Children who ostracize or gossip about other kids have likely picked up that behavior from their peers, families or teachers, according to new study findings.

In a study of identical and fraternal 6-year-old twins, a group of Quebec researchers found that approximately 60 percent of children's physical aggression - biting, hitting or slapping another child - is inherited. In contrast, only 20 percent of social aggression - more subtle forms of cruelty, such as gossiping, or excluding another child - is fueled by a child's genetic makeup.

This suggests that most children who are socially cruel to other children have likely learned it from their environment, meaning the people around them, study author Dr. Mara Brendgen of the University of Quebec at Montreal stated.

Brendgen added that the study also showed that physical aggression tends to lead to social aggression, but not the other way around, which helps explain why physical aggression often diminishes with age, while social aggression increases.

Typically, children are more likely to be punished for physically attacking another child than for socially attacking them, the researcher explained, so as children age, they may transition toward tactics that they are more likely to get away with.

"We as a society are responsible for teaching children to switch their aggressive ways, instead of unlearning aggression," Brendgen said in an interview. "We have to get the message across that this is not acceptable," she added.

During the study, Brendgen and her colleagues interviewed the peers and teachers of 234 twins aged 6 years old about the children's tendencies toward physical and social aggression. Identical twins have exactly the same genetic makeup, Brendgen said, while fraternal twins share only half of the same genes. Both types of twins share the same environment, since they're raised together.

Given those circumstances, the researchers reasoned that if identical twins are more similar to each other than fraternal twins, those similarities are likely genetically driven. Based on the results, Brendgen and her team estimated what percentage of each behavior is driven by genetics. They report their findings in the journal Child Development.

Brendgen added that the findings also suggest that the same genes are fueling physical and social aggression, but both habits are triggered by different environmental factors. The identity of those genes and environmental factors, however, remains a mystery, she added. "That's the big question."

SOURCE: Child Development, July/August 2005.