By Trevor Turner and Maja Sandaker
Introduction
Domestication is defined as a process whereby wild species are bought under the control of man. Thus a domestic species is one which has undergone selection, natural or otherwise, in order to better adapt it to life around men. This has been one of the most important process in the evolution of society. Over the years, man has domesticated many animal species, including farm and pet animals, plant species, which take the form of almost all the vegetables and fruit we eat today, insects such as the silk worm, and more recently bacterial and viral species, which are used in the production of a wide range of products and treatment of disease. All of these have resulted in a drastic change in phenotype.
This is perhaps a wider use of the term domestication than is in general circulation. The most common interpretation is used to describe the process by which modern domestic animals have been bent by the will of man for his own gain. The subject of this essay will be the domestication of the dog and how this has impacted its wild behavior.
In common with all wild species which have been subject to domestication, the dog is a social animal. It is a necessary pretext of domestication that animals, especially those used to produce food, are able to be kept in large groups. There are parts of the world where to dog I even considered a delicacy, such as Korea. Perhaps the only exception to this rule is the domestic cat, which is thought to be descended from solitary wild cats.
However, it has often been said that man has not domesticated the cat, rather that the cat has domesticated man. It could also be noted that the cat’s more distant cousins, such as the lion, do live in groups or rather prides. Without domestication of food animals able to live in herds and plants able to be grown at high densities, it is unlikely that modern society could have progressed to its current level, supporting as it does such a large number of individuals.
The domestication of the dog
This subject is a matter of much debate. There are two main schools of thought, with differing hypotheses.
1. a. The domestication of the dog occurred in many different areas. This is based on the fact that dogs remains have been collected from many different archeological sites around the world.
b. The dog is a descendant of a number of different species. This is based around that fact that the domestic dog can be interbred with a large number of its close relative from the genus canidae. The best examples of this phenomenon are all have the same number of chromosomes, and are coyotes, jackals and the wolf. The relationship between the latter of the three and the domestic dog brings up an interesting point of classification.
Linneas, one of the forefathers of the modern zoological classification system, names the dog as a separate species within the genus, Canis familiaris. As previously mentioned, the dog can breed successfully with other canids. This is one of the basic notions of the concept of species. This, and the modern science of DNA analysis, has led to the reclassification of the dog as a vulpine subspecies by the International Commission of Zoological nomenclature. Thus the dog has become Canis lupus familiaris to the European wolf’s C. lupus lupus and the American wolf’s C. lupus occidentalis. This evidence is enough to prove that this part of this theory is incorrect. (As in many other branches of science, such as bacteriology, the reclassification of former species into subspecies has lead to rather unwieldy and complicated species names. Most biologists, and indeed the authors, have therefore chosen to maintain the classical binomial nomenclature when describing old species).
Another problem when discussing this subject is that the word "dog" is often used to describe all members of the family canidae, and the colloquial name for many species also contains the word dog, for example the bush dog, the African wild dog, and the raccoon dog.
c. Domestication started some 10-15 (14) thousand years ago. This is based around the discovery of dog remains around human dwellings of the Paleolithic era. However, as we have seen in the previous section, the dog and wolf are in fact very similar entities. It is likely that the dog underwent many phenotypic changes before reaching its modern form. Perhaps wolf like remains of domestic dogs have been disregarded in excavations of earlier sites.
You will perhaps have noted that the analysis of DNA, a very fashionable modern science, plays no role in the previous hypothesis. This, and other objections as explained above, has lead the authors to believe that the following, and also more modern hypothesis, is closer to the truth. It is not without its own faults, however.
2. a. The wolf is the sole ancestor of the dog. This is based on many morphological and behavioral studies, but perhaps more importantly in this day and age on the study of DNA. More specifically mitochondrial DNA was examined. The region chosen (control region) undergoes mutation very fast and so could be used to determine the differences between a young species such as the dog and other canids. The least differences were found between the dog and the wolf. The study also showed that there had been many interbreedings between dog and wolf since the first domestication (Vila et al. 1997).
b. The domestication of the dog took place around 135 thousand years ago. This was the conclusion of the same study by Vila. It is particularly interesting because it suggest that men and dogs have been together since the dawn of man. The DNA of the dog and wolf were used as a "molecular clock". The time taken for the two species to diverge was estimated based on the product of the time taken for genetic differences/mutations to occur and the number of mutations. The calibration of the clock maybe called into question. Although the number of mutations is a set quantity, the time taken for mutations to occur was based on modern dogs. This time may not have been uniform throughout the dogs development. The main sticking point is that wolves breed seasonally and once a year and seasonally, while dogs breed twice a year regardless of season, increasing the likelihood of mutation.
c. The domestication of the dog took place once only. This hypothesis can again be broken down into differing schools of thought.
