Throughout evolutionary history, pathogens have imposed strong selection pressures on humans. To minimize humans’ exposure to pathogens, a behavioral immune system that promotes the detection and avoidance of disease-connoting cues has evolved. Although most pathogens cannot be discerned by our sensory organs, they produce discernable changes in their environment. As a result, a common denominator of many disease-connoting cues is morphological deviance—figurative disparity from what is normal, visual dissimilarity to the prototype stored in memory. Drawing on an evolutionary rationale, we examine the hypothesis that activation of the behavioral immune system renders people more sensitive to morphological deviance and more prone to perceive dissimilarities between stimuli. In Study 1 (N = 343), participants who scored higher on disgust sensitivity demonstrated greater differentiation between normal and disfigured faces, reflecting greater sensitivity to morphological deviance in the bodily domain. In Study 2 (N = 109), participants who were primed with pathogen threat demonstrated greater differentiation between perfect and imperfect geometrical shapes, reflecting greater sensitivity to morphological deviance even in stimuli that have nothing to do with health or disease. In Study 3 (N = 621), participants who scored higher on disgust sensitivity perceived pairs of neutral pictures as less similar (i.e., more dissimilar) to each other. Literature on the relations to social deviance and implications for social perception and for social behavior is discussed.
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