Every time you feel your heart pounding before a difficult conversation, your palms sweating before a presentation, or a sudden jolt of alertness when something startles you – that’s your body’s stress alarm going off. This automatic reaction has a name: the fight-or-flight response. It is one of the most fundamental survival mechanisms in human biology, and understanding how it works – and where its limits lie – tells us a great deal about how we experience and manage stress.
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Cannon’s theory: where it all began
Walter Bradford Cannon, an eminent American physiologist at Harvard Medical School, was the first to systematically describe the body’s physiological reactions to stress in the early twentieth century. Working initially on digestion, Cannon noticed that when his experimental animals were frightened or disturbed, normal stomach activity would halt abruptly. This observation drew him toward a deeper investigation into the physiology of emotion.
Cannon identified that when an animal – or a person – perceives a serious threat, a cascade of reactions is triggered almost instantly. He named this the fight-or-flight response, first formally described around 1915. The core idea is straightforward: faced with danger, the body mobilizes all available resources to either confront the threat (fight) or escape from it (flight). There is no conscious decision-making involved; the response is automatic.
Central to Cannon’s framework is the concept of homeostasis – a term he himself coined – which refers to the body’s ability to maintain stable internal conditions like blood pressure, temperature, and respiration. According to Cannon, the fight-or-flight response is a built-in mechanism that temporarily disrupts homeostasis in order to protect it in the long run. By mobilizing energy and directing resources toward survival, the body gives itself the best possible chance of overcoming a threat and returning to a stable state.
Cannon proposed that this response is triggered by the sympathetic nervous system (SNS) – one branch of the autonomic nervous system, which operates largely outside conscious control. The SNS works in tandem with the endocrine system, particularly the adrenal glands, to produce a rapid, body-wide reaction to perceived danger.
What actually happens in your body during stress
The fight-or-flight response sets off a chain of physiological events designed to maximize the body’s ability to act quickly and forcefully. When the brain perceives a threat, the hypothalamus – a small region deep in the brain – signals the adrenal glands to release adrenaline (epinephrine) and noradrenaline (norepinephrine) into the bloodstream. These hormones are the primary drivers of the acute stress response.
As adrenaline circulates through the body, a number of rapid changes take place. The heart beats faster, pushing more blood to the muscles and vital organs. Breathing quickens to bring in more oxygen. Pupils dilate to sharpen vision. Muscles tense in preparation for rapid movement. Digestion slows – resources that the body normally devotes to processing food are redirected toward more immediate survival needs.
Alongside adrenaline, cortisol – the primary stress hormone – is released from the adrenal cortex. Cortisol raises blood glucose levels, giving muscles and the brain a quick supply of energy. It also temporarily suppresses functions that are not critical in a crisis, including the immune response, digestion, and reproductive processes. The result, as described in StatPearls, is a body primed for strenuous physical activity: stronger, faster, and more mentally alert than under ordinary conditions.
The specific physiological changes and their purpose
The fight-or-flight response produces a coordinated set of changes, each serving a specific function. Increased heart rate and blood pressure ensure that oxygen-rich blood reaches the muscles rapidly. Bronchodilation – the widening of the airways – maximizes oxygen intake. Blood is diverted away from the digestive system and toward the large muscle groups needed for action. Blood glucose rises to provide immediate fuel. Even blood clotting speeds up, which would limit blood loss in the event of physical injury.
The autonomic nervous system manages all of this without any conscious input. Once the threat passes, the parasympathetic nervous system – sometimes called the “rest and digest” system – brings the body back to its baseline. Heart rate slows, breathing returns to normal, digestion resumes, and cortisol levels drop. In healthy, short-term stress situations, this recovery is relatively swift.
The problem arises when the stress response is activated repeatedly or remains switched on for prolonged periods. Chronic cortisol exposure weakens the immune system, contributes to weight gain, elevates blood pressure, and increases the risk of cardiovascular disease. This is why stress management matters not just psychologically, but biologically – the fight-or-flight response was never designed to run continuously.
Critiques and limitations of the model
Cannon’s theory was groundbreaking, but it was developed primarily through research on male animals. For much of the twentieth century, stress research followed the same pattern. Up until 1995, females made up only about 17% of participants in studies investigating the fight-or-flight response, with researchers often excluding female subjects due to variability caused by hormonal fluctuations across the menstrual cycle. This exclusion had a significant consequence: it meant that the dominant model of the stress response was built almost entirely on male biology.
