The decline of marriage is upon us. Or, at least, that’s what the zeitgeist would have us believe. In 2010, when Time magazine and the Pew Research Center famously asked Americans whether they thought marriage was becoming obsolete, 39 percent said yes. That was up from 28 percent when Time asked the question in 1978. Also, since 2010, the Census Bureau has reported that married couples have made up less than half of all households; in 1950 they made up 78 percent. Data such as these have led to much collective handwringing about the fate of the embattled institution.

But there is one statistical tidbit that flies in the face of this conventional wisdom: A clear majority of same-sex couples who are living together are now married. Same-sex marriage was illegal in every state until Massachusetts legalized it in 2004, and it did not become legal nationwide until the Supreme Court decision Obergefell v. Hodges in 2015. Two years after that decision, 61 percent of same-sex couples who were sharing a household were married, according to a set of surveys by Gallup. That’s a high take-up rate: Just because same-sex couples are able to marry doesn’t mean that they have to; and yet large numbers have seized the opportunity. (That’s compared with 89 percent of different-sex couples.)

The move toward marriage has not been driven by young gay and lesbian couples rushing to the altar. In both the year before and the year after Obergefell, only one out of seven people whom the Census Bureau classified as in a same-sex marriage was age 30 or younger, according to calculations I’ve done based on the bureau’s American Community Survey. In fact, half of them were age 50 or older. The only way that could have happened, given that same-sex marriage has been legal for less than 15 years, is if large numbers of older same-sex couples who had been together for many years took advantage of the new laws. In other words, changes in state and federal laws seem to have spurred a backlog of committed, medium- to long-term couples to marry.

Why would they choose to do so after living, presumably happily, as cohabiting unmarried partners? In part, they may have married to take advantage of the legal rights and benefits of married couples, such as the ability to submit a joint federal tax return. But the legal issues, important as they are, appear secondary. In a 2013 survey conducted by the Pew Research Center, 84 percent of LGBT individuals said that “love” was a very important reason to marry, and 71 percent said “companionship” was very important, compared to 46 percent who said that “legal rights and benefits” are very important.

Yet the emphasis on love and companionship is not enough to explain the same-sex marriage boom. Without doubt, most of the middle-aged same-sex couples who have married of late already had love and companionship—otherwise they would not have still been together. So why marry now? Marriage became for them a public marker of their successful union, providing them the opportunity to display their love and companionship to family and friends. One reason, of course, was the desire to claim a right so long denied, but that only further underlines the way in which marriage today signals to the wider community the success of a long-standing relationship.

In this sense, these gay couples were falling right in line with the broader American pattern right now: For many people, regardless of sexual orientation, a wedding is no longer the first step into adulthood that it once was, but, often, the last. It is a celebration of all that two people have already done, unlike a traditional wedding, which was a celebration of what a couple would do in the future.

Consistent with this shift in meaning, different-sex couples, like the many of the same-sex couples who have married recently, are starting their marriages later in their lives. According to the Census Bureau, the median age at first marriage—the age at which half of all marriages occur—was 27.4 for women and 29.5 for men in 2017. That’s higher than at any time since the Census began keeping records in 1890. It is six years higher than when I got married in 1972 (at the typical age of 24). In my era, a young couple usually got married first, then moved in together, then started their adult roles as workers or homemakers, and then had children. (I scandalized my parents by living with my future wife before I married her.) Now marriage tends to come after most of these markers are attained.

The main distinction in marriage patterns today is between Americans who have attained at least a bachelor’s degree and those with less education. The college-educated are more likely to eventually marry, even though they may take longer to get around to it. In addition, nearly nine out of 10 wait until after they marry to have children, whereas a majority of those without college educations have a first child before they marry. Rates of divorce have been dropping across the board since about 1980, but the drop has been steeper for the college-educated. In the mid-20th century, people’s educational level had less impact on when, whether, and for how long they married. Today, marriage is a much more central part of family life among the college educated.

Nevertheless, the last-step view of marriage is common across all educational groups in United States. And it is being carried to the nth degree in Scandinavia. In Norway and Sweden, a majority of the population marries, but weddings often take place long after a couple starts to have children, or even after all of their children are born. The median age at first marriage in Norway is an astounding 39 for men and 38 for women, according to a recent estimate—six to eight years higher than the median age at first childbirth. In Sweden, one study found that 17 percent of all marriages had occurred after the couple had had two children. Why do they even bother to marry at such a late stage of their unions? Norwegians told researchers that they view marriage as a way to demonstrate love and commitment and to celebrate with relatives and friends the family they have constructed. This is capstone marriage: The wedding is the last brick put in place to finally complete the building of the family.

Americans have tended to rank marriage as more important than Europeans do for as long as there have been Americans. The transatlantic difference extends back to the Calvinist settlers who believed in the exalted place of marriage found in Martin Luther’s theology. And the difference has persisted: Between 2005 and 2009, the World Values Survey asked samples of people in various Western countries whether they agreed with the statement, “Marriage is an outdated institution.” Just 12.6 percent of Americans agreed, which is smaller than the proportion who agreed in any of the Western European nations surveyed, including heavily Catholic Italy (where 18.1 percent agreed) and Spain (31.6 percent).

Justice Anthony Kennedy reflected this high American regard for marriage when he wrote for the majority of the Court in Obergefell, “Rising from the most basic human needs, marriage is essential to our most profound hopes and aspirations.” Although many on the cultural and political left applauded the Court’s decision, Kennedy’s language was quite traditionalist. In fact, plenty of Americans view marriage as, at best, one of many lifestyle choices and, at worst, a deeply flawed heterosexual institution that should be transcended. Some go as far as to argue that families headed by married couples should be replaced by networks of friends and past and present romantic partners.

The alternative visions are far from replacing marriage. It is an open question, however, how much longer marriage will continue to dominate American family life. According to the General Social Survey, a national survey of Americans conducted every other year, the percentage of Americans who agreed with the statement, “It is alright for a couple to live together without intending to get married,” increased from 41 percent in 1994 to 57 percent in 2012, the last time the question was asked. Moreover, the material foundations of marriage have weakened. America is well past the heyday of the farm family in which a husband and wife united in labor and raised children to help work the land. Marriage seems to operate best today for parents who pool two incomes and invest heavily in their children’s development. Yet these investments could be made by parents in long-term cohabiting relationships. The dominance of marriage may simply be due to what the sociologist William Ogburn called “cultural lag”: the tendency of attitudes and values to change more slowly than the material conditions that underlie them.

There may soon be a slowdown in the proportion of same-sex couples who choose to marry. Sometime soon, the backlog of same-sex couples wishing to marry will be depleted. At that point, marriage rates among same-sex couples will depend largely on what younger people in recently formed relationships do. Many of them may do the same things that younger different-sex couples are doing: live together in cohabiting relationships, postpone marriage, and ultimately choose marriage less frequently than their parents’ generation did. If that happens, the rate of same-sex marriage will slow. But it will surely persist—more, to be sure, as a common last step into adulthood than as a first.

Andrew Cherlin is a professor of public policy and sociology at Johns Hopkins University.