In Jack London's classic novel, The Call of the Wild, the issue of how Buck's primal instincts slowly return to him plays a major role. If it were not for these impulses, Buck most likely, would not have survived his long journey. However, Buck didn't learn these things. They were in fact recovered. That detail is what makes this aspect of the story so out of the ordinary. It is the fact that he didn't need to learn new skills to survive. They were already there, within him.
At one point in Chapter 4, this is quite evident. This quote explains the feelings he had: "Far more potent were the memories of his heredity the instincts, which had been lapsed in later days, and still later, in him, quickened and became alive again." Other examples are the visions that Buck has of the "different man", who seems to be some ancient person from Buck's primal past. This man reappears throughout the book, as a sign of Buck's primordial feelings. Buck was not homesick at all. He even mentions how "such memories had no power over him". He was adapting to his surroundings with ease, and soon became the leader for Francois and Perrault.
Buck's primal intuitive thoughts were another way he was becoming more like his wild ancestors. One illustration of this was in Chapter 5, while Hal, Charles, Mercedes and the dogs stopped at John Thornton's camp. Thornton warned the group of the obvious danger that lied ahead if they went on. Buck already knew this. He sensed the "impending doom" as soon as the group came into the came. Buck's life was saved, partially because he followed his instinct.
Towards the end of the novel, Buck starts getting wild impulses like never before. He would just be lying around, when all of a sudden; he would feel a yearning. He would run into the woods, for hours, sometimes days, just enjoying the splendor of the nature. One night, he heard an actual call, from a wolf. He followed him, and almost kept going, before he remembered about Thornton.