Childhood Aggression: Rooted in Genetics, Influenced by Environment

Summary: While both reactive and proactive aggression in children appears to be genetic, it is the environment the child is exposed to that determines whether the behavior gets worse or better as the child ages, a new study reports.

Source: University of Montreal.

Over the past few months, many local cases of assault and harassment have come to light and been widely discussed in the news, both here and in the U.S. and Europe. Why do people have these types of aggressive impulses? To look for an answer, Stéphane Paquin, a PhD candidate in sociology at Université de Montréal working under the supervision of Éric Lacourse and Mara Brendgen, led a study on 555 sets of twins to compare incidences of proactive and reactive aggressive behaviour. His results demonstrate that, at age 6, both types of aggression have most of the same genetic factors, but the behaviour diminishes in most children as they age. Increases or decreases in aggression between the ages of 6 and 12 appear to be influenced by various environmental factors rather than genetics.

“Too often we forget that aggression is a fundamental part of a young child’s social development,” said Paquin. “Human beings show the highest levels of aggressive behaviour 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.”

Proactive aggression refers to physical or verbal behaviour meant to dominate or obtain a personal advantage at the expense of others, whereas reactive aggression is a defensive response to a perceived threat. While some children only exhibit reactive aggressive behaviours, proactive and reactive aggression are generally closely related.

Twins under the microscope

The study’s cohort of Quebec twins, which included 223 sets of monozygotic twins (with an identical genetic code) and 332 sets of fraternal twins, made it possible to determine whether the individual differences observed in proactive and reactive aggression were due to genetic or environmental factors. The children’s aggressive behaviours were assessed and documented in a report by their teachers at ages 6, 7, 9, 10 and 12. The results of the study also demonstrated that genetic factors influencing aggression at age 6 are different than those associated with changes in behaviour up to age 12. This suggests a common genetic maturation process is taking place, including the maturation of cognitive functions such as planning, decision-making, control and concentration.

kids fighting
Reactive and proactive types of aggressive behaviour in 6-year-old children share most of the same genetic factors. However, their evolution over time seems to be influenced by environmental factors. image is adapted from the University of Montreal news release.

With these results, researchers can now move on to study specific social factors associated with 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.”

He added: “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.”

About this neuroscience research article

Funding: This study was funded by the Social Sciences and Humanities Research Council, the Canadian Institutes of Health Research, the Fonds de recherche du Québec – Santé and the Fonds de recherche du Québec – Société et culture.

Source: Julie Gazaille – University of Montreal
Publisher: Organized by
Image Source: image is adapted from the University of Montreal news release.
Original Research: Full open access research for “Heterogeneity in the development of proactive and reactive aggression in childhood: Common and specific genetic – environmental factors” by Stéphane Paquin, Eric Lacourse, Mara Brendgen, Frank Vitaro, Ginette Dionne, Richard Ernest Tremblay, and Michel Boivin in PLOS ONE. Published online December 6 2017 doi:10.1371/journal.pone.0188730

Cite This Article

[cbtabs][cbtab title=”MLA”]University of Montreal “Childhood Aggression: Rooted in Genetics, Influenced by Environment.” NeuroscienceNews. NeuroscienceNews, 20 December 2017.
<>.[/cbtab][cbtab title=”APA”]University of Montreal (2017, December 20). Childhood Aggression: Rooted in Genetics, Influenced by Environment. NeuroscienceNews. Retrieved December 20, 2017 from[/cbtab][cbtab title=”Chicago”]University of Montreal “Childhood Aggression: Rooted in Genetics, Influenced by Environment.” (accessed December 20, 2017).[/cbtab][/cbtabs]


Heterogeneity in the development of proactive and reactive aggression in childhood: Common and specific genetic – environmental factors

Few studies are grounded in a developmental framework to study proactive and reactive aggression. Furthermore, although distinctive correlates, predictors and outcomes have been highlighted, proactive and reactive aggression are substantially correlated. To our knowledge, no empirical study has examined the communality of genetic and environmental underpinning of the development of both subtypes of aggression. The current study investigated the communality and specificity of genetic-environmental factors related to heterogeneity in proactive and reactive aggression’s development throughout childhood.

Participants were 223 monozygotic and 332 dizygotic pairs. Teacher reports of aggression were obtained at 6, 7, 9, 10 and 12 years of age. Joint development of both phenotypes were analyzed through a multivariate latent growth curve model. Set point, differentiation, and genetic maturation/environmental modulation hypotheses were tested using a biometric decomposition of intercepts and slopes.

