The economist Melissa Kearney has been both vilified and praised for her new book, The Two-Parent Privilege: How Americans Stopped Getting Married and Started Falling Behind.

In the book, released last month, Kearney points out a rather obvious fact: Children raised by two parents have a much higher chance of success than those raised by one. Yet she goes even further to argue that whether parents are married or not impacts their children's success.

Her argument goes against the trend in the U.S.; American children are increasingly being born and raised by single mothers. The U.S. has the world's highest rate of children living in single-parent households, according to a 2019 Pew Research Center study. Almost a quarter, or 23% of U.S. children under age 18, live with one parent and no other adults.

Kearney finds that this arrangement hurts children, widens inequality and ultimately damages society. She is ringing the alarm bells, and she wants people to hear them and start thinking of solutions. Judging by the book's reception, she has managed to achieve at least the first part of that.

"I've done exactly what I wanted, which was to start a conversation," Kearney tells NPR. "But I get frustrated that a lot of the initial reaction is an initial knee jerk reaction."

Kearney's argument that children who grow up in unmarried households are fighting the odds has progressives miffed and accusing Kearney of stigmatizing single mothers. Conservatives are celebrating her findings as validating their support of marriage.

"There are a lot of folks who are uncomfortable with the idea of prioritizing one family type over another," says Kearney, whose research and work as an economist at the University of Maryland focuses on issues that most would consider progressive: poverty, inequality, family and children.

"I'm not prioritizing one. I'm just recognizing the data and the evidence and the reality."

The realities about unmarried mothers

One fact is undeniable in all this: More women are deciding to have children and also remain single. Almost half of all babies born in the U.S. were born to unmarried women in 2019, a dramatic increase since 1960, when only 5% of births were to unmarried mothers. And it's not because of divorce; today's unpartnered mothers are also more likely to have never been married.

Some children who are raised by single mothers go on to achieve great things. But on the aggregate, the data shows that the odds of graduating from high school, getting a college degree and having high earnings in adulthood are substantially lower for children who grow up in single-mother homes.

Kearney notes that families headed by a single mother are five times more likely to live in poverty than families headed by a married couple. It's simple math, she says: Having two adults in the home who can bring in income lessens the chance that a family is poor. As any parent will readily attest, raising children takes a lot of resources: money, time, emotional energy and more.

Most single mothers start from behind; they're less likely to have a college education or a high income. Single motherhood is a lot less prevalent in higher-educated women. This college gap exists for white, Black and Latino families.

Data also shows that many single mothers don't have help from any other adult, like a grandparent or other family member. That means it's mom who both supports the family financially and serves as the primary caregiver. There's nobody to pick up the slack when she's tired or sick or just needs to talk after the kids go to bed.

Kearney focuses her research on single mothers because of their outsize number. It's not like there aren't single dads. But they're a fraction (a quarter) of single moms.

Kearney is especially worried about boys falling behind and no role models around them. "We've got millions of boys now growing up without dads in their home," she says. Data shows that boys from disadvantaged homes are more likely to get in trouble at school and with the criminal justice system.

Altogether, this has a compounding effect of undermining social mobility and perpetuating inequality across generations, she argues.

But what's marriage got to do with it?

Kearney's endorsement of the institution of marriage seems antiquated and out of touch. Marriage rates have declined, with more people deciding to remain single for longer.

Kearney says it's easy to assume that Americans are adopting a European lifestyle of raising children in partnerships, living together, free of labels.

"You get a knee jerk reaction from a lot of people like, 'Oh, well, it doesn't matter if they're married as long as they stay together,'" says Kearney. "The problem is, unmarried parents very rarely stay together."

In the U.S., she says, unmarried adults who decide to live together do it for a much shorter duration than in Europe. Children in many of these households are more likely to experience two or three parental partnerships by age 15.

Kearney wants to veer clear from the politics and emotions surrounding the topic of marriage. She says she views her job as a social scientist who bases her work on facts and evidence and is unwilling to examine the complexities of marriage.

"I don't know exactly what it is about marriage, but it is a very practical matter," says Kearney, chafing at all the criticism. "If you just look in the data, marriage is what delivers kids a stable, long-term, two-parent household in this country."

But marriage is a loaded word that means different things to different people. It can be a religious union for some, a celebration of a romantic union, a legally binding contract for others and even an oppressive patriarchal institution.

Kearney says she's not advocating that children live in a household filled with marital tension or where parents are unhappy or mistreating each other. As an economist, she sees marriage as a long-term contract between two individuals to pool their resources and share household responsibilities, including raising children. Two is greater than one. The genders of the parents are irrelevant.

Where are the dads?

One of the biggest issues is that women seem to be giving up on men, particularly those without college degrees. The economics hasn't been kind to this demographic: Since the 1980s, those men have seen their earnings stagnate and employment rates fall.

In the same period, more women entered the workforce and their average earnings increased regardless of their education level. This change has stripped many men of their traditional role as breadwinner for the family and, in simple terms, made them less desirable marriage partners. Research shows that in parts of the country where men's earnings have fallen, so too have marriage rates.

Kearney cites sociologists Kathryn Edin and Maria Kefalas, who interviewed 162 single mothers for Promises I Can Keep: Why Poor Women Put Motherhood Before Marriage.

Their book suggests that many women don't marry the father of their child not because they reject the concept of marriage, but because they do not see him as a reliable source of economic security or stability. They appear to have a higher bar for a potential spouse than their partners, or the fathers of their children, have met.

Kearney says she wants to grab the attention of both conservatives who say they care about children's well-being and progressives reluctant to talk about family structures, because the link between single parenting, inequality and mobility in America is too strong to deny.