One holds that the dog was domesticated in the Jarno cave region in the east of modern Iraq. Ironically this is the very region of the world where American soldiers are searching ancient caves for the fugitive Osama Bin Laden and his dastardly crew of followers. This is based on archaeological evidence, morphological evidence also points to an east Asian origin of the domestic dog, because an osteological jaw feature found in domestic dogs is also found in east Asian wolves, but is absent in all other wolves, and molecular DNA evidence, which shows that wolves from that region show the least genetic divergence from dogs. Statistical analysis even narrows the source to a group of five females. (Salvonian et al. 2002)
The other school of thought is that domestication occurred in ancient china. Statistical analysis suggests that all domesticated dogs are descendant of only three original female wolves.
Although differing greatly, these two hypotheses can be used to draw some conclusions. Firstly, it is possible to say with little doubt that the wolf is the sole ancestor of the dog. Secondly the dog is descended from the East Asian wolf and this domestication happened once only. Thirdly this process occurred at least 15 thousand years ago. The proof of the latter point is that there are Neolithic cave paintings depicting man and dogs together as early as the Neolithic, and also that native American dog breeds are descended from the same east Asian grey wolves and old world dogs, and not North American wolves. The Bering Strait, the land bridge between Siberia and Alaska, was flooded some 15 thousand years ago, so man and dog must have crossed together before this. This process therefore occurred long before the domestication of any other species, plant of animal.
The changes domestication has brought
The wolf is a fairly uniform species. The weight, height and bone structure vary little between different subspecies, although the coat colour does how wider range, for instance between the pure white of arctic wolves in the winter and typical mixture of grey, black and brown of timber-wolves. This is compared with the domestic dog, with enormous breed differences in size (from the 85kg great dane to the 1kg yorkshire terrier) bone structure (the greyhound compared to the dachshund) coat colour, length and texture (the puli compared to the Mexican bald dog) and inherent behavior (the Labrador retriever and the rotwieller). The domestic dog also breeds twice a year with males fertile all year round, the wolf only once.
Interestingly, modern dog breeders have tried to emulate the wolf by producing a breed like it. The result is the German shepherd or alcasian, one of the most popular dog breeds in the world. Whether this is similar to the wolf is questionable, because it is impossible to reverse thousand of years of evolution. In the authors’ opinion, the resulting animal, prone to hip dysplasia, epilepsy, paranoia and other physiological disorders, is a failure when compared with the hardiness and mental balance of a wild wolf. A better way of achieving a vulpine dog is direct breeding with wolves. This is the strategy of the Eskimo in the breeding of the Alaskan husky, which is bred back with wolves every eighth generation. Ownership of such wolf/dog hybrids is strongly restricted in most countries.
Other physical changes include the appearance of floppy ears, a shorter nose and smaller skull compared to body size.. The size of the eyes compared to the rest of the face is also bigger. This is typical of wolf cubs around four months old (Coppinger and Coppinger, 2001). Tails also tend to be curved and carried above the back. These are all traits typical of wolf pups, who have floppy ears, erect tails and ess angled facial features. This process has been described as paedeomorphosis, or the retention of juvenile traits in adults. Thus many people now belive that dogs are paedeomorphic wolves. These traits in wolf pups trigger a response in adults causing them to care for their young.
Behavior has perhaps undergone a less pronounced change, although it too has moved towards the juvenile. Starting at birth, the imprinting period, in which animals learn who their parents are, is more prolonged in dogs than wolves (eight to twelve weeks as opposed to three). Domestic dogs are known for their bark, which is often worse than their bite. This is not the case in wolves however, who barks only a pups. Wolves also grow out of whining ans submissive behavior, except that which is involved in maintainence of the social hierachy. The hunting instinct of some dogs has also been destroyed. For example, the Himalayan mountain dog will catch and kill animals, but will wait for the shepherd to cut the carcass open before it can begin to eat.
The pack instinct of dogs has not been destroyed, but rather its target changed. The dog will regard its owner as the pack leader (provided it has been appropriately trained) and other members of the family as subordinate or superior. This is why most dog attack victims are family, or rather pack, members who the dog has considered lower in the hierarchy than itself and chosen to dominate, like the elderly of small children. Most canine behavioral faults can be solved by looking at the dogs family as a pack and trying to make it the most subordinate member. This can be achieved using the same methods as dominant individuals use in the wild, for example taking aggressive stances, towards the dog or feeding the family first.
Experimental examination of the domestication process
As mentioned in the previous section, many aspects of the dogs physical and mental characteristics have undergone changes when compared to the wolf. Defining these changes in scientific terms is difficult because the domestication process occurred many thousands of years ago, and would be difficult to repeat.
In Russia in the 1940’s and experiment was carried out on a population of fur farm silver foxes (Vulpes vulpes) in which the domestication process of this species was examined. The authors realize that this is a different species entirely to the domestic dog, however it is a close relative of the dog (when compared with, for example, a whale). However, some of the observations of the experiment were found to relate to the dog, and so we feel it is valid to examine here.
