The human alien
Eli Doyle is an archetypal character. Namely, he is an anti-Christ figure because he descends to heaven. His story is defined by his unique nature; he is the sole remnant of the trip from alien worlds. He also has supernatural powers with alien origins. There are more similarities between him and a messiah-figure in literature: he starts a community for instance, and he meets people alone in the desert. But, instead of being a symbol for life and hope, he is the opposite symbol. He rapes many people and impregnates them with demonic and horrifying children, like the fallen gods in the Book of Enoch.
The instinct parasite
The parasite that infects this survivor astronaut is a symbol for one's own potential, because the parasite gives superhuman strength and energy to a person, but with a parasitic intention; by making the host stronger and more libidinous, the parasite ensures its own survival by animal copulation of the host. The parasite symbolizes humankind's own animal nature therefore, because the virus simply amplifies all the aspects of human nature which are rooted in instinct. This "ad infinitum" shows that Eli's evil is rooted in his own nature and amplified by circumstance.
The insulated family
The perfect victim of Eli's insidious torment is the insulated family from Southern California. They are defined by their insulation from life's problems. The post-apocalypse might be rending Los Angeles nearly unlivable, but the Maslin family lives there in a wealthy way, insulated by gates and walls and home security measures, so that the chaos of their degrading civilization does not effect them. The family might be an allusion to the apocalyptic tale of Lot and his own two daughters. The question of rape also arises in that story, so there are multiple similarities.
The anti-children
Human life is warped by the alien virus. Horrific monsters are born, like the legendary Nephilim from the book of Eli's namesake—the Old Testament Bible. The alien halfbreeds are so archetypal that the story of horrifying and superstrong alien halfborns occurs within the very first book of the Bible, almost at the beginning. Here, we see that motif referenced as a symbol. In the context of the book, the anti-children called clayarks, are a reference to the generations of life on earth, but with a monstrous spin which is informative by inverted symbolism. Subtract the apocalyptic and horrific elements of the book, and a philosophical argument can be seen about human nature.
