Introduction
In the dystopian sci-fi film Children of Men, set in 2027, the world is on the brink of collapse; no children have been born for nearly two decades. Against the backdrop of an acute fertility crisis, the movie's protagonist, played by Clive Owen, is tasked with protecting the first pregnant woman in nearly 20 years. Although fictional, the story now seems ominously prescient, as birth rates worldwide have plummeted to worryingly low levels.
Contrary to predictions of a looming population bomb in the mid-to-late 20th century, we’re now experiencing the beginning of a population implosion. Even in many developing and middle-income countries, like in Latin America, birth rates are quickly dropping below prior forecasts from the UN:
In East Asia, countries like China, South Korea, and Japan lead the fertility crisis, where birth rates have fallen so low that the countries’ total fertility rates have dropped to around or below one.
Nearly every country except for those in Sub-Saharan Africa is experiencing below replacement fertility rates, aging populations and depopulation of rural areas.
Although the global population is still increasing, the peak is getting closer than most would have thought just 10 years ago.
Despite this issue largely escaping the public’s consciousness, governments around the world have become increasingly concerned about it. In Sweden, known for its generous parental benefits and subsidies, the fertility rate has fallen to a record low of 1.4 children per woman, prompting the government to issue an investigation into its causes.
This may seem a strange concern; isn’t it good that population growth is slowing? For as long as I can remember, the standard story has been that the Earth can’t sustain the world’s population, let alone a larger one. Resource depletion, climate change, and overpopulation seem like a catastrophe in the making.
Yet, as I’ve explored previously at length, larger populations and economic growth aren’t incompatible with a sustainable, prosperous world. We no longer live in a Malthusian, zero-sum world where overpopulation leads inexorably to famine. Technology and economic growth have made it possible to sustain a population many times larger than during pre-industrial times. Arguably, a world with 100B people can be much better than one with 10B or 2B.
Indeed, population growth appears to be a crucial input to long-term economic growth. Improving economic productivity is primarily driven by technology, resulting from new ideas. More people have, therefore, historically been closely tied to economic growth and increasing prosperity.
What was once perhaps a necessary correction from, at times, unsustainable population growth is now a worrying trend in the opposite direction. Fertility rates have been declining continuously in nearly all Western and developed countries since the Industrial Revolution, with earlier declines in some countries and later in others. But the overall trend is clear.
In pre-modern times, most societies had fertility rates of 5-6 children per woman or higher; today, they’re around or below 2.1—the replacement level—in most countries. The average fertility rate in 2024 was 2.2.
The decline is not just confined to wealthy countries anymore:
Even so, high-level charts like these understate the dramatic change in fertility rates in many countries over the last 10-15 years. While rates were low but stable in most countries for decades, the decline has attenuated in the 2010s.
The U.S. had a fertility rate of around 2 until the late 2000s or early 2010s, after which it fell to around 1.5. The same trend can be detected in countries as different as Chile, South Korea, and Sweden. (OWID’s data set actually understates the decline, as it doesn’t span past 2023 yet. In Sweden, fertility has declined further, approaching 1.4 in 2025.)
But what is “fertility” exactly? In everyday language, fertility usually refers to how easily someone can get or make someone pregnant (“fecundity”). Among demographers, it refers to the actual birth rate or number of children born per woman. The total fertility rate (TFR) represents the average number of children a woman is expected to have throughout her lifetime, based on current age-specific fertility rates.
In case it wasn’t clear, the issue isn’t that people can’t have kids but that they increasingly won’t.
Despite the widespread (mistaken) belief in Malthusian ideas about unsustainable population growth, such as those promoted in the book “The Population Bomb”, most people actually want 2-3 children. This is good news because the challenge isn’t just one of trying to convince people to do something they don’t want to do. The challenge is that despite people’s desire to have more kids, they’re having fewer and fewer.
In The Children of Men, the cause is eminently obvious—women can’t have children. In our case, the cause is much less clear. Understanding the socio-economic factors driving this trend is crucial if we are to reverse it and address the demographic challenges.
Why population decline is a problem
Historically, raising fertility rates has largely been the hobby horse of conservatives, religious fundamentalists, and ethnonationalists in order to further their political, religious, or ideological agendas. This makes it hard to talk about the challenges of demographic change and decreasing fertility without getting bucketed into the same category as those who’d prefer a return to traditional gender norms or dream of ethnic and racial purity in their country.
I approach this issue as a believer in progress, socially and economically. I worry about fertility decline and a shrinking population because it may lead to stagnation, degrowth, poverty, and, if we’re unlucky, the end of civilization as we know it.
Countries like Japan, which have had low birth rates for decades, flat or negative growth, and rapidly aging populations, are already seeing the consequences of below-replacement fertility: labor shortages, strained social safety nets, and declining economic dynamism.
Now, others are catching up. In Europe, countries like Italy and Spain are rapidly aging, with over 25% of their populations aged 65 and above, straining their welfare systems and economic growth. The rise of populism, nationalism, and authoritarian leaders across the continent can be seen, in part, as a result of these broader changes, with immigration more of a symptom.
