In a new Canadian study, researchers from the Université de Montréal set out to investigate the genetic and environmental factors in childhood that may be responsible for aggressive behavior.
They observed 555 sets of twins to compare incidences of proactive and reactive aggressive behavior. Their findings show that, at age 6, both types of aggression share a majority of the same genetic factors, but the behavior tends to diminish in most children as they get older.
Proactive aggression is defined as physical or verbal behavior meant to dominate or gain a personal advantage at the expense of others. Reactive aggression refers to a defensive response to a perceived threat. While some children only exhibit reactive aggressive behaviors, proactive and reactive aggression are generally closely related.
“Too often we forget that aggression is a fundamental part of a young child’s social development,” said researcher Stéphane Paquin, a Ph.D. candidate in sociology at Montréal.
The researchers also found that, between the ages of 6 and 12, any increases or decreases in aggression appear to be influenced by various environmental factors rather than genetics.
“Human beings show the highest levels of aggressive behavior towards their peers between the ages of 2 and 4. 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,” said Paquin.
The study’s twins included 223 sets of monozygotic twins (with an identical genetic code) and 332 sets of fraternal twins, allowing researchers to determine whether the individual differences observed in proactive and reactive aggression were due to genetic or environmental factors.
The children’s aggressive behaviors were evaluated and documented in a report by their teachers at ages 6, 7, 9, 10 and 12.
The findings of the study also reveal that genetic factors influencing aggression at age 6 are different than those associated with changes in behavior up to age 12. This suggests a common genetic maturation process is taking place, including the maturing of cognitive functions such as planning, decision-making, control and concentration.
With these results, researchers can now move on to study the specific social factors related to changes in proactive and reactive aggression in childhood.
“This work will also have a direct impact on clinical practices and prevention programs,” said 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.”
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