People are not eschewing romantic relationships, but people move in and out of romantic partners.

Stephanie Coontz, a professor at The Evergreen State College in Washington state and director of research and public education at the Council on Contemporary Families, has written widely on marriage and family life. A recent New York Times column, for instance, explored “the new instability” in family life due to rising socioeconomic inequality coupled with greater gender equality. In researching our recent report Meet the New Family, we talked to Coontz about some of the ways families around the globe are changing and what’s driving these shifts.

As more people forego marriage and long-term partnerships in some cases, do you see a rise in finding familial fulfillment through friends?

One of the things I think is important to understand about that is a lot of people are not eschewing romantic relationships, but people move in and out of romantic partners. You have a significant uptake in “living apart together.” A lot of the increase in solo living is because of the delay in the age of marriage and then later, divorce. But most people transition through several of these family archetypes. They’re not just set in stone.

What do you mean by “living apart together”?

About 7 percent of California couples are in this. It’s frequent enough in the Nordic countries that they have this phrase for it. It means that these people are in a committed relationship but do not live in the same house. They may take turns staying at each other’s house, but it’s different than just dating. It’s a very committed relationship, but they don’t feel like living together.

Because you’ve had the breakdown of this lockstep idea that people have to transition into marriage by a certain age, people have become much more free to follow their individual idiosyncrasies. And there are people, especially ones with a certain amount of capital or economic affluence, who can afford to live in separate houses and prefer to have their separate space and yet consider themselves committed couples. I don’t think this is going to become a majority trend, but it’s an interesting little niche that has developed and probably will continue to develop at a modest pace.

How do Millennials feel about pursuing different family models?

Along with this increased freedom to follow your own path is the increasing socioeconomic inequality that is occurring, not just in the United States but across many countries in the developed world. The decline of marriage among educated individuals is actually much less extreme than among low-income individuals and much more connected to choice and idiosyncrasies.

It is the culmination of women’s increased options, the increased tolerance for non-family relationships,—but also men’s declining ability to actually offer themselves as a stable partner who can contribute, who will hold down a job and will have rising real wages like they did in the ’50s and ’60s. The culmination is not purely choice. There’s a big element of necessity in the decline of marriage among less educated and low-income people.

In Asia, we’ve seen the rise of “golden misses”—women who cannot find a partner of equal or higher socioeconomic status, so they choose not to marry.

At the low-income level, these women are not golden at all, and that’s why they often move into cohabiting relationships in order to share expenses, reluctant to commit to marriage because they are afraid they may end up having to support this guy.

Why do you think there’s been such a dramatic increase in same-sex marriages?

From my own research on the history of marriage, the stunning rapidity of the acceptance of same-sex marriage is not really a sign of declining morals anywhere. It’s actually a sign of how much heterosexual marriage has changed. Until the 1970s, there were hidden master laws and legal requirements as to the roles that men and women could legally play in marriage. Since the 1970s, we’ve repealed those, and more and more marriages are based not on a set of specialized activities between husband and wife but on gender-neutral organizations. The spread of same-sex marriage is almost the inevitable result of the transformation of heterosexual marriage.

Marriage remains the highest level of commitment that most Americans can imagine. What’s changed, really, is that we have much higher standards. We don’t need marriage to organize and bring together people who have totally different skills and resources. We don’t need it for social respectability. The decline in marriage does not reflect the lessened importance of marriage, because in many ways the decline of marriage represents the higher emotional expectations of it: We’re not going to marry the way people married in the ’50s, after knowing each other for six months, and just say, “Well, it’s time to get married.”

Another trend we’re examining is multiple generations increasingly living together under one roof. Why is this?

Throughout history, this was very common, and then we went through a period in the United States and Britain and many European countries of really emphasizing the nuclear family and calling upon Freudian psychology. Marital therapists called upon young people to actually break with their parents and put them in a nursing home rather than take them in. Go back to films like Marty from the 1950s, where the moral is you shouldn’t live with your mother, you should leave your mother and her sister on their own or put them in a nursing home, and go off with your new bride.

We are seeing an uptick of this intergenerational cohabitation for a combination of economic reasons. And also because childbearing has become so much more democratic. There’s no longer that sense that there’s a huge generational gap, and there’s more respect for the independence, which makes it possible for people to move back and not feel completely stifled by it.

Research shows that the vast majority of Americans say their families are as close if not closer than the ones they grew up in. That includes extended kin who are not co-residents. For the ones who do move back home, there is a certain ambivalence, because you still have the American values of individualism and self-sufficiency that are being countered both by closer relationships between adult children and their parents and by economic necessity.

What do you see happening outside the U.S.?

The long-term trend is toward women’s permanent entry into the workforce and a decline in fertility rates, which changes the dynamics of marriage, and an increase—which varies from society to society—in the options of women outside marriage. All these trends toward delayed marriage, toward more singles, toward the challenges of re-evaluating traditional male/female values about male/female relationships are occurring everywhere.

The idea of trying to roll back by going back to more traditional values seems to be completely wrong. In Singapore and Japan, [the marriage rate] is falling really, really fast, and the fertility rates are falling very fast too. Because at this point in history, if women have to choose between having kids and work, many of them will choose work, and they will not have kids at all. The only countries that have kept up fertility are countries like France and the Nordic countries, where you have very good work/family policies.

How will the globe’s aging population change the way family looks?

There are huge debates among people as to what extent this is going to be a crisis of the aging and to what extent it could be an opportunity. It’s certainly a major challenge to all governments. It’s also becoming an increasing challenge most obviously in China, where the one-child policy, coupled with it being a crime not to take care of your parents, means that one kid has to take care of four grandparents often.

The other side of it—one of the reasons China has just left India in the dust—is, because of this one-child policy, they’ve been able to modernize and put in place economic infrastructure that India completely lacks.