Aggression is defined as any behavior that is intended to harm someone. Several studies have shown that exposure to television violence increased aggressiveness and that aggressive children tend to look for the more violent programs.
Theorists believe that human nature is aggressive because aggression has a long history and is found within all cultures. Aggression is inborn and that it cannot be eliminated. Psychologists studying aggressiveness propose that aggression evolved from only the 'survival of the fittest' instinct.
The biological factor in aggression is genetics. It is believed that some individuals are likely to inherit irritable temperaments and to engage in aggressive behaviors. However this does not mean that individuals have to behave aggressively because aggression also develops from other factors.
Many people believe that humans are violent because we are naturally and unavoidably aggressive. This widely held theory provides us with harmful expectations, self-fulfilling prophesies, and with excuses for being aggressive.
The good news is that the evidence shows that humans can in the right circumstances and with the appropriate training be kinder to one another.
In closing, there is still an immense amount of work to be done in explaining the development of aggression. There will always be one side that says there is a certain factor that causes aggression.