It is likely that aggression in humans results from an interaction between genetic inheritance and environmental influences. The evidence for a genetic basis for human aggression is admittedly controversial, but it is at least clear that there are important biological influences on aggression, such as hormonal effects and the sensitivity of specific elements of the nervous system to aggressive cues. However, we also learn to behave aggressively through exposure to aggressive role models, particularly during early development. The Frustration-Aggression hypothesis proposes that frustration generates hostile aggression, particularly when our motivation to achieve some goal is very strong and we are completely blocked from attaining that goal. In these circumstances, our aggression may sometimes be redirected to a target not responsible for our frustration.
Aggression is stimulated by various aversive experiences, including pain, physical attack and heat.
It is also stimulated by a high level of general arousal and by crowding. People in a crowd often show a combination of reduced accountability resulting from anonymity and reduced self-awareness resulting from intense stimulation. This phenomenon is known as deindividuation and it can result in an extreme form of violence that the perpetrators would never show in isolation. The print and electronic media also play a role in stimulating antisocial aggressive behaviour. There is correlational and empirical evidence suggesting a link between the availability of pornography and the incidence of sexual violence in adult males.