One of the primary themes of I Am Legend is alienation, and it is hard to imagine someone who is more literally alienated than Robert Neville. He is an absolutely normal American man, or at least he was until the world changed around him. Simply by remaining who he is, he becomes first alone (when his family dies), then a criminal (when he decides not to bury her), then the target of frenzied attacks (as the vampires try to kill him), and finally the only remnant of actual humanity left alive after the world has mutated and moved on. At the close of the novel, Robert Neville is experiencing an alienation that is both evolutionary (on the species level) and metaphysical. This is indicated by the title itself. Simply by being who he is, Neville transitions from being ordinary to being mythic. He shifts from being a forgettable man to being an unforgettable legend.
Conservatism and Change
The relationship between conservatism—a conscious attempt to stay the same—and change is complex in I Am Legend. On one hand, Neville is aware of how much life has changed. The omnipresent storms that blow in, covering everything with dust, are a good example of this. I Am Legend was first published in 1954. Imagine the social ideals of the time, as seen in television shows like Leave It to Beaver, which aired starting in 1957. Those communities were planned, and order and cleanliness were their watchwords. At the same time, however, the 1950s were marked by the Cold War with the Soviet Union, and fear about atomic testing rippled through these safe, ideal communities. It is only addressed briefly, but there is a recognition in I Am Legend that the human race has brought about its own destruction. Humanity caused the mutation that is replacing it.