For example, some news reports have claimed that a recent shooting rampage resulted when one young man was jilted by his girlfriend. Athletes scream obscenities at officials ruling foul behavior. Shoppers fight over the last remaining item at a sale. But frustration doesn't have to lead to aggression. Some people seem more prone to aggression than others.
Aggression also runs in families.
Researchers, reasoning from animal models of territorial aggression, aggression within social groups, and selective breeding for aggressive traits, argue that genetics contributes to aggression and violence. Another hypothesis is the observational learning hypothesis. According to this hypothesis, aggression is perpetuated by observation and modeling of aggressive behavior. Thus, children are aggressive not so much because they inherited aggression genes from their parents but because they have observed aggression and violence in their homes. Aggression and violence are complex behaviors and likely have complex causes.