The Evolution of Stress

This is part 1 of a series of blog posts discussing the ins and outs of stress: its many forms, when it’s helpful and when it’s harmful, optimizing your stress response, and survival strategies for living in a modern world with a primal nervous system. Part 2 and Part 3 available too.

We Only Have One Stress Response

The body is constantly striving to achieve balance. This becomes apparent when we observe how every cell, organ, system, and the entire organism as a whole is ultimately working to attain a stable internal environment in which the cells can function efficiently…otherwise known as homeostasis. Remember that term from high school science class? It basically means balance, or stability, which is slightly misleading because it implies a still state. You don’t ever ‘achieve homeostasis’ and then you’re done trying. Rather, each second our bodies are making physiological adjustments at the micro cellular level, and behavioral adjustments at the macro level to keep us alive amidst the constantly changing environmental circumstances that we call life. Thus, stress researchers have coined a newer term, allostasis, which more accurately describes the ongoing micro and macro (physiological and behavioral) processes that the body undergoes in order to restore stability, or dynamic equilibrium.

Due to the dynamic nature of existence on this planet (things are always changing), our bodies are constantly working away at both the micro and macro levels to maintain our body temperature, pH, oxygen levels, blood glucose, hormones, (etc.) within a very narrow range necessary for our survival. The amazing thing is that all of this occurs in a dynamic and ongoing process that never stops or rests, without us ever having to think about it.

When we get thrown off balance by a stressor, we experience stress. The word stress has many meanings, but in this context, it is the body’s reaction to various life challenges, or stressors. Good ol’ Wiki defines a stressor as “a chemical or biological agent, environmental condition, external stimulus, or an event that causes stress to an organism.” A stressor can take almost any form. It can be an actual physical threat, an infection or illness, a psychological threat or strong emotion…the point is that the body turns on the same stress response regardless of the stressor. We only have one stress response.

A few examples of stressors include: physical pain, emotional pain, illness, injury, infection, loud sounds, lack of movement, over-exercising, fear, loss, a fight with a loved one, stress at work, not getting enough sleep, working too many hours, a sick friend, malnutrition, leaky gut, hearing some bad news, a scary movie, insecurity, a poor diet, financial worries, bad traffic, or in its most extreme form, the fear or reality that your life is currently in danger.

What’s important to understand is that our body reacts to all of these different stressors the same way each time, because we only have one stress response. It doesn’t matter what the stressor is, or whether it is real or imagined; your body’s physiological response (which I’ll discuss more in my next post) is always the same. So whether you are stressed about your job or your crummy relationship, or you are running for your life from a bear in the forest… your body is responding identically on the micro and macro levels, producing the same predictable “fight or flight” chemicals, hormones and behaviors each time you are “stressed out.” There is only one stress response, and it’s been that way since the dawn of human existence.

Stress Didn’t Kill the Caveman

Our nervous system has evolved very little since the days of our primal ancestors. As a result, our stress response, which is largely mediated by the nervous system, is essentially the same as it was millions of years ago. Everyone’s heard the saying “stress kills”, but why is this? The fact of the matter remains, as much as stress does lie at the root of many diseases, it also keeps us alive on a minute-to-minute basis. Especially if you need to run away from a bear in the woods. So why does stress get such a bad rap? Here’s the problem in a nutshell: while the types of stressors humans are exposed to have changed over time, our stress response has essentially not changed at all. Inside of each modern human is the nervous system of a caveman trying to cope with the stressors of living in a fast-paced and rapidly-evolving (technologically-speaking that is) society.

