Aggression
Some scholars believe that behaviors like aggression may be partially learned by watching and imitating people's behavior, while other researchers have concluded that the media may have some small effects on aggression. There is also research questioning this view. For instance, a long-term outcome study of youth found no long-term relationship between playing violent video games and youth violence or bullying. One study suggested there is a smaller effect of violent video games on aggression than has been found with television violence on aggression. This effect is positively associated with type of game violence and negatively associated to time spent playing the games. The author concluded that insufficient evidence exists to link video game violence with aggression. However, another study suggested links to aggressive behavior.
Behavior mutation
Aggression is a survival trait that can be favoured by Natural Selection in nearly any species. Aggressive individuals can be better able to compete for resources including food, territory and mates, as well as more successful in protecting themselves and their progeny from predators. It can also be energetically costly, and extreme or out of context aggression can be disadvantageous or deleterious, especially in social organisms. Aggression is a complex trait that is regulated by many interacting genes and gene expression is highly variable depending on environment (phenotypic plasticity). Mutations in genes that influence aggressive behaviours can potentially increase aggression or passivity.