Immune System - The Evolutionary Root of Emotions and Behaviour
Evolution of emotions as function of the immune system to optimise survival and reproduction
Original research article
by James Berryhill, 2024
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Abstract
The main thesis proposed is that emotions evolved as regulatory mechanisms shaped through interactions between the immune system, nervous system and endocrine system to promote optimal survival and reproduction.
Drawing from principles of evolutionary theory and evidence across multiple disciplines, it is argued that the immune system played a crucial but underappreciated role in this process as a sensory system that influences emotional and behavioral responses.
The immune system defends the organism at a physiological level through detection and elimination of pathogens. However, it also perceives stimuli and modulates emotional states through cytokines and communication with the brain. Negative emotions like fear and anxiety motivate behaviors that avoid health threats, while positive emotions approach bonding opportunities that enhance group survival.
Through an evolutionary lens, emotions are analyzed as conserved brain states that emerged selectively to drive adapted responses mediating physiology, cognition and behavior according to homeostatic needs and environmental challenges perceived by the immune system. Neurological, genetic and developmental evidence suggests emotions serve fundamental functions across species despite superficial differences.
The complex bidirectional relationship between immune activation, physiological changes, and emotional/behavioral flexibility is explored. Chronic stress impacts immunity, and positive/negative emotions respectively enhance or suppress immune function. This calibrated interplay between immune signaling, emotions and motivated behaviors provides an integrated framework for understanding human psychology from an evolutionary perspective rooted in biology.
The paper forwards the novel idea that emotions originated through immune system regulation as a sensory system fine-tuning survival and reproductive strategies. This model integrates traditionally distinct domains and offers new insights into the evolutionary design of human emotions and mind-body relationships.
Key points
Evolutionary perspective:
- The paper proposes an evolutionary perspective, noting that all living organisms evolve to maximize survival and reproduction, which is the ultimate purpose that shapes biological traits and systems.
- It argues that emotions and psychological processes evolved not for their own sake, but to serve the end of maximizing fitness and passing on genes to succeeding generations.
- The immune system in particular plays a crucial role in defending the organism against threats to survival like pathogens, injuries etc. Emotions then evolved in coordination with the immune system.
Immune system regulates emotions:
- The immune system communicates with the brain through molecules like cytokines that can influence emotional states, mood, and behaviors.
- Inflammation and immune activation trigger physiological stress responses regulated by the HPA axis, leading to emotions like fear, anxiety etc.
- Positive emotions are also regulated to promote behaviors like social bonding that enhance survival and reproduction.
- The paper provides examples of how different emotions like fear, joy, empathy etc. motivate adaptive behaviors regulated by the immune system.
Evolutionary origins of emotions:
- Emotions evolved as conserved, functional brain states that modulate physiology, cognition and behavior in response to stimuli.
- They emerged through evolutionary processes as modulated by the immune system to drive adaptations to threats and opportunities.
- Evidence from conserved neurological circuits, neurotransmitters, and emotional expressions across species show emotions fulfill adaptive roles.
Immune system as a sensory/inference system:
- It argues the immune system perceives internal and external stimuli through receptors and classifies them as self, non-self, reward to mount appropriate responses.
- This allows it to guide "active inference" and engage in probabilistic perception, prediction and inference about stimuli similar to the brain.
Bidirectional immune-brain interactions:
- A complex bidirectional relationship exists where emotions influence immunity and vice versa through pathways like cytokines, HPA axis, neurotransmitters etc.
- This allows dynamic calibration of emotional and immune responses based on physiological state and environmental challenges through feedback loops.
This paper presents a coherent evolutionary argument grounded in evidence that emotions are closely intertwined regulatory mechanisms that evolved through interactions between the immune, nervous and endocrine systems to promote optimal survival and reproduction in varying contexts. It develops the novel idea that the immune system acts as a sensory/inference system influencing emotional and behavioral responses. Overall, it provides a compelling synthesis of the emerging understanding of emotions and mind-body connections through an evolutionary lens, with implications across fields.
Interesting story, but where is the evidence?