Furthermore, humans are unique from animals in that we have the ability to think stressful thoughts, which elicits the exact same physiological response as if we were actually in physical danger. Moreover, if we are continually thinking stressful thoughts and repeatedly activating our stress response systems, eventually the stress itself can start causing damage to our bodies and predispose us to the so-called “stress-related diseases.” As put by author and stress researcher Robert Sapolsky: “Viewed from the perspective of the evolution of the animal kingdom, sustained psychological stress is a recent invention, mostly limited to humans and other social primates.” It is also important to point out that
it’s not the stressor itself that’s the problem, but rather our interpretation and reaction to the stressor, which dictates a person’s stress response. It would be more accurate to say (as Robert Sapolsky explains so eloquently in his book Why Zebras Don’t Get Ulcers) that “chronic or repeated stressors can potentially make you sick or can increase your risk of being sick. Stressors, even if massive, repetitive, or chronic in nature, do not automatically lead to illness.” A large body of evidence suggests that personality plays a huge role in all of this. For example, it’s well documented that ‘Type-D’ individuals (‘D’ is for ‘distress’) are more likely to develop heart disease, compared to those who are more adept at turning off their stress response, despite exposure to the same stressor.

Acute vs Chronic Stress

Is stress “Paleo”? This may sound like a silly question, until you stop for a moment to consider the fact that our caveman forebearers were not exposed to the ongoing (chronic) stress that we modern humans face. Their stress was short-lived (acute) and often involved escaping or winning a fight for dinner. Acute stress literally saves lives (think of the mom who uses the surge of adrenaline to lift a car up off her child, or the caveman who managed to out-maneuver the saber-toothed cat chasing him, or your body fighting off an infection). The surge of adrenaline that we feel during acute stress episodes is a normal function of the human body trying to protect itself from real or perceived threats.

There are two distinct, but overlapping responses to stress, which depend on the intensity and duration of the stress: acute (short-term) and chronic (long-term). In general, acute stress is not the issue when it comes to all those stress-related diseases we hear about: heart disease, obesity, stroke, infectious disease, anxiety disorders, depression, autoimmunity, ulcers and other GI issues, to name a few. The type of stress that significantly contributes to a multitude of modern-day health concerns is called chronic stress, which is basically an acute stress response that won’t turn off. Chronic stress is what the saying “stress kills” is referring to. Not only does chronic stress underlie several ‘diseases of modern civilization’, but in my opinion, it’s totally not Paleo. To answer my own question, “is stress Paleo”, I would say that acute stress is Paleo, but chronic stress is not.

Evolution of Stressors

So the title of this article (The Evolution of Stress) is pretty misleading, because the stress response has not really evolved at all since Paleolithic times. What has evolved, however, are the types of stressors that people are exposed to. Therein lies the key to understanding how “stress kills.” Our nervous systems were designed to protect us from acute stressors that are relatively short in duration (around 30 minutes or less). The types of danger that our cavemen ancestors were exposed to is very much akin to the dangers that animals face living in the wild: they had to hunt food, escape from predators, and fight to defend their territory. Danger could be lurking behind every boulder, and the human stress response was designed to respond to acute threats that were short-lived (often literally), and that certainly didn’t drag out for days on end. Today humans face mainly social and mental threats, yet our primal stress response reacts to these threats on the micro and macro levels much in the same way that we did as cavemen.

Primarily what has changed between then and now, is the chronic and psychological nature of stress. Our not-all-that-distant ancestors did not experience the ongoing (chronic) stress that we modern humans are subject to. Much like animals, once the stress was gone, they returned to being relaxed, playing and socializing…until the next time their lives were threatened. The difference is that our ancestors didn’t sit around in fear of when the next threat was going to emerge. Rather they dealt with the stressors as they emerged, as quickly as possible, and then they moved on.

Nesse and Young summarize the social and mental threats of modern man well in the
following statement: “Most stresses in modern life arise not from physical dangers or
deficiencies, but from our tendency to commit ourselves to personal goals that are too many and too high. When our efforts to accomplish these goals are thwarted or when we cannot pursue all the goals at once and must give something up, the stress reaction is expressed. In short, much stress arises, ultimately, not from a mismatch between our abilities and the environment’s demand, but from a mismatch between what we desire and what we can have.” Perhaps that’s why the Buddhists believe that ‘the root of all suffering is attachment, and a desire for particular outcomes.’ I’ll leave you with that food for thought, until part 2 of this blog series, where we’ll shine some light on living with a caveman nervous system in a modern, stressed-out world.

In good health,

Kinsey Jackson, MS, CNS®