Why do you think London emphasises the connection between Buck and his ancestors ?

The focus on Buck's ancestors explains inherited traits. It explains the part of Buck that yearns to be free and wild. The call of the wild is instinctive.... the instinct of a wild animal that hasn't been tamed.

One can reframe Buck's journey in The Call of the Wild as a search for companionship. Buck is never alone in the novel, but instead travels between a various number of humans and other dogs, often wondering why he is not completely happy. At the beginning of the novel, Buck does not seem to lack for anything. One might wonder whether Buck is actually better off at the end of the novel, if he never felt unfulfilled in his Santa Clara home. But, it seems likely that Buck was simply young, and as he grew older he would have felt the lack of true companionship more strongly.

Buck encountered several positive kinds of companionship along his journey. First Francois and Perrault, then the Scotchmen, engaged him in meaningful relationships based on work, along with the rest of the dog team. Though Buck was sometimes tired and uncomfortable, he was fulfilled by his work. His relationship to John Thornton was obviously superior to these, and it was at its peak when he was able to work for John Thornton, fulfilled by his labor and inspired by his love. But, throughout these times, he was restless and knew something was missing.

Buck always dreamed of his companionship with wild man, because only that partnership was completely equal. Then, Man and Dog were united by mutual goals, mutual labor, mutual fears and mutual desires. When Buck meets the lone wolf in the woods and runs with him for a few hours, he finally understand the meaning of the call that he has felt. His relationship with the wolves is like his relationship with wild man. When John Thornton dies, Buck is free to go with the wolves. He mourns John Thornton, because he loved him, but the story suggests that Buck's final home among the pack of wolves is the right one.