Darwinian medicine (the application of Darwinian ideas to our understanding of disease) is relatively new, to the extent that most doctors are not familiar with the term. In this book two psychiatrists (one a Jungian analyst, the other a former National Health Service psychiatrist and Senior Lecturer in Psychological Medicine) propose a new model of psychiatry based on Darwinism.
Although both authors are medically qualified, they disagree with the prevailing 'medical' model for psychiatric disorders. While not questioning the view that there are genetic and biological influences at work in disorders such as depression and schizophrenia, they think that mental function and dysfunction cannot be adequately understood unless they are seen in an evolutionary context. Many psychological disorders, they argue, are manifestations of ancient adaptive strategies that are no longer always appropriate in modern circumstances.
The authors consider psychological disorders in three broad categories. The first is disorders of attachment and rank. Depression, they suggest, is connected with loss in personal relationships: for example, loss of an attachment figure (such as a maternal figure) or to loss of 'rank' in a social group. Other disorders discussed in this context include personality disorders, obsessions, anxiety and phobias, and eating disorders. Phobias are obviously easy to explain in evolutionary terms, but some of the others are perhaps more difficult to accommodate.
The second category is what the authors call spacing disorders. By this they mean dysfunctional states characterized by difficulty in forming and maintaining personal relationships and in functioning appropriately in a social group. Schizophrenia is the characteristic disorder found in this category but it lies at one end of a spectrum of symptoms. Most psychiatrists today regard schizophrenia as a primarily biological disorder, with a genetic component, but this raises the question: why has selection not eliminated the gene or genes responsible?
The theory advanced by Stevens and Price is that people with a schizoid personality (but not full-blown schizophrenia) are suited to taking on the role of charismatic leader, and such leaders, they argue, would have been advantageous in early hunter-gatherer societies because they would facilitate the splitting up of groups which were tending to grow larger than the optimum size (about 50 individuals). In the first edition this theory was linked to group selection, but they have now reduced their emphasis on this.
The third category to be considered is reproductive disorders, including homosexuality and sadomasochism. Actually, Stevens and Price don't regard homosexuality as a disorder, since they think it is adaptive in certain circumstances and is widespread among many male primates. They manage to construct a reasonably plausible evolutionary explanation for this apparently non-adaptive behaviour, at least so far as male homosexuality is concerned; they have little to say about female homosexuality, probably because relatively little seems to be known about this. Sadomasochism, again, is mainly a male preoccupation and is therefore discussed in that context.
The first edition of the book was criticized by a number of people, including me, on the grounds that although it was intended to put forward a scientific theory, it made few predictions by which that theory could be tested. The authors have responded by including a chapter on research, in which they make a number of suggestions for ways of testing their ideas. New material has also been included on obsessional, anxiety, phobic, eating, and mood disorders.
There is an important new chapter on paedophilia. In keeping with their generally non-judgemental attitude, the authors adopt a factual approach to the subject and in so doing supply a valuable anthropological corrective to some of the prevailing popular notions on this touchy subject. From reading the popular press you might easily get the impression that paedophilia is a modern aberration, a horrific pandemic of perversion, but in reality sexual contacts between children and adolescents are probably less common now than previously, though public condemnation and the risk of prosecution make it difficult to be certain about this. A number of earlier societies did not share our censorious attitude. In seeking an explanation for paedophilia the authors reject the idea that most child abusers were themselves abused as children (large-scale surveys don't support this) and instead put forward the theory that care-giving and sex-mating have become fused during ontogeny in individuals who display a paedophilic orientation.
Not everyone would agree that animal evolution can tell us anything useful about human psychology; see, for example, Kenan Malik's Man, Beast and Zombie. But human beings are, after all, the product of the evolutionary process, and although it's true that this doesn't explain everything, it is surely self-evident that our mental functioning must be to a considerable extent conditioned and shaped by evolution. And it's also certainly the case that current psychiatric explanations for mental disorders are unsatisfactory. Stevens and Price make a good case for their view that the evolutionary approach gives a better understanding of psychiatry than does the current medical model.