Activation of the Behavioral Immune System: Putting the Brakes on Affiliation.

Evolutionary psychologists propose that humans evolved a first line of defense against pathogens: the behavioral immune system (BIS). The BIS is thought to be functionally flexible such that the likelihood and magnitude of BIS activation depends on the individual's perceived vulnerability to disease (PVD). Because conspecifics are sources of infection, the BIS has implications for affiliation. By priming and measuring chronic levels of PVD, we examined PVD's relation to affiliation in zero-acquaintance situations in the laboratory, online, and during speed-dating events. Elevated BIS activation was associated with decreased attraction and affiliative behavior in situations that varied in the trade-off between social reward and potential risk of infection. These results were not due to attachment style, personality traits, or disgust sensitivity. This suggests that in social interactions, approach motivation associated with the need to belong may be weighed against avoidance motivation associated with the need to protect the self from disease.