As we have mentioned several times Darwin was a very smart and perceptive guy. But when it came to dogs even Darwin underestimated the power of selection (here artificial selection rather than natural selection). Darwin thought that the current array of dog breeds must have been descended from a number of different wild canine species such as such as jackals, coyotes and wolves. We now know this is not the case and all 350+ distinct breeds are, in fact, descended from one species, the grey wolf. This raises the question of just where all the variety in dogs came from.
A paper in Genome Research by Matthew Webster of Trinity College Dublin, Ireland, and colleagues at Uppsala University in Sweden has proposed an explanation. They analysed the complete mitochondrial DNA genome in 14 dogs, six wolves, and three coyotes. This data suggests that mutations in the canine genome have played a bigger role in dog evolution than previously thought. Natural selection usually weeds out mutations in wild species if they offer no survival advantage. But if that pressure is removed, these mutations will get passed on. This provided dog breeders with a wide inventory of traits in the DNA to exploit. Others disagree, Webster et al. only studied mutations in mitochondrial DNA, which tends to accumulate more quickly than in nuclear DNA which forms the largest part of the genome. Far fewer mutations may have occurred in genes in the nucleus compared with mitochondria. Much of the variation we see in dogs may have to do with pre-existing variation from the ancestral wolf-dog population.