What is the source of evil in this novel?

This is a tough question because of the intricate nature
of Roy's work.  She provides no easy answers.  In my mind, I think that if there is one
source of evil or a location for it, the class system and system of social
stratification based on caste might be a good candidate for where evil lies.  The system
of segregation that was imposed on the Indians by the British was internalized to the
point where such divisions ended up demarcating personal relationships.  It is for this
reason that Vellya Paapen kills his son, and why Ammu and Velutha are punished so harsh
for what they do in the hopes of transcending it.  The fact that individuals take this
social segregation into the realm of the private and into their own states of being,
internalizing the failures of society as personal shortcomings, becomes a main reason
for the evil and cruelty in the novel.