The standard story was that as countries develop and reap their demographic dividend1, birth rates decline, population growth slows, and everyone’s rich and happy forever. Demographers projected that as this process runs its course, the world population will peak at around 10 billion by the century’s end, and it would just stay like that… forever? There will be a lot of old people for a while, but eventually, the demographic pyramid will revert, and we’ll be good.
Unfortunately, if current trends continue, the world population will not level off but will keep declining. This is problematic for several reasons.
Global challenges. Although a shrinking population is celebrated by environmentalists and degrowthers as a good thing. A declining population may, surprisingly, make it harder to address global crises like climate change, poverty, and conflict due to its negative impact on societal stability, innovation, and economic growth. Ironically, continuing to grow the population (conditional on continued technological growth and prosperity) may be the most straightforward way to deal with climate change and other civilizational challenges long-term.
Culture. As population size stagnates and then declines, many fundamental aspects of modern society that we take for granted will inevitably change. Progressive, cosmopolitan values could disappear. More localized, mercantilist systems may replace the broadly positive-sum global economic systems that created the prosperous modern world. Smaller populations will lead to social fragmentation and a shift towards more traditional and parochial values as the pie gets smaller for everyone. High-fertility subcultures (like the Amish) with distinct norms will make up a larger share of the population and may replace the rest of society culturally.
The economy. Smaller, declining populations have numerous adverse effects that collectively contribute to economic decline. Fewer young workers means less innovation and dynamism, a trend already seen in Europe. Labor shortages and smaller consumer markets harm businesses, leading to fewer incentives to start them and lower profits, resulting in fewer investments, less R&D, and less innovation, exacerbating the downward spiral. Deurbanization as cities are no longer a place of opportunity for people and less of an economic driver. Falling property values negatively impact many people’s savings. Decreased demand, deflation, stagnation.
Social welfare. Fewer working-age people will eventually collapse the welfare systems, safety nets, and public services in developed nations due to a worsening dependency ratio (working-age to retired/child population). Countries may cut benefits to people without kids to afford welfare costs while incentivizing childbirth. We should expect to see more measures like these in the coming decades.
Perhaps most worryingly, if population decline reaches a sufficiently low threshold, we may reach a tipping point where reversing it becomes extremely difficult or impossible. Changes in the demographic structure of society can irrevocably alter economic, political, and cultural landscapes, leading to a world that becomes decidedly zero-sum.
Fertility decline: the standard explanations
To explain declining global fertility rates, demographers, economists, and researchers typically point to a common set of factors associated with lower fertility. These include rising income and economic development, female education and labor force participation, child care costs, access to contraception, declining child mortality, changes in religiosity and societal values, and more.
Despite many of these being strongly associated with lower fertility rates, it’s hard to figure out what’s actually going on, as correlation does not imply causation. To see why, let’s examine these explanations in more detail.
Rising income and economic development
The usual explanation for declining fertility rates is economic development. This appears to align with global patterns, where the poorest countries tend to have the highest fertility rates, while the developed world has the lowest.
This correlation is so strong that demographers call it the “iron law of fertility.”
Yet this doesn’t tell us much about the factors affecting birth rates within countries.
Economic development and rising incomes may be effects of falling fertility as much as they precede it. Countries don’t develop and become richer in a vacuum; many cultural, technological, and demographic forces change in tandem with the economy.
In developed societies, people tend to have fewer children and spend more money and time on each, limiting the number of children they want and can afford. Economists refer to this as the quantity-quality trade-off, which suggests that as countries develop economically and people get richer, parents opt to have fewer children but invest more in each child’s education and upbringing.
Moreover, people in wealthier countries tend to have more career and life options, meaning that the opportunity cost of having and raising children, especially at a young age, is greater, both in terms of time and income.
All this makes sense intuitively, but empirical research has shown mixed results, and as we shall see, there are plenty of counterexamples.
Higher education and employment for women
Economic development often coincides with increased women’s labor force participation, directly delaying and reducing fertility.
The opportunity cost of having children increases as women focus on higher education, enter the workforce, and pursue careers. This delays marriage and childbirth, making having children less appealing, especially earlier in life.
When women get educated, they become more knowledgeable about children's health, demand access to contraceptives (potentially reducing childbirth to their desired level), and invest more in their children, too.
And, of course, when given a choice, many women don’t much like the idea of spending the “best years” of their lives pregnant, pumping out babies. Although childbirth is an incredibly empowering and transformative experience for many, it’s also horrifically painful and can maim women for life.
Within countries with high fertility, the more education a woman has, the lower her fertility rate:
However, this trend doesn’t hold as neatly within countries with lower fertility (most developed countries). What’s more, the period of the baby boom—when fertility increased substantially—coincided with rising education and labor force participation among women.
Cost of childcare
Even though people are much wealthier today, children also cost more while providing no financial gain to parents until they are much older, if ever.
In the past, most people lived near their extended families and helped each other raise children. Today, most live in small, nuclear families and may not even receive help from grandparents. It takes a village to raise a child, but few have one.
In many developed societies, governments have attempted to fill the role of “the village” by providing support in the form of child subsidies, affordable and flexible childcare arrangements, and other services. Despite this, fertility keeps falling. But it would likely be worse without this support, as these do improve fertility rates, albeit only slightly.2
It’s tempting to think high childcare costs prevent people from having more children, but I think the explanation largely goes the other way: childcare costs are high because people have fewer kids and can afford to spend more on each one.
