Why Zebras Don’t Get Ulcers

The preface invites us to look at a man in a bookshop who seems absorbed in a Stephen Hawking book: he has no leprosy, no smallpox, no fever — but his cholesterol is high and he calms his nerves with tranquillisers. Sapolsky's starting point is that our pattern of disease has changed: where infectious diseases once killed people, today it is damage that accumulates slowly over years — heart disease, cancer, stroke. He reminds us that the 1918 flu pandemic killed more people than the First World War. He also notes that for the third edition he added two new chapters, on sleep and on addiction, and rewrote between a third and a half of the older ones.

Chapter 1 opens with a familiar scene: it is two in the morning, there is an important meeting tomorrow, sleep won't come, and suddenly the thought arrives — «what if I have a brain tumour?» Sapolsky wryly notes that nobody lies awake on such nights worrying about leprosy. Then comes the book's central comparison: for a zebra, stress means a lion's attack, a wound, hunger — a short, physical danger. The body is perfectly designed for exactly that: «either the stress is over or you are». We, however, switch on the same response over loans, taxes, public speaking, even thoughts of our own mortality — dangers that exist only in our heads. Examples such as chess grandmasters whose bodily strain during a match approaches that of a running athlete make the point well.

The most memorable part of the chapter is the story of Hans Selye. In the 1930s the young Selye injected rats with an extract from sheep ovaries, but did it very clumsily — dropping the rats and chasing escapees out from behind the sink with a broom. Months later all of them had stomach ulcers, enlarged adrenal glands and shrunken immune tissue. The control group had received only sugar water, yet showed the same changes. Instead of giving up, Selye reasoned that what the groups shared was the miserable procedure itself. When he exposed rats to cold, heat or exhausting exercise he got the same result, and discovered that the stress response is a general reply given to every threat.

Sapolsky then explains the logic of the stress response: energy is sent straight to the muscles and the heart speeds up; «long-term projects» such as digestion, growth, reproduction and immunity are put on hold; pain is dulled and memory sharpens. Selye's mistake was to think that illness sets in when the hormones «run out»; in fact, as the author puts it, the body's army never runs out of bullets — it spends so much on defence that nothing is left for repair and upkeep. This is called «allostatic load», and the book illustrates it with the image of two elephants trying to balance on a seesaw. There is also an important distinction: stress does not directly cause disease, but it raises the chance of getting ill or of failing to fight an illness off.

On the basis of the part read, the book's greatest strength is its voice: Sapolsky jokes even while discussing hormones and brain regions, illustrates every complex idea with an image from daily life, and says openly that he had other specialists check his text. The Turkish translation is by the clinical psychologist Nesrin Hisli Şahin; terms are chosen carefully, though some sentences are heavy and there are typos. At roughly 600 pages, some chapters read like a textbook; since the chapters are nearly self-contained, it is also possible to pick and read the ones that interest you.

• A style that explains every scientific idea with an everyday image and a joke
• A running comparison between animals (zebras, lions, baboons) and humans
• A structure in which each chapter covers one body system and can be read on its own