Buck learns to steal food to survive when eating with other dogs. Being larger, he requires more food, and the other dogs frequently steal his rations. Initially, he fights back, but this only allows others to finish his food. Observing his companions, Buck adapts by stealing from Francois and Perrault, recognizing that survival in the harsh environment demands abandoning old notions of fair play and fastidiousness.

John Thorton is a man of the wilderness, whose life revolves around the freedom and purity of nature. He is deeply in love with his dog, Buck, and enjoys living a simple life with his dog in the wild. John's idyllic life becomes threatened when he is attacked by Indians who seek to steal from him. As a result of this attack, John and Buck are forced to separate for a short time as Buck travels through the wilderness alone to evade the pursuing tribe. During this time, Buck shows signs of reverting back to his wolf-like instincts and he begins hunting animals such as bears, moose and even fish out of rivers like a wolf would do.

Buck's feelings for Thornton are marked by deep devotion and genuine love, unlike the angry revulsion he felt toward previous masters. With earlier owners like Perrault and Francois, Buck showed respect but no affection, while with Hal and Charles, he felt irritation and bitterness due to their cruelty. Thornton's rescue of Buck from abuse and his caring nature fostered a passionate bond, a love Buck had never experienced before, even with Judge Miller.