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 ce ntury. As the attention shifted from an instinctual paradigm to a drive par adigm and a social learning paradigm, what have we learned on the developme nt of aggressive behaviour during childhood! Are children born with an aggr essive instinct or do they have to learn to aggress? This question has deep philosophical roots, but it also has important practical implications. Sho uld 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 adolesce nts and elementary school age children, there appeared to be an implicit as sumption that aggression is learned during these developmental periods. It is argued that to understand the origins of aggressive behaviour and preven t chronic cases of physical aggression we will need to focus on the develop ment of aggressive behaviour during the first few years after birth, and di fferentiate among forms of aggressive behaviour. The form of agressive beha viour that is generally considered more "serious" or "socially unacceptable " (physical aggression) is clearly ontogenetically antecedent to less "seri ous" forms of aggressive behaviour, such as verbal aggression or indirect a ggression. Furthermore, as a rule the frequency of physical aggression appe ars to decrease with age. However, infants' physical aggression has general ly not been considered developmentally significant. This is probably becaus e 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.