Chronic stress: an evolutionary mismatch?

The other day, my ten year old nephew told me he was stressed.  I was shocked. At that age he shouldn’t even have heard the word, let alone suffer from it. It’s striking how the term ‘stress’ has taken root in our lives.  Expressions like ‘I’m so stressed out’ are part of our everyday life – as if it’s quite normal to feel like this from one moment to the next. But what does this stressful lifestyle actually do to our health?  I’d like to spend a moment or two reflecting on this from an evolutionary standpoint, as usual.

What is stress?

If there is a mismatch in our internal balance (homeostasis), or the even the perception of a threat, we call this stress. The body has a complex mechanism of adaptive responses that can be adjusted to recover from it.  But these responses have been selected because they are responses to the dangers that have typically threatened the human race throughout most of its history.

How does my body react to stress?

At a time of stress, the body goes into survival mode.  The central nervous system becomes more focused, more aware and alert.  On the periphery, an increased supply of oxygen and nutrients goes to the brain, heart and muscle, gearing up the cardiovascular and respiratory system and producing more energy. At the same time, this means that every function that isn’t to do with survival is inhibited.  So, if the stress is prolonged, other systems such as digestion, reproduction and regeneration are significantly affected.
To put it another way, stress response gets the body ready to think about the threat (this response is unique to humans); and, if necessary, to fight or run away.
These reactions are responses typically adapted to the kind of dangers we humans have been used to facing for most of our history, namely::

  1. Lack of food
  2. Lack of water
  3. Infection by a pathogen
  4. Contact with an enemy
  5. Exposure to danger
  6. Damage to the tissues

So if you’re exposed to one of these situations, your body knows the best way to deal with it.  We’ve spent thousands of years fighting these threats, and the very fact that you’re here now means that you’re a descendant of all those others who’ve successfully overcome them. The problem is that, nowadays, the threats we face are different.  But the body’s responses are the same, and that causes problems for us.
We call this situation an ‘evolutionary mismatch’.

The evolutionary mismatch

If there’s one thing that distinguishes us from the rest of the animal kingdom, it’s our brain. Our ratio of total weight to brain weight (the coefficient of encephalization) far exceeds that of any other mammal.  Basically, the brain is our main weapon for survival. Our brain is able to anticipate dangers and develop creative strategies ahead of the difficulties. This is what gives us our special status of being the creature best able to adapt.  The human species can live in many different environments, from the desert to the arctic.
We’re the animal that is most adaptable, but not the best adapted.
One of the functions that this organism carries out is to sum up the environment and anticipate dangers.  If it detects a hostile environment, it will react by becoming alert. The problem, which we call ‘evolutionary mismatch’, is that we have evolved to live in environmental, social and cultural conditions that are seen by the brain as hostile.  99% of human generations have lived in a natural environment. What, in its time, was a necessary evil has now become a necessity.  Our habitat is natural.
You can prove this for yourselves by looking at one of these photos, and checking the sensations you feel.
urbanización con stress
When we look at the picture of nature, the brain feels a sensation of peace, and our vital functions slow down.  We are in our natural habitat (or at least that’s what our brain is telling us).
When we look at the photo of concrete we become tense.
And that’s just one example.  It becomes clearer by the day that what we see as normal aspects of our daily lives are not what our physiology is adapted to,  and it perceives them as threatening. Here are a few examples:

  • Unnatural surroundings
  • Lack of exposure to sunlight
  • Pollution
  • Food that doesn’t suit us
  • Individualism: we’re a very social animal
  • We don’t have the muscle capacity that we need
  • Secondary rewards (money)
  • Bio rhythm
  • Loss of our old friends (the microbiome)
  • Taboos, both emotional and sexual

So the evolutionary mismatch theory suggests that we’ve evolved to live in specific conditions.  When we don’t find them, we react by going into a state of alarm and easily generate the stress response.   Stress is about getting us ready to face the dangers of the past, so our bodily response doesn’t address these new risks: and as a result it doesn’t go away.  Over time it becomes prolonged: so what is good for us in the acute stage can then become a problem.

Ancestral threat
Adaptive response
Pathology if prolonged
Lack of food Energy Conservation Metabolic Syndrome/ Obesity
Dehydration Liquid and electrolyte conservation Hypertension / Liquid retention
Infections Powerful immune reaction Autoimmunity / allergy
Enemies INcrease in tension and fear Anxiety / allergy
Dangers Social withdrawal Depression
Damage to Tissues Increased tension in the tissues Symptoms of pain an exhaustion



Unnatural Surroundings Spend time with nature. Remember this post
Lack of exposure to sunlight Expose yourself to the midday sun. Remember this post
Pollution Spend time with nature.
Food that doesn’t suit us Eat what your body is adapted to. Remember this post
Individualism: we’re a very social animal Cultivate your friendships. Remember this post.
We don’t have the muscle capacity that we need Use coherent movements. Remember this post.
Secondary rewards (money) Eat when you’re hungry, drink when you’re thirsty, Make love with passion. Remember this post
Bio Rhythm Devote some time every day to doing nothing. Meditate.
Loss of our old friends (microbiome) Avoid being ultra hygienic. Remember this post
Taboos, both emotional and sexual Say what you really feel.  Accept your emotions.


The stress response is a very useful reaction to the basic threats we have faced for most of our history.  The stress response was brief and intense, but did not last long.  For the most part,  we should be spending our lives in peacefully. The risks we face have changed, but our bodily responses have not. This means that the response can easily become chronic. So, as far as possible, let’s go back to giving our brains that serenity which is the best antidote to chronic stress.

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