The most recent theory I've read is that the wolf half domesticated itself by raiding human garbage dumps. They had to evolve the ability to not run or attack when a human approached to distances that a true wild wolf would react to. Then humans finished the job. The Russian Silver Fox project shows how a fox (and presumably a wolf) could be bred to dog in as little as 50 years. A lot less than once thought. Quicker perhaps with the half domesticated wolves they (apparently) started with, the guy who started the project may well have seen results.