FRIDAY, March 16 (HealthDay News) -- Using spanking as a method of discipline for kids who have a genetic predisposition to aggressive behavior likely makes them even more aggressive, especially boys, new research suggests.

"There's an intricate interplay between nature and nurture," said study co-author J.C. Barnes, an assistant professor of criminology at the University of Texas at Dallas School of Economic, Political and Policy Sciences. "Most people know that genes matter, but genes and environment can coalesce, and we see things above and beyond what's expected."

While the study found this effect was statistically pronounced in males, Barnes said that the combination of aggressive genes and being spanked as a child likely influences girls' behaviors, too. He said it might be that the combination of these two factors didn't reach statistical significance in girls because boys tend to act out more, and so present more opportunities to have that behavior seen in a study.

The findings were published recently in the journal Aggressive Behavior.

The use of spanking as a disciplinary tool has been linked to a number of adverse outcomes in children and teens, such as aggression and criminal behavior, according to background information in the study.

Last month, researchers reported in the Canadian Medical Association's journal, CMAJ, that children who had been physically punished had higher levels of aggression against their parents, siblings, peers and spouses.

And, it may be that children who are genetically predisposed to aggression are the ones most likely to be spanked for their behavior, but the current study by Barnes and his colleagues suggests that spanking in response will just increase that type of behavior.

Data for the current study came from a nationally representative sample of children born in 2001. The entire group involved almost 11,000 children.

To assess genetic predisposition, the researchers looked at a group of about 1,500 twins. They compared the behavior of identical twins to fraternal twins. Since identical twins share 100 percent of their genetic makeup, the researchers said that behaviors under genetic influence would be more common in identical twins than in fraternal twins. Fraternal twins share about 50 percent of their genetic makeup.

The researchers then looked at the effect of genetic predisposition and the use of corporal punishment and how those factors influence a child's behavior both separately and together.

They found that for both boys and girls having a genetic risk for aggressive behavior increased the risk of antisocial behavior in children. The use of corporal punishment also increased the risk of antisocial behavior in both sexes, according to Barnes.

But, when the two factors were combined -- genetic risk and corporal punishment -- only boys seemed to have an even greater likelihood of antisocial behavior, according to the study.

"I'm not surprised to see that they're concluding that there's evidence proving that genetic factors are involved in the development of aggressive behaviors. There's a complex interaction between genetics and environment," said Dr. Roya Samuels, an attending physician in the department of general pediatrics at the Steven and Alexandra Cohen Children's Medical Center of New York.

"Many studies have shown detrimental long-term effects from the use of corporal punishment in children. But, it still occurs with great frequency in this country," she said.

As children get older, it becomes especially difficult for parents who've relied on corporal punishment to discipline effectively, she noted.

Instead of physical punishment, Samuels suggests developing a supportive, nurturing relationship with your child. She said parents should reinforce positive behaviors, and give structure and a daily routine in a child's life. Parents should set consequences for negative behavior, she said, and in the toddler years, timeouts can be an effective form of discipline instead of spanking.

More information

Get advice of disciplining children from the Nemours Foundation's KidsHealth.