Ultra-Darwinists think that anything biological that exists must be advantageous to the survival of an organism or at least to the propagation of its genes, or at the very least must once have been so. And this, of course, includes anything ‘psychobiological’. This Panglossian viewpoint none the less imposes a duty on its adherents to demonstrate the alleged advantage. And with a little ingenuity it can usually be done. Even if you do not believe, as Stevens & Price do, that psychology and psychiatry have been revolutionised in the past decade by the advent of evolutionism, and that as a result we now ‘have a pretty good idea’ why people become depressed, phobic, jealous and sadomasochistic, their attempt to explain the ‘survival’ of schizophrenia is a tour de force.

Incomplete penetrance and phenotypic plasticity allow the existence of the famous formes frustes of schizophrenia. So the same nasty genes that determine the negative symptoms — lethargy, emotional blunting and suchlike — can, in certain circumstances (note the envirome creeping in), turn the positive symptoms — hallucinations and delusions — into creative innovation and charismatic leadership.

Stevens & Price do not argue that biblical prophets or modern cult leaders such as David Koresh of the Branch Davidians had schizophrenia: only that they were ‘schizophrenicish’. Such people often arise in situations of economic hardship or social instability and tend to attract the downcast and the disaffected. They preach with apocalyptic vision and succeed in commanding extraordinary loyalty from their followers, even to the point of sexual slavery and human self-sacrifice. Moreover, the force of their personal conviction, however bizarre, becomes the focus for a breakaway society to be formed. They may provide the impetus for a revitalisation of culture. Therefore, unlike those categorised as having schizophrenia, they have a higher than average chance of spreading their genes.

But if, as Stevens & Price tell us, the prophecies of cult leaders are rarely innovative and usually consist of an amalgam of preexisting religious clichés, it is difficult to see how they could revitalise anything. I begin to get lost. Certainly I have failed to do justice to the authors' scholarship, their synthesis of the relevant literature and their nicely written text. I do recommend you read the book for yourself.