Early Aggression in Children Could Have More to Do With Genes Than Earlier Thought

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Childhood aggression may have more to do with a child’s genes than his or her surroundings, a new study has found. But environment and parenting remain key factors in the upbringing of young children, according to child development experts.

Montreal researchers claim that genetic factors may contribute more to a small child’s tendency to be physically aggressive than environmental factors.

To arrive at the root causes of physical aggression in young children, researchers at the University of Montreal conducted a study and posted new findings that could help clear up the perennial nature-versus-nurture debate.

Their findings: that the genetic makeup has more impact than does surrounding environment on whether a child likely will act out aggressively toward other children, adults or possessions.

“Quite surprising,” remarked University of Montreal researcher Eric Lacourse.

As part of the study, Lacourse, an associate professor in the school’s sociology department, and his team of researchers followed 667 pairs of twins, identical and fraternal, for three and a half years. Tendency toward physical aggression, or PA, “was assessed for each twin as part of a large questionnaire administered to mothers” at key points in the children’s developmental process; ages 20, 32 and 50 months.

The study then took the mother’s reports and used three different models to calculate shared and non-shared environmental factors. There was no direct observation of the individual home environments, (i.e. shared environment,) of the twins, however.

“The statistics we derived always depends on the type of environments we find in the sample. For instance, because we are dealing with a population sample, the environments of the twins may not be as adverse as those we find in more at risk sample,” said Canada Research Chair in Child Development and co-researcher Michael Boivin.

Identical twins, with identical genetic makeup, tended to display similar tendencies toward aggressive or non-aggressive behavior. But fraternal twins, sharing the same environment, often showed different tendencies toward aggression, a way of suggesting genetic influence.

“At first we thought that it would be even,” Lacourse said, commenting on the influence of genetic factors versus environmental ones. Identical twins were used as a comparison group. They share 100 percent of the same DNA while fraternal twins share about 50 percent. Within both the identical and fraternal twin sets, every twin lived in the same, shared environment as their sibling.

“We expected more correlation of similarity among the fraternal twins,” Lacourse said. But the scientists were surprised to discover that shared environments “had no effect on the stability, initial status and growth rate of PA,” the study noted.

Based on the mothers’ completed questionnaires, Lacourse was quick to clarify that young children often grow out of their physically aggressive behavior. PA “[is] normative and can be frequent during this age period,” Lacourse said.

“I do not want to make parents not responsible for their parenting,” he said. Even if a child is genetically prone to PA, there are ways parents and caregivers should react to decrease the likelihood of continued PA in later years.

“If parents respond badly, it will make PA worse over time,” Lacourse said.

Denise Duval Tsioles, a child psychologist at Child Therapy Chicago, also emphasized that parent involvement is crucial, and her experience leads her to slightly different conclusions.

“What I tend to see is a lot of environmental factors. They play a huge role,” Duval Tsioles said. Children may have “similar genetic backgrounds but depending on certain factors their emotions come out differently.”

How children develop a sense of self plays a large role in their ability to control their emotions. Children who have caregivers that “help them regulate their emotions by being physically and emotionally responsive to their needs are more capable of modulating their emotions and are able to begin to internalize” the correct behavior that is expected, Tsioles said.

“The bottom line is that very early risk factors (of genetic origin) are at play that makes it more likely (it’s not destiny!) that some children will use physical aggression over time early in life,” said Boivin. “These findings militate for an early prevention approach to physical aggression, before other factors (some environmental, others, of genetic origin) kick in to reinforce this behavioral tendency.”

Illustration by Mike Fisher / MCT