Parents today are heavily involved in all aspects of their children’s lives, committing enormous amounts of time and resources. In the past, when everyone was poor, people still had large families. The costs were lower not because it was cheaper, but because parents didn’t — or couldn’t — invest as much in each child.
So while costs matter, they’re mostly downstream of deeper cultural and structural changes.
Urbanization and density
The global decline in fertility has coincided with increasing urbanization over the past centuries. Many big cities are, unsurprisingly, not very child-friendly.
Much like with economic development, there is a strong negative association between density and fertility, even when controlling for socioeconomic factors. That is, the denser a country, the fewer kids people have. This effect is magnified for lower-income families, whereas higher-income families come closer to their desired fertility levels even in denser environments.
While this makes sense intuitively, high population density probably explains much less of the decline because the standard measure of population density is often too crude. When looking at population-weighted density instead, which better captures the actual lived experience, the negative association is less pronounced. This measure better adjusts for countries with one or a few very dense cities, but they are otherwise largely uninhabited (like Egypt), making it appear as if the country has low density when, in fact, it has high density where people actually live.
Some countries and regions with nominally high densities continue to have higher fertility rates. In Nigeria and South Africa, increased urbanization and density correlate with higher fertility, as shown in this study. Although this is primarily due to the high proportion of people living in slums, it suggests that, without factors such as economic development, education, and cultural norms, fertility remains high even in highly dense areas.
So, while extremely dense environments probably do deter family formation and birth rates, most cities aren’t that dense, and the negative connection between fertility, urbanization, and density is likely driven by other underlying factors.
Decline of religion and traditional values
Religions typically promote “family values” like marriage and fecundity. They urge their adherents to “be fruitful and multiply”. There are also strict rules and norms around sex before marriage, out-of-wedlock children, and abortion, to name a few examples.
Within countries and when accounting for socio-economic status, more religious groups tend to have slightly higher fertility rates than less religious or irreligious groups.
Nevertheless, with the exception of insular groups like the Amish and Ultra-Orthodox Jews, fertility has also fallen across most overtly religious groups and conservative, religious countries. While the Amish still have very high fertility rates, they are trending in the same direction as society overall.
In Iran and Saudi Arabia—conservative Muslim countries—fertility rates have fallen from +5 in the 80s/90s to 1.7 and 2.2 in 2023, respectively.3 Similarly, Orthodox Christian countries like Russia and Greece have fertility rates of 1.4 and 1.3. Rates also vary widely between countries with the same religion, like Afghanistan and Iran.
While strong religious beliefs or ideological commitments matter for fertility, other factors clearly influence the impact of religious beliefs and appear to be more significant overall.
Reproductive technology
Contraception—preventive, like a pill, or reactive, like abortion—allows women to choose and approach their ideal number of children. Similarly, prioritizing education and career is an implicit choice to delay or avoid having them. In all these ways, broadened personal autonomy and individual choice are drivers of lower fertility, and birth control enables these choices.
Despite a strong correlation between contraceptive prevalence and TFR, it's likely not a significant cause. Fertility decline and demographic transitions have occurred in various societies throughout history, even before the advent of modern contraceptive technology. For example, some European countries saw their fertility decline to below replacement-level fertility already in the 19th century, long before "the pill" was invented.
People have always known how to control their fertility fairly well through “traditional means” (e.g., the pull-out method). While not as reliably as in modern times, it was still enough to avoid having children every time they had sex.
This is another way to say that while birth control has had an impact, it may not be as pivotal as it appears at first glance.4
Declining child mortality
Lower child mortality and increased life expectancy reduce the need to have many children, as most will survive into adulthood, reflecting a change in reproductive strategy.
When half of your children won’t survive until reproductive age, having 5-7 children ensures at least 2-3 survive into adulthood. When you can be reasonably sure all children survive, you can have as many or as few as you want.
(This is why the world population didn’t explode exponentially over many millennia, despite a high total fertility rate—children just died in droves, so the effective fertility rate (children surviving into reproductive age) has been closer to 3. Which explains why the human population has increased linearly over the past 2-3 centuries.)
So while declining child mortality has undoubtedly played a role in reducing TFR from >6 to <3 per woman, this quantity/quality trade-off doesn’t explain why fertility would fall from replacement levels to <1 in many developed East Asian countries.
Going deeper: Understanding the causes of fertility decline
I suspect that all or most of these factors above have some degree of explanatory power, depending on the time and place. Yet there are plenty of local, regional, or temporal exceptions that don’t fit the standard story.
It can’t be just about economic development, because the fertility decline isn’t confined to developed countries. Poor countries like Albania have fertility rates comparable to Portugal (1.4). Some developed countries, like Israel, stand out with comparatively high fertility rates (about 2.8).
It can’t be just about religion because even traditional and religious societies like Iran have seen fertility drop sharply.
It can’t be just about humanism and feminism because TFR has declined in places where women’s lives are still heavily restricted, like in Saudi Arabia or (many parts of) India.
