Evolutionary Stress Response

I have been thinking a lot about Ellie’s presentation about our stress reactions and how they affect our bodies and our brains. The way our nervous systems respond to stressful or scary events has developed in such an interesting way.  Ellie repeatedly used the word amazing to describe our bodies’ reactions to those types of situations, and I can’t agree with her more.  I know it is super, super nerdy to talk about how amazing the biology of our bodies is, but the idea that these processes developed through evolution is pretty cool.  In our evolutionary history, those with strong stress responses who were able to use their adrenaline to muster a strong “fight or flight” response were the ones able to escape from danger, or defeat it, and survive.  But given the changes that have occurred in the world with the development of civilization, will evolution now work in a diametrically opposed way to favor those who have more muted stress responses?  Today in America and in western civilization in general, in many cases the situations that are considered stressful are very different from those that were considered stressful in the past.  Currently, taking important exams, giving presentations in school or at work, participating in a big sports game or dance performance, having an important or difficult conversation with a friend or family member are all examples of what would today be considered stressful situations.  But acting in a “fight or flight” way, being combative or exhibiting avoidance behavior, would actually be unhelpful in such situations.  Responding “overanxiously” to these types of situations that we face frequently today would make us less likely to be healthy and succeed in the world, and from an evolutionary standpoint, less likely to be able to reproduce successfully and share our genes with the next generation. So I wonder and, in a sense, hypothesize that evolution in the future will lead to a population of people who respond with diminished stress reactions.  This can only hold true, of course, if we as humans are still affected by evolution. Medical expertise and technology that can reduce the type of strong nervous system reaction I described above may alter evolution.

2 thoughts on “Evolutionary Stress Response

  1. A strong physiologic reaction can be problematic when clear thinking is needed (e.g., a pilot crash landing a plane, a fire officer sizing up a burning house where children are trapped, a police officer in a shoot out with a criminal, a soldier surrounded by the enemy). My understanding is that the fight or flight reaction causes impaired cognitive function, loss of fine motor skills, loss of peripheral vision, auditory exclusion, and time distortions. The brain reverts to a more primitive state (this has been referred to as the “monkey brain”). When that happens you fall back on your training, whether good or bad. There’s one story of a police officer who found empty brass ammo casings in his pocket after a shootout. Apparently the lieutenant who ran the shooting range was strict about police officers picking up the spent ammo so they would often fire and then pick up the spent rounds. He was not consciously aware that he did it in middle of a life-or-death situation. I don’t know if this story is apocryphal but it sounds plausible. This is one of the reasons that in aviation there is a checklist for everything (even crash landing an airplane). We can’t change the fact that we are animals but we can create mechanisms to improve our situational awareness and effectiveness during acute stress reactions.


  2. I am very intrigued by this idea: Can changing stressors in our lives affect our bodily response to stress? I see how one would think that our advanced world presents us with a whole different type of stress than our early ancestors experienced. Hunting and fighting, for example, are things that we associate with primitive cavemen. Clearly, a fight or flight response for a caveman being chased by a wild animal should not be identical to the response a businessman has when arguing with the CEO. Although the second scenario is much more common in the 21st century, there are still plenty of situations in which people need the full benefit from our fight or flight response. Soldiers in wars face high-intensity situations every day. People in rural areas of Africa and South America still hunt. Even citizens of the US, such as police officers, must engage in activities that rely on a bodily stress response to perform optimally. So, will evolution cause our stress responses to become muted? Maybe, but I don’t see it happening for a long time.


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