The world's most powerful economies are growing increasingly alarmed by declining birthrates, and there is no shortage of theories as to why. SpaceX founder Elon Musk has suggested society is "teaching a fear of pregnancy," while policymakers in France appear to believe young people are simply forgetting to procreate—and sent reminder letters to 29-year-olds as a result. Other explanations are more mundane: the cost of raising a child is too high, or would-be parents worry the world is already running out of the resources needed to support current population levels. The stakes are economic as much as demographic: sustained low fertility means fewer future workers and taxpayers supporting a growing retiree population, with knock-on pressure on pension and health-care systems. In the U.S., the total fertility rate has hovered around 1.6 births per woman in recent years—well below the roughly 2.1 level needed for a population to replace itself—while countries including South Korea and Italy record even lower figures.

A working paper by Claudia Goldin, a Nobel prize-winning economic historian at Harvard University who was awarded the 2023 Nobel Memorial Prize in Economic Sciences for her decades of research on women's labor-market outcomes, proposes an alternative: perhaps hardworking, highly educated women are concerned about the autonomy they would sacrifice if their partners do not share the workload of raising children.

"Women who undertake greater investments in themselves will be more likely to have children if they can reap the financial and personal rewards from their education while raising their children," Goldin writes. "In the absence of that assurance, they will be more likely either not to have children or not to undertake the initial investment in themselves."

She adds: "The more that men can credibly signal they will be dependable 'dads' and not disappointing 'duds,' the more investment in women's education and careers, and the higher will be the birthrate in the face of greater female agency."

A neat theory, contested

The theory is tidy—and has attracted criticism as a result. Some observers point out that birthrates have continued to fall even as household work has been carried out more equitably. Data from the Bureau of Labor Statistics shows that over the decade between 2016 and 2026, the hours men spend on household activities have fractionally increased while the hours carried out by women have slightly decreased. Birthrates have nonetheless continued to decline. Other critics suggest the data used in the research is inconsistent, and skeptics also question what "dependability" in dads actually entails. Goldin's analysis, moreover, arrives in the form of an NBER working paper—a format the bureau circulates for discussion and comment before formal peer review—leaving ample room for the debate she openly invites.

Goldin does not claim to have all the solutions to the questions her work raises. "When women did not have any choice, [having children] is what they did," she tells Fortune. "But now they are given a choice." Men now face a choice as well, she adds: how to demonstrate whether they are a dud or a dad. But "we don't really know the answer [to] what sort of commitment mechanisms [men] have," Goldin says.

Perhaps attuned to this dynamic through her research, Goldin says she can spot anecdotal indicators among her students: "I can pretty much tell who the good dads are. There's no question—they are the individuals who are clearly going to share and [are] going to engage in what I would call couple equity."

"Couple equity doesn't mean equality—it doesn't mean you're doing exactly the same things … but it does mean that each of them has decided that they're willing to give up a certain amount of income and prestige to raise a child or two, or three together."

No new phenomenon

While Goldin's methodology can be debated—and indeed, the historian is open to feedback—the research is nonetheless making waves. On a superficial level, Google searches for Goldin's name have increased 400% over the past year compared with a year prior. More broadly, the topic of birthrates is climbing the political agenda: President Trump has even suggested he'd be known as the "fertilization president", courtesy of policies aimed at supporting birthrates, such as increasing access to IVF. Governments elsewhere have already leaned on fiscal levers: South Korea has spent years rolling out cash incentives and expanded parental leave, while Hungary has offered subsidized housing loans and tax breaks for larger families—yet fertility in both countries remains well below replacement level.

So why the sudden focus? The trends driving Goldin's formula are nothing new: women have been investing in their education in increasing numbers over the past 50 years. The Bureau of Labor Statistics' (BLS) latest reporting, for the year 2024, found that among recent high school graduates ages 16 to 24, 69.5% of women were enrolled in college, while 55.4% of men had done the same. Meanwhile, Census data from 50 years prior shows that in 1974, 45.87% of 14- to 24-year-olds enrolled in college were women.

In addition to women wanting to build careers for their enjoyment and fulfillment, there has been a growing economic need for them to do so. Brookings found in a 2020 study that without women's earnings, middle-income households would have seen virtually no income growth between 1979 and 2018.

Myra Strober, a labor economist and Professor Emerita at the School of Education at Stanford University, sees an answer both simpler and broader than the data from the past half-century suggests: the need for children has shifted from the household level to the societal.

"Historically, people had children because they needed them," Strober tells Fortune. "In an agricultural economy, you needed children to do the work … as agriculture has become a less and less important part of our economy, people don't need children the way they did before.

"And people had lots of children because the infant mortality rate was high. You couldn't be assured that the children you had would live to adulthood, and so you better ensure you have plenty of children to help around the farm. Once agriculture declines and the infant mortality rate goes way down … people don't need children in the way that they did."

Strober founded the famous Stanford course "Women and Work" (later renamed "Work and Family"), where she met student Abby Davisson, now an entrepreneur and consultant. The pair co-authored their book Money and Love in 2023, which is now required course reading at Stanford's Graduate School of Business.

At the end of the duo's book, they examine the extent to which public policy trickles down into household decision-making. "Yet we have not changed our policies around … work expectation or cultural norms. It's much easier to change policy than it is to change culture," Davisson tells Fortune.

"There is a cultural conversation piece that's tricky here, even if we have the best geopolitical policies and … everyone holds hands and agrees on that, if the culture—the expectations for parents do not change, if the expense for raising children does not change—I don't see how we're going to see different behaviour at the individual level, because it's not just this one piece of policy."

"We should be thinking about the economy as a whole and public policy rather than bedroom policy," Strober echoed.

An economic boon

Whether or not equity in partnerships is the cause of declining birthrates, Goldin, Strober, and Davisson are united in advocating for it—the latter duo even include checklists in their book to prompt conversations between couples. But that does not mean equity is no longer a significant economic concern.

"If you begin with the thought that you have a distribution among women and men of talent and creativity, why would you not want to use both distributions and take the top of each to run your economy and your society?" Strober poses. "In terms of economic well-being, social well-being, use of resources, you want to look equally among men and women."

Davisson, mom to two boys, chimes in: "I really value the fact that my children see their father in food preparation mode all the time—he's the family chef—like they're going to grow up thinking that that is totally normal. The value is both for the workplace and for the citizens in that workplace."

This story was originally featured on Fortune.com.