At the start of the experiment, the fur farm foxes were wild. That is to say, they feared man and were nearly impossible to tame. In this way they are similar to true wild dogs like the kelpie and new Guinea singing dog which cannot be tamed. The foxes were bred for one trait, tameness around people.
During the experiment, various physiological parameters were closely monitored. Perhaps most notably, corticosteriod production by the adrenal gland was reduced. These hormones are responsible in some degree for aggression and fear type behavior, so the effect of their reduction would have been to produce calmer animals. Another neurotransmitter whose concentration changed was serotonin. This is held responsible for creating a feeling of "well being" in the brain, promoting calm. Its concentration was found to increase. In terms of physical characteristics, there was also found to be a move towards paedomorphosis ie. Shorter wider noses, larger eyes, curled tails (due to reduced number of vertebrae) etc.
There are two possible explanations for this results. Firstly, the reduction in the production of these two hormones could have had an effect on the development of the foxes. Secondly, the gene for behavioral change (or reduced production of serotonin and corticosteroids) could have been linked to another gene for these paedomorphic characteristics on the chromosome, so when the former was selected, so was the latter. This phenomenon, whereby the selection for one trait also results in the selection of one or more other traits, is called selection. This is why many domestic animal breeds share common genetic diseases, for example malignant hyperthermia in Danish land race pigs (a problem now more or less eliminated) or narcolepsy in Dobermans.
Although this experiment is a good analogy for the domestication of the dog, it is flawed in many ways, apart from the obvious fact that it involved silver foxes and not wolves. Many of the technologies and methods used were not available to pre-Neolithic man, such as bottle for bottle feeding. Also, the amount of time required to raise a wolf cub is immense, more time than a hunter gatherer on a subsistence existence could afford. Also the sheer number of test subject required to produce the result is greater than a caveman could have supported.
The domestication process
This brings us on to the question of whether domestication was an intentional process on the part of humans, or one of "self domestication" by ancient wolves. The answer, as is typical in such situations where two ideologies oppose each other, is a compromise, just as Hegel predicted, as part of a dialectic process. Initially the domestication process was one of natural selection, with wild wolves finding living easier around human settlements where they could scavenge for food. Many dogs today in more rural settlements still live just like this, with no intentional human care.
Those wolves who were more puppy like and friendly, and vitally less scared of humans, would have done better and been selected. Later, man would have seen the potential for domestication and put these "proto-dogs" to work. It has been said that man is at his most creative when it comes to food or war. The dog could have been utilised for both, running down wounded prey and guarding human encampments from intruders.
Conclusion
The general trend in the domestication process, in the authors’ opinion, is that dogs have been bred from wolves towards paedomorphosis. Many of these characteristics, for example larger eyes size as compared to the face, are shared with human babies. These characters have been shown in humans to stimulate an instinctive response, ultimately resulting in the protection and care for an infant, or in this case dog. All members of the class mamallia use similar tactics to cause adults to care for their young, so this "cross reaction" is not so surprising. Thus many dogs act as surrogate children for people, becoming the focus for their natural parenting behavior.
Perhaps this brings into question the idea that the relationship between man and dog as a symbiosis. We naturally regard ourselves as the leader of the pack, the controlling partner in the relationship. Dogs, however, appear to have developed a way of almost forcing us to care for them. As an example, look at the multimillion dollar pet care industry, or highly financed charities like the British RSPCA. The loss of the hunting instinct, and the resulting dependence on humans for food, has reduced the dog to an almost parasitic entity. Deprived of the ability to fully mature, they live a life of perennial puppyhood.
Early in the history of our coexistence, the flow of benefit between partners was more balanced, the dog performing duties such as hunting and guarding. Nowadays, only a tiny percentage of dogs can be said to work for their living. Most of the worlds' canine population are scavengers or pets. In evolutionary terms, this is an advantage to the dog. They have found their niche and are exploiting it to its full. Their continuing existence, although irretrievably linked to humans, is ensured, and with little effort of their own.
The domestication of the dog has been an arduous process. The dog has become an integral part of life in cultures throughout the world, accompanying man on his journey through civilization since its birth. Along the way, they have done less and less for us, and we have done more and more for them. Their elevation to "pet" animal has relived them of the basic challenges of living. Which begs the question, who really is the master?
References
http://www.ualberta.ca/~jzgurski/dog.htm
http://www.ananova.com/news/story/sm_713600.html
http://www.bordercollie.org/kpbehav.html
http://www.canineworld.com/ngsdcs/
Early Canid Domestication: The Farm Fox Experiment Published by American Scientist, Vol. 87 No. 2 (March-April 1999). L. Trut
The behaviour of the domestic dog (Canis familiaris) (handout by Peter Kabai for vet students)
Sophie’s World – Jostein Gaarder
Almost like a whale – Steve Jones
Professor F. Hajos of the Faculty of Veterinary Science, St. Istvan Universty,
Budapest