domestic dog, "Canis lupus familiaris" and "C. l. dingo", recognized by the International Code of Zoological Nomenclature (ICZN Code). Beginning with the advent of dog shows in the mid-19th century in England,