The History of Dog Domestication
This is my 2007 course paper for Systematics class at the University of Miami. I think it might be of general interest.
Carnivores of genus Canis are among the best-studied mammals, but their systematics still present numerous challenges due largely to high genetic similarity and to the ability of many species to produce fertile hybrids in the wild. Traditionally, eight extant species have been recognized. A few more species, closely related to gray wolf and differing mostly in size, have gone extinct in the last 100,000 years. Below is the list of extant species (based on Nowak, 1999, with corrections), their distribution and major taxonomic problems.
1. Gray wolf (C. lupus). Historically North America south to Mexico, Eurasia except the tropical rainforest zone, many islands such as Greenland and Britain. Form lupaster of Egypt and Libya has been alternatively assigned to this species and to C. aureus; now the majority of sources seem to favor the former, but the population itself is apparently extinct. Form lycaon of southeastern Canada has been shown to be either a separate species or (more likely) a subspecies of C. rufus (Wilson et al, 2004). Other highly distinct populations are known from Japan (extinct), Queen Charlotte Islands, and India.
2. Red wolf (C. rufus). Described as inhabiting the Southeastern USA, now extinct in the wild (unless the form lycaon is included), except for small reintroduced populations.
3. Coyote (C. latrans). Historically southwestern Canada, western USA and Mexico; in the last 300 years has colonized most of Alaska, Central America and eastern North America. In areas where wolves are very rare, both wolf species produce fertile hybrids between themselves and with the coyote. Eastern populations of the latter are probably of hybrid origin to some extent.
4. Golden jackal (C. aureus). Historically Balkan Peninsula, Northern Africa and Southern Asia east to Myanmar; currently expanding and has reached Hungary, Vietnam and Malawi.
5-7. Striped jackal (C. adustus), black-backed jackal (C. mesomelas), and Simien wolf (C. simensis). Sub-Saharan Africa. The latter is critically endangered.
8. Dog (C. familiaris). Described from a domestic European specimen, it has occurred in association with humans on all continents (except the Antarctic) prior to European contact. There are still no dogs in the Antarctic due to an international ban, but domestic animals now inhabit every country. Many of 400-450 known domestic breeds show remarkable behavioral and physiological differences, particularly the basenji of West Africa, some Chinese and Amerindian breeds (Dinets & Rotshild, 1998).
Feral populations exist in many areas, including some remote oceanic islands such as the Galapagos. Two of them - the dingo (C. f. dingo) of Australia and the singing dog (C. f. hallstromi) of New Guinea (now apparently extinct in the wild) are many thousands of years old. Feral populations of tropical Asia (pariah dogs) are remarkably similar to dingoes and singing dogs in appearance, and are included in species C. dingo in some classifications, such as Corbett (1995). It has been suggested (reportedly, with supporting DNA evidence) that a feral population known as Carolina hunting dog has originated from an ancient introduction of pariah-like dogs to North America. (There are no scientifically published sources yet, but Wikipedia entry on "Carolina dog" contains a list of links to brief online articles).
Due to the recent trend to name domestic animals as subspecies of their wild ancestors, the dog is sometimes called C. lupus familiaris, but in my opinion it is wrong for reasons mentioned below. Unfortunately many popular sources, including Wikipedia, have followed this trend.
Dogs are known to hybridize in the wild with both species of wolf, the coyote and the golden jackal, especially where the wild species is close to extinction. All such hybrids are fertile. However, there is conspicuous lack of records of wolf-dog hybrids from the Middle East, India and China, even though local wolves often inhabit the vicinity of human settlements. In parts of northern Eurasia, populations of wolf-dog hybrids became a serious problem for wildlife management and public safety.Where normal wolf pack structure is still maintained, wolves regularly hunt dogs, often preferring them to any other prey (Dinets & Rotshild, 1997).
In some areas of the Arctic, crossing domestic dogs with wolves is traditionally practiced (Dinets & Rotshild, 1998); such hybrids are now kept as pets in many Western countries, but have been outlawed in some US states (Willems, 1995).
Originally, some experts believed that the golden jackal and/or coyote had played a part in the dog's origins, but that theory is now largely rejected based on genetic evidence discussed below. The gray wolf is now generally believed to be the sole ancestor.
The oldest archaeological remains certainly attributable to dogs are 14,000-12,000 years old (from Germany, Israel and China), although wolf-like bones have been found in association with human sites as old as 100,000 years. The only other domestic animals for which domestication earlier than 10,000 years ago has been established are the cattle (Bos primigenus taurus, B. p. indicus) and the reindeer (Rangifer tarandus) (Dinets and Rotshild, 1998).
