Psychologist Leanne ten Brinke, an associate professor at the University of British Columbia, has spent decades studying toxic personality traits such as psychopathy, narcissism, Machiavellianism and sadism. Her new book, Poisonous People: How to Resist Them and Improve Your Life, explores how these 'dark personalities' exist on a continuum and affect everyday life.
Ten Brinke's interest began after a disturbing encounter with a sex offender during her studies in Halifax, Nova Scotia. While volunteering at a parole office, a rapist in a treatment group stared at her and described how his victim resembled her, saying she was 'his type'. The experience made her reconsider working with convicted criminals, but she remained fascinated by dark traits, which she found prevalent not only in criminal settings but also in politics, business and the media.
According to Ten Brinke, about 1% of the general population have clinical levels of psychopathy, while up to 18% show elevated traits. In prisons, around 20% of inmates meet the clinical threshold. However, these individuals are often highly persuasive and may convince parole boards to release them. Despite the low prevalence of clinical cases, those with elevated dark traits cause disproportionate harm to society.
Ten Brinke emphasises that both nature and nurture contribute to these traits. Early intervention for children with callous-unemotional traits and persistent aggression can lead to changes over time. For adults, treatment in criminal justice settings can reduce recidivism, particularly violent reoffending, though it typically modifies behaviour rather than personality.
