The Mutation of Domestication
The transition from wolf to domesticated dog happened over thousands of years, in fact, the people of this time may have not even noticed an overall change happening. Dogs at this point still looked and probably acted pretty much like wolves.
Regardless, about 15,000 years ago, people began to have greater and greater impact on dogs, not only in their relationships with them, but on their appearance as well.
The levels of domestication varied around the world with location, time, need, and even with different types of wolves. For this discussion, we're interested in the groups that migrated from Asia to the americas over the Bering land bridge and the dogs they brought with them, or those that followed them.
Human grave sites in the americas, dating as far back as 9,000 years ago, revealed that the dogs were burried with people, giving us a glimpse at just how much these people valued their animals. But something even more interesting was found.
Amidst all the bones, even of wolves and coyotes, there were two types of dogs. One was a very large dog, much larger than the wolf, and the other was a very small dog. We know that the ancient peoples of the americas were masters of the their environment, but were they also masterful breeders? Serious changes were taking place to our friend, the wolf.
Furthermore, a modern discovery sheds light on some other changes that may have been occurring. Science has found that the act of domestication not only changes the behavior of a dog, essentially preventing maturity and creating dependency, but it will actually change the genetic make up, which then can be transferred to other generations.
The breeding for 'tame', characteristics of a more amiable dog, will actually create mutations in the wolf. The more superficial changes are the genetic mutations of floppy ears and curled tails which are caused from the reduction of adrenaline. The most significant change is to the shape of the skull.
If I understand all the scientific research, it goes something like this. Changes to the wolf's ability to mature, from any human interference that truncates or retards the wolf's natural aging process, results in a dramatically different skull type in adults. Essentially, they continue to be softer and rounder looking as in puppy-hood.
I wanted to throw this last bit in because it bridges the gap in physical appearance between dogs and wolves. With or without knowing, we basically created an entire species of mutant wolves.