Although, these unprovoked violent outburst decreased in the second year of life.
What’s more, the aggressive infant did not show any signs of obvious distress.
What is also interesting, researchers scored the violent toddlers as higher in their tendency to show pleasure. It suggests that they use force as a form of fun interaction, not as a way to vent their anger. Also, provoked and unprovoked aggression showed different developmental trajectories.
Dahl, A. (2015). “Infants’ unprovoked acts of force toward others Developmental”, Science, Volume 19, Issue 6, November 2016, Pages 1049–1057