A second limitation is that the fight-or-flight framework assumes a fairly narrow set of behavioral options. In reality, people respond to stress in far more varied ways. Some freeze. Some fawn – becoming overly accommodating to defuse a threat. The model’s binary framing does not fully capture the range of human stress responses, and more recent models, such as the defense cascade proposed by Schauer and Elbert, attempt to address this by outlining a broader sequence of reactions that unfold as threat intensity escalates.
Taylor’s ‘tend and befriend’: an alternative framework
In 2000, UCLA psychologist Shelley E. Taylor and her colleagues published a landmark paper in Psychological Review that challenged the universality of the fight-or-flight model. Taylor and colleagues proposed that while fight-or-flight may describe the primary physiological stress response for both males and females, the behavioral response of females is better characterized as “tend and befriend.”
Tending refers to nurturing activities – protecting offspring, reducing distress in dependents, and promoting safety. Befriending refers to the creation and maintenance of social networks that provide mutual protection and support. Taylor argued that from an evolutionary standpoint, a pure fight-or-flight response would have been disadvantageous for females who were pregnant, nursing, or caring for young offspring. As Taylor explained, fighting could result in injury that would leave offspring unprotected; fleeing could mean abandoning them entirely. A tend-and-befriend response offered a safer evolutionary path – one that maximized both the female’s survival and that of her young.
The biological mechanism Taylor identified at the core of this response is oxytocin – a hormone released during stress that, rather than amplifying arousal, actually downregulates the sympathetic nervous system. Taylor noted that oxytocin encourages bonding and nurturing behavior, and its effects are amplified by estrogen and dampened by androgens like testosterone. This hormonal difference, she argued, helps explain why women tend to seek social support during stress more readily than men do – a finding supported by a meta-analysis of 26 studies, all but one of which showed that women turned to others for support under stress.
Subsequent research has added important nuance to Taylor’s theory. While women are somewhat more likely to engage in tend-and-befriend behaviors, men also exhibit these responses – just to a lesser degree and through somewhat different social pathways. Importantly, studies have found that attachment style – how individuals relate to others in close relationships – may be a stronger predictor of tend-and-befriend behavior than biological sex alone. This suggests that the story is more complex than a simple male/female divide.
What this means for how we understand stress
Together, the fight-or-flight model and the tend-and-befriend framework offer a richer, more complete picture of the human stress response. Cannon’s contribution remains foundational – the physiological mechanics he described are well established and apply across sexes. But Taylor’s work highlights an important gap: when research is conducted predominantly on one group, the resulting models may not represent the full range of human experience.
This has practical implications. Understanding that some people – particularly women – may instinctively move toward connection and caregiving under stress, rather than confrontation or withdrawal, can shape how stress support is designed in clinical, workplace, and educational settings. It also challenges the cultural assumption that the aggressive, individualistic fight-or-flight response is the universal human norm.
What do you think? If the tend-and-befriend response is partly rooted in biology but also shaped by socialization, how might gender norms influence whether someone feels free to seek social support during stressful situations? And as stress research continues to develop, what other groups or identities might be underrepresented in models that have long been treated as universal?
References
- https://pmc.ncbi.nlm.nih.gov/articles/PMC1447286/
- https://courses.lumenlearning.com/waymaker-psychology/chapter/studying-stress/
- https://psychology.pressbooks.tru.ca/chapter/12-3-understanding-stress/
- https://www.health.harvard.edu/staying-healthy/understanding-the-stress-response
- https://www.mayoclinic.org/healthy-lifestyle/stress-management/in-depth/stress/art-20046037
- https://www.ncbi.nlm.nih.gov/books/NBK541120/
- https://www.britannica.com/science/fight-or-flight-response
- https://www.psychologytools.com/resource/fight-or-flight-response
- https://www.stress.org/news/understanding-the-bodys-stress-response/
- http://www.personalityresearch.org/papers/mccarthy.html
- https://pubmed.ncbi.nlm.nih.gov/10941275/
- https://www.psychologicalscience.org/observer/taylor-takes-on-fight-or-flight
- https://www.apa.org/monitor/jan04/habit
- https://levylab.la.psu.edu/wp-content/uploads/sites/9/2022/01/LevyHlayetal2019tendandbefriend10.1007_s40806-019-00197-x.pdf
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