Silver Fox (vulpes vulpes)
I find the origin of dogs and how their history is so closely intertwined with ours a fascinating topic.
There are a few different theories on how the domestic dog emerged. However, the actual event and where it happened will most likely never be known. As a matter of fact the existence more than one origin looks more and more likely.
The two domestication theories most frequently cited, “adoption” and “self-domestication,” are both verifiable as possibilities but neither can be effectively disproved. In addition, the question as to whether or not domestic dogs evolved from wolves, coyotes, jackals, or a common ancestor can neither be proven nor disproven given the current fossil record and mitochondrial DNA (mtDNA) information.
The oldest known fossil of a domesticated dog, a part of a jaw estimated to be from 14,000 years ago, was discovered in Germany. The next oldest was discovered in Iraq and is estimated to be 12,000 years old. But there is no fossil evidence for an intermediate species between wolf and the smaller dogs identified from this time period, leaving the question of the early dogs’ ancestry and date of origin unknown.
Recently, mtDNA evidence has lead some to place the origin of the dog as far back as 135,000 years ago in Asia. This interpretation of the mtDNA record assumes that mtDNA evolves at a steady, linear pace, which is not the case. Even the study admits this means the 135,000-year estimate “may be inflated,” without providing an adjusted estimate.
Given such a wide range of time estimates, a lack of agreement on how dogs emerged as a species would not be surprising. However, many authors indicate or assume that dogs descended from wolves, with some papers even treating this as a fact. Mitochondrial DNA analysis indicates that dogs and wolves are much more closely related than dogs are to coyotes or jackals, with significantly more variations between dogs and coyotes and jackals than there is between dogs and wolves. As a matter of fact, there is only as much variation between dogs and wolves as there is between different breeds of dog!
In 1993 the Smithsonian Institution and the American Society of Mammalogists changed their designation for the domestic dog from canis familiaris to canis lupus familiaris. This change is not universally recognized and some scientists explicitly reject this designation as it can be interpreted as settling the debate over the dog’s origins by designating it as a subspecies of the Gray Wolf.
A frequently cited theory on the origin of the dog is that man domesticated the wolf. This theory posits that early man took wolf cubs, raised them and somehow selected based on tameness. The remains of wolves, wolf cubs and other evidence of wolves living in or near human settlements dating 10,000 years before present (and earlier) support this idea. However, the time, effort and expense required in domesticating and training wolves must have been difficult, if not impossible, for early man. The effort required to not just tame a wolf, but teach it skills that would make it a useful member of the group, such as tracking or hunting, would have been substantial.
Early researchers found that wolf cubs, when separated from their mothers and socialized with humans daily, still preferred canine contact to human by the time they are 8 weeks of age. Mesolithic man would have had great difficulties problem obtaining puppies young enough, successfully separating them from their mothers, keeping them alive and healthy, and adequately socializing the puppies. If wolves ever were successfully “adopted” it would have required considerable effort, if not a great deal of fortune.
The adoption theory also implicitly assumes that dogs are descended from wolves, the same theory has not been proposed for coyotes or jackals, most likely because those species would not have been useful to Mesolithic man for anything other than food. However, for the same reason that the theory has only been proposed for wolves, it requires wolves be reshaped into a generalist role from that of a predator.
The self-domestication theory posits that wolves gradually evolved into the domestic dog because of adaptive pressure they encountered scavenging for food in and around Neolithic villages. Scavengers that had a shorter flight distance are able to gather more food and would have had greater reproductive success. Belyaev’s experiment with Silver Foxes (link to pdf) provides compelling evidence about how selective pressure on flight distance effects evolution.
In thirty generations of selection for tameness, Belyaev’s foxes were not just tolerant of humans; they solicited and competed for human attention. The foxes also developed significantly different appearances, with floppy ears, barking, curled tails, variations in the size of their skulls and jaws, and piebald coats. Significant changes in the levels of corticosteroids in blood plasma, the response of the adrenal cortex to stress as well as brain chemistry were documented.
The selection was based exclusively on the foxes’ reaction to the approach of humans at various stages of development. This experiment effectively tested and verified the effect selective pressure can have on the ability to tolerate close contact with humans. In evolutionary terms, thirty generations is a very short period of time, making it possible for Coppinger’s scenario to transpire very quickly, perhaps many times over in many different places.
New information regarding the origin of the dog hit the news last week. Researchers collecting DNA sample in Africa and South America have found evidence that the origin of the domestic dog might not be Asia. They found striking genetic diversity in Africa, which indicates a possible origin in those areas. My opinion is that this reinforces the notion of multiple origins. The “self-domestication” scenario could have transpired many times in several different continents over the course of many thousands of years.
Researching and discussing the origin of the domestic dog is a rewarding and challenging endeavor, but it’s important to keep in mind that the dog is a domesticated species and the single biggest difference between the domestic dog and the wolf is its relationship to us. Ian Dunbar put it very well in an interview with the San Francisco Chronicle: “Learning from wolves to interact with pet dogs makes about as much sense as, ‘I want to improve my parenting — let’s see how the chimps do it!’ ”
This PBS show provided a great look into the origin of the dog:
Dogs that Changed the World
These papers are also very helpful. A few require paid access though.
Belyaev, D. K. (1979). Destabilizing selection as a factor in domestication. Journal of Heredity,70, 301-308.
Clutton-Brock, J. (2006). Origins of the dog: domestication and early history. In J. Serpell (Ed.), The Domestic Dog (Tenth printing ed., pp. 7 – 20). United Kingdom: Cambridge University Press.
Coppinger, R., & Coppinger, L. (2002). Dogs: A new understanding of canine origin, behavior and evolution (2002 ed.). Chicago 60637: The University of Chicago Press.
Frank, H., & Frank, M. G. (1982). On the effects of domestication on canine social development and behavior. Applied Animal Ethology, 8, 507 – 525.
Koler-Matznick, J. (2002). Origin of the dog revisited. Anthrozoos, 15(2), 98 – 118.
Leonard, J. A., Wayne, R. K., Wheeler, J., Valadez, R., Guillen, S., & Vila, C. Ancient DNA Evidence for Old World Origin of New World Dogs. Science, 298, 1613-1616.
Olsen, S. J. (1). Origins of the domestic dog The fossil record. Tucson, Arizona: The University of Arizona Press.
Rafkin, L. (2006, October 15). The Anti-Cesar Millan. San Francisco Chronicle.
Savolainen, P., Zhang, Y.-P., Luo, J., Lundberg, J., & Leitner, T. (2002, November 22). Genetic Evidence for an East Asian Origin of Domestic Dogs. Science, 298, 1610-1613.
Vila, C., Peter, S., Jesus, M. E., Isabel, A. R., John, R. E., Rodney, H. L., et al. (1997). Multiple and ancient origins of the domestic dog. Science, 276(5319), 1687 – 1689.
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