Leanne ten Brinke opens her new book not with a serial killer but with a Supreme Court justice. William O. Douglas, a celebrated figure of mid-20th-century liberal jurisprudence, would probably meet “modern definitions of psychopathy,” according to the psychologist — despite never committing a prosecutable offence.
The book is Poisonous People, published by Simon & Schuster. Ten Brinke directs the Truth and Trust Lab at the University of British Columbia and argues that psychopathy’s damage extends well beyond prison walls.
The formal diagnosis was dropped in 1952 over stigma concerns, replaced by frameworks like antisocial personality disorder. It returned in the 1980s through the Psychopathy Checklist Revised, a tool designed to assess dangerous criminals and their likelihood of reoffending.
People who score as clinical psychopaths represent around 1 per cent of the population. By some estimates, the report states, they account for half of all serious crime.
The Wider Pool
Ten Brinke pushes beyond that clinical threshold. She estimates that 10 to 20 per cent of people score high on traits associated with psychopathy without meeting the full clinical definition. “We find these people everywhere,” she writes.
Her framework draws on the dark tetrad — a personality model built around four traits: psychopathy, Machiavellianism, narcissism, and sadism. These are not binary categories. Each sits on a spectrum, and a person’s score on one trait operates independently of the others.
Those in the elevated 10 to 20 per cent share a particular talent for “eroding ethical standards and sowing fear and mistrust,” she writes.
Situational Psychopaths
The more unsettling argument targets the remaining 80 per cent. Ten Brinke says these traits are malleable — dialled up or down by environment. Through case studies, she shows how “cultures of rot” can push otherwise empathic people into behaviour she labels “situational psychopathy.”
The triggers she identifies range from sleep deprivation and extreme heat to sports fandom’s in-group dynamics. “Kind and empathic people are prone to infection by dark personalities,” she writes.
The book offers practical guidance — establishing explicit rules, for instance, because people with dark traits exploit unwritten ones. But the larger portion is a call for self-examination.
Ten Brinke asks why these individuals keep getting promoted, elected, and hired. The assumption that dark personality traits produce effective leaders is addressed directly, and she dismantles it.
The case of Douglas anchors the argument throughout: the wreckage he left behind touched every life around him, professionally and personally, without ever attracting a criminal charge. Ten Brinke’s point is that this is the more common pattern — harm at scale, operating entirely within the law.
Photo by Brian Wangenheim on Unsplash
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