It also can’t be limited to urban lifestyles and cosmopolitan norms, because TFR has declined in traditional places, like rural Guatemala and Turkey.
Noah Smith thinks we basically have no idea. I think we can do better, but the complex nature of this problem suggests we’re missing an underlying theory (or several) to connect the dots across time and place. We need to dig deeper.
Income and fertility
As we’ve seen, fertility rates are negatively correlated with income. However, this association obscures complex underlying variations and says nothing about the causal relationships, especially within countries.
For example, most Arab Gulf states, like the UAE, retain similar or higher TFRs compared to other countries in the MENA region, despite having a much higher GDP per capita.
In the US, fertility rates vary across income levels within different ethnic groups, suggesting underlying cultural norms interact with increasing incomes in different ways. There’s no clear association between income and fertility at this level.
Traditional religious groups like the Amish and Ultra-Orthodox Jews have retained high fertility rates into “modernity” (though even their fertility has declined), almost irrespective of incomes.
Another huge expectation is the mid-20th-century baby boom, when TFR increased across the Western world alongside broad-based economic growth.
In other words, higher incomes don’t deter having children. Yet many assume that only poor people have lots of kids. Urban, wealthy people sneeringly picture rural, poorer women uncontrollably pushing out baby after baby. As it turns out, though, this picture isn’t accurate anymore, if it ever was.
Once you correct for the age at which women give birth (younger women generally have lower income than older women) and cultural differences (a significant factor), the relationship between income and fertility becomes muddled or even positive for many groups; families with higher incomes tend to have more children.
Another aspect is that income has a noticeable effect on male fertility but not a big effect on female fertility. In other words, men with higher incomes have more children, while women’s earnings have little or no impact.
Studies on lottery winners show that men who win lotteries and become rich see their fertility rate increase. There’s no such impact on women.
Lyman Stone highlights the distinction between earnings and income: A woman’s income (overall wealth of her family) may increase when she marries a man who is wealthier, but her earnings (wages) may not change. Women with high earnings tend to want to marry men with equal or higher earnings.5
Perhaps relatedly, some evidence suggests that men with higher cognitive abilities tend to have more children, even after adjusting for factors such as income, education, and marital status.
All in all, the effect of income on fertility is largely positive rather than negative when you look past high-level correlations. This is quite intuitive: when people have more money, they can afford to have more kids. Similarly, during good times, people will want to have more children than during bad times. And this is actually what the data shows when you dig deeper.
The way to reconcile this with the “iron law of fertility” is that income and fertility may be negatively correlated between countries, but positively correlated within an individual country, at least in recent decades.
Thus, cross-national data tell us more about the differing cultural norms surrounding child-rearing and marriage rather than the direct effect of income itself. Wealth and income influence fertility, but their effects are deeply shaped by culture.
Ideology and culture
There’s long been a debate between those who believe that economic and other “objective” forces drive the fertility decline, and those who believe that it’s due to culture.
The demographic history of France helps us answer this question. Instead of economic development preceding or coinciding with declines in fertility, France’s fertility began to decline during the 18th century, almost a century before other countries and before the Industrial Revolution came into full force.
This change wasn’t driven by industrialization and economic development, but by a shift in ideology toward secularization. Or in other words, culture:
”The regions that secularized experienced a much earlier decline in fertility than those that did not. The difference between Provence, a stronghold of dechristianization, and Brittany, a stronghold of Catholicism, is almost as large as that between France and England. According to the genealogical data, these places did not have lower fertility before: the fertility transition only took place after dechristianization. I also find that the effect persisted for generations, as persons born in secular places passed their secular values on to their children, even after moving to places with different institutional and cultural norms. This means that dechristianization was not only institutional but rather, and above all, cultural.”
To see the magnitude of this impact, we can look at England, which followed a different path but ultimately ended up in the same place in terms of fertility. In England, fertility began to fall only during or after the Industrial Revolution.
This suggests that culture and social variables may be more influential than economic development (such as income) in shaping fertility rates, or at least that they can change them independently of direct economic forces.6
Cultural norms and ideologies shape people's perceptions of what constitutes a “normal” family size, the importance of getting married and having children, and whether having children is a choice at all.7
Anti-natalist values
Liberal and cosmopolitan norms have diminished the appeal of parenting and family life. Pro-family norms are seen as “traditional” and even oppressive to women. The so-called normative lifestyle focuses on personal fulfillment and career advancement. Having children early is generally viewed as low-status.
In addition, fears of overpopulation, overconsumption, and climate change give many people intellectual reasons to delay or forgo having children.
My sense is that most people in the West, while generally supportive of families and want to have children themselves, nevertheless believe that there are too many people alive, and that a smaller population would probably be better. The reason to have children is purely selfish. Moreover, among many academics and in institutions like the UN, falling fertility levels have generally been celebrated as something good, due to the association between poverty, child mortality, and high birth rates.
What’s going on here, I think, is that having children has become more of an explicit lifestyle choice, for women, in particular, rather than the default path through life.
As a result, some people choose not to have children (or at least don’t realize they want children until they are too old, or at least old enough that finding a partner is challenging).
Although the number of children people want is lower now than in the past, it’s not zero. So, despite the prevalence of anti-natalist sentiments within mainstream society, there has to be more to the story.
