The phrase "fight or flight" is so familiar it sounds timeless, but it has a precise origin and a century of evolution behind it. What began as a Harvard physiologist’s description of how the body mobilises under threat has grown, through decades of research and clinical observation, into the four-part model — fight, flight, freeze, and fawn — that trauma therapists use today. Tracing that history does more than satisfy curiosity; it shows why each response is real, where the science is solid, and where the model is a useful clinical map rather than a law of physiology. Here is how the idea grew from Walter Cannon’s laboratory to the 4F framework.
Cannon and the Birth of Fight or Flight
In 1915, the physiologist Walter Cannon published Bodily Changes in Pain, Hunger, Fear and Rage, describing how animals and humans respond to threat by mobilising the body for action. He detailed the surge of adrenaline, the racing heart, the diverted blood flow — the whole sympathetic-nervous-system cascade that prepares a creature to either fight the danger or flee it.
Cannon’s insight was revolutionary: he showed that the stress response was a coordinated, measurable physiological event, not a vague emotional state. "Fight or flight" entered the language as the foundational description of how bodies handle emergencies, and it anchored stress science for the rest of the century.
Adding Freeze
Cannon’s active pair could not explain everything researchers observed. Animals under inescapable threat often went still — the "tonic immobility" of prey that plays dead. Humans, too, reported freezing, numbing, and dissociating in the face of danger they could neither fight nor flee. The active model needed a passive counterpart.
Over the twentieth century, work on the defense cascade and dissociation established freeze as a distinct survival state — a braking response for situations where mobilising would fail. Freeze took its place alongside fight and flight as the third F, the body’s answer to helplessness rather than to a winnable or escapable threat.
Porges and the Polyvagal Map
In 2011, Stephen Porges’s polyvagal theory gave freeze a physiological home. Porges described a hierarchy of nervous-system states governed by the vagus nerve: a social-engagement state for safety, a sympathetic state for fight-or-flight mobilisation, and an older "dorsal vagal" shutdown state for overwhelming threat — the physiological basis of freeze.
Whatever debates surround the finer points of polyvagal theory, it offered a compelling framework for why the body sometimes shuts down instead of mobilising, and it gave clinicians a vocabulary for states they had long observed. It deepened the model from three behaviours into a layered map of the nervous system.
Walker and the Fawn Response
The fourth F came not from physiology but from the therapy room. Working with survivors of complex, prolonged trauma, therapist Pete Walker noticed a pattern the existing model missed: people who managed danger by appeasing, pleasing, and merging with the needs of others. In his 2013 book on complex PTSD, he named this the fawn response and completed the 4F model.
Fawn is best understood as a clinically observed survival behaviour rather than a formal physiological category. That distinction matters for honesty about the model: fight, flight, and freeze rest on rigorous physiology, while fawn is a powerful clinical concept. Together they form a practical framework, not a closed scientific law.
Why the History Matters
Knowing where the model comes from keeps it honest. The 4F framework is genuinely useful — it helps people recognise and work with their survival patterns — but it is a map, not the territory. Treating it as a rigid scientific verdict overstates it; treating it as pure pop psychology understates the real physiology beneath three of its four parts.
Held with that balance, the model becomes a tool for self-understanding rather than a label. To see which of the four leads for you, take the Trauma Response Test, then read the science of the trauma response for how it works in your body today.