The study convincingly shows that parenting, and not just genes, contributes to the development of risky callous-unemotional traits.
Washington: Parents, take note! A harsh environment at home and less emotional warmth can make children aggressive and antisocial, a study has found.
Researchers from University of Pennsylvania and Michigan State University in the US analysed small differences in the parenting of 227 identical twin pairs.
They wanted to determine whether these differences predicted the likelihood of antisocial behaviours emerging.
The study, published in the Journal of the American Academy of Child and Adolescent Psychiatry, showed that the twin who experienced stricter or harsher treatment and less emotional warmth from parents had a greater chance of showing aggression as well as a set of characteristics known as callous-unemotional (CU) traits.
"Some of the early work on callous-unemotional traits focused on their biological bases, like genetics and the brain, making the argument that these traits develop regardless of what is happening in a child's environment, that parenting doesn't matter," said Rebecca Waller, an assistant professor at University of Pennsylvania.
"We felt there must be something we could change in the environment that might prevent a susceptible child from going down the pathway to more severe antisocial behaviour," said Waller.
The work is the latest in a series of studies from researchers using observation to assess a variety of aspects of parenting.
The initial research, which considered a biological parent and child, confirmed that parental warmth plays a significant role in whether CU traits materialise.
A subsequent adoption study, of parents and children who were not biologically related, turned up consistent results.
"We couldn't blame that on genetics because these children don't share genes with their parents," Waller said.
"But it still didn't rule out the possibility that something about the child's genetic characteristics was evoking certain reactions from the adoptive parent," he said.
In other words, a parent who is warm and positive may have a hard time maintaining those behaviours if the child never reciprocates.
Using 6- to 11-year-old participants from a large, ongoing study of twins that Burt directs, the team turned its attention to identical twins.
For 454 children (227 sets of identical twins), parents completed a 50-item questionnaire about the home environment.
They also established their harshness and warmth levels by rating 24 statements such as "I often lose my temper with my child" and "My child knows I love him/her."
The researchers assessed child behaviour by asking the mother to report on 35 traits related to aggression and CU traits.
"The study convincingly shows that parenting -- and not just genes -- contributes to the development of risky callous-unemotional traits," said Luke Hyde, an associate professor at University of Michigan.
"Because identical twins have the same DNA, we can be more sure that the differences in parenting the twins received affects the development of these traits," said Hyde.
The next step is to turn these findings into useable interventions for families trying to prevent a child from developing such traits or to improve troubling behaviors that have already begun, researchers said.