Genetics may trump environment in kids’ aggression

Those toddler temper tantrums may have more to do with genes than environment, a new study finds. But experts continue to stress the importance of parenting and environment for young children.

University of Montreal scientists find that genetic factors may contribute more to a small child’s tendency to act out aggressively toward other children, adults or possessions than does their surrounding environment.

“It was kind of surprising. Quite surprising,” says Eric Lacourse, researcher and associate professor at the department of sociology at the University of Montreal.

Lacourse and his team of researchers followed 667 pairs of twins, identical and fraternal, for three and a half years. Tendency toward physical aggression “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,” says 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 says. Identical twins were used as a comparison group.

The scientists were surprised that shared environments “had no effect on the stability, initial status and growth rate of (physical aggression),” the study notes.

However, Lacourse is quick to clarify that young children often grow out of their physically aggressive behavior based on the completed questionnaires. Aggression is “normative and can be frequent during this age period,” he says.

“I do not want to make parents not responsible for their parenting,” he says. Even if a child is genetically prone to physical aggression, there are ways parents and caregivers should react to decrease its likelihood in later years.

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

Denise Duval Tsioles, a child psychologist at Child Therapy Chicago, also emphasizes 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 says. 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, Duval Tsioles says.

“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,” Boivin says.

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