Aggression is defined as

• The act of initiating hostilities or invasion.
• The practice or habit of launching attacks.
• Hostile or destructive behavior or actions.

Aggression in humans is partly genetic, with origins going as far as to our reptilian ancestors, and partly a result of the upbringing. One of the genes primarily responsible for aggression and antisocial behaviour is МАОА . However, studies in macaque and humans showed that its negative effects can usually be compensated by better parenting.

Aggression is one of the most important and most controversial kinds of motivation. Its use as a category in the psychology of motivation has often been criticised, because it is clear that it encompasses a vast range of phenomena, from modern war to squabbles between individuals, and it is far from clear that these have anything in common other than the risk that someone gets hurt. There is a constant danger that concepts and explanations that are useful in the study of one kind of aggression will be misapplied in a different field. However, it remains one of the most important topics in many areas of psychology and other social sciences, including:

• motivation
• ethology and comparative psychology
• social psychology
• psychoanalysis and other kinds of depth psychology
• game theory
• social anthropology
• criminology
• international relations

Not all aggression is direct or readily identifiable, especially aggression which occurs between girls. Such aggression may occur in the context of what appear to be friendships. Such Relational aggression may involve domination, even sadism as the more powerful friend torments the weaker through threats of exclusion. Indirect aggression involves such actions as spreading rumors about others, even lies; as may social aggression which attacks self esteem or social status. Together these are characterized by Rachel Simmons in Odd Girl Out as alternative aggression .

Further reading

• Rachel Simmons, Odd Girl Out: The Hidden Culture of Aggression in Girls, Harcourt, 2002, hardcover, 296 pages, ISBN 0151006040