The tone of the novel is reflective and sympathetic: London often dwells on small details and imagines what it would be like to be Buck. For example, in Chapter 7, London writes:
There is a patience of the wild—dogged, tireless, persistent as life itself—that holds motionless for endless hours the spider in its web, the snake in its coils, the panther in its ambuscade; this patience belongs peculiarly to life when it hunts its living food; and it belonged to Buck as he clung to the flank of the herd, retarding its march, irritating the young bulls, worrying the cows with their half-grown calves, and driving the wounded bull mad with helpless rage.
At this point in the novel, Buck is patiently hunting a wounded moose, and he is trying to get the moose away from the rest of the herd. It is taking a long time because the herd keeps coming back for it. London might choose to sympathize with the moose in this moment. Instead, he sticks close as ever to Buck's perspective. Even when Buck is preying on other living beings, then, London is relentlessly curious about his inner experience.
This curiosity and sympathy is not just because London loves dogs. More than that, it is emblematic of his naturalist approach. His novel aims to explore the effect of the natural, social, and political environment on an individual's life and behavior, and his chosen case study is a dog who is kidnapped from a life of luxury and plunged into a difficult working life in the Yukon. Still, London's ability to take this reflective and sympathetic tone towards a dog suggests that he has a certain respect for dogs' inner worlds. He does not afford this same respect to people of color in the novel (for instance, the "Yeehats" are presented as villains whose perspective London leaves unexplored) or outside the novel (he was an explicit white supremacist).