In Chapter 4, London uses a simile comparing the sled dog team's work to that of a machine:
Buck did not like it, but he bore up well to the work, taking pride in it after the manner of Dave and Sol-leks, and seeing that his mates, whether they prided in it or not, did their fair share. It was a monotonous life, operating with machine-like regularity. One day was very like another.
By comparing the dog team's work to that of a machine, London evokes the idea of an industrial factory. As technology and industrialization continued to advance in London's lifetime, a huge part of the labor force became concentrated in factories, where they operated machines on an assembly line and functioned essentially as further cogs in those machines. London had his own experience with "monotonous life, operating with machine-like regularity." He grew up poor and spent his young adult life working at low-paying jobs. Eventually, he decided that this life was dehumanizing. He became a socialist who stood for workers' rights and more even distribution of wealth (at least among white men, considering that he held racist views). The simile suggests that London sees some of his younger self in Buck, who has not yet realized that he can refuse to "bear up well to the work."
The simile also hints at the complicated dynamics of the political landscape London was writing from, and it also hints at London's own troubling politics. The beginning of the 20th century was an especially bleak time for laborers in the United States. Following the passage of the 13th, 14th, and 15th amendments to the Constitution at the end of the Civil War, corporations began to take advantage of the new legal protections for Black people. The Supreme Court allowed corporations to assert rights over their employees, whereas workers' rights were still in their infancy. As long as workers were not technically enslaved, they could be forced into any number of inhumane situations. London believed that laborers deserved a share of their corporate employers' wealth and that it was wrong to exploit people as Buck and the rest of the dogs are exploited.
However, he also thought of the workers whose rights he was defending strictly as white men. He was not alone in pitting working-class white men against people of color who were even more mistreated, but he did write explicitly white-supremacist defenses of white male workers. London's use of a sled dog team to advocate for white workers' rights in The Call of the Wild demonstrates that he (like many other white activists at this time) saw more humanity in animals than in people of color.