This is how Delroy Paulhus from the University of British Columbia in Canada describes the results of his work on "evil".

The nature of evil is elusive. Why do some people take pleasure in cruelty? Not just psychopaths and murderers – but school bullies, internet trolls and even apparently upstanding members of society such as politicians and policemen.

Paulhus’s interest began with narcissists, stretching to Machiavellianism, the coolly manipulative. Psychopathy is another variable, with its callous insensitivity and immunity to the feelings of others. The three traits seem to be largely independent, though they sometimes coincide, forming a “Dark Triad” of nastiness.

Studies comparing identical and non-identical twins suggest a relatively large genetic component for both narcissism and psychopathy, though Machiavellianism seems to be more due to the environment – you may learn to manipulate from others.

But whatever we’ve inherited cannot take away our personal responsibility.