Reciprocal actions are important to social psychology as they can help explain the maintenance of social norms. If a sufficient proportion of the population interprets the breaking of a social norm by another as a hostile action and if these people are willing to take (potentially costly) action to punish the rule-breaker then this can maintain the norm in the absence of formal sanctions. The punishing action may range from negative words to complete social ostracism.
In public good experiments, behavioral economists have demonstrated that the potential for reciprocal actions by players increases the rate of contribution to the public good, providing evidence for the importance of reciprocity in social situations (Fehr and Gatcher, 2003).
In the animal world reciprocity exists in the social behaviour of Baboons. Male Baboons will form alliances with one another in order that one baboon will distract the Alpha-male, who has monopolized reproductive females, and the other will copulate with a female. The roles will be reversed later for "payback."