The original question had to be edited down. I would suggest that there is much in the text to depict a theme of predation that exists in the interactions of human beings. The friendship between Lennie and George is so unique to the other men on the farm precisely because it lacks this predatory element. Steinbeck shows that the condition of predator and prey underscores the nature of human beings. In doing so, attention is raised in the hopes of changing such a condition.
In Steinbeck's rendering, the world is shown to be fairly brutal. Men like Carlson and Curley are in the position of power, looking to exact more for themselves at the cost of others. Curley's need to always pick a fight, demanding respect through confrontation, is a part of this. Carlson packing a gun and seeking to initiate violence as a part of his mechanism to solving problems is another example. Both men display a construction of human existence where there is a clear predator and a clear prey. Candy's dog and Lennie at the end of the narrative become this prey. It acquires meaning that George tends to Lennie at the end, preventing the predatory mob from exacting its perceived revenge on him. At the same time, Steinbeck displays this theme in chapter five when Curley's wife encounters Crooks, Lennie, and Candy. They are her prey as her venom strikes at their powerless condition. This was precededed by Crooks striking at Lennie with constructions of fear and abandonment. In this predation, Crooks wishes, if only for a moment, to be a predator in a world where his social and economic condition makes him out to be prey. In an even sadder construction, consider that Lennie's interactions with animals such as mice and puppies is one in which he is a predator and they die as his prey. Lennie, the embodiment of goodness and purity, is incapable of extricating himself from the cycle of being in which there is a clear prey and a distinct predatory. Predation becomes a part of Steinbeck's construction of being in the world and a thematic reality of the novel.
Steinbeck's narrative depicts sad people. One reason they are sad is that they are caught in a state of consciousness where the nature of human existence is one in which there exists a clear and defined notion of predator and prey. The novel displays how this theme underscores human consciousness. The social realism to which Steinbeck is wedded demands that individuals see this reality in their own life and seek to change it.