This is an interesting experiment conducted in the USSR with foxes that seems to suggest that there were certain genetics that made certain canines within a species more apt to become tame. The foxes in the study were bred for tameness, the results were intruiging:
The domesticated foxes were more eager to hang out with humans, whimpered to attract attention, and sniffed and licked their caretakers. They wagged their tails when they were happy or excited. Further, their fear response to new people or objects was reduced, and they were more eager to explore new situations. Many of the domesticated foxes had floppy ears, short or curly tails, extended reproductive seasons, changes in fur coloration, and changes in the shape of their skulls, jaws, and teeth. They also lost their "musky fox smell."
So, seemingly, at some point, canines which tended to be more tame were attracted to humans, most likely for our garbage. At some point, humans took advantage of that tameness and started the domestication process, and further bred for tameness, which resulted in physiological changes.
It would seem that the dates for this process keep getting pushed further and further back, that dogs have been our companions for some time now.