Housing
At first glance, it makes sense that a lack of affordable housing would drive down fertility:
”The more expensive an extra bedroom is, the more expensive it is to have more (or any) children. Expensive housing can force people to wait before having kids and move out of city cores and into cheaper suburbs when they do. This means losing many of the amenities and social life benefits of city life, adding a long commute to their day, and probably reducing their number of job options.”
But it’s not just the cost of housing. Places like Tokyo and Seoul have fairly affordable housing, yet some of the lowest birth rates. Studio or single-bedroom apartments, even if affordable, aren’t great for family formation. It may be easy for people to move out of their parents' house, but many cities lack family-friendly neighborhoods or building styles.
Living in small or crowded apartments in highly dense areas contributes to lower fertility, but the “fertility penalty” is reduced substantially for larger apartments or houses, even in dense areas.
Another aspect is that the longer people live with their parents, the fewer children they tend to have later in life, even when controlling for things like their desired number of children, socioeconomic status, etc. A guy in his late twenties, still living with his parents, is not a particularly attractive marriage option for most women, not to mention the increased crowdedness of sharing living space with multiple adults while having a family.
Fertility is also inversely correlated with the share of the population living in apartments.
Notice, though, that the difference between a country like Ireland (low share of pop. in apartments) and Spain (high share) is around 0.5. We’re not talking about major differences of 1-3 additional children on average.
Still, I don’t think city life or apartments are inherently anti-natal. The problem in many city centres, packed with high-rise buildings, isn’t necessarily the density in and of itself, but the way that apartments have been constructed (many single or two-room apartments), and the lack of family-friendly public areas (e.g., parks). This makes it both expensive and less practical for many couples to raise families, and certainly not large ones, so they don’t or move out of cities.
Entertainment, the Internet and smartphones
The rise of personalized and on-demand entertainment has coincided with a sharp drop in fertility rates (around the 2010s); it’s not just online dating, doom scrolling on social media, or pornography, but also video streaming, gaming, and other forms of highly accessible and cheap on-demand entertainment.
Social Scientist Alice Evans’ work shows how entertainment technology contributes to declining birth rates in two ways. First, through the spread of “western” feminist/liberal values that promote women’s empowerment and “small family” norms through social media, TV, and movies:
"Telenovelas may have helped create a habit of having smaller families in Brazil. Telenovelas – TV soap operas – often depict small families, in part because it makes the plot more manageable for showrunners and writers. This paper found that the more Brazilian women were exposed to telenovelas, the fewer children they had."
Similarly, entertainment and access to social media spread values that promote singledom, which enables “cultural leapfrogging," especially for young women in otherwise traditional societies. This rapid cultural shift has led many young women in patriarchal societies to break with established gender norms and marriage expectations within the span of just a decade or two.
In contrast, where gender gaps in internet and smartphone usage between poor men and women are larger, like in Bangladesh, marriage rates remain higher, possibly as women aren’t exposed to modern/western gender norms to the same extent.
Second, the accessibility of on-demand entertainment worldwide has made single life more palatable, even desirable. Why bother with dating, facing rejection, or going out when you can have “just as much fun” at home in front of your computer or smartphone?
In the EU, a third of the population lives alone. Sweden stands out, with half of its households comprising single individuals. Singledom is now the norm.
This is reflected in modern pop culture, with an abundance of portrayals of strong, independent women, but not nearly as many of mothers, motherhood or family life.6
I’m generally quite skeptical of narratives blaming social media or smartphones for all our contemporary woes. But in this case, the strong association between the widespread increase in highly personalized and accessible entertainment (mainly through smartphones) and the concomitant decline in fertility since the 2010s seems at least partly causal.
An interesting data point is that when curfews have been imposed on societies, fertility rates have temporarily increased. When entertainment choices are limited, people tend to have more children instead. This adds further evidence to the claim that one reason fertility rates have decreased is that adults have many other options for how to spend their time.
Delayed marriage and family formation
With many remaining single for longer, people marry much later, if ever, and couples end up having fewer children overall. The decline in marriage rates (nuptiality), tracks the decline in fertility rates quite well. Interestingly, within marriages, fertility actually hasn’t fallen much in recent years and is quite stable in most countries.
Historically, at least in the US, declining fertility rates were initially driven by a decline in births within couples following the Baby Boom, and only in recent decades by lower rates of coupling.
The depressive impact on fertility rates from delaying or forgoing marriage entirely is perhaps best evidenced by looking at East Asian cultures, where intensive parenting strategies and increasing relationship frictions push many to remain single.
When people delay having their first child until they’re much older, they won’t have time to conceive as many children, given the biological time constraints that exist for women in particular, but also for men.
Evidence from Sweden also suggests the decline in first births as an important factor in the fertility decline, as birth rates of second or third children haven’t declined as much.
“The fertility decline in Sweden during the 2010s was largely confined to first births. Rates for subsequent births (second or higher) remained stable. This suggests that factors influencing the decision to start families play a critical role in the fertility decline”.
Lyman Stone has again compiled data showing how fertility rises and falls strongly in unison with marriage rates.
