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  • Writer's pictureAmy Loughman, PhD

Ancient Stress Response vs Modern Life

Updated: Jan 9, 2020

Who wins in the contest between our neanderthal stress-response system and the demands and joys of our modern lives? Spoiler alert — neither. It’s a zero sum game.

Stress is one of the biggest psychological triggers of physiological changes in the body. It is a key intersection of mind, body and microbiome — the perfect example of the interconnectedness of it all. It worries me a little, stresses me out even, how ubiquitous stress seems to be, and how we seem to have accepted it as our lot in modern life. There is mounting evidence that stress contributes to most of our modern chronic illnesses, from depression to heart disease to cancer.

At least this guy has 3 heads, 6 hands (and a tailor made shirt) to make it all happen with. The rest of us are making do with just the standard body parts. Image credit Andrés Nieto Porras via Creative Commons.

At least this guy has 3 heads, 6 hands (and a tailor made shirt) to make it all happen with. The rest of us are making do with just the standard body parts. Image credit Andrés Nieto Porras via Creative Commons.

It is probably at the level of the mind that we first think of stress. The feelings of overwhelm, busyness, tension and worry. Those feelings are the canary in the coal-mine of a whole cascade of events happening in the depths of your body at the cardiovascular, digestive and immune systems (at a minimum). And even deeper in the bowels of, well — in our actual bowels, there are the gut microbiota busy at work. It turns out that they’re pretty sensitive to stress and it puts them out of whack, wreaking further havoc on our health.

So how exactly does stress happen in the body, and how does it impact our long-term health? And how can we harness what it was intended for?

Stress: how nature intended it

In psychological terms, stress is the reaction to something that threatens our physical or mental equilibrium. So the cause can be of any material nature — say looming deadlines, a hungry lion escaped from a zoo running after you, poverty, illness, or a fight with your significant other. But the result, stress, is the psychological and physical reaction to the cause. When some stressful event occurs, the autonomic nervous system responds with its well-intentioned (but usually not so helpful) emergency system that you’ve probably heard about: ‘fight or flight’.

Through the release of stress hormones such as cortisol and adrenaline, the ‘fight or flight’ response has rapid effects on multiple bodily systems. Some things are increased: heart rate, blood pressure, muscle tension, perspiration, narrow focus of attention and food seeking behaviour (for energy). Some things are decreased: such as digestion and immune function. As the name suggests, the fight or flight response was designed for a short-term physical response to a paleolithic stressor; a threat to life such as a predator or an angry enemy with a spear. By increasing heart rate and redirecting blood flow and energy to limbs and away from digestive and immune systems, the fight or flight response helped our ancestors battle the predator or run really fast away from it. Our ancestors who were successful in fighting or flighting gave birth to our great-great-grandparents (approximately), and so the fight or flight response was part of the evolutionary advantage of the fittest people who survived and procreated. All going well so far, thank you sympathetic nervous system, thank you ancestors.

The stress response — unsuited to modern life

Fast forward to the stressors of this modern day, and you can see that our stress response is not quite so well adapted to them. Stressful work-life, cyber bullying, rising house prices and the pressure to discover your “authentic” self and live the life you really want. None of these really benefit from being able to run from a tiger or fight an angry cave-man. Not only that, but our modern stressors cannot be solved in an afternoon, or even within a week. So what happens when our well-intentioned but unsuitable fight or flight response tries to help us with long-term modern stressors? With the prolonged release of stress hormones, blood pressure goes up, the cardiovascular system is taxed to do its job, the immune system is weakened, digestion doesn’t happen properly, you get headaches and have trouble winding down. Not to mention a reduced ability for learning and memory, partly because the resources of the attentional system are being directed rigidly towards immediate threats, rather than flexibly and curiously to all the other interesting things going on in life.

So our stress response is doing pretty much the same things as it was doing for our ancestors, but for longer periods. A short burst of adrenaline gives us motivation and energy for the challenges in life, but a steady stream of it just makes us run down. It turns out this takes a serious toll on the body, known as allostatic load. Chronic stress plays a sizeable role in mental illness and pathological physical states such as high blood pressure, cardiovascular disease, obesity and immunosuppression. This is at least in part due to systemic inflammation that occurs when cortisol is in oversupply.

“Stress contributes to many disabilities worldwide and represents a severe economic burden.” De Palma et al. 2014

Stress is in the (mind’s) eye of the beholder

Just to put my psychologist hat on for a moment, it’s important to remember that the impact of stressful situations depends a lot on your individual perception of the situation (how bad it is, how much control you have, whether you were expecting it, how optimistic you are about things getting better etc). So one person’s stressor may be another person’s playground. Well maybe not quite that much fun, but it might not bother them as much.

Stressed-out gut bacteria

Back to stress and the body, stress has specific effects on the gut and gut bacteria too. Specifically, the overflow of stress hormones increases the permeability of the gut lining. This is a bad thing, because as much as I love all things gut, most things should stay inside the gut rather than flow on into the bloodstream, which can happen if the gut wall isn’t tightly closed. If bacteria are detected passing through the gut wall, a whole cascade of immune system responses kick in, and this can cause oversensitivity or allergies to some food, and also changes the composition of the gut microbiome. As demonstrated in a recent study on red squirrels, rat pups separated from their mums too early (yes, mean) and in kids with early life neglect (really, really mean), the greater the stress, the lower the diversity of the gut bacteria.

We are still in our infancy in understanding gut bacteria and their role in health, but so far diversity seems to be a good thing. Fewer numbers of different species present in the gut has been associated with gastrointestinal, allergic and neurological conditions. What exactly high diversity does for us hasn’t been completely worked out, but the gut microbiota function as a community. Different species and types have unique roles to play, and many rely on one another to be comfortable and happy. A bit like human societies really, which also benefit from a diverse community.


It is best to use the stress system we’re equipped with for short bursts of focussed energy — this is what it is made for. If you can curb chronic stress and maintain a general baseline of calm and relaxation (perhaps through mindfulness-based stress reduction practices) then you are likely to be respond more effectively to the occasional high-stress situations that life throws you.

So for the sake of your mind, body and microbiome, it is worth keeping your stress levels in check. A little bout of adrenaline and acute stress once in a while won’t do you any harm, but we simply weren’t made for the chronic stress that many of us experience. The impact is cumulative, long-term and serious and we’re seeing this with the rise of chronic illness at a public health level. A fantastic Australian documentary The Connection: Mind your body tells the quite extraordinary stories of chronic stress, serious illness and recovery, with pleasing amounts of scientific explanation for people who need a bit more depth.

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