The Stress Response: Evolution and Implications

The Stress Response
When the human body perceives a threat to its survival, the sympathetic nervous system (SNS) activates the stress response commonly known as the Fight-or-flight response. This activation redirects blood flow away from the organs and into the limbs in preparation for physical action. “The SNS also increases heart and respiration rates and adrenal gland production, which then increases stress hormones such as cortisol. Awareness is focused to the immediate surroundings, and overall muscle tone increases" (Byerly 2015, p. 31).
Evolution of Stressors
In order to survive, hunter-gatherers had to hunt for food, escape from predators, and fight to defend territory. These stressors activated the stress response, which was designed to protect the body from life-threatening and otherwise dangerous situations. Once the body escaped the situation, the stress response would turn off. Therefore, any stress response was short-lived, caused by an acute stressor.
Fast-forward to contemporary industrialized society (CIS) where life is experienced with a luxury and comfort that hunter-gatherers never could have comprehended. Food and water security, consistent shelter, technological innovation, industrialization and medical advances all contribute to the relative stability of CIS. For most people within CIS, meeting survival needs on a day-to-day basis is a given.
Modern common stressors might include prolonged inactivity, consistent lack of sleep, over-working, over-stimulation, a fight with a loved one, bad traffic, an emotional or physical insecurity, or worrying about anything from finances to social life (Jackson 2015).
Stressors can take practically any form, whether it is real or imagined. Yet, the body reacts to all stressors in the same way because there is only stress response, and it has not adapted to human's drastic lifestyle evolution. So whether you are stressed about bumper-to-bumper traffic, or you are running for your life from a bear in the woods, your body responds in the same exact way (Jackson 15).
"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 society" (Jackson 15).
Acute vs Chronic Stress
Acute Stress
As blood flows away from the organs and into the limbs when the SNS is activated, all attention is directed away from the body’s organs responsible for digestion, elimination, and immunity (Byerly 2015; Mcleod 2010). For hunter-gatherers, this trade-off would not have been harmful because any stress response was short-lived and shut off once there was no longer a physical threat. Therefore blood flow activity and maintenance in the organs would resume once again.
Chronic Stress
Modern humans however experience stressors that are less often connected to physical, short-lived threats and more often connected to mental, emotional, and social threats and are therefore long-lasting and perpetuated by over-thinking and over-stimulation.
When the stress response does not shut off or is continually re-activated daily, the SNS becomes over-activated, and the parasympathetic nervous system (PNS) becomes suppressed. Overtime, Chronic stress increases heart rate, blood pressure and blood cholesterol levels, suppresses the immune system's ability to fight infection, and inhibits the digestive system. This leads to an increased risk of infection and disease (Mcledo 2010) as well as "memory problems, changes in the brain, depression, osteoporosis, and insulin resistance" (Byerly 2015, p. 32).
Is Any Stress Good For You?
To consider the notion that some stress is good for you, the duration and intensity of the stress must be taken into account.
I argue that acute stress serves as a useful protective reaction to short-lived threats. Consider the adrenaline rush a mother would receive when lifting a car off of her child. Because the stress response quickly activates and rushes blood to the mother's limbs, she is able to react fast and use strength she otherwise wouldn't have.
However, prolonged, stressful thinking as an example of chronic stress clearly is harmful to the body.
The Power of Positive Thinking
Balancing an Over-activated SNS

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