(AP Photo/Damian Dovarganes, File)

There could be an unlikely contributor to the decline of marriage in this country. And it's free pornography on the Internet.

A team of researchers, who published their findings in The Institute for the Study of Labor (IZA) in Germany, determined that the rise of free Internet pornography is not only correlated with a pronounced decline in percentage of young adult males who are married, but might actually be contributing to the trend.

"The results in this paper suggest that such an association exists, and that it is potentially quite large," the study notes.

The researchers used data from the General Social Survey (GSS), a comprehensive, nationally representative survey, to analyze how 18-to-35 year-old men used the Internet between 2000 and 2004. They focused on  how many hours each participant spent on the Internet per week, and how many reported having used the Internet to view pornography in the past 30 days, but also observed other activities, including the use of religious websites.

"We asked ourselves, what is helping determine whether people are married or not?" said Dr. Michael Malcolm, a professor at the University of West Chester, Pennsylvania, and one of the study's authors. "One of those things, we thought, could be the use of pornography."

In order to test the hypothesis, Malcolm adjusted for a number of variables, including age, income, education, religiosity, and employment, all of which have been shown to correlate with marriage. He also adjusted for the possibility marriage has an impact on pornography use, and never the other way around.

He then measured the correlation between pornography use and marriage rates among the more than 1,500 participants studied.

Broadly, higher Internet usage was associated with lower marriage rates. But pornography use in particular was more closely linked to those participants who were not married than any other form of Internet use, including regular use of financial websites, news websites, sports websites, and several others. The opposite, for comparison, was true for religious website use, which was positively correlated with marriage.

The natural reaction might be to dismiss the findings as confirmations of an obviousness: that men who are married tend to look at porn less frequently precisely because they are married. While that might very well be true, and likely helps explain some of the relationship, it doesn't explain all of it.

The researchers, while careful to say that their findings fall short of being conclusive, insist that the relationship between the two also "likely runs in the direction that we assert."

The reason, Malcolm explains, is likely tied to the relationship between marriage and sexual gratification. If pornography is viewed as a means of alternative sexual gratification, then it could be undercutting the need for marriages to serve this function, at the very least during a younger age. Think of it as a milder form of premarital sex.

The decline of marriage in the United States is well-documented. Marriage rates have been falling for decades. Divorce rates, while leveling off, are still historically high. Even those couples who are still tying the knot are doing so later and later as time passes.

There are many reasons for the trend. One of the most provocative is the rise of wealth inequality. Andrew J. Cherlin made this point in a recent op-ed in the New York Times: Historically, low and stable inequality has coincided with periods of higher marriage rates among all socioeconomic groups. Marriage can be a expensive institution, especially without two sustainable sources of income. It's likely of little coincidence that the United States is particularly unequal today, and its poor are particularly less likely to marry than the rich.

Some have argued that a decline in traditional values has made marriage less of a priority than it once was. The country is certainly less religious today than it has been in the past, and religious people do tend to get married more often, and younger.

Another, albeit much less central issue, seems like it could be the proliferation of free pornography. Between 2009 and 2010, erotic content accounted for roughly 13 percent of all Internet searches, according to Forbes. In addition, a 2008 study found that nearly 90 percent of men think it's acceptable. It might be time to dive a bit deeper into how the societal shift is influencing things happening beyond all the closed doors.