yogaMany of the biochemical processes that go on inside the human body strive to maintain a steady state of equilibrium or homeostasis. This homeostasis exists more as an ideal than an achievable condition, as environmental factors continuously cause an upset in the balance, leading to a flux moving about the homeostatic set point.

In its broadest sense, the word stress refers to any external or internal forces, or “stressors“, which alter the dynamic equilibrium or homeostasis of an organism, thereby inducing a stress response.

Physical activity, consumption of dietary phytochemicals, and many other components of our lifestyle can be included under the stress umbrella as they all jeopardise homeostasis. However, to keep the concept of stress from getting too broad and inclusive, this article will primarily revolve around acute stress as most people look at it (e.g., narrowly avoiding a car crash, escaping a dangerous animal), as well as chronic stress (e.g., unpleasant job situation, chronic illness).

There are three main forms of stress:

  • Acute stress: Immediate threat to an organisms homeostasis that occurs within a short span of time. Acute stress activates the sympathetic nervous system and leads to a “fight-or-flight” response.
  • Chronic stress: A persistent presence of sources of frustration and anxiety, which induces a long-term activation of the fight-or-flight response.
  • Traumatic stress: A type of stress that can follow a life-threatening event.

An ancient adaptation

When our ancient ancestors first ventured down from the trees in Africa about 5-8 million years ago and began a more upright existence, they subjected themselves to greater danger from predators on the ground. The fossil data indicate that the first hominins had bodies that were in-between that of a quadruped ape and a bipedal man (1). They hadn’t yet evolved the capability to run long distances in the heat, and they hadn’t yet developed the technology that later in our evolutionary history aided in the protection against dangerous animals.

One thing early hominins did have however – which further evolved over the following millions of years – was an ancient adaptation that helped them deal with stressful events. For our primal ancestors, acute stress was the dominant form of stress, and how they responded to an attack by a snake or big predator clearly had a major impact on their ability to survive and reproduce.

Ever since the dawn of time, life in nature has been a battle for existence, and traits that helped organisms deal with attacks from other animals would have been obvious targets for natural selection.

Following the perception of an acute stressful event there is a plethora of changes in the nervous-, cardiovascular-, endocrine-, and immune-system. In the short-term, these changes are adaptive. Stress hormones such as epinephrine and cortisol are released, energy stores are made available for the body’s immediate use, a new energy distribution pattern leads to the diversion of energy to systems that become more active during stress (e.g., brain, muscles), and the immune system is activated. We also become more alert, our heart rate goes up, and all of the systems that are involved in activities that are less crucial at the time being – such as the digestive system and reproductive system – are down-prioritized.

Our primal ancestors routinely encountered predators and other immediate dangers, and as a result, we have evolved effective adaptive mechanisms for dealing with short-term, acute stresses.

A stressful modern life

The acute stress experienced by our ancient ancestors has now largely been replaced by chronic stress. For many people, stress is synonymous with the mental challenges that come with a life that consists of long work hours, constant connection with other people through social media, e-mail and telephone, kids who need to be driven to school, guitar lessons, and sports events, traffic jams, and energy-consuming relationships. When living a life in the fast-lane it can be difficult to keep a cool head and prioritize correctly.

In today’s industrialized society we have a lot of distractions, avenues, opportunities, and temptations in front of us. While our ancient ancestors could simply absorb everything and “give in” to their environment, we now live in a world filled with supernormal stimuli, stimuli that weren’t a part of our existence for 99% of our evolutionary history (2).

Given the rapid pace of technological change, one has to wonder whether or not our brains (and bodies) have been able to keep up with all the new stimulation that is available. Some research suggests that a few of the things we enjoy today might be classified as “supernormal stimuli,” a term evolutionary biologists use to describe any stimulus that elicits a response more strongly than the stimulus for which the response evolved, even if the supernormal stimulus is artificial (2).

What is important to remember is that from an evolutionary perspective, our hectic, high-tech way of life is novel and abnormal. Many of the things that people find stressful about today’s lifestyle only came into existence during the last couple of decades – and if we go even further back, to our days as hunter-gatherers, it’s clear that we today experience a level of chronic stress that was unheard of for most of our evolutionary history.

The dangers of chronic stress

For 99% of all the species on earth – and also for our species throughout most of our evolutionary history – acute stress is the dominant form of stress. While the short-term stress our ancient ancestors faced when they got attacked by a predator led their bodies to adapt to rapidly changing environmental conditions, the repeatedly or continuously activated stress response that often accompanies life in the 21st century can become maladaptive. In other words, natural selection never equipped us with mechanisms for dealing with a constant stimulation of the fight-or-flight response and a steady supply of stress hormones such as catecholamines.

  • Chronic stress is a risk factor for high blood pressure, mood swings, depression, suppressed immune function, and several types of chronic diseases (3, 4).
  • Chronic stress can disrupt sleep (1).
  • Chronic stress can promote weight gain by inducing hormonal dysregulation and cravings for energy-rich foods (1).
  • Studies in animals have shown that stress-related increases in the expression of proinflammatory genes contribute to an increased risk of diseases associated with chronic exposure to adverse social environments, and that chronic stress can set the stage for changes to the human microbiome by altering the composition, diversity and number of microorganisms living in the gut (5, 6). There’s little doubt that these types of effects extend to humans as well, albeit to which extent is still unclear.

It’s not just the levels of chronic stress we experience that have changed dramatically since the Paleolithic era, but also the types and amount of acute stress we face. Compared our primal ancestors, modern humans are “soft”: we rarely – if ever – have to evade dangerous animals, we live in perfectly temperature-regulated homes, and we take hot, comfortable showers instead of toughening up our bodies with some cold water.  Just like too much of something can be bad, too little of something is rarely optimal either. 

The conclusion is that many of us in the 21st century experience chronic stress that falls in the category of being too new and too much. Also, most of us could benefit from experiencing more of certain forms of acute stress.

Practical applications

Strategies that can help you take control of your stress levels:

  • Don’t let ancient adaptations that are mismatched to the modern environment control your behaviour. In other words, don’t let your temptations get the best of you, but instead plan your life according to what you know is best for your long-term health and happiness.
  • Establish boundaries so that technology does not rule your life.
  • Avoid unnecessary “noise”. E.g. constantly checking e-mails and phone messages, spending hours on social media looking at what other people do.
  • Include some occasional bursts of acute stress into your life. E.g., cold showers, “facing your fears”.
  • Regular exercise, a healthy diet, and adequate sleep are all important for preventing chronic stress.
  • Plan your life according to what’s important for you.
  • Try to resolve energy-consuming relationships, difficult job situations, etc.
  • Seek out and nurture meaningful relationships instead of focusing on online communications.

Picture: Creative Commons picture by a4gpa. Some rights reserved.


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