Summary
The next morning, as François harnesses the dogs, he tries to install Sol-leks in the lead position. But Buck refuses to accept this. He wants to be the lead dog, and will not settle for anything less. François and Perrault at first try to beat him into obedience, but Buck keeps out of reach. Eventually Buck wins the battle of wills and is installed as the lead dog. He excels in the position, and quickly restores discipline in the team. Two more dogs, Teek and Koona, are acquired, and Buck breaks them in. The weather is comparatively benign and they make good progress, averaging forty miles a day for fourteen days until they reach Skagway.

François and Perrault are ordered elsewhere by the government, and leave Buck behind. He makes the trip back to Dawson with his team under a new master. They are extremely tired but get only a two-day break before setting off once more. At nights, Buck has visions of life from long ago; he sees a caveman and large beasts of prey. He is fascinated by these visions, which take him further back into primitive times.

The dogs get more and more weary, and Dave in particular weakens. He is taken out of the traces, but he resents this. He wants to continue to do his job despite the fact that he is too weak to do to. So his driver puts him back in harness, and Dave continues to pull, falling down several times. They reach camp at night, but in the morning Dave is too weak to travel. The dog-sled moves out without him, and the Scotch half-breed who is in charge goes back and shoots Dave in an act of mercy.

Analysis
Buck quickly shows that he is a worthy pack leader, since the dog-team makes the run to Skagway in record time. This makes François and Perrault local celebrities, but it is to Buck that they owe their success.

François and Perrault then depart from Buck's life for good. They were hard men, but they treated Buck fairly, and he respected them. They are both examples of men who adapted well to their harsh, uncivilized environment. Perrault in particular is described in terms that could also be applied to Buck ("Nothing daunted him"). They show that when men, like the dogs, also revert to a more primitive way of life and behavior, it is possible to do so with honor. Buck's next experience with humans, in chapter 5, will show the other side of the coin.

The significance of the vision of the cave-man is that Buck is tapping into the collective memory of the species, not his own personal memories. It is this that makes him so quick to adapt to primitive ways of life. Something in him remembers the lives of his ancestors, even though at a personal level all he can remember is his luxurious, easy life at Judge Miller's ranch.