My daughter and I watched a show about dog evolution on NOVA last night. It was narrated by John Lithgow. Very interesting stuff. The scientists interviewed scoffed at the idea that humans adopted, then domesticated wolves.
Their reasoning goes like this:
1) Dog training and selective breeding are very difficult. They require a lot of resources and some sophisticated knowledge.
2) While archaeological evidence shows that humans and dogs have cohabited for at least 15,000 years, genetic clock evidence indicates that the dog line goes back about 100,000 years.
3) Dog's brains are smaller than wolves' brains.
From these facts some researchers conclude that dogs became at least partially domesticated BEFORE humans adopted them. They suggest that as early human groups began to throw away garbage, some wolves filled a niche by becoming scavengers. (Scavengers generally have smaller brains than predators.) Those scavengers had an evolutionary advantage over the wilder ones who had to struggle much harder to get their food. Over generations, populations of these animals gradually lost their fear of humans and lived alongside them. That is, they became dogs in this process.
An interesting factoid from the show: the earliest dogs seemed to be playthings for royalty and looked a lot like modern salukis.