Are your relatives strange or simply replicas?

There is probably not a single act, however odd, that has not been performed by some human being. Psychiatrists have classified many of the recurring forms of bizarre behaviour although for the most part they can neither treat them nor understand their causes. Louis Franzini and John Grossberg describe 12 of these disorders, illustrating them by numerous case histories, a literary genre made popular by Oliver Sacks. Since the cases the authors report are taken from historical records, they lack both the immediacy of Sacks's accounts and the charisma he exhibits.

Some of the activities described are revolting, for example, necrophilia, whether it necessitates killing for the purpose of having sex with a corpse or whether the necrophiliac continues to make love to his or her deceased partner. Others, like erotomania, are merely annoying: oddly this condition is found mainly in women. They fall wildly in love usually with a celebrity whom they have never met. They believe that he is in love with them and consummation is prevented only by his wife or his agent. They bombard him with letters, telephone calls and gifts, and occasionally attempt to kill or injure him when they finally realise he does not reciprocate their passion. Although this is surely no more than wishful thinking carried to an extreme, psychoanalysts attribute the disorder to an unresolved Oedipal complex - but then they hold that complex to be the source of all human aberration.

A few other disorders can be partially explained. In a variation of Munchhausen's syndrome, mothers feign illness in their child, by, for example, wounding him and making him swallow his own blood in the expectation that it will appear in his stools. The child is moved from one hospital to another with simulated illnesses. Its feigned ailments allow the mothers to demonstrate their maternal love. Moreover, they receive attention and praise from doctors and nurses for the care they give. Again, the Stockholm syndrome, in which captives come to like and identify with their captors, as Patti Hearst did with her kidnappers, can also be explained in psychological terms. In order to gain favours she had to be nice to her evil captors, but because she had to justify this behaviour to herself, she exonerated them by adopting their values and joining in their crimes.

Many other of the disorders detailed defy explanation, though the authors always make the attempt. Why should people compulsively pull out their own hair? And why should some people believe that their relatives or friends have been replaced by replicas? There is a suggestion that the latter delusion is caused by neurological damage, which can cause other odd but highly systematic disorders, such as Tourette's syndrome. It is curious that the authors never discuss the nature of a compulsion. Are necrophilia, exhibitionism, or masturbating while asphyxiating oneself, compulsive acts or are they performed voluntarily? Anyone who has suffered from a compulsion will swear that they have done their best to resist it but in the end they have to give way. How is it possible to recognise that another person is acting under a compulsion?

Eccentric and Bizarre Behaviors makes interesting if sometimes gruesome reading but it raises more questions about the vagaries of the human mind than it solves. It is a book that should be brought to the attention of those research workers in artificial intelligence who believe that by writing programs that behave intelligently they are simulating the human mind. Their simulations will achieve credibility only when they replicate the bizarre and irrational characteristics of people.

Stuart Sutherland is emeritus professor of psychology, University of Sussex.