Aggression in children are often a symbol of the many different underlying problems. It’s a very polymorphic thing, a commonality for any number of different psychiatric conditions, medical problems, and life circumstances. Aggression in children can take many forms: Angry tantrums; hitting, kicking, or biting; hot-headed outbursts that destroy property; cool-headed bullying; verbal attacks; attempts to control others through threats or violence. Aggression differs from what's commonly called assertiveness, although the terms are often used interchangeably among laypeople. Predatory or defensive behavior between members of various species might not be considered aggression within the same sense. Biological approaches conceptualize aggression as an internal energy released by external stimuli, a product of evolution through natural selection, part of genetics, a product of hormonal fluctuations.