Emotion is a ubiquitous phenomenon in human social behaviour.
As a mechanism selected in the course of evolution it subserves adaptation to significant changes in the physical and social environment by allowing the flexible choice of response alternatives. However, emotions at the same time automatically produce action tendencies that prepare adaptive action. The signalling function of emotional expression is of particular importance for socially living species allowing the negotiation of interactive moves. Finally, the feeling component plays a major role of for monitoring and regulating emotional reactivity. Given its key function in adaptation, it is not surprising that emotion involves virtually all organismic subsystems, which are synchronised during the emotion episode to muster all the resources of the organism in an effort at adaptation.