All modern dogs are descendants of wolves, though this domestication may have happened twice, producing groups of dogs descended from two unique common ancestors.
If dogs evolved from wolves, which seems to be the case, then wolves must have had the capacity for this diversity somewhere in their genomes. Thus, Vilà and his colleagues decided to compare the mitochondrial DNA of dogs and wolves in an attempt to understand the genetic consequences of these species’ different lifestyles: domesticated versus wild. (Remember, both dogs and wolves evolved from a common ancestral wolf species, so wolves are an ideal control with which to study the consequences of dogs’ life with humans.) The mitochondrial genome was used because of earlier work by Vilà that showed the nuclear genomes of dogs and wolves to be too similar to study their molecular evolution. On the other hand, this research indicated that mitochondrial lineages are clearly distinguishable for the two species.
Genetic studies indicate that the grey wolf is the closest living relative of the dog. Attempting to reconstruct the dog’s lineage through the phylogenetic analysis of DNA sequences from modern dogs and wolves has given conflicting results for several reasons. Firstly, studies indicate that an extinct Late Pleistocene wolf is the nearest common ancestor to the dog, with modern wolves not being the dog’s direct ancestor. Secondly, the genetic divergence (split) between the dog’s ancestor and modern wolves occurred over a short period of time, so that the time of the divergence is difficult to date (referred to as incomplete lineage sorting). This is complicated further by the cross-breeding that has occurred between dogs and wolves since domestication (referred to as post-domestication gene flow). Finally, there have been only tens of thousands of generations of dogs since domestication, so that the number of mutations between the dog and the wolf are few and this makes the timing of domestication difficult to date.
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