Humans are born with a set of five social instincts that vary in intensity across the population; add to this consciousness (that also varies) as well as civilisation (culture) and the historical use of alcohol, and you have the makings of a theoretical framework that explains the most common forms of clinical anxiety and depression. This is the core contention of Jeffrey Kahn in this book.

Although the book is written in the style of popular science, it is, in fact, an innovative and scholarly work that deserves to be studied by mental health specialists. Kahn places his arguments and hypotheses within the broader evolutionary and historical context. His thesis is that five of the most common psychiatric disorders can be related to the five ‘social instincts’ underlying the ‘Big Five’ personality factors. The book's structure follows the same line, with a chapter devoted to discussing each of these disorders: panic anxiety which kept us close to the group; social anxiety which kept us in our place within the social hierarchy; obsessive-compulsive disorder that helped us live safely within the group; atypical depression that kept us well behaved for a cooperative group; melancholic depression that stopped us from using resources when no longer useful to the group; and finally, consciousness that kept us responsive to group members and the environment. Kahn presents a plausible and insightful model for the roots of these disorders in the evolved social instincts. Some are existing hypotheses and others are new or modified by the author. However, the overall model and the way it has been put together are new. The model has good face validity and gives rise to testable predictions that can be answered by future research. What is not clear, however, is the process the author believes to be implicated in these disorders. Is it ‘mismatch’ between the design of the instincts and the current human environment, or is it ‘trade off’ between the advantages of having an evolved functional system on average but which dysfunctions at the extremes of the trait? There are hints by the author that one or other of these processes may be at play in the various disorders but these issues are not explicitly discussed.

The insights into the nature of atypical depression are particularly illuminating. The author makes a sharp distinction between atypical depression and melancholia and puts forward a sound case for considering these as entirely separate conditions that arise from distinct evolved brain systems (instincts). This is in contrast with conventional classifications (both DSM and ICD) that place most depressions within the same diagnostic groupings. The author rightly points out that such practice can and does lead to invalid research findings regarding aetiology and treatment.

In contrast to the easy flow of the anxiety and depression chapters, the chapters on consciousness and schizophrenia are less lucid. For example, the discussion of the emergence and function of human consciousness seems to take place in the abstract rather than relating to what we know about human evolutionary history and the human environment of evolutionary adaptedness. Also, despite the empirical evidence that Kahn presents in support of his thesis that schizophrenia can be classified along the same lines of the five social instincts combined with the effects of reduced consciousness (e.g. through hypofrontality), the arguments in favour of his model are less compelling. Nevertheless, the author does present some novel and testable hypotheses such as his contention that Scheiderian first-rank symptoms are related to the socially phobic variant of schizophrenia.

The fascinating story of the role of alcohol as the ‘great leveller’ of social hierarchies over many millennia of human history is told with both its positive effects in ameliorating the negative effects of social instincts and its well-known harmful effects highlighted. Also, the author draws attention to a little-known and intriguing observation that all known alcohol-free societies are (or have been) polygamous as males in these societies tend to have more rigid hierarchies resulting in sharper disparities in access to mates. In contrast, monogamy prevails when alcohol is socially permitted.

The book contains other astute observations and suggestions. One such is taken from Darwin, who observed that most domesticated animals have floppy ears, in contrast with animals in the wild, which have erect ears. This suggests a biological link between floppy ears and lowered fears. Clearly, humans do not have floppy ears, which is consistent with the author's observation of the high levels of human angst compared with our primate cousins. Another interesting idea is that premenstrual dysphoric disorder (PMDD) may be the biological remnant in human females of the ‘oestrus’ phenomenon that exists in mammals but not in humans.

The author eschews much of the modern terminology of evolutionary psychology and psychiatry, such as adaptations and behavioural strategies, in favour of the more archaic ‘instincts’; neither does he mention other key concepts, such as kin selection, in relation to his formulations. The omission of kin selection is particularly pertinent to the discussion of melancholia which, other authors have argued, is a form of altruism towards kin rather than being ‘for the good of the group’.

However, these observations aside, this book makes a powerful case for a scientific approach to psychiatry firmly based within the framework of evolutionary theory. This contrasts sharply with the current atheoretical approach of psychiatry that has given birth to ever-enlarging compendia of disorders without any common thread or any chance of improving our understanding of the origin of our uniquely human angst.