The Naturalism of Steinbeck certainly is evident in his characterization of Lennie whose gait is like that of a bear and hands are described as "paws." That there is a Darwinian determinism to the characters is clearly apparent. For, the opening chapter defines the action of the final chapter as the George and Lennie are by the river in the clearing where George instructs Lennie to go if he gets into trouble. Of course, Lennie does find the "trouble"; he waits for George, but in the end, he is the mouse who dies.
I agree that a major contribution to characterization in this novel is the use of the third person narrator. However, the other mechanics of character development are not difficult to understand. There are several sources of information about characters. 1. What does the narrator tell us about him/her either directly or through imagery. 2. What do others tells us about the character. 3. How do two or more characters interact with one another. 4. What does their physical description tell us? 5. What does the character do or say that would tell about him/her? Now follow the number pattern below for examples for each of these points.
1. the narrator describes Lennie as large, slow moving man who follows in the footsteps of George, a smaller man. Hence, for all his size, Lennie follows George's lead. 2. George refers to Lennie as being "slow", a "nice guy", a great worker, he warns that if angered Lennie can be dangerous, he tells the boss Lennie is incredibly strong, and Candy as well as Slim note that he is definitely-not mean. 3. Lennie interacts with George as a follower, with Curly as a frightened but dangerous fighter, with Crooks we see his loyalty to George, with Curly's wife we see his childishness. Obviously, we learn much about him as interacts with mice, puppies, and pieces of velvet which are, of course, not characters. 4. Lennie is described as a "bear" a "neighing horse", powerfully built, with eyes that seem to be a little to closely set-perhaps hinting at mongolodism. The meaning in this is obvious. 5. Lennie tells us a great deal about himself in argument with George over the dead mouse, with Crooks, and with Curly's wife as well as in the deluded conversation had with a giant rabbit and his deceased aunt. Just add all the peices of information up and you get a nice portrait of Lennie Small.
I think that Steinbeck is able to develop his characters through an effective use of the third person narrative. His role is that of an outsider, and while this is impersonal, Steinbeck is able to construct personal settings and the development of character in a way that allows the reader to fully embrace and understand these characters' longings and hopes. Dialogue is a part of this process. When George and Lennie talk, there is much revealed between them. Whether it is the discussion of the farm, the animals, or how life will be outside of their current existence along the Salinas, it is dialogue between both characters that allows the reader to fully "get" or grasp these characters. From a thematic point of view, I think that Steinbeck's use of dreams, as a concept, helps the reader fully understand the characters as well. George's vision of life outside the migratory setting, such as being his own boss or going to a ball game, helps understanding about his character. Lennie's aspirations to have a farm and have animals on it reflects his own sense of childhood hope, while Curley's wife's dreams of being someone more than what she is helps us understand how misguided she feels her state of being is right now. The employment of dreams is an element that allows us to get to know the characters in Steinbeck's work.