A common function defining aggression is as elusive as a common cause. Agonistic inter actions do not invariably produce injuries or increase individual distance, nor are they the sole cause of injury and spatial relations. Ag gression includes intentional movements and ritualized communications that only indicate a high probability of imminent attack. Aggression need not include attack and may serve as an instrument to modify the behavior of another acting in a manner perceived to be detrimental to the subject’s self-interest (as in defense, com petition, or getting another to comply with a previous communication). Aggression can also be directed to a third party with whom there was no prior conflict, as in redirections and coalitions. Moreover, aggression may serve a socialization function in which “incorrect” be havior is “punished,” which thereby benefits the recipient in the long run.