Much of Schaller's psychological research has examined the subtle cognitive processes that contribute to stereotypes and prejudices.
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).
[2] Another line of research focused on communication processes as they relate to the emergence and change of group stereotypes.
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).