"Psychopaths really do exist, they're just not all out to kill you."

Forensic psychologist Paul Wilson.

Psychopaths are usually egocentric and often experience little guilt or remorse for their actions.

The successful TV series Dexter, based on Jeff Lindsay's novels of the same name, follows Dexter Morgan, a forensic blood spatter expert for the Miami Dade Police Department.

He hunts down people who have escaped justice and then kills them. Quirky, charming but often murderously violent Dexter's character oscillates between normality and controlled psychopathic fury.

But does Dexter represent the typical psychopathic serial killer? For that matter do psychopaths really exist or are they, as some psychologists believe, simply a media and writers' beat-up, a condition that has never been scientifically established?

While I am sceptical about many psychological categorisations and believe that it is always difficult to pigeon-hole humans into neat diagnostic packages, there is a great deal of evidence that psychopaths really do exist. …