Written by: Eileen Johnson
Edited by: Caroline Harms
This piece was written in collaboration with the 2025 ComSciCon-MI Write-A-Thon.
Stress is part of everyday life, and while some stress is healthy for growth and safety, an overstimulated stress response can cause mental and physical harm. Understanding the evolutionary pathways that organize this stress response and how to manage them can help us find a healthy balance between stress and rest.
Instincts are the summary of inherited survival knowledge an animal depends on to survive. Information is accumulated and distilled over generations until it is embedded in every member of the species. Automatic and potent, the brain responds to both internal and external stressors by flooding the body with chemicals called stress hormones. The sympathetic nervous system is responsible for producing these hormones and inducing one of three main reactions: fight, flight, and freeze. How hormones turn into instincts depends on the shared experiences of long-lost ancestors, guiding the functional changes in mind and body to improve survival chances.
For example, imagine a common brown squirrel. If two squirrels grab the same acorn, they are probably going to duel over who gets to claim it. However, if the threat is too big to challenge directly, going on the offensive isn’t always a good idea. If a curious dog comes to investigate, they’ll probably scamper into a tree, or if a human yells at them, they’ll halt in their tracks. Each reaction is fueled by a cascade of stress hormones working together to help the squirrel do whatever would give it the best chance of survival: fight to win dinner, flight to escape predators, or freeze to avoid discovery. Buried beneath layers of rational thought and consciousness, humans still have a reactionary internal alarm system. So what happens when the stressors we encounter no longer act how our ancestors would expect?
As animals living after the Industrial Revolution, where humans have delegated most of our survival tasks to machines, most instincts are useless at best. Exchanging blows over the last box of cookies, running from a difficult conversation, or staying very still so that a stressful email won’t find you are no longer viable forms of survival. Chronic stress is dangerous, even if that stress is mild. Normally, once danger has been conquered, the parasympathetic nervous system begins the “rest and digest” cycle. But if the stressors remain unaddressed, the sympathetic cycle repeats and more stress hormones flood the body. This can cause heart problems from increased work, stomach problems from inflammation, immune problems, and problems with mental health. What’s more, the brain is densely packed with connection points for stress hormones, and if these connections are overloaded with stress, thinking can become difficult and memories are harder to make.
Stress hormones are great for action, but that is only one part of survival. It is our ability to think beyond our instincts that makes us so successful. A broken leg is a death sentence to the majority of mammals, but there’s evidence of ancient humans who thrived with long-healed femur bones. By choosing to take care of one another, Homo sapiens practically doubled their average lifespan. Our ability to talk requires a shorter tongue, increasing the chance of choking but providing complex communication. While this would be a death sentence for most other animals, the potential benefits vastly outweigh the risks, and humans now have thousands of different languages to use.
We build communities because we are social creatures, and ancient humans gained the ability to shout, “Careful, there’s a bear behind you!” because it was more effective than a couple of primal grunts. Our instincts brought us together because that is how we best survive. The landscape of a modern stress response is largely unexplored because we still rely on our ancestors’ instincts, but community remains one of our most powerful survival tools.
The sympathetic nervous system often gets the spotlight, and while the parasympathetic rest and digest may not be as exciting as a high-energy stress response, it is just as important. Any damage done during fight, flight, or freeze – for example, a broken femur bone – is meant to be healed during the parasympathetic cycle. It’s also easier to build community when at rest and not actively fighting or flighting or freezing. All we need to do is make the space and time for rest to happen.
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