The Call of the Wild Theme of Loyalty

In The Call of the Wild, loyalty is rare, but strong, when it exists. It is forged by the extremities of circumstance (Thornton saved Buck from death) and repaid with similar intensity (Buck saves Thornton repeatedly). The big question in this novel is whether Buck has greater loyalty to the wild and his own feral nature or to the man that has saved his life. Buck is unable to commit to his life in the wild until Thornton dies, perhaps suggesting that his love and loyalty for the man are stronger than his ancestral urges.

1. Does Buck choose to love John Thornton, or is it just an instinct, like everything else? What's the difference between instinct and choice? Are all choices instinct in the end, like Buck ending up in the wild?
2. Does Thornton have to die because he’s standing in the way of Buck answering "the call?"
3. What is going on with all the violence involved in Buck's love of Thornton? You know, how Buck bites his hand and Thornton verbally curses at him and so on. It's almost makes their love seem savage and primitive.

Buck's love for Thornton develops while he is adapting to the wild, but this love is incompatible with the natural world because of its domestic nature.

The difference between love and loyalty is illustrated in the contrast between the loyalty Buck feels to François and Perrault as opposed to the love he feels for Thornton.