The differences between dogs and wolves are larger than between any domestic animal and its wild ancestor. Dogs have 30% smaller relative brain size, noticeable differences in dentition, adaptations to an omnivorous diet in their digestive tract, and numerous other anatomical differences; even their gait and tracks are different. There are very significant behavioral differences: for example, dogs can't feed their puppies by regurgitating food. Adult dogs display many neotenic behaviors, such as tail wagging and barking (Dinets & Rotshild, 1998).
Experiments on red foxes (Vulpes vulpes) have shown that many of those differences can be reproduced simply by selection for friendliness to humans. By using this method over 30-40 generation of foxes, D. Belyaev produced animals with dog-like tails, floppy ears, irregular coloration, early sexual maturity and many neotenic behavioral traits (see Trut, 1999, for English summary). However, some of the differences between dogs and wolves probably needed a very long time to evolve.
Vila et al. (1997) have compared wolf DNA from 27 populations in Europe, Asia, and North America with DNA from 67 dog breeds worldwide. Not surprisingly, the study found that some dog breeds show traces of recent hybridization with various wolf subspecies. But it also estimated the date of original wolf-dog split as 150-400 thousand years ago. The authors (and many groups that later conducted similar research with similar results) have interpreted this result as the date of the first domestication event, presumably in Sub-Saharan Africa prior to the dispersal of Homo sapiens to other continents. However, to my knowledge, there are no wolf fossils from Sub-Saharan Africa.
In 2002, Savolinen et al. examined mtDNA sequence variation among 654 dogs representing all major populations worldwide. Based on levels of genetic variation and phylogenetic pattern, they concluded that all domestic dogs originated from an East Asian ancestor about 15,000 years ago.
However, the "domesticated wolf" theory has serious problems. Some features of dog anatomy, particularly brain structure, resemble jackals and coyotes, but not wolves. Although the most primitive dog breeds and the oldest feral populations all look similar, they do not particularly resemble wolves, having typical dog anatomy and mostly reddish or yellowish coloration. There is absolutely no archaeological evidence of any transition from wolves to dogs from human sites. And, most interestingly, pariah dogs of Asia are not known to hybridize with sympatric wolves, even where both forms coexist in very close proximity.
A much better explanation for all known facts is that dogs have existed in tropical Asia prior to the arrival of modern-type humans and subsequent domestication (Dinets & Rotshild, 1998).
In a little-noticed publication, Koler-Matznik (2002) summarized evidence that the ancestor of the dog was not the gray wolf, but a closely related, smaller extinct canid. The author suggests Canis (lupus) variabilis, an extinct wolf that occurred in present-day China 100-200 thousand years ago, as the most likely candidate. A Middle Eastern form similar to grey wolf and golden jackal seems to be another possible candidate.
Corbett, L.K. 1995. The dingo in Australia and Asia. Comstock/Cornell Univ. Press, Ithaca.
Dinets, V. & V. Rotshild. 1997. Mammals of Russia. Encyclopedia. ABF, Moscow [in Russian]
Dinets, V. & V. Rotshild. 1998. Domestic animals. Encyclopedia. ABF, Moscow [in Russian]
Koler-Matznick, J. 2002. Origins of the dog revisited. Anthrozous 15(2): 98 - 118.
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Nowak, R. M. 1999. Walker's Mammals of the World. 6th edition. The John Hopkins Univ. Press, Baltimore and London.
Savolainen, P., Y. Zhang, J. Luo, J. Lundeberg, T. Leitner. 2002. Genetic Evidence for an East Asian Origin of Domestic Dogs. Science 298: 1610-1613.
Trut, L.N. 1999. Early Canid Domestication: The Farm-Fox Experiment, American Scientist, 87: 160-169
Vila, C., P. Savolainen; J. E. Maldonado; I. R. Amorim; J. E. Rice; R. L. Honeycutt; K. A. Crandall; J. Lundeberg; R. K. Wayne. 1997. Multiple and ancient origins of the domestic dog. Science 276:1687.
Willems, R. A. The Wolf-Dog Hybrid - An Overview of a Controversial Animal. 1995. AWIC Newsletter. USDA, Baltimore.
Wilson, P. J., S. Grewal, I. D. Lawford, J. N.M. Heal, A. G. Granacki, D. Pennock, J. B. Theberge, M. T. Theberge, D. R. Voigt, W. Waddell, R. E. Chambers, P. C. Paquet, G. Goulet, D. Cluff, B. N. White. 2004. DNA profiles of the eastern Canadian wolf and the red wolf provide evidence for a common evolutionary history independent of the gray wolf. Can. J. Zool. 78: 2156-2166