Much of Schaller's psychological research has examined the subtle cognitive processes that contribute to stereotypes and prejudices. One line of research focused on intuitive statistical reasoning processes. This work revealed that people form erroneous stereotypes when they engage in overly simplistic statistical reasoning, but that these erroneous stereotypes are less likely to emerge if people can be trained to engage in a more sophisticated reasoning process (analogous to a statistical analysis of covariance). Another line of research focused on communication processes as they relate to the emergence and change of group stereotypes. Additional lines of research, informed by the adaptationist reasoning characteristic of evolutionary psychology, focused on the ways in which specific kinds of perceived threats (e.g., threat of interpersonal violence), and contextual cues connoting vulnerability to those threats (e.g., ambient darkness), trigger specific kinds of prejudices against specific categories of people.
Within his program of research on threats and prejudices, Schaller developed a broader line of research on the perceived threat of infectious disease and its implications for psychological functioning. In this context, he coined the term "behavioral immune system" to refer to a suite of evolved psychological mechanisms that serve as a crude first line of defense against infectious diseases. The behavioral immune system includes sensory mechanisms that allow people to detect the presence of pathogens in objects (including people) in their immediate environment, as well as stimulus-response mechanisms that trigger aversive affective, cognitive, and behavioral reactions to those things (and persons). Schaller and his colleagues, as well as other behavioral scientists, have documented many implications that the behavioral immune system has for emotion, for prejudice, for human social cognition and social behavior more generally, for the origins of cross-cultural differences, and for actual immunological functioning.
Schaller has also published scientific research on a variety of other topics pertaining to human psychological functioning. These topics include: the implications of evolutionary fundamental human motives on social behavior, the psychology of kin recognition, and the psychological consequences of fame.
Schaller, M., & Murray, D. R. (2008). Pathogens, personality and culture: Disease prevalence predicts worldwide variability in sociosexuality, extraversion, and openness to experience. Journal of Personality and Social Psychology, 95, 212-221.
Park, J. H., Schaller, M., & Van Vugt, M. (2008). Psychology of human kin recognition: Heuristic cues, erroneous inferences, and their implications. Review of General Psychology, 12, 215-235.
Maner, J. K., DeWall, C. N., Baumeister, R. F., & Schaller, M. (2007). Does social exclusion motivate interpersonal reconnection? Resolving the "porcupine problem." Journal of Personality and Social Psychology, 92, 42-55.
Ackerman, J. M., Shapiro, J. R., Neuberg, S. L., Kenrick, D. T., Becker, D. V., Griskevicius, V., Maner, J., & Schaller, M. (2006). They all look the same to me (unless they're angry): From out-group homogeneity to out-group heterogeneity. Psychological Science, 17, 836-840.
Maner, J. K., Kenrick, D. T., Becker, D. V., Robertson, T. E., Hofer, B., Neuberg, S. L., Delton, A. W., Butner, J., & Schaller, M. (2005). Functional projection: How fundamental social motives can bias interpersonal perception. Journal of Personality and Social Psychology, 88, 63-78.
Schaller, M., Park, J. H., & Faulkner, J. (2003). Prehistoric dangers and contemporary prejudices. European Review of Social Psychology, 14, 105-137
Conway, L. G., III, & Schaller, M. (2002). On the verifiability of evolutionary psychological theories: An analysis of the psychology of scientific persuasion. Personality and Social Psychology Review, 6, 152-166.
Schaller, M., Conway, L. G., III, & Tanchuk, T. L. (2002). Selective pressures on the once and future contents of ethnic stereotypes: Effects of the communicability of traits. Journal of Personality and Social Psychology, 82, 861-877.
Schaller, M. (1997). The psychological consequences of fame: Three tests of the self-consciousness hypothesis. Journal of Personality, 65, 291-309.
^Schaller, M., Asp, C. H., Rosell, M. C., & Heim, S. J. (1996). Training in statistical reasoning inhibits the formation of erroneous group stereotypes. Personality and Social Psychology Bulletin, 22, 829-844.
^Schaller, M., & Conway, L. G., III (1999). Influence of impression-management goals on the emerging contents of group stereotypes: Support for a social-evolutionary process. Personality and Social Psychology Bulletin, 25, 819-833.
^Schaller, M., Conway, L. G., III, & Tanchuk, T. L. (2002). Selective pressures on the once and future contents of ethnic stereotypes: Effects of the communicability of traits. Journal of Personality and Social Psychology, 82, 861-877.
^Schaller, M., Park, J. H., & Faulkner, J. (2003). Prehistoric dangers and contemporary prejudices. European Review of Social Psychology, 14, 105-137.
^Schaller, M. (2006). Parasites, behavioral defenses, and the social psychological mechanisms through which cultures are evoked. Psychological Inquiry, 17, 96-101.
^Schaller, M., & Duncan, L. A. (2007). The behavioral immune system: Its evolution and social psychological implications. In J. P. Forgas, M. G. Haselton, & W. von Hippel (Eds.), Evolution and the social mind: Evolutionary psychology and social cognition (pp. 293-307). New York: Psychology Press.
^Oaten, M., Stevenson, R. J., & Case, T. I. (2009). Disgust as a disease-avoidance mechanism. Psychological Bulletin, 135, 303-321.
^Faulkner, J., Schaller, M., Park, J. H., & Duncan, L. A. (2004). Evolved disease-avoidance mechanisms and contemporary xenophobic attitudes. Group Processes and Intergroup Behavior, 7, 333–353.
^Navarrete, C. D., Fessler, D. M. T., & Eng, S. J. (2007). Elevated ethnocentrism in the first trimester of pregnancy. Evolution and Human Behavior, 28, 60–65.
^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, 440-447.
^Schaller, M., & Murray, D. R. (2010). Infectious diseases and the evolution of cross-cultural differences. In M. Schaller, A. Norenzayan, S. J. Heine, T. Yamagishi, & T. Kameda (Eds.), Evolution, culture, and the human mind (pp. 243-256). New York: Psychology Press.
^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, 649-652.