Common genetic factors accounted for 64% of the total variation of proactive and reactive aggression’s intercepts. Two other sets of uncorrelated genetic factors accounted for reactive aggression’s intercept (17%) on the one hand, and for proactive (43%) and reactive (13%) aggression’s slopes on the other. Common shared environmental factors were associated with proactive aggression’s intercept (21%) and slope (26%) and uncorrelated shared environmental factors were also associated with reactive aggression’s slope (14%). Common nonshared environmental factors explained most of the remaining variability of proactive and reactive aggression slopes.

A genetic differentiation hypothesis common to both phenotypes was supported by common genetic factors associated with the developmental heterogeneity of proactive and reactive aggression in childhood. A genetic maturation hypothesis common to both phenotypes, albeit stronger for proactive aggression, was supported by common genetic factors associated with proactive and reactive aggression slopes. A shared environment set point hypothesis for proactive aggression was supported by shared environmental factors associated with proactive aggression baseline and slope. Although there are many common features to proactive and reactive aggression, the current research underscores the advantages of differentiating them when studying aggression.

“Heterogeneity in the development of proactive and reactive aggression in childhood: Common and specific genetic – environmental factors” by Stéphane Paquin, Eric Lacourse, Mara Brendgen, Frank Vitaro, Ginette Dionne, Richard Ernest Tremblay, and Michel Boivin in PLOS ONE. Published online December 6 2017 doi:10.1371/journal.pone.0188730

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  1. Not too odd for the conclusions from the data. I would suggest looking to multi-generation affects in the generational affects on any one generation’s behavior. Specifically, look at denial, through fear of “genetic fault” implications.

    I had to deal with a 1 year older brother who was extremely violent, getting worse with time, surrounded through time with behaviors I am told are now termed Narcissistic Personality Disorder. Because he looked very much like our paternal grandmother, who lived only 10 miles away, his behavior was excused, or denied, because it might reflect badly on her. She was, herself, always unwilling to accept any implication that she was the source, either genetic or environmental, of anyone’s bad behavior. She also always excused less bad behaviors in herself. She died still excusing herself, and blaming her choice in marriage for bad results in the family.

    A pattern of family behavior, stemming from her, is now visible at several decades remove. At 7, in 1957, my older brother planned and attempted to kill me for the first time. The incident was denied, using the words, “That sort of thing doesn’t happen in *our* family!” This attitude perfused the family, and continued through the next 2 attempts, when he was 12 and when he was 17. By 12 he had picked up a belief about dealing with others that, as he put it, “You’re either on top, or you’re sh*t-on-the-ground, and *I* know which I intend to be”.

    By the time he was 22, in 1972, I had left for college, and my younger brother was the target, getting slashed from hip to collar bone. That got Bob a choice between jail and the voluntary commitment which he chose for a few months. Because the family still chose not to believe any of the reports I yet again spoke to them, and did not pass those on to doctors, his diagnosis was simply Paranoid Schizophrenia.

    Over the next 5 years he was in and out of mental hospitals. In 1978 he was in a halfway house in Portland, Oregon, and attacked the head of the house, an elderly lady, apparently after several incidents where she had praised me in front of him. She died 3 months later when blood clots from the attack broke free and caused a brain stroke. He was placed under the Psychiatric Security Review Board (PSRB), and housed in the security wing of the State Hospital in Salem, Oregon. I interviewed with his physician at this time, and gave him my full history with Bob.

    In spite of this, Bob was, at our Mother’s request, in 1982, given a 1-Day pass, and I went with her to take him on a trip to the Pacific, at Astoria. There, after we climbed the Astoria Column, and Mother wandered to the other side, he tried to grab my pants belt loops from behind and throw me from the top of the column. Being weaker than I by then, he failed, but on the drive home, anticipating something bad happening on return, he jumped from the car on the I-5 freeway, at 70 Mph. His forehead was dented, with much blood, but that was repaired in surgery. In 1989 he failed to win release from the PSRB, and 3 months later committed suicide.

    In each case that Bob’s behavior was denied, it worsened. However, he responded to restrictions when actually inside a hospital. Such affects of the family on individuals are not always the same. My younger brother is accused of NPD traits by his own grown sons, but he never attempted to kill anyone. I have never married, because I was born with Asperger Syndrome, and recognized before Asperger’s was an “official” diagnosis in the US that my differences with people had to do with a lack of social nimbleness that I did not want to pass on.

    I urge you, when looking at environmental effects on those already genetically disposed to violence, to look closely at denial because of fear of fault-finding against the family itself, as a important factor in worsening behaviors over time.

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