The key ideas

Why Zebras Don't Get Ulcers: The Acclaimed Guide to Stress, Stress-Related Diseases, and Coping

Robert M. Sapolsky, 1994

Why does a zebra that has just escaped a lion go back to grazing a minute later, while a person can fall ill from years of worrying about the future? Robert Sapolsky shows how the stress response, built for short chases, hits the heart, the stomach, growth and memory when it never switches off. You will learn what makes the same setback light or devastating, and which levers you really have.

Who it is for

For anyone tired of constant worry who wants to understand what it does to the body. And for anyone who loves biology told with humour and good stories.

Essentially, we humans live well enough and long enough, and are smart enough, to generate all sorts of stressful events purely in our heads.

The zebra is already grazing, and you are still running

The savanna, midday. A lion charges the herd, the zebras race away, and one escapes the chase at the very last second. A few minutes later it is grazing calmly again. Its heart was pounding and its muscles were burning, but the danger is over, and the body has switched off the alarm.

Now picture an ordinary person's evening. Nobody is chasing them. They lie in bed thinking about the loan, about tomorrow's talk with the boss, about what the doctors will say in a month. And their body switches on the very same system the zebra used. Only there is nothing to switch it off with, because the lion lives in their head.

Robert Sapolsky is an American neuroscientist at Stanford who studies stress hormones and spent many years watching baboons in Kenya. His book came out in 1994, and the third edition in 2004. In it he asks a simple question: why don't zebras get ulcers, while we do? His answer: the stress response is a brilliant invention of evolution for short emergencies, but we have learned to trigger it with our thoughts, for days and years on end.

From this book you will learn what exactly stress does to the heart, the stomach, growth and memory. And above all, what makes the same setback light one time and devastating the next. Sapolsky writes with wit, with jokes and stories about rats, baboons and Londoners under the bombs, so it will not be a frightening read.

The body fights the fire and puts off the repairs

What happens to a zebra during the chase? Sapolsky describes the stress response as a rearrangement of the whole household in seconds. The adrenal glands release adrenaline and glucocorticoids. These are hormones that move energy out of storage and straight into the blood. The heart beats faster and blood pressure rises, so the fuel reaches the muscles sooner.

At the same time the body pauses everything that works for the future. Digestion stops, growth and reproduction are put off, and the immune system is reorganised. The logic is simple: there is no point digesting lunch if in a minute you might become someone else's lunch.

For a zebra this is the perfect deal. The chase lasts minutes, then the stores are refilled and the repairs carry on. Trouble starts when the fire never goes out. If the body spends energy and postpones repairs for weeks, it wears out, grows less well, repairs itself less well and falls ill more often.

And here is what sets humans apart. The response switches on not only at a blow but at the mere thought that a blow could come. We can worry about something that will happen in thirty years, and the body reacts as if the lion were already close.

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About the author

Robert Sapolsky is an American neuroscientist and primatologist, a professor at Stanford University. For many years he studied stress hormones and watched baboons in Kenya.

All books by this author: Robert M. Sapolsky

Why Zebras Don't Get Ulcers: The Acclaimed Guide to Stress, Stress-Related Diseases, and Coping Quiz

Terms from the book

  • Endorphins
  • Hippocampus
  • Adrenaline
  • Friedman
  • Beecher
  • Williams
  • Baboons
  • Adrenal glands
  • Immune system
  • Marmot
  • Stress response
  • Atherosclerosis
  • Marshall
  • glucocorticoids: A group of adrenal hormones, the main one in humans being cortisol. They mobilise energy during stress and, in long excess, can harm the body.
  • Selye: Hans Selye (1907 to 1982), an endocrinologist who worked in Canada. He brought the concept of stress into medicine in the 1930s.
  • endocrinologist: A scientist or doctor who studies hormones and the glands that produce them.
  • hypertension: Persistently high blood pressure.
  • Rosenman: Ray Rosenman (1920 to 2013), an American cardiologist and co-author of the description of Type A.
  • Type A: A style of behaviour described by cardiologists: constant hurry, competitiveness and irritability. It describes behaviour, it is not a diagnosis.
  • Warren: Robin Warren (1937 to 2024), an Australian pathologist, co-discoverer of the role of Helicobacter in stomach ulcers.
  • Helicobacter: Helicobacter pylori, a bacterium that lives in the stomach. Most stomach ulcers are linked to it.
  • stomach lining: The inner layer of the stomach, which protects its wall from the stomach's own acid.
  • Widdowson: Elsie Widdowson (1906 to 2000), a British nutrition scientist. She studied the growth of children in post-war Germany.
  • psychosocial dwarfism: Stunted growth in a child caused by a harsh environment and stress, not by a lack of food or by illness.
  • Anzio: A town on the coast of Italy where the Allies fought long battles against German forces in 1944.
  • Weiss: Jay Weiss, an American psychologist who in the 1960s and 1970s studied in rats what determines whether stress leads to ulcers.
  • displaced aggression: Anger taken out not on the source of the trouble but on someone weaker.
  • Blitz: The massive German bombing of London and other British cities in 1940 and 1941.
  • hierarchy: The order of rank in a group: who gives way to whom and who answers to whom.
  • Whitehall: Long-running British studies of the health of civil servants. They are named after the street in London where the government offices stand.

All terms

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