Fertility
Statistics
A global unraveling of fertility
“In the United States, the share of young adults aged 18-29 reporting no sex in the past year doubled between 2010 and 2024 — from 12% to 24%. The increase was driven by men. At the 2018 peak, 28% of men under 30 reported no sex in the past year, compared to 18% of women.
On dating apps, women’s average match rate is 31%; men’s is 2.6% — a 12-fold difference. The most desirable men receive overwhelming attention while the majority receive almost nothing.
In South Korea, the 4B movement (no dating, no sex, no marriage, no childbirth) has contributed to the lowest fertility rate ever recorded: 0.72 children per woman. Deaths outnumber births. In Japan, 40% of never-married adults aged 18-34 have never had sex. The population is projected to fall from 124 million to 87 million by 2070.
If you’re older than 45, you likely live in a world where people still got married. The figures above may feel like dispatches from another planet. They’re not. They’re dispatches from the other half of your own country. Among women born in 1980, 71% of college graduates were married by 45. Among those without degrees, it was only 52%. Marriage has become a luxury good. And all groups are converging toward the same destination: below replacement fertility.”
- Aporia [1]
History
Aporia:
- How the fertility crisis was solved last time around:
"This may not be the first time a civilization has run into the problem of weakened norms of pair-bonding combined with (apparently) effective contraception. The Romans had their own version of the Pill: Silphium, a plant from the Libyan coast, was believed to be an effective contraceptive. (The historical analog isn’t perfect, as Roman silphium was so expensive it was limited to the elite class of Rome.)
Still, birth rates among the senatorial class declined so sharply that they could no longer sustain their own population. Senators chose to remain unmarried; those who did marry avoided having children. It preserved their wealth, limited entanglements and gave them freedom. Emperor Augustus responded with legislation: the Lex Julia in 18 BC and the Lex Papia Poppaea in 9 AD encouraged citizens to marry and have children. Unmarried men couldn’t inherit property or attend public games. The childless could only inherit half their bequests. Women who bore three or more children received legal privileges. Adultery became a public crime.
The irony was not lost on contemporaries. The Lex Papia Poppaea was proposed by two consuls, Marcus Papius Mutilus and Quintus Poppaeus Secundus, both of whom were unmarried and childless. The law encouraging Romans to have children was sponsored by men who refused to do so themselves.
The laws were deeply unpopular. Roman elites found loopholes and staged sham marriages. Marriage and birth rates among the elite did not rise significantly. Augustus had to banish his own daughter Julia for adultery, and later his granddaughter too. The quick legislative fix failed.
Silphium was expensive, so only the elite could afford it. Moreover, they had harvested it to extinction by the first century AD. The last stalk was apparently given to Emperor Nero.
Yet Rome did not go extinct. While senