The Boys from Brazil is a novel by Ira Levin that explores themes of morality. The most prominent theme is the concept of evil, which is represented by the character Mengele, who is based on the real-life Nazi physician, Josef Mengele. The historical figure Mengele was notorious for conducting unethical experimentation on Jews and other prisoners in the Auschwitz concentration camp during World War II.

Levin examines the psychological mechanisms of a psychopath like Mengele, and how people can develop evil traits. It can be theorized that war creates a lawless society, and psychopaths like Mengele are "liberated" from the constraints of the legal system, social norms, and codes of morality within this lawless environment.

On the other hand, Liebermann represents goodness. He is an older gentleman who is tasked with tracking down the Nazi war criminals, especially Mengele. The theme of the evil-good duality are dependent on these two central characters, in the same way God and Satan are depicted in Judaism, Christianity, and Islam.

The other theme is the haunting nature of history. There are two perspectives proposed in the book. The first perspective is that atrocities in history could teach future generations about repeating evil acts. The second perspective is that humans are inherently prone to evil acts because human behavior is unpredictable. A person could be born with neurological defects that lead to the development of psychopathy. Likewise, a person could develop amoral and immoral viewpoints in life based on their experiences. This is why even atrocities like genocide could not "teach" future generations about repeating history.