The behavioral, not physiological, immune system

The behavioral, not physiological, immune system

Who knew that we have a behavioral immune system? Or that when it’s activated it may put the brakes on our drive to connect with our peers socially? Before reading a recent research paper out of McGill University, I didn’t know anything about the behavioral immune system. This is what I learned.

Evolutionary psychologists propose that apart from physiological immune system defenses, which are triggered after a pathogen enters our body, there are also behavioral counter measures against infectious pathogens. In its purest form, the behavioral immune system is thought to detect cues of pathogens in the immediate environment, and trigger emotional and cognitive responses, which in turn facilitate avoidance behaviors. 

The argument for the existence, and evolutionary basis of the development, of a behavioral immune system is linked to the repeated devastation of ancient human populations by infectious diseases. As infections killed thousands upon thousands of people, the early signs and symptoms of illness became recognized. Apart from developing fear, people became disgusted by yellow discharges and other body products associated with deadly diseases. The disgust is thought to have led people to avoidance behaviors. Over long spans of time, in addition to the early physical cues of infection, other cues developed, which were mistakenly identified as significant. Certain behaviors that may have overstepped cultural norms, the unaccustomed behaviors of strangers, or unusual facial appearances or body shapes caused avoidance behavior and an associated sensation of disgust. 

In the subsequent thousands upon thousands of years of ongoing human evolution, infection avoidance behaviors and the related disgust feelings became culturally adopted and reinforced and, possibly, through natural selection, eventually genetically encoded. Evolutionary psychologists now think that just like inappropriate physiological immune system reactions may lead to various disorders, mistaken behavioral avoidance reactions and the associated affective experiences may have become the underpinnings of social and interpersonal problems. These problems may relate to attraction, sexual behavior, mate choice, and societal leader selection, and may also have implications for stigmatization and prejudice against people who may be physically disabled, elderly, or obese. 

The research paper used a perceived-vulnerability-to-disease scale to assess study subjects’ tendency to experience heightened emotional discomfort when exposed to real or false pathogen-related cues and beliefs about their susceptibility to infectious disease. The scale can serve as an indication of behavioral immune system activation. In this study, behavioral immune system activation was associated with decreased attraction and affiliative behavior in the various laboratory, online, and speed-dating events set up by the researchers. 

The study, “Activation of the behavioral immune system: Putting the brakes on affiliation,” was published in Personality and Social Psychology Bulletin.

While this was a small study with marginal results, it adds to the slowly growing understanding of the psychological underpinnings of major personal and social issues. 

How strange, that all this may be related to the devastating infectious disease epidemics of the ancient human times.
—George Szasz, CM, MD

Suggested reading
Sawada N, Auger E, Lydon JE. Activation of the behavioral immune system: Putting the brakes on affiliation. Pers Soc Psychol Bull 2018;44:224-237.
Schaller M. The behavioral immune system. In: Buss DM, editor. The handbook of evolutionary psychology. 2nd ed. Vol 1. New York: Wiley; 2016. p. 206-224.


This posting has not been peer reviewed by the BCMJ Editorial Board.

Bill Gardner says: reply

You have still got the chops; good article. Bill

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