You only need to look at the anti-heroes of popular culture – James Bond, Don Draper or Jordan Belfort in the Wolf of Wall Street – to realise that dark personalities have sex appeal, a finding supported by more scientific studies. Further clues to the benefits might come from another basic human characteristic – whether you are a morning or evening person. Lyons and her student, Amy Jones found that “night owls” – people who stay up late but can’t get up in the morning – tend to score higher on a range of dark triad traits. They are often risk-takers – one of the characteristics of psychopathy; they are more manipulative – a Machiavellian trait – and as narcissists, they tend to be exploitative of other people. That might make sense if you consider our evolution: perhaps dark personalities have more chance to steal, manipulate, and have illicit sexual liaisons late while everyone else is sleeping, so they evolved to be creatures of the night.

Whatever the truth of that theory, Paulhus agrees there will always be niches for these people to exploit. “Human society is so complex that there are different ways of enhancing your reproductive success – some involve being nice and some being nasty,” he says.

Dark corners

Recently, he has started probing even further into the darkest shadows of the psyche. “We were pushing the envelope, asking more extreme questions,” he says – when he found that some people will also readily admit to inflicting pain on others for no other reason than their own pleasure. Crucially, these tendencies are not simply a reflection of the narcissism, psychopathy or Machiavellianism, but seem to form their own sub-type – “everyday sadism”. For this reason, Paulhus now calls it a “dark tetrad”.

The “bug crushing machine” offered the perfect way for Paulhus and colleagues to test whether that reflected real life behaviour. Unknown to the participants, the coffee grinder had been adapted to give insects an escape route – but the machine still produced a devastating crushing sound to mimic their shells hitting the cogs. Some were so squeamish they refused to take part, while others took active enjoyment in the task. “They would be willing not just to do something nasty to bugs but to ask for more,” he says, “while others thought it was so gross they didn’t even want to be in the same room.” Crucially, those individuals also scored very highly on his test for everyday sadism.