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
"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
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
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
"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,"
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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