Signal value of stress behaviour

Physiological and psychological stress are accompanied by nonverbal behaviour across a wide range of species. The function of this ‘stress behaviour’ is not well understood but is often assumed to be read by others as a cue to stress. Displaying signs of weakness is, however, difficult to understand from an evolutionary perspective and therefore further investigation into why these behaviours exist is needed. Here, we test whether displacement behaviours (i.e., those known to be associated with stress) are reliable indicators of stress in humans. Self-directed displacement behaviours and self-reported stress were both associated with stress ratings given by observers. Therefore, such behaviours can provide reliable information to others and can be considered communicative. Individuals producing more nonverbal stress behaviour were rated as more likeable by observers (perhaps presenting as more honest signallers), indicating a benefit and potential adaptive function of displaying stress....