At its core, this is a story of nature versus nurture; is Ben the way that he is because he is both spoiled by Harriet and reviled by her at the same time, or is he more the result of a personality defect, some kind of psychopathic make-up that made him different to his siblings from the moment he came into being? Harriet feels that he is different from the point of conception, almost as though he is possessed by an evil or an other-worldliness that she and David cannot begin to fathom.
The couple's other children are part nature, part nurture. Until the arrival of Ben,they are happy-go-lucky, carefree and rather fond of each other. They are a tight family unit and others love to visit their home because the love and happiness within it seems contagious. The children are nurtured but not spoiled, and they are raised to care for others. When Ben arrives, the entire family is plunged into emotional disarray. The changes that occur in his siblings are more to do with the way in which they find themselves marginalized than their innate qualities. For example, Paul becomes emotionally nervous through a lack of nurturing. He feels cast aside, frightened and dismissed, and this is not his nature, it is the result of the changes in the way he is treated by his mother.
Ben, for his part, is manipulative and clearly a sociopath. He has his own nature and no amount of nurturing or mental health assistance is going to change that. He has his own path and would rather follow it than follow the path that has already been trodden by his siblings. He does not fit in at home but Harriet is surprised to find that he is considered a social leader at school. This has nothing to do with her nurturing of him; it is simply the way that he is.
