Psychopathy seems to be caused by specific mental deficiencies

WHAT makes people psychopaths is not an idle question. Prisons are packed with them. So, according to some, are boardrooms. The combination of a propensity for impulsive risk-taking with a lack of guilt and shame (the two main characteristics of psychopathy) may lead, according to circumstances, to a criminal career or a business one. That has provoked a debate about whether the phenomenon is an aberration, or whether natural selection favours it, at least when it is rare in a population. The boardroom, after all, is a desirable place to be—and before the invention of prisons, even crime might often have paid.

To shed some light on this question Elsa Ermer and Kent Kiehl of the University of New Mexico, Albuquerque, decided to probe psychopaths’ moral sensibilities and their attitude to risk a little further. Their results do not prove that psychopathy is adaptive, but they do suggest that it depends on specific mechanisms (or, rather, a specific lack of them). Such specificity is often the result of evolution.

Past work has established that psychopaths have normal levels of intelligence (they are only rarely Hannibal Lecter-like geniuses). Nor does their lack of guilt and shame seem to spring from a deficient grasp of right and wrong. Ask a psychopath what he is supposed to do in a particular situation, and he can usually give you what non-psychopaths would regard as the correct answer. It is just that he does not seem bound to act on that knowledge.

Dr Ermer and Dr Kiehl suspected the reason might be that, despite psychopaths’ ability to give the appropriate answer when confronted with a moral problem, they are not arriving at this answer by normal psychological processes. In particular, the two researchers thought that psychopaths might not possess the instinctive grasp of social contracts—the rules that govern obligations—that other people have. To examine this idea, as they report this week in Psychological Science, they used a game called the Wason card test.

Playing by the rules

Most people understand social contracts intuitively. They do not have to reason them out. The Wason test is a good way of showing this. It poses two logically identical problems, one cast in general terms and the other in terms of a social contract.

For instance, the first presentation might be of four cards, each with a number on one side and a colour on the other. The cards are placed on a table to show 3, 8, red and brown. The rule to be tested is: “If a card shows an even number on one side, then it is red on the other.” Which cards do you need to turn over to tell if the rule has been broken?

That sounds simple, but most people get it wrong. Now consider this problem. The rule to be tested is: “If you borrow the car, then you have to fill the tank with petrol.” Once again, you are shown four cards, one side of which says who did or did not borrow the car and the other whether or not that person filled the tank:

Dave did not borrow the car
Helen borrowed the car
Brianne filled up the tank with petrol
Kirk did not fill up the tank with petrol

Once again, also, you have to decide which cards to turn to see if the rule was broken.

In terms of formal logic, the problems are the same. But most people have an easier time answering the second one than the first. (In both cases it is cards number two and four that need to be turned.)

Ordinary people are similarly attuned to questions of risk (“If you work with tuberculosis patients, then you must wear a mask,” for example), and the Wason test shows this, too. It is not, however, a matter of the problem being cast in natural language. Descriptive sentences that are not about social contracts or risk (“People from California are patient; John is patient”, etc) are as difficult for normal people to deal with as colours and numbers.

Dr Ermer and Dr Kiehl wanted to know how psychopaths would fare at this task. To find out, they recruited 67 prisoners and tested them for psychopathy. Ten were unambiguously psychopathic. Thirty were non-psychopaths. The rest were somewhere in between. When the two researchers probed the prisoners’ abilities on the general test, they discovered that the psychopaths did just as well—or just as poorly, if you like—as everyone else. In this case the average score for all was to get it right about a fifth of the time. For problems cast as social contracts or as questions of risk avoidance, by contrast, non-psychopaths got it right about 70% of the time. Psychopaths scored much less—around 40%—and those in the middle of the psychopathy scale scored midway between the two.

The Wason test suggests that analysing social contracts and analysing risk are what evolutionary psychologists call cognitive modules—bundles of mental adaptations that act like bodily organs in that they are specialised to a particular job. This new result suggests that in psychopaths these modules have been switched off.

Further research will be needed to see how the risk and social-contract modules that govern psychopathy are actually controlled. But other phenomena that look like diseases are known to be maintained by natural selection. Sickle-cell anaemia, caused by genes protect against malaria, is the most famous example. Psychopathy may be about to join it.