Violent impulses and outbursts are nothing new in society, and a fundamental question of human existence is how violent tendencies arise in people. Twins provide researchers with a unique opportunity to look at how genetics plays a role, or not, in the developmental of mental and physical disorders and can illustrate whether the environment has a more significant influence than the genetic background a person possesses. Scientists investigating aggressive behavior in people turned to a study that included 555 sets of twins to look at proactive and reactive aggressive behavior.
Stéphane Paquin, a doctoral candidate in sociology at Université de Montréal mentored by Éric Lacourse and Mara Brendgen has found that at six years of age, both types of aggression consists of similar genetic factors. But, changes in aggression levels between the ages of six and twelve seem to have more to do with the environment than with genetics. The data has been reported in PLOS One.
"Too often we forget that aggression is a fundamental part of a young child's social development," noted Paquin. "Human beings show the highest levels of aggressive behavior towards their peers between the ages of two and four. As children grow, they learn how to manage their emotions, communicate with others and deal with conflict. They are able to channel their aggressive impulses, whether proactive or reactive."
Aggressive behavior has been classified into two groups. Physical or verbal actions that seek to create a personal advantage or dominate others to their detriment is called proactive aggression. Reactive aggression consists of defensive responses to some perceived threat. Some kids exhibit only reactive aggression, but both types are considered to be closely related.
For this work, 223 sets of identical or monozygotic twins participated, while 332 sets of fraternal twins helped show whether genetics or the environment played a bigger role in the development of aggressive behaviors. Teacher’s reports served to document the actions of the children at ages six, seven, nine, ten and twelve. The result suggests that some common genetic mechanism is at work as cognition matures, and planning, impulse control, concentration and decision-making skills develop.
This research will enable investigators to assess the various social factors that are associated with alterations in reactive and proactive aggression in childhood. "This work will also have a direct impact on clinical practices and prevention programs," noted Paquin. "Our results have revealed the importance of developing different prevention methods for reactive and proactive aggression, specifically by offering support to families and providing interventions in schools."
"Our findings also corroborate those of other studies, demonstrating that programs designed to prevent reactive aggression should focus on reducing experiences of victimization, whereas those meant to counter proactive aggression should be based on the development of pro-social values,” Paquin concluded.
The video above explains more about how twin studies help researchers learn about the role of genes, and the environment, in traits.