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Study Debunks Theory On Teen Sex, Delinquency
Looked at from a similarly high altitude, she said, people might conclude that red meat is a health food, since people live longer in countries where more is eaten. Only when the issue is studied within one country does red meat's link to chronic diseases appear.
Suspecting such an error in the Haynie study, Harden and three colleagues, including her adviser, Eric Turkheimer, an expert in behavioral genetics, studied more than 500 pairs of twins in the same national survey analyzed by the Ohio team. Because twin pairs share similar or identical genetic inheritances (depending on whether they are fraternal or identical) and the same home environment, twin studies are useful for seeing through false cause-and-effect relationships.
The team looked at identical twin pairs in which one twin initiated sex younger than the other, then team members tallied subsequent problem behaviors. If sex really adds to the chances of delinquency, then early-sex teens should end up delinquent more often than their later-sex twins.
"It turns out that there was no positive relationship between age of first sex and delinquency," Harden said.
The way to reconcile that with the previous evidence of a link is to conclude that some other factors are promoting both early sex and delinquency, she said. In an e-mail, Haynie agreed. And the Virginia study, to appear in the March 2008 issue of the Journal of Youth and Adolescence, offers some clues.
It found that identical twins, who have the same DNA, were more similar to one another in the ages at which they lost their virginity than were fraternal twins, whose DNA patterns are 50 percent the same -- an indication that genes influence the age at which a person will first have sex. Other twin studies have found the same pattern for delinquency.
Together, those findings suggest that some genes -- perhaps, for example, those that increase impulsivity and risk-taking -- may underlie both behaviors.
"You need to have some appetite for risk-taking to be a delinquent. And the same if you're 13 and going to have sex for the first time," Harden said.
Efforts to prevent delinquency can hardly take aim at people's genes. But the Virginia study also indicates that social factors, as yet unidentified but perhaps involving relationships with family and friends, have an even bigger impact than genes on whether a child will become delinquent. Those are the things that should be identified and targeted by delinquency-prevention programs, said Jeanne Brooks-Gunn, co-director of Columbia University's National Center for Children and Families.
"I wouldn't be focusing on early sexuality . . . to alter rates of delinquency," she said.
Perhaps most surprising, the Virginia study found that adolescents who had sex at younger ages were less likely to end up delinquent than those who lost their virginity later. Many factors play into a person's readiness for sex, but in at least some cases sexual relationships may offer an alternative to trouble, the researchers say.
Even then, there are emotional and physical risks. Young adolescents, in particular, are less likely to use condoms and so are vulnerable to sexually transmitted diseases and unwanted pregnancies.