Why Zebras Don’t Get Ulcers: Book Overview

This article is an excerpt from the Shortform book guide to "Why Zebras Don't Get Ulcers" by Robert Sapolsky. Shortform has the world's best summaries and analyses of books you should be reading.

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Want an overview of Why Zebras Don’t Get Ulcers? Why are people today more stressed than ever before?

In Why Zebras Don’t Get Ulcers, biologist and neuroscientist Robert Sapolsky argues that stress in modern society is causing major physical and mental harm. Fortunately, there are steps you can take to reduce stress in your life and curb the damage caused by chronic stress.

Keep reading for an overview of Robert Sapolsky’s book Why Zebras Don’t Get Ulcers.

Why Zebras Don’t Get Ulcers: Overview

In the book Why Zebras Don’t Get Ulcers, neurologist Robert Sapolsky argues that people today are facing constant psychological stress and that our mental and physical well-being are suffering because of it. As a biologist who specializes in the study of primates and neuroscience, Sapolsky looks at stress from an evolutionary perspective, noting that the way human behavior has changed since our time as hunter-gatherers leads to high levels of stress in the modern world. Because of this, diseases and illnesses caused, or at least exacerbated, by stress are now the leading cause of death across the globe.

The Evolutionary Explanation for Our Constant Stress

Sapolsky writes that due to advances in medicine, health, and agriculture, our lives have become both longer and much less immediately dangerous than our ancestors’. Instead of having short-term stressors like famine, childbirth, and predators, our stressors are long-term, like financial or career concerns. However, our stress response hasn’t evolved to cope with such long-term stressors, which results in our feeling constantly stressed. 

How the Stress Response Works and How Chronic Stress Influences It

To better understand how stress affects the body, let’s take a look at how the stress response works and how chronic stress affects its functioning. In Why Zebras Don’t Get Ulcers, Sapolsky points out that when you identify a stressor, your brain has two main ways of activating your stress response. The first is through the release of neurotransmitters by the autonomic nervous system. The second is through the release of hormones. When you’re chronically stressed and these systems are activated too often, it can disrupt the body’s functions and potentially cause harm.

Autonomic Nervous System

According to Why Zebras Don’t Get Ulcers, the autonomic nervous system controls involuntary processes (like the stress response), and it consists of two key parts: the sympathetic and parasympathetic nervous systems. These two systems work in tandem to respond to and then recover from stress.

The sympathetic nervous system turns on during times of stress (fight or flight) and helps your body respond almost immediately during a perceived emergency. It does this by releasing neurotransmitters through the nerve endings all over your body. The two key neurotransmitters the sympathetic nerve endings release are the closely related epinephrine (more commonly known as adrenaline) and norepinephrine. Both of these neurotransmitters make your body immediately react to a stressor. 

The parasympathetic nervous system is best understood as working in opposition to the sympathetic nervous system. It promotes calm, vegetative activities, like growth, energy storage, and digestion. After a stressful event, the parasympathetic nervous system slows your heart rate and returns blood flow back to the rest of your body.

In a healthy person, there’s a balance between the sympathetic and parasympathetic systems—you get stressed, so the sympathetic activates. The stressful event ends, so the parasympathetic kicks into gear. When you’re consistently stressed, however, you’re constantly turning on your sympathetic nervous system and turning off your parasympathetic one. This can, among other things, cause harm to your cardiovascular and metabolic systems, lower your immune response, and affect your brain functioning, leading to many health problems (some of which we’ll cover in depth later in the guide).

Hormonal Release

The second way your body reacts to stress is through the release of hormones. Similar to its effect on the autonomic nervous system, the constant activation of the stress response caused by chronic stress disrupts the balance of the hormonal system, causing health issues.

Chronic Stress and Its Effect on Your Body

Sapolsky’s main argument is that the chronic stress humans regularly feel can be extremely damaging to their bodies.

Stress and Cardiovascular Health

In Why Zebras Don’t Get Ulcers, Sapolsky states that the harmful effects of psychological stress are seen most clearly in cardiovascular health. Since stress causes your blood pressure to increase, chronic stress can cause chronically high blood pressure, also known as hypertension. Hypertension can lead to a self-reinforcing cycle: As blood pressure increases, your blood vessels have to work harder to regulate the blood flow and ensure your body is getting adequate oxygen and nutrients. As they work harder, they become stronger and more rigid, and thus more resistant to blood flow. Now there is a constant cycle of increasing vascular resistance and blood flow, driving blood pressure higher and higher. 

Stress and Metabolic Health

Sapolsky argues that chronic stress can cause a variety of metabolic issues. During intense physical stressors, your body doesn’t need to digest food and store the energy for later—it needs energy now. To get this energy, the sympathetic nervous system activates, decreasing the secretion of insulin, the hormone responsible for storing energy. Also, glucocorticoids are released to stop nutrients from being transferred to fat cells, which basically cancels out the effects of any insulin left in the bloodstream.

Stress, Anxiety, and Depression

Chronic stress doesn’t just impact your physical health: It also impacts your mental health. In Why Zebras Don’t Get Ulcers, Sapolsky argues that there’s a significant link between stress and mental disorders such as depression and anxiety, which both involve a person inadequately dealing with stress.


Sapolsky states that there’s a significant link between stress and depression and that chronic stress can be a precursor to a depressive episode. Depression has long been linked to an imbalance or deficiency of neurotransmitters such as norepinephrine, which, as we’ve discussed, makes your body immediately react to a stressor. Furthermore, people suffering from major depression usually have elevated levels of glucocorticoids, a sign of an overactive stress response.


Like people with depression, people with anxiety disorders usually have overactive stress responses. The main difference, according to Sapolsky, is that while depressed people have more or less given up on trying to cope with stress, people with anxiety are still able to use coping mechanisms. The problem is that people with anxiety disorders constantly mobilize their stress responses, even when they don’t need to. They’re hypervigilant, overestimating dangers and letting their imaginations lead to a constant state of dread or foreboding. Unsurprisingly, people with anxiety disorders are much more likely to suffer from the many diseases exacerbated by chronic stress.

Psychological Factors of Stress

As we’ve explored, the main argument of Why Zebras Don’t Get Ulcers is that chronic stress arises because our bodies are responding to constant psychological stressors. But there are outside factors that can impact the degree of stress we experience.

Venting frustration: Sapolsky claims that humans can deal with stress better if they have a way to relieve it. Perhaps you’ve experienced this yourself—maybe you feel less frustrated if you exercise, yell into a pillow, or simply do something you enjoy.

Social support: According to Sapolsky, people who feel they have social or communal support are often much less stressed. A number of studies support this effect: When dealing with a relatively small stressor like public speaking or arguing with strangers, people with a supportive friend present show less of a cardiovascular stress response.

Predictability: Furthermore, Sapolsky claims that if you can predict when your next stressor will be, you’ll be less affected by it. This is because when you know that a stressor is coming, you can prepare for it. Additionally, knowing when the stressor won’t happen lets you relax during that time.

Control: According to Sapolsky, a sense of control over a situation can also alleviate stress. For example, he observes that people are generally more afraid of flying in a plane than driving a car, even though it’s widely known the latter is much more dangerous. This is because when you fly, you cede complete control to the pilot of the plane. 

How You Can Learn to Better Cope With Stress

In Why Zebras Don’t Get Ulcers, Sapolsky contends that you can reduce stress by finding ways to displace frustration, lean on social support, and implement a sense of predictability and control in your life. There are, however, caveats and exceptions to these methods you should be aware of. The key is to find the right strategies and coping mechanisms for certain situations and to figure out which ones work best for you. Let’s look at some of the strategies you can use to reduce psychological stress in your life while keeping in mind some of their caveats.

Exercise as a Way to Vent Frustration

According to Sapolsky, a popular, well-studied, and effective way to reduce stress and vent frustration is to exercise. Remember, the stress response is preparing your muscles to exert energy, so by exercising, you give your body the chance to release that energy. Exercise can also reduce stress by simply taking your mind off the stressful event.

Make Your Life More Predictable

We’ve noted that predictability can help reduce stress in humans. Therefore, Sapolsky claims that it can be helpful to make your life more predictable: Make schedules based on various timeframes (daily, weekly, yearly), make a budget to keep track of expenses, look up the weather before going to an outside event, and so on.

Develop Your Sense of Control

According to Sapolsky, a sense of control reduces stress by letting you believe that your actions and decisions have meaning and that you can change a bad outcome or maintain a good one if you work hard enough. In general, people who believe their actions matter, also known as having a strong “internal locus of control,” are better equipped to deal with the psychological stresses of everyday life. For instance, if you are struggling financially, the belief that through determination and effort you can get yourself out of that rut might help you achieve that goal and be less stressed because of it.

Seek Social Support

Sapolsky claims that having the social support of a community can greatly reduce stress. Even in highly individualized societies, people still long to be a part of something. Therefore, he recommends that to become better at managing stress, you strengthen your current relationships with friends and family and build new ones that are intimate, supportive, and communal. 

Why Zebras Don’t Get Ulcers: Book Overview

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Like what you just read? Read the rest of the world's best book summary and analysis of Robert Sapolsky's "Why Zebras Don't Get Ulcers" at Shortform.

Here's what you'll find in our full Why Zebras Don't Get Ulcers summary:

  • The physical and mental harm chronic stress does to your body
  • The steps you can take to reduce stress in your life
  • Why you should make your life more predictable

Emily Kitazawa

Emily found her love of reading and writing at a young age, learning to enjoy these activities thanks to being taught them by her mom—Goodnight Moon will forever be a favorite. As a young adult, Emily graduated with her English degree, specializing in Creative Writing and TEFL (Teaching English as a Foreign Language), from the University of Central Florida. She later earned her master’s degree in Higher Education from Pennsylvania State University. Emily loves reading fiction, especially modern Japanese, historical, crime, and philosophical fiction. Her personal writing is inspired by observations of people and nature.

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