is overt, often harmful, social interaction with the intention of inflicting damage or other unpleasantness upon another individual. It may occur either in retaliation
or without provocation
. In humans, frustration
due to blocked goals can cause aggression. Human aggression can be classified into direct and indirect
aggression, whilst the first is characterized by physical or verbal
behavior intended to cause harm to someone, the second one is characterized by a behavior intended to harm social relations of an individual or a group.
In definitions commonly used in the social sciences and behavioral sciences
, aggression is a response by an individual that delivers something unpleasant to another person. Some definitions include that the individual must intend
to harm another person. Predatory or defensive behavior between members of different species may not be considered aggression in the same sense.
Aggression can take a variety of forms, which may be expressed physically, or communicated verbally or non-verbally: including anti-predator aggression, defensive aggression (fear-induced), predatory aggression, dominance
aggression, inter-male aggression, resident-intruder aggression, maternal
aggression, species-specific aggression, sex-related aggression, territorial
aggression, isolation-induced aggression, irritable aggression, and brain-stimulation-induced aggression (hypothalamus). There are two subtypes of human aggression: (1) controlled-instrumental subtype (purposeful or goal-oriented); and (2) reactive-impulsive subtype (often elicits uncontrollable actions that are inappropriate or undesirable). Aggression differs from what is commonly called assertiveness, although the terms are often used interchangeably
among laypeople (as in phrases such as "an aggressive