If China hopes to avert a fall in its population by raising the maximum number of children per mother from two to three, it’s going to have its work cut out.

That’s because declining fertility, once started, tends to be an inexorable force that few nations have managed to arrest, let alone reverse. Of the 85 countries where fertility had fallen to less than 2.1 births per woman in 2009 — the so-called “replacement level,” below which population decline tends to set in — only Tunisia had managed to just about creep back above replacement 10 years later.

Even that achievement could suggest a measurement problem more than genuine policy success. Women tend to have children later in life as education levels and employment prospects improve. That can sharply depress fertility in the early years of the demographic shift as women wait longer to have children, before leading to a modest rise in the birth rate later as they catch up in their 30s.

Apparent phenomena as diverse as declining fertility in northern Europe and the supposed higher fertility rate of Hispanic women in the U.S. are as likely to be the result of having children later rather than having fewer children. Birth rates in the European Union, for instance, barely changed in a generation once the shift to later maternity was complete:

A three-child policy will certainly help on that front. Given replacement levels of 2.1 births per mother, it’s by definition impossible to stabilize your population when you can’t have more than two children. Still, there are reasons beyond population policy that China may struggle to spark a baby boom.

Consider what’s happening in other countries in the region. Japan and the four Asian “Tiger Economies” of Hong Kong, Singapore, South Korea and Taiwan have so strikingly few babies that the term “ultra-low fertility” has been coined to describe them. The four tigers, along with Macau, take the bottom five places globally in the Central Intelligence Agency’s latest ranking of countries by fertility rate, with Japan not far behind:

There’s evidence that this isn’t just about the delayed maternity that caused Europe’s fertility slowdown. The ongoing decline since 2000 in South Korea is being driven instead by women having fewer or no children, according to a 2018 study by Sam Hyun Yoo and Tomas Sobotka of the Wittgenstein Centre for Demography and Global Human Capital.

What can be done to reverse this? Reducing the human and financial cost of rearing children will be vital, as my colleague Clara Ferreira Marques has written. That means not just funding for child care, schooling and parental leave, but a change in attitudes in the workforce, property law and the home so that women don’t shoulder all the burden of raising a family.

Measures to address this in China were announced alongside the three-child policy, though it’s unclear whether promised or even enacted changes will be enough. Japan has some of the world’s most generous paternal leave policies in an attempt to get fathers more involved in child care, but only about 3 percent of men take any time off at all.

Switching away from an economic model built on a constant cycle of real estate investment might also help. China’s major cities, where property is as expensive per square foot as in far richer global cities, aren’t particularly attractive places to raise large families.

The good news for China is that, given the right incentives, most people in the world seem to want to have the two or three children needed to balance populations for the long term. The only question is whether the two dozen 60-something men (and one woman) on the Politburo will have the insight needed to change nearly five decades of anti-natalist policy.

David Fickling is a Bloomberg columnist.