The development of aggressive behaviour during childhood: What have we learned in the past century?

Research on human aggression has been a flourishing industry in the 20th century. As the attention shifted from an instinctual paradigm to a drive paradigm and a social learning paradigm, what have we learned on the development of aggressive behaviour during childhood? Are children born with an aggressive instinct or do they have to learn to aggress?This question has deep philosophical roots, but it also has important practical implications. Should interventions prevent children from learning to aggress or should they help children learn to inhibit aggressive reactions? Since most of the 20th century work on the development of aggression was concentrated on adolescents and elementary school age children, there appeared to be an implicit assumption that aggression is learned during these developmental periods. It is argued that to understand the origins of aggressive behaviour and prevent chronic cases of physical aggression we will need to focus on the development of aggressive behaviour during the first few years after birth, and differentiate among forms of aggressive behaviour. The form of agressive behaviour that is generally considered more “serious” or “socially unacceptable” (physical aggression) is clearly ontogenetically antecedent to less “serious” forms of aggressive behaviour, such as verbal aggression or indirect aggression. Furthermore, as a rule the frequency of physical aggression appears to decrease with age. However, infants’ physical aggression has generally not been considered developmentally significant. This is probably because of “the weakness of their limbs” and the apparent lack of “intentionality”. To have a relatively complete description of the life-span developmental trajectories of human aggressive behaviour by the end of the 21st century, we will need to start recruiting pregnant women very soon.