Defense Mechanims from an evolutionary Perspective

Assignment – Discussion – Personality Theory & Research: Discuss the cause and effect relationship between biology and behavior/experience. To what extent do genes affect our personality? Consider an emotion that we generally consider to be negative and apply concepts from evolutionary psychology to explain how these may have evolved because they serve adaptive functions for the species. Finally, what can we learn about human personality from studying personality in other species?

Fight-Flight and Freeze-Faint Mechanisms from an Evolutionary Perspective

Funder (2016) describe that the capacity to deal with adversity and stress appears to be the bedrock of evolution and species development. Throughout millions of years, organisms have encountered numerous difficult and challenging situations, forcing them to evolve and develop new functions. From single-celled organisms in the oceans has life evolved into multicellular reptiles, mammals, and finally humans. Evolution occurs in response to new challenges in accordance with the Red Queen hypothesis, which states that a species evolves continuously through gradual changes caused by facing various challenges and competition with other species (Van Valen, 1973). Or, as more recent research by Pagel et al. (2010) demonstrated, rare environmental events such as genetic mutations, climate change, or new threats from other species, force a species to rapidly undergo a quantum leap in development as a way to avoid likely extinction as a result of the sudden change. No matter if evolution occurs in gradual small steps or in sudden big leaps, nature develops new functions to meet new challenges. This has resulted in the gradual development of the brain and nervous system in reptiles, mammals, and humans, according to phylogenetics, the study of evolutionary relationships between biological entities. Associated with these anatomical and neurological changes, is the development of various stress responses, such as the fight-or-flight response, associated with the sympathetic nervous system, and the freeze and faint response, which is part of the parasympathetic nervous system. (Bracha, 2004).

Interestingly, as described by Levine (2010) and Porges (2010) the parasympathetic nervous system evolved before the sympathetic nervous system, implying that food had to come to an organism before it could move. The sympathetic nervous system developed many millions of years later as a response to various organisms beginning to move toward food or away from something attempting to eat them. While the parasympathetic nervous system, dorsal vagus nerve, and digestive nerves evolved approximately 500 million years ago in multicellular organisms, jawless fish, and fish with a cartilage skeleton, the sympathetic nervous system, spinal cord, and movement nerves evolved approximately 300 million years ago in bony fish, amphibians, reptiles, and simple mammals. Around 80 million years ago, the social engagement system, the ventral vagus nerve, and nerves associated with communication evolved in more advanced mammals such as dogs, monkeys, and humans. Thus, simultaneously with the development of the brain and nervous system, novel functions and behaviors are adapted in response to environmental and competitive threats. To gain a better understanding of the relationship between behavior, cognition, and emotional states, let us consider the primary functions of the various nervous systems during homeostasis and in response to danger.

Let us begin with the parasympathetic nervous system, the first developed nervous system. When no real stress is present, this system is in charge of resting and digesting food, also known as the rest-and-digest response. Then, under conditions of stress or when it perceives a threat to life, this system has only one response: it shuts down to varying degrees, activating the freeze-or-faint response. When this occurs, opiates are produced to aid in numbing the pain, dissociating from the experience, and immobility as a means of pretending to be dead and increasing the likelihood of survival. While this system results in inaction on a behavioral level, it protects us from pain on a cognitive level by tuning out, which means our mind goes elsewhere. The associated emotions that aid us in being passive include feelings of being trapped, helpless, shame, lack of energy, depression, and a sense that life is meaningless.

The sympathetic nervous system, the second developed nervous system, supports daily activation and movement in the absence of stress or danger. Then, in response to stress it activates the fight-or-flight response. In relation to the flight mechanism, feelings such as anxiety, fear, and panic are gradually increasing in relation to perceived levels of stress and danger. That is, as danger increases, so do nervous system activation, or arousal, as a means of producing enough energy to flee the threat. According to Jackson’s theory of dissolution (Hays, 2019), if an animal is unable to flee, the fight response is activated (maybe a little too simplified but nonetheless). Feelings such as irritation, frustration, anger, and rage are produced to aid in protecting one’s boundaries and fighting off a perpetrator.

Finally, the Social Engagement System, according to Porges’ (2011) Polyvagal Theory, is the most recently developed nervous system (it is actually a component of the parasympathetic nervous system, but for the sake of simplicity, I refer to it as the third nervous system here). When there is no stress, this system is associated with social engagement, communication, empathy, and the emotions of love and compassion. This is the first card to play when stressed, and particularly at relatively low levels of stress, by attempting to deescalate a potentially dangerous situation by tending to and befriending the perceived threat. If this is unsuccessful, the sympathetic nervous system and the fight-or-flight response gradually take control. over.

To conclude, I like to pose a few reflection questions, either for ourselves or for our clients. What is our personality like when the various stress responses are inactive, resulting in the absence of the various feelings and defensive behaviors that aid us in dealing with stress? When my nervous system is truly deregulated, who am I, how do I feel, and how do I behave? This person is probably closer to my authentic self than to my defensive self, which is so easily triggered by the various stressors we face on a daily basis.


Bracha H. S. (2004). Freeze, flight, fight, fright, faint: adaptationist perspectives on the acute stress response spectrum. CNS spectrums9(9), 679–685. (Links to an external site.)

Funder, D. (2016). The personality puzzle (7th ed.). Norton & Company.

Hays, S. (2019). Nature as Discourse: Transdisciplinarity and Vagus Nerve Function.

Transdisciplinary Journal of Engineering & Science 10(1) DOI:10.22545/2019/0112

Levine, P. (2010). In an unspoken voice: How the body releases trauma and restores goodness. Berkeley, CA: North Atlantic Books 

Pagel, Venditti, C., & Meade, A. (2010). Phylogenies reveal new interpretation of speciation and the Red Queen. Nature (London), 463(7279), 349–352. (Links to an external site.)

Porges (Links to an external site.), S. (2011). The Polyvagal Theory: Neurophysiological Foundations of Emotions, Attachment, Communication, and Self-regulation. Norton & Company.

Van Valen, L. (1973). A new evolutionary law. Evolutionary Theory, 1(1)–30.

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