The infidelity business is booming. In a recent interview, Noel Biderman, the CEO of Ashley Madison, a website for people seeking extramarital affairs, observed, “I don’t see an appetite for unfaithfulness waning around the world.” Indeed, the company has 36 million members in 46 countries and is hoping to launch an IPO in London in the not too distant future.

To what does Biderman attribute the company’s success? “Female equality,” he explained to Business Insider recently. “Women are getting greater equality and are generally getting married later than those in two or three generations ago. They are now more willing to put their marriage at risk. That’s only going to increase because economic conditions for women are better and it gives them more choice.”

If an evangelical pastor had said that, he would have been denounced as a retrograde hick trying to keep women barefoot and pregnant by suggesting that women’s liberation would destroy the traditional family. But Biderman can not only point to his company’s bottom line but also decades of social science research to confirm his suspicions.

Most marriage researchers I’ve interviewed concluded long ago that “opportunity” is the single biggest factor in predicting infidelity in a marriage. Lots of marriages are unhappy. A couple will fight over money or children. They will have a less than satisfactory sex life. But what most distinguishes the husbands and wives who are unfaithful is that opportunity was practically knocking down the door. And while some of those opportunities will present themselves on a girls’ weekend away—what happens in Vegas… you know—the workplace romance is also alive and well.

Even before the existence of dating websites, offices could provide a kind of alternate universe for men and women away from their spouses. Advice columns are filled with women who refer to their “office boyfriends” or men who find themselves flirting with coworkers on business trips.

According to a 2001 paper in the Journal of Family Psychology, “Two variables … considered indexes of opportunity for [extramarital sex], income and employment status, were both significantly related with infidelity.” The authors speculated that it might not be the income itself that produces this result. Instead, income “might make it easier to hide the costs of entertainment or other expenses incurred as a result of being with a third person.” Also, they wondered whether “individuals with higher incomes might be considered to have higher status, to travel more or to interact professionally with more appealing individuals.” (That last part may be a little academic snobbery—who would want to sleep with that guy the waitress met in a diner?)

It could also be true, as Biderman notes, that as women work outside the home more and are less dependent on the spouse for support, they are more inclined to put their marriage at risk.

So will the growth of Ashley Madison know no bounds? It’s possible. It does seem as if women’s equality is spreading across the globe. But the same paper also found that younger men and women seem to be reporting a lower level of infidelity.

Perhaps that’s partly because only people who really believe in marriage bother to get married anymore and so the sample is skewed. Or maybe the fact that the partners in these younger marriages are on a more equal footing might lead to lower levels of infidelity. The highest level of infidelity seemed to occur when one spouse (most often the husband) worked and the wife stayed home. The authors suggest that a “discrepancy in relationship power” could also be a cause of infidelity.

Biderman suggests that his company is bound to grow because it’s based on “human conditions.” Even if people have the motive, though, Ashley Madison is providing the opportunity.