Modern Life, Ancient Physiology, and the Misinterpretation of Normal Human Function

Our understanding of the factors that influence human health and well-being continues to expand as chronic disease rates rise across the globe. Advances in epidemiology, neuroscience, and evolutionary medicine are increasingly converging on a shared insight: many of the conditions now considered pathological may arise not from biological failure, but from a fundamental mismatch between ancient human physiology and modern living conditions.

Human physiology has changed remarkably little over the past several thousand years. The neurological, hormonal, and autonomic systems that evolved to support survival in a vastly different environment remain largely intact today. What has changed—dramatically—is the context in which these systems now operate.

For the majority of our evolutionary history, humans lived nomadic or semi-nomadic lives. Daily survival required sustained physical movement, environmental awareness, and periodic exposure to real, immediate threats. The nervous system evolved to detect danger rapidly and mobilize energy efficiently, while equally prioritizing recovery once safety was restored. These systems were adaptive, flexible, and exquisitely tuned to environmental cues.

Modern humans, however, no longer live in the conditions that shaped these regulatory mechanisms. We are rarely required to move our bodies to source food. We face few physical threats that demand coordinated action and resolution. Yet our brains remain just as capable of detecting danger as they were when that danger might have been life-threatening. Today, a traffic delay, a hostile email, or social conflict can trigger the same physiological stress responses once reserved for survival-critical situations.

At the same time, circadian rhythms that evolved to synchronize with natural cycles of light and darkness are now disrupted by artificial lighting, screens, and urban light pollution. The nervous system receives constant signals that blur distinctions between day and night, activity and rest, safety and threat. In this context, it becomes increasingly difficult for the body to return to baseline regulatory states.

This raises an important question: are we interpreting normal human physiology as pathological simply because it is operating in an environment it was never designed for?

Behavior as Regulation, Not Failure

One of the central aims of health coaching is identifying the underlying drivers behind behaviors that negatively impact physical health. Chronic, lifestyle-related diseases continue to rise, and many of the conveniences of modern life amplify behaviors that appear maladaptive on the surface.... This can look like overeating, sedentary patterns, disrupted sleep, and chronic stress.

Yet human behavior does not arise randomly. Behind every repeated behavior lies a biological or psychological need. If behavior is viewed solely through a lens of willpower or discipline, the opportunity for meaningful change is limited. Sustainable change requires understanding why a behavior exists in the first place.

Stress plays a central role in this dynamic. Chronic stress is now well established as a contributor to metabolic dysfunction, cardiovascular disease, immune suppression, and mental health disorders. But stress also shapes behavior. When individuals experience prolonged or repeated stress, they do not simply “choose poorly”, their nervous systems adapt in predictable ways to restore balance.

It was at the intersection of stress physiology and behavior that my research began. What initially appeared to be a pattern of maladaptive coping in health coaching clients (particularly stress-driven eating) revealed itself as something far more biologically coherent. Rather than representing a breakdown in self-control, these behaviors may reflect ancient regulatory mechanisms attempting to function in an unfamiliar environment.

The Autonomic Nervous System and the Brainstem’s Role in Regulation

To understand this process, it is essential to examine the autonomic nervous system (ANS), which governs the body’s unconscious physiological functions. The ANS consists of two primary branches: the sympathetic nervous system, responsible for mobilization and threat response, and the parasympathetic nervous system, which supports recovery, digestion, immune activity, and restoration.

During perceived threat, sympathetic activation redirects blood flow away from non-essential systems such as digestion and reproduction toward the heart, lungs, and skeletal muscles. This response is adaptive and necessary in short bursts. However, when perceived stress becomes chronic (as it often does in modern life) these systems remain suppressed for extended periods.

The parasympathetic nervous system acts as the counterbalance to this state, allowing the body to disengage from threat and return to physiological equilibrium, often referred to as allostasis. Importantly, access to parasympathetic regulation is largely mediated through the brainstem and the cranial nerves.

The twelve cranial nerves emerge directly from the brainstem and innervate the face, head, neck, and visceral organs. These nerves serve as bidirectional communication pathways, carrying sensory information from the body to the brain and motor commands from the brain to the body. Because of their direct connection to brainstem nuclei involved in autonomic control, cranial nerves provide a powerful entry point for bottom-up regulation of the nervous system.

This is why a wide range of evidence-based interventions like eye movement desensitization and reprocessing (EMDR), vagus nerve stimulation, sound and music therapy, acupressure, and olfactory stimulation can rapidly influence stress states. While these modalities differ in application, they share a common mechanism: targeted stimulation of cranial nerve pathways that signal safety to the brainstem and promote parasympathetic activation.

Chewing as an Overlooked Evolutionary Regulatory Mechanism

Within this framework, one behavior stands out as both ubiquitous and poorly understood: mastication, or more commonly known as "chewing".

Across species, mastication is closely linked to states of safety and resource availability. From an evolutionary perspective, chewing would have reliably occurred after successful threat resolution once food had been acquired and immediate danger had passed. In this context, mastication may have served as a biological signal that it was safe to transition out of sympathetic mobilization and into parasympathetic restoration.

Chewing activates multiple cranial nerves, most notably the trigeminal nerve (cranial nerve V), which has extensive connections to brainstem regions involved in autonomic regulation. Rhythmic jaw movement, proprioceptive feedback from the jaw and face, and orofacial sensory input provide direct bottom-up stimulation to the brainstem. This pathway is strikingly similar to those targeted by modern neuromodulatory techniques designed to reduce stress and anxiety.

From this perspective, the drive to chew (particularly during or after stressful experiences) may represent an ancient, subconscious attempt by the nervous system to downshift from sympathetic activation into a state that supports digestion, repair, and recovery.

In modern environments, however, this mechanism has become profoundly distorted. Psychological stressors that do not require physical resolution continue to activate threat circuitry, while chewing is often engaged in isolation from genuine safety cues. Ultra-processed foods intensify reward signaling without completing the physiological loop that once accompanied nourishment, movement, and social cohesion.

As a result, stress-driven eating may feel compulsive yet unsatisfying. The nervous system is attempting regulation through a familiar evolutionary pathway, but the environmental inputs fail to deliver the resolution that pathway evolved to expect. What was once adaptive now contributes to metabolic dysfunction, shame-based narratives around self-control, and the growing burden of chronic disease.

Rethinking Pathology in the Context of Modern Life

A growing body of work in evolutionary medicine supports the idea that many symptoms we attempt to suppress (such as anxiety, inflammation, fever, or gastrointestinal distress) are not defects, but protective responses shaped by natural selection. As Randolph Nesse and others have argued, these mechanisms evolved for damage mitigation, not comfort. In modern contexts, they are often misunderstood and prematurely labeled as dysfunction.

When viewed through this lens, behaviors associated with stress may warrant reinterpretation. Rather than asking how to eliminate them, a more productive question may be: what regulatory function are they attempting to serve, and why is that function no longer being fulfilled?

Chewing, in this framework, represents a compelling example of misapplied physiology. It is not inherently pathological. Instead, it reflects a nervous system attempting to regulate itself using tools that evolved under radically different conditions.

Understanding this distinction has profound implications for health coaching, clinical practice, and public health. It shifts the narrative away from blame and toward biological literacy, offering new avenues for intervention that work with the nervous system rather than against it.

Reference

Staggs, K. (2025). Chewing as a Brainstem-Mediated Stress Modulator: An Evolutionary Hypothesis Linking Orofacial Neural Activation to Emotional Eating and Obesity. Zenodo. https://doi.org/10.5281/zenodo.15611696