John Steinbeck includes more of the tale of Genesis: 4 than is actually told in the bible. The basis of this is a Jewish story involving twin sisters of both Cain and Abel. The two disputed over Abel's twin whom Abel was to marry. Cain murdered Abel and wed the twin sister of his brother. The story differs also in that it is Abel who leaves his home instead of Cain. Abel found his Eden, represented by Salinas Valley, but lost it after fathering a second generation very similar to the first, Caleb representing Cain and Aron representing Abel. The story is changed by Steinbeck to illustrate the idea that men naturally have both good and evil tendencies within them, and that this mixture compels men to choose between the two. The story told is similar to an alternate interpretation of Genesis: 4 called timshel. This alternate reading introduces the idea that Cain feels evil and kills Abel because of the jealousy he feels towards his brother and God's love for Abel.
The relationship of good to evil is found in many different ways throughout East of Eden. One way is the opposition between the two. Such a relationship is illustrated through the Cain and Abel allusions in the novel. Another relationship is that the two must coexist. This relation is represented by the arrival of both the church and the brothel in town at the same time. Good comes from evil is the third relationship. Cathy making Adam appear all the more pure shows this relation. The last relationship is that both terms are relative. Caleb Trask is illustrated as being a man more evil than others are. This innate wickedness varies from the immoral values of other characters such as Charles or Cathy-Kate. The wickedness is attributed to Caleb's ability to choose between good and evil and his choosing of the latter . In East of Eden, good is associated with individual morals. Examples of such would be abstinence from sexual activity and virtues like generosity and self-respect.