Why did early human ancestors keep dog's ancestors?

I read a lot of things in a lot of places, and most the time I remember some piece of information, or severaal pieces that lead to a total, but I don't remember where I read them. I'm guessing maybe an issue of Nat Geo (my auto mechanic has them in the waiting area) or a Nat Geo special, or something on Animal Planet. I've also been to a few workshops by animal behaviorist Patricia McConnel. She might have mentioned something. I do remember something on TV a number of years back about the basic southern "Yellow Dog" which a naturalist realised strongly resembled African tribal dogs that were suspected of being the closest thing to domestic dog's ancient ancestor. I know I saw the article about the Russian fox project in Nat Geo maybe a year or so ago.