Nova had a show about dogs/wolves. They said that some researchers in Russia raised silver foxes and selectively for friendlyness. It turns out the the smaller the adrenal glands on these foxed the less angry they were and less likely to bite people. Over ten generations they bread the foxes to be very human friendly. The friendly foxes were more like cudley dogs. But the genes that control the adrenal glads size were also tied to the color of the fur. Foxes with more white fur also were friendlier.
They said that wolves that were more tame were cared for by early humans and those that were mean were killed or driven away. Over generations we got the domesticated dogs. This took 30,000 years to accomplish.