Evolution of the dog
Today domesticated dogs bear little resemblance to their progenitor, the wolf. Genetically they are similar, but physically and behaviorally they are very different. This paper will summarize how the dogs we know today evolved from wolves, and what caused the changes that we see between dogs and wolves today.
While the general consensus is that the domestic dog (Canis Familiaris) evolved from the gray wolf (Canis lupus), it is important to note that there are others who disagree. One competing hypothesis states that the dog originated from a wild Canis other than jackal or C. lupus (Koler-Matznick, 2002). While the questions this theory generates are worth exploring, due to the preponderance of evidence presented by other scholars, it will be assumed that the domestic dog did, in fact, evolve from the gray wolf.
There are various theories surrounding how, when and where wolves became domesticated. One theory states that humans would have played a large part in domesticating wolves by using selective pressure and creating an ecological niche where a tamer wolf would succeed. According to Clutton-Brock, in order for a species to be domesticated, it is a result of reproductive isolation from their wild progenitors combined with natural and artificial selection in association with human societies. (Clutton-Brock, 1999) Wolves would have been brought into human settlements and tamed, and over time, those wolves would breed with other tamed wolves until after many generations, the tamed wolves would develop into domestic dogs.
The biggest argument against this theory is that this would require reproductive isolation, which would be very difficult if not impossible for the hunter-gatherer humans of that time. They were often on the move, and would most likely not be devoting much time to domesticating their wolf pups. Even if two tamed wolves were to breed, the resulting offspring would not automatically be tame – they would still need extensive socialization as pups to become tame.
The leading theory regarding how wolves became domesticated was proposed by Raymond Coppinger, and it states that wolves became domesticated dogs by carving out a niche for themselves in the dumps of human settlements. He proposes that when humans gave up their nomadic lifestyle and began to gather in human settlements, a new ecological niche was created in the dumps of these human settlements. Wolves that had a higher “flight distance” tolerance would avoid these dumps, or spend more time and energy running away from the dumps when people approached than they would scavenging. Wolves with a lower “flight distance” would not startle and run from humans as easily, and this would allow them to eat more and succeed in this new niche. This flight distance gene would be passed on to future generations, with the tamer wolves having more success in the new environment. Over time, the wolves would develop a shape more suited to scavenging, with a smaller body and smaller brain, which would require less energy. Coppinger uses evidence of domestic dogs found in dumps in societies around the world to support his theory. (Coppinger, 2001)
Archeological evidence indicates that the dog was the first species of animal to be domesticated and that this occurred towards the end of the last Ice Age when all human subsistence still depended on hunting, gathering and foraging. (Serpell, 1995). However, genetic evidence may contradict this. According to one study based on mitochondrial DNA from 162 wolves and 140 domestic dogs, wolves were determined to be the ancestors of dogs, and the evidence suggested that dogs originated more than 100,000 years ago. (Vila, C., 1997) If this time period is correct, Clutton-Brock’s theory may garner more support. At this time however, the majority of archeologists, biologists and geneticists believe that the time period of 12,000 – 14,000 years is a more accurate time-frame.
Where wolves first turned into dogs is also an issue that scientists disagree on. Peter Savolainen, a molecular biologist from Sweden’s Royal Institute of Technology found that 95% of all domestic dogs could be traced back to just three females from East Asia, most likely China. (Savolainen, 2002). Another expert, anthropologist Stanley Olsen, states that fossil evidence from hundreds of human archeological sites in Europe, the Near East and Asia suggests that dogs evolved from different wolf populations in different places at different times. (Cohn, 1997) A study by Ben Koop, a biologist at the University of Victoria in British Columbia found that all domestic dog breeds form a single group, suggesting a single origin, with the exception of the Arctic elkhound which apparently evolved separately from all other dog breeds. It is the only breed known to have done so. (Cohn, 1997).
An interesting experiment was done by Dmitry Belyaev, a Russian geneticist. He established a multi-generational breeding program involving over 45,000 foxes. The foxes were bred with only one trait in mind – tameness. After six generations, a new class of tame fox was created that avidly sought out human contact, unlike the previous generations of foxes that had been bred. With each generation, a greater percentage of pups were in this tame class. Although only behavior was being selected for, physical changes were also noted during this experiment. By the eighth to tenth generation, the coat color changed, then floppy ears and curled tails showed up. After 20 generations, the foxes had shorter tails and legs. And after forty generations, the tame foxes had a longer reproductive season, their skulls were smaller in height and width, and their snouts were shorter and wider. They also had lower levels of activity in the adrenal glands and higher levels of serotonin which lower aggressive impulses. (Page, 2007) This experiment demonstrates how physical characteristics can be linked to behavioral characteristics. As wolves became tamer over time, similar physical changes could have resulted, causing a natural selection process in dog appearance. After some time, humans also would play a part through artificial selection based on physical and/or behavioral characteristics.
Whether the changes were caused by wolves being tamed as pets by humans, or taming themselves to take advantage of human dumps, the end result is the same – a change to the species resulting in both physical and behavioral differences, giving us the domesticated dog.
References:
Clutton-Brock, J. (1999) A Natural History of Domesticated Mammals. The Natural History Museum.
Cohn, Jeffrey (Dec 1997) How Wild Wolves became Domestic Dogs. BioScience, 47(11), 725-728.
Coppinger, R., & Coopinger, L. (2001). Dogs A startling new understanding of canine origin,behavior & evolution. New York, NY: Scribner.
Koler-Matznick, J. (2002) The Origin of the Dog Revisited. Anthrozoos, 15(2), 98-118.
Page, J. (2007) Dogs: A Natural History. HarperCollins Publishers Inc.
Savolainen, P., Zhang, Y., Luo, J.,Lundeberg, J. & Leitner, T. (Nov 22, 2002) Genetic Evidence for an East Asian Origin of Domestic Dogs. Science, 298(5598), 1610-1613.
Serpell, J., Barrett, P. (1995) The Domestic Dog: its evolution, behaviour, and interactions with people. Cambridge, UK: Cambridge University Press.
Vila, C., Savolainen, P., Maldonado J., Amorim I., Rice, J. Honeycutt, R. Crandall, K. Lundeberg, J. Wayne, R. (June 13, 1997) Multiple and Ancient Origins of the Domestic Dog. Science, 276, 1687-1689.
