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The concept of a behavioral immune system is seen by evolutionary psychologists such as Mark Schaller and L A Duncan as a coherent set of adaptations, responses and behaviors that have been shaped by evolutionary forces to help protect higher organisms from bacteria, viruses, parasitic disorders and infections. This system is seen to complement the biological immune system

The behavioral immune system is a phrase coined by the psychological scientist Mark Schaller to refer to a suite of psychological mechanisms that allow individual organisms to detect the potential presence of disease-causing parasites in their immediate environment, and to engage in behaviors that prevent contact with those objects and individuals.[1][2][3]

These mechanisms include sensory processes through which cues connoting the presence of parasitic infections are perceived (e.g., the smell of a foul odor, the sight of pox or pustules), as well as stimulus–response systems through which these sensory cues trigger a cascade of aversive affective, cognitive, and behavioral reactions (e.g., arousal of disgust, automatic activation of cognitions that connote the threat of disease, behavioral avoidance).[2][4]

The existence of a behavioral immune system has been documented across many animal species, including humans. It is theorized that the mechanisms that comprise the behavioral immune system evolved as a crude first line of defense against disease-causing pathogens.[2]

Implications for human behavior

Within the psychological sciences, there is extensive research linking the behavioral immune system to a variety of prejudices—including prejudices against people who aren't actually diseased but are simply characterized by some sort of visual characteristics that deviate from those of a subjectively prototypical human being. The disease–avoidant processes that characterize the behavioral immune system have been shown to contribute to prejudices against obese individuals, elderly individuals, and people with physical disfigurements or disabilities.[5][6][7]

In addition, the behavioral immune system appears to contribute to xenophobia and ethnocentrism.[8][9] One implication is that these prejudices tend to be exaggerated under conditions in which people feel especially vulnerable to the potential transmission of infectious diseases.

Additional lines of research on the behavioral immune system have shown that people engage in more reticent and conservative forms of behavior under conditions in which they feel more vulnerable to disease transmission. For instance, when the potential threat of disease is made salient, people tend to be less extraverted or sociable.[10] Evidence suggests that the behavioral immune system also incorporates mechanisms designed to search out and process (heuristic) signs of disease at the level of basic visual attention.[11]

Implications for human culture

The behavioral immune system also has consequences at a cultural level of analysis. Under ecological circumstances in which diseases are more prevalent, people also tend to display more reticent and socially restricted forms of behavior, and human cultures are defined by more conservative norms and value systems.[12][13]

Implications for immunology

Some research suggests that the behavioral immune system has implications for the functioning of the "real" immune system too. One study found that the mere visual perception of diseased-looking people stimulated white blood cells to respond more aggressively to infection (as indicated by the production of the proinflammatory cytokine Interleukin 6 in response to a bacterial stimulus).[14]


Physical attractiveness and mate selection

Stigmatization and prejudice

See also


  1. Schaller, M. (2006). Parasites, behavioral defenses, and the social psychological mechanisms through which cultures are evoked. Psychological Inquiry 17 (2): 96–101.
  2. 2.0 2.1 2.2 Schaller, M. (2007). "The behavioral immune system: Its evolution and social psychological implications" J.P. Forgas, M.G. Haselton & W. von Hippel Evolution and the social mind: Evolutionary psychology and social cognition, 293–307, New York: Psychology Press.
  3. Schaller, M. (2011). The behavioral immune system (and why it matters). Current Directions in Psychological Science 20 (2): 99–103.
  4. Oaten, M., Stevenson, R.J. & Case, T.I. (March 2009). Disgust as a disease–avoidance mechanism. Psychological Bulletin 135 (2): 303–21.
  5. Park, J.H., Faulkner, J. & Schaller, M. (June 2003). Evolved disease-avoidance processes and contemporary anti-social behavior: Prejudicial attitudes and avoidance of people with physical disabilities. Journal of Nonverbal Behavior 27 (2): 65–87.
  6. Park, J., Schaller, M. & Crandall, C.S. (2007). Pathogen-avoidance mechanisms and the stigmatization of obese people. Evolution and Human Behavior 28 (6): 410–4.
  7. Duncan, L.A. (October 27, 2009). Prejudicial Attitudes Toward Older Adults May Be Exaggerated When People Feel Vulnerable to Infectious Disease: Evidence and Implications. Analyses of Social Issues and Public Policy 9 (1): 97–115.
  8. Faulkner, J., Schaller, M.; Park, J.H.; Duncan, L.A. (2004). Evolved Disease–Avoidance Mechanisms and Contemporary Xenophobic Attitudes. Group Processes and Intergroup Relations 7 (4): 333–53.
  9. Navarrete, C.D., D. Fessler, S. Eng (2007). Elevated ethnocentrism in the first trimester of pregnancy. Evolution and Human Behavior 28 (1): 60–5.
  10. Mortensen, C.R., Becker, D.V.; Ackerman, J.M.; Neuberg, S.L. & Kenrick, D.T. (2010). Infection breeds reticence: The effects of disease salience on self-perceptions of personality and behavioral tendencies. Psychological Science 21 (3): 440–7.
  11. Ackerman, J.M., Becker, D.V.; Mortensen, C.R.; Sasaki, T.; Neuberg, S.L. & Kenrick, D.T. (2009). A pox on the mind: Disjunction of attention and memory in the processing of physical disfigurement. Journal of Experimental Social Psychology 45 (3): 478–85.
  12. Fincher, C.L., Thornhill, R.; Murray, D.R.; Schaller, M. (2008). Pathogen prevalence predicts human cross-cultural variability in individualism/collectivism. Proceedings of the Royal Society B 275 (1640): 1279–85.
  13. Schaller, M. (July 2008). Pathogens, personality, and culture: Disease prevalence predicts worldwide variability in sociosexuality, extraversion, and openness to experience. Journal of Personality and Social Psychology 95 (1): 212–21.
  14. Schaller, M., Miller, G.E.; Gervais, W.M.; Yager, S.; Chen, E. (2010). Mere visual perception of other people's disease symptoms facilitates a more aggressive immune response. Psychological Science 21 (5): 649–52.


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