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With this book, Robert Sapolsky successfully achieves two aims; to offer lay readers an explanation of how stress may cause diseases, and second, to convey his own enthusiasm for science. He argues that disease is caused when natural stressor responses fail to turn on, fail to turn off, or function inappropriately.

He contrasts the unhealthy 20th century life of homo sapiens with the life of other mammals, arguing that man is exposed to chronic psychological stressors which produce an inappropriate, chronic stress response. This is too expensive for the body to maintain without cost; hence ulcers, heart disease, decreased immunity and other ills. On this account, the zebra does not get ulcers because the zebra is not exposed to the same psychological stressors as man - something akin to being permanently on the verge of becoming a lion's breakfast.

This is an enormous topic, and Sapolsky has to cover extensive anatomical and physiological ground in each chapter, requiring some effort on the part of the reader. It is effort well spent, however, and while the lay reader is getting to grips with the basic structures of the general stress response, the professional can enjoy the comprehensive endnotes.

The book concludes with advice on stress management. Predictability, perceptions of our ability to control events, and the availability of social supports are important, and can be protective. Sapolsky cites several studies which show that supportive interpersonal relationships can protect against stress. Just as other humans are probably the most common cause of psychological stress, so it seems right that they should also be a source of stress relief, with important implications for the provision of psychological therapies.

The extensive coverage of the physiology means that the psychological dimension of stressors becomes somewhat marginalised. Maybe this is my professional bias; but I would have been interested to see Sapolsky's views on the psychological experience of being stressed. For example, is not the most potent stressor faced by homo sapiens the knowledge of our own vulnerability and mortality? "Timor mortis conturbat me" is a reminder that the belief that death is imminent is a potent psychological stressor. I saw a patient with a severe case of post-traumatic stress disorder who had survived the sinking of the Herald of Free Enterprise in Zeebrugge harbour. After struggling to escape to safety, he watched the water rising towards him, and said to himself: "I'm dead." This experience was much more than simple perception of threat or risk; rather, it seemed to affect a crucial aspect of personal identity, producing severe and chronic disability.

A related issue is time, and memory of time. Most mammalian stressors are not only acute, but comparatively brief. In contrast, many humans endure persistent stressors (such as family violence) which continue for hour after hour, week after week. And humans have memories of stressors, which can themselves be stressful; do zebras have traumatic memories of lions, which haunt them long after the lion is gone?

I think there is another danger in Sapolsky's exposition, which relates to notions of "internal" and "external". If an external stressor can produce internal, unwanted stress effects, which is easier to manipulate - the internal or the external? Most biological solutions emphasise internal solutions to stress; treatment, management. The danger is that external stressors are accepted as "natural", and efforts to prevent them are reduced.

An obvious example of a potent stressor are those cultural attitudes which put interpersonal relationships low on a list of human priorities, or make vulnerability equate with low social status. Even if they appear to occur in nonhuman primates, such attitudes are not "natural" for homo sapiens. Even if considered "natural", this does not imply they are immutable or inevitable.

This stimulating book is both enjoyable and academic - more so than the slightly cutesy title would suggest. Not many scientific books make me laugh out loud; Sapolsky has certainly succeeded in his second aim to entertain. I also liked the cover, of zebras in a Matisse-like circular dance, happily avoiding ulcers.

Gwen Adshead is lecturer in forensic psychiatry, Institute of Psychiatry, London.