John Burn-Murdoch from FT calls it a “relationship recession”; across the world, the decline in coupling tracks the decline in birth rates.
The reverse happened during the baby boom, where increasing nuptiality drove increases in birth rates, even though the magnitude of this effect differed across countries. In fact, the baby boom was probably a marriage boom, even though within-marriage fertility also increased slightly.
As Alice Evans has noted, only love remains as the main requirement for marriage. When marriage was purely transactional, more people married, but when marriage depends on finding love—and true love is hard to find—marriage becomes increasingly rare.
Men are an insurance policy
The reason women generally seek to partner with men who have (more) money is not because they don’t want to or can’t make their own money, but because men are a form of financial insurance. As Lyman Stone writes, a committed partner can help fill the income gap most women inevitably experience when having kids:
”Women know that having kids will create a big negative income shock at the exact moment they need more money for the aforementioned kid. So they want spouses who can help with consumption smoothing during that episode, and ensure that their children don’t suffer during any other periods of disemployment or economic weakness”
We know that men’s income matters for marriage more than women’s, not just because it’s what we observe anecdotally, but because of natural experiments that researchers have studied, namely lotteries:
"When women win the lottery, there is little to no effect on their marriage rates. But when men when the lottery, they get married. Seriously, they (buy homes and) get married. Even in Taiwan, they get married. When men are wealthier, they are more attractive, and so women marry them, which means men’s and women’s marriage rates rise."
It’s hard for women to predict a man’s future parenting skills, but it’s relatively easy to gauge his income.
Women are overtaking men
Men’s relative status, in terms of both education, employment, and income, has been falling as women in most Western societies have begun to catch up and surpass men. While this is something to celebrate, it changes how men and women approach coupling and marriage.
Young men and women are diverging sharply in terms of their ideological and political views. Young women are becoming increasingly progressive across a wide range of issues, while young men are trending more conservative. This widens the gap, breeding resentment among young men, who effectively become incels or part of incel culture. This may help explain the sharp fall in coupling rates among young people worldwide.
Most well-paying jobs today demand extensive education and experience, while demand for manual and lower-skilled labor has declined (so-called skill-biased technical change). This has made it harder for young men without college degrees in particular to achieve the same social status at a young age, compared to their fathers or grandfathers.
When men have lower incomes, even if they’re higher in absolute terms, they offer in terms of financial security, which is one, but not the only reason, to marry. Given that women tend to want partners of equal or higher status, many young men have effectively become unmarriageable.
Looking back at the post-war baby boom, we can observe this effect in reverse: increasing male incomes made men more marriageable, which contributed to higher marriage and fertility rates.
In the US, the increase and subsequent decrease in the male-female income ratio tracks the rise and decline in fertility rates during the same period, and may help explain the baby boom and subsequent bust.
In the past, men whom women found unattractive could at least lean on traditional marriage norms and higher incomes to attract women. Today, women no longer have to rely on men for income and can be choosy, so they won't just settle for anyone.
The status game
The opportunity cost of balancing family life with a career is undoubtedly a major contributor to lower fertility rates. But these “costs” are not strictly financial; they’re social.
People look at others in their social group to determine what is high or low status. As “high-status” people don’t seem to have children until much later in life, if ever, building families early in life is perceived as low-status.
Traditionally, men were granted status as the primary breadwinners or through religious or societal hierarchies. Women could maintain or acquire status by marrying, and having children didn’t detract from that; it contributed to it. A patriarchy, in other words.
Men and women didn’t play the same status games, and women therefore had a lot of potential mates of higher status to choose from (even if, as is the case with arranged marriage, the choice was made by their family).
Today, men and women compete in the same kind of status games. Both prioritize their careers, making money, and accumulating experiences as individuals. Women, like most men, don’t want to be stay-at-home moms.
It’s not that family life is seen as low status per se, though it can be; it’s that it detracts from everything else that grants people status in modern society.
As much as we want to see ourselves as equal, and as much as we downplay the role of money, women do, in general, still tend to “marry up” in status. Ironically, modern life and egalitarian gender norms have made it harder for women to find men, despite being freer to choose than ever before.
Demographic transitions through history
A neat way to bring these factors discussed above together is to map out the fertility decline in stages. Each stage has a different composition of drivers pushing birth rates (mostly) downward.
By focusing on the West as a proxy for trends that would later spread to much of the rest of the world, the blogger Arctoherium describes the fertility decline across five stages:
Pre-industrial Western European marriage pattern: Absolute monogamy and religious condemnation of family planning within marriage were the norm, keeping fertility rates high. Couples would only marry when financially self-sufficient and independent, which increased birth rates during economically good times and decreased them during bad times, controlling fertility rates in a Malthusian manner.
First demographic transition: Fertility declines to around the replacement level or below, as early secularization spread and the church became less influential, changing family planning norms. Although marriage rates were high, fertility rates within marriages declined.
Baby boom: Changing labor force participation among women and increases in male income, among other things, drove an increase in nuptiality and fertility within marriages, pushing fertility above replacement rates.
Baby bust (second demographic transition): Fertility rates fall below replacement level and stay there throughout the rest of the 20th century. Possibly driven by changing marriage norms and progressive values (second-wave feminism in particular).
