He said that while some research has indeed linked excessive porn consumption with personal problems, it has failed to demonstrate that pornography was the cause.
"It's the chicken-or-the-egg thing," he said. "Which came first? Were they depressed first and turned to porn, or was it the other way around?"
But Ralph DiClemente, a researcher at Emory University in Atlanta, said establishing strict causation is an unfairly high standard. If enough evidence points a certain way, parents, educators and lawmakers shouldn't need a "smoking gun" to be concerned, he said.
He is finishing a federally funded study that aims to provide some of the most precise answers yet about teens and Internet porn. Randomly selected young volunteers from around the country agreed to have software installed on their computers that allowed researchers to observe the websites they visited. Every two months, the teens answered survey questions designed to measure changes in attitude and behavior.
DiClemente said he couldn't reveal much about the results, but said it was clear that some of his subjects watched quite a bit of porn. A paper he aims to publish in a scientific journal will examine whether that appears to speed a child's initiation into sexual activity or affects sexual risk-taking.
"While they're seeing (pornography) on the computer, it may be telling them that that's what a relationship is: a lack of intimacy and a whole lot of risky sex," he said.
But one complication to the idea that porn influences behavior is evidence suggesting that young people are becoming more sexually conservative even as Internet pornography becomes more widespread.
A federal study released last year found that a declining percentage of teens are having sex. And figures from the Guttmacher Institute indicate that teen pregnancy rates are down sharply from the early 1990s, when Internet access was limited to academics and hobbyists.
"Right now, teens are looking like they're acting more responsibly than they were 10 or 20 years ago," said Jennifer Manlove, who studies adolescent sexuality for Child Trends, a Washington, D.C., research center.
Still, Alex Montesantos, 17, a junior at Elmhurst's York High School, said he believes ubiquitous online porn has produced a certain flippancy in his generation's views toward sex. Connecting the act with love has come to seem "lame or weird or awkward" among many of his peers, he said.
"They don't look at sex as consequential or emotional," he said. "They almost see it like you can do it for fun, hook up with someone you never met before. They don't necessarily see it as another generation would see it -- a very personal thing, a deep emotional connection."
Shira Tarrant, an author and gender studies professor at California State University Long Beach, said she thinks porn has had even subtler effects on young people. It has affected notions of female beauty, ideas of normal sexual behavior -- even certain grooming habits, she said.
But vilifying or censoring porn is ill-advised, she said: Adults should respond through education, reminding teens to summon their powers of critical thinking when they encounter sexually explicit material.
"Porn is like any other form of media," she said. "If I'm watching 'Keeping Up With the Kardashians,' I'm getting an idea of what sexy looks like. If I'm watching a music video, I'm being shown what sexy dancing looks like. It's a script given through media. Pornography is no different."
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