The correct interpretation of this excerpt is: As Buck lives in the wild, he summons his natural instincts for survival.
In this passage, Buck is experiencing a deep connection to his ancestral instincts and heritage as a wild creature, revealing how living in the wild awakens those instinctual behaviors within him. The reference to how he learns to fight and howls like a wolf highlights his return to a primal state, emphasizing the transformation he undergoes as he adapts to his environment and taps into his innate survival instincts.