Contemporary collapse during the 2010s (third demographic transition?): Sharp decline from slightly below replacement-level fertility to significantly below replacement, primarily among younger, unmarried, less-educated individuals. Potentially driven by technology (i.e. widespread access to on-demand entertainment), delayed marriage or no marriage.
Conclusions
In the search to understand why fertility is declining, I started out looking for the one thing that could explain most, if not all, of it.
What I’ve learned instead is that it can be better explained as a result of changing norms and new circumstances across different times and places. The forces that drive societies from a TFR of >6 to <3 are different from those that push it 1.5 or lower.
Nevertheless, there are a few recurring themes.
Norms and culture
Given that fertility began to decline before the Industrial Revolution in France, and that it has declined before some countries fully developed economically in contemporary times, one can conclude that shifting cultural norms and practices must play a significant role.
Culture and norms influence desired family size, the purpose of marriage, when someone is considered “ready” to have a family, the role of women, and what it means to get ahead in society. When beliefs and norms around these things align with marrying earlier and having children, fertility rates are higher; when they don’t, fertility rates drop.
Technology
Technology, broadly construed, has always had an enormous impact on people throughout history. It’s hard to disentangle it from culture, as technology shapes culture and culture impacts technology adoption and diffusion.
The sustained reduction in child mortality across most of the world, driven in large part by medical discoveries and technologies such as handwashing and vaccines, has reduced the need for larger families as parents can trust their offspring to reach adulthood.
The availability of reliable birth control has given women greater control over whether and when they have children.
The rise of personalized, on-demand entertainment via the Internet and smartphones has had a negative impact on fertility, making single life more appealing.
The proliferation of smartphones has exposed even remote, traditional communities to liberal, individualistic values, impacting women's beliefs and aspirations, in stark contrast to the prevailing gender norms in those societies.
Income and the economy
The standard story about how increasing incomes drive down fertility rates is largely wrong, and the reverse is actually the case on a personal level. People (men in particular) with higher incomes tend to have more children.
Like technology, economic factors impact people’s decisions, both practically (not having a big house or high earnings) and immaterially (in lacking or having social status).
Economic pressures and the drive to achieve higher status present financial opportunity costs, leading most to prioritize education and careers over family life.
Although people clearly used to have many children when poor, income does matter, especially to young men, and affects women’s marriage choices.
Social status
The way one attains status in society influences the importance of marriage and family life.
We’ve seen how the falling status of young men contributes to lower rates of coupling. Conversely, the rising status of women and the fact that men and women now play the same status games means family life takes a back seat.
The opportunity costs women face when choosing between careers and education versus family life and children are exacerbated by how social status is acquired in modern societies.
Marriage
Although marriage isn’t necessary for having children, most people and women in particular, do want to get married (or live in stable, long-term relationships) before having kids.
Marriage used to be more transactional, which made it a matter of convenience and necessity. Today, true love is also a requirement for marriage, so it’s no surprise that marriage rates are falling. When marriage and coupling rates decline, fertility rates tend to follow.
So what’s the solution?
The fertility crisis is, in many ways, an unexpected consequence of social changes that have otherwise been overwhelmingly positive—greater personal freedom, gender equality, secularization, and the erosion of oppressive traditional and religious norms. But we may have thrown out the baby with the bathwater. Modern society risks becoming a victim of its own success.
Unfortunately, there is no simple solution to this dilemma. Governments have been trying to reverse the fertility decline for decades, with little success.8
Any solution needs to address the underlying factors discussed above that have been pushing birth rates ever lower. There has been much written about how to do this by many here on Substack and elsewhere. (For example, see Cremiuex, Hanson, Stone, Evans.)
Overall, solutions typically come in three variants: policy levers, cultural changes, and infrastructure. Some emphasize the need for financial incentives, such as tax credits or subsidies. Others focus on ways of creating a more pro-natal culture that raises the status of family life. Still others focus on physical and social infrastructure: affordable housing, family-friendly cities, and better public services.
To solve the fertility crisis, we will need to do all of these things to varying degrees. But as this article is already too long, I will have to return to what I think the best solutions are in a future essay.
In any case, a hopeful sign is that people actually want more children than they’re having, so the challenge isn’t about convincing people to do something they don’t want, but to create the right circumstances that enable them to do that.
The Demographic Dividend: Most societies that have become wealthy over the past two centuries have done so in part by leveraging the effects of demographic dividends, which have now largely dissipated, except in high-fertility countries (e.g., sub-Saharan Africa).
The dividend meant that countries that came out of high-fertility periods with droves of kids and working-age people, and that also got access to modern medicine and industrialized at the same time, had access to 1-2 generations of very large labor pools. This helped grow their economies very quickly, with very few dependents (children or retirees) per working-aged person. As their fertility declined, subsequent generations became smaller, and the large (baby-boom) generations started to retire, the population pyramid started to work against economic growth.
A common explanation for smaller family sizes and declining fertility is that modern nation-states provide more extensive support to adults and the elderly through national pension schemes. So couples needn’t rely on having many children to care for them in old age. While there’s probably some truth to this (e.g., some researchers argue the baby bust following the baby boom was partly driven by broadening support for the elderly), it doesn’t explain much of the contemporary decline.
