Protecting resources might involve territorial disputes, a common cause of aggression. Biology has also been used to explain aggression. Damage to brain structures has been shown to increase aggression, as has high levels of the hormone, testosterone. According to Bandura, humans learn aggressive behavior either through the direct experience of rewards for that behavior or the vicarious learning experience of observing someone else's behavior and the consequences. In other words, we can observe a person be aggressive and if she is in any way rewarded, we will adopt the model's behavior.
Children are particularly susceptible to models, which is why TV violence is of such concern.
Children observe aggression on TV and vicariously learn to model this behavior. Additionally, repeated exposure to violence makes it seem more acceptable and numbs the viewer to the impact of it. Similarly, behavior of parents and family members is extremely influential. Many studies have shown that people, who grow up in abusive homes, are more likely to exhibit violence towards their own family or others.