Signs of death in the form of abandoned gear litter their paths. In the spring gold is found. There is nothing for the dogs to really do except muse by the fire. This lack of work causes Buck to remember his vision of the early man. In his mind he wanders in this early, undefined world.
Fear is the most salient point with it.
Buck and the man are always vigilant and searching. Akin to this vision is the call that Buck hears nightly in the forest. Eventually he is unable to sit still, night or day. The call becomes too much to resist, and one night Buck goes looking for it. He comes upon a timber wolf.