Saudi fertility differs greatly between natives and foreign-born, e.g., immigrant workers.
It’s revealing that Catholics across the world, despite the Church’s strong and longstanding opposition to contraception, now have nearly as low fertility rates as others in the same countries, in most cases at or below replacement level.
This isn’t a normative statement about what I think is right; it’s a descriptive statement about social norms in most societies, whether due to the “patriarchy” or due to innate, evolved preferences among men and women.
In a similar manner, Lyman Stone argues that one possible driver of fertility decline in developing countries is a concept known as Developmental Idealism. The idea is that people and governments in developing countries mimic the surface-level attributes of developed regions, for example, by having smaller families, assuming that the path to achieving greater wealth necessitates a reduction in the standard family size (among other things). Of course, this puts the cart before the horse and is essentially a form of cargo culting.
Although Developmental Idealism may be part of the story in some countries, it seems unlikely to me that governments can demand such a profound change in societal norms from the top down, except in cases like China’s One-Child policy, which was very coercive.
An interesting example is the case of Israel, a developed and largely secular country that has retained a TFR of around 2.8. The Substacker NonZionism suggests that a form of Socially Recursive Fertility largely explains Israel’s high birth rates:
People look around their social circles and determine how many kids they want based on how many kids others have, memetically. Orthodox Jews have a lot of children, conservative jews have less but more than average, and secular Israelis have the fewest but are still culturally influenced by them. The visible presence of large families within more or less close communities shifts the cultural baseline of what’s considered “normal” or acceptable.
Another explanation is existential nationalism. Israel is a small country with a history of existential threats and a population that generally believes in the importance of national survival. In this context, procreation becomes a civic duty.
That’s not to say that pro-fertility or pro-natal policies never work. It could very likely be worse without it. But what has been tried so far doesn’t seem to work well enough to reverse the trend.
This is pretty comprehensive, but there's some errors.
I'm really glad that this post mentioned birth control, since most people never think about it. But I don't it emphasized its importance enough (https://zerocontradictions.net/faqs/overpopulation#why-birth-rates-declined). Increasing birth control was more important than increasing education and employment for women, because that never could've happened in the first place without widespread birth control.
Declining child mortality does not reduce fertility. They might be correlated, but there's no valid causal connection. https://zerocontradictions.net/pdfs/demography-and-destiny.pdf
Population density may correlate with lower fertility, but it does not cause lower fertility. https://zerocontradictions.net/faqs/overpopulation#density-fertility
This post didn't describe how the modern state has liberated women from men (https://zerocontradictions.net/pdfs/modern-romance.pdf). Since women no longer need men (nor want, in some cases), this made the mating game harder, thus reducing fertility rates.
I've written a list of ideas for raising fertility rates here: https://zerocontradictions.net/faqs/eugenics#boosting-western-fertility
But we should also be cautious about raising fertility rates. Ideally, they fertility rate should match the death rate. Having some population decline would actually be a good thing, since the Earth is overpopulated. https://zerocontradictions.net/faqs/overpopulation
Aside from those things, this is a good post.
I appreciate the thought you’ve put into all of this. It’s a really good overview of the current thinking on this problem. I’ve been trying to figure this out since around 2013 and I’ve finally arrived at something that could explain all of it. My latest substack post goes into more detail than I can explain here but this is the short version-
The transition from hunter gathering to agriculture 12,000 years ago meant that ppl suddenly went from working 4 hours a day to working a lot more than that. Humans aren’t well adapted to working that much and fundamentally it’s a mismatch between our environment and our needs. We need more rest and leisure time than whats available to most of us, to really thrive. Children are a threat to the remaining scraps of leisure time that we do have, so we’re not going to choose to have children in that environment. Bc it makes it even harder for us to meet our basic needs.
The obvious question is how can it possibly be that when fertility only started to decline within the past couple hundred years. The reason is bc between the dawn of agriculture and the Industrial Revolution, kids were an economic necessity. You needed them for farm labor, soldiers for protection, security in old age. People weren’t having kids to reproduce themselves, they were farming resources they needed for survival. That allowed humanity to survive and grow the population even though something was fundamentally broken in our environment’s ability to meet our needs.
People are willing to sacrifice their needed rest and leisure time if necessary to secure other more critical needs like food and safety.
The cultural and religious reinforcement of high fertility developed downstream of the economic reality that required it. That’s how culture and beliefs work- they’re stories we tell ourselves to justify and normalize the stuff we were going to do anyway.
When the economic need for children at an individual level ended with the Industrial Revolution, that’s when the fall in birthrates started because kids were no longer a source of wealth and power. We didn’t need to have a lot of babies to survive anymore, so we stopped having a lot of babies. It didn’t happen immediately bc for a while it was reinforced by the culture and religions that had been created to support it, and it took some time for all that to unravel.
People think the problem started with the Industrial Revolution but really it started with the dawn of agriculture and was masked by the fact that kids could be exploited for labor, until technology evolved to the point where there was a better alternative to exploiting children for labor. Now the dysfunction that was there all along has been laid bare.
It’s the only explanation I’ve ever come up with or encountered that is consistent with every observation.