The Origins of Stress: An Evolutionary Explanation

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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What are the origins of stress? Have we evolved to cope better with stress?

According to neurologist Robert Sapolsky, people today are facing constant psychological stress and our mental and physical well-being are suffering because of it. In his book Why Zebras Don’t Get Ulcers, he explains the origins of stress from an evolutionary perspective.

Keep reading to learn about the origins of stress, according to Sapolsky.

The Origins of Stress in Evolution

Do you feel overworked, exhausted, and constantly stressed? If so, you’re not alone. In 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 the origins of 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.

Hunter-Gatherers and Old Age

Sapolsky contends that people are now much more likely to live long enough to suffer the long-term effects of stress. It’s important to note, however, that a fair amount of our hunter-gatherer ancestors did live to old age, and it’s mainly higher infant mortality rates that dragged their average life expectancy down.

Other research suggests that it wasn’t uncommon for hunter-gatherers to live well past the age of fifty. Hunter-gatherers lived much healthier lives than the average person today—they were constantly on the move and had much healthier dietary habits, which lowered their risk of cardiovascular disease. They also weren’t exposed to the many toxins that modern humans are in the industrialized world which would have lowered their chances of developing cancer.

For most of our evolutionary history, we were hunter-gatherers. Hunter-gatherer societies were relatively small, social groups. Like most other animals (such as zebras), hunter-gatherers’ main sources of stress were short-lived, intense, physical stressors—which is where the origins of our modern stress lie. Our ancestors were concerned with being chased by a predator, or hunting down your prey so that you didn’t starve.

These sorts of events are extremely stressful, and surviving them requires an intense physiological response. And because these sorts of stressors were the most common for most of our evolutionary history, our bodies are fine-tuned to deal with these types of stressors. That is, we’re able to quickly and efficiently recover from this type of stress without long-term damage to our minds and bodies. Therefore, the origins of our stress come from short-lived stressors.

(Shortform note: Another term for short-term stress is acute stress. However, acute stress isn’t necessarily a response to a physical threat, as Sapolsky suggests: It’s just a response to an immediate threat, whether physical, emotional, or psychological. People usually experience acute stress multiple times a day and are usually able to deal with it quickly and avoid bodily damage. But you should be careful about the amount of acute stress you experience because enough instances of acute stress can build up to chronic stress rather quickly.)

Now, think about the main stressors in your life. These are likely ongoing psychological and social stressors, unlike the origins of stress that were acute and short-lived. You might be worried about how your career is advancing, how you’re going to pay your bills, or how your date went last night. We’ve invented countless things to be stressed about, and we can stimulate a stress response just by thinking about them.

The problem with this is that our bodies haven’t evolved to deal with these never-ending mental stressors. When you’re stressed, whether you’re running for your life or thinking about that humiliating social encounter you had five years ago, you turn on similar physiological processes. Remember the origins of stress evolved to deal with short-term, physical crises, yet your body turns on this response constantly when there is no immediate danger, only sustained, imagined danger. This type of chronic stress can have disastrous consequences, which we’ll discuss in a later section.

(Shortform note: A 2019 study performed on rats provides additional insight into the effects of physical and psychological stress. The research suggests that although physical and psychological stress have similar effects on the mind and body, there are some key differences. The behavioral and mental effects of physical stress appear more quickly than the effects of psychological stress; but over time, the effects of psychological stress are more severe. Furthermore, the damage from long-term psychological stress is harder to reverse than the damage from physical stress. This shows that even when it occurs regularly, physical stress is less damaging than psychological stress, especially long-term.)

The Origins of Stress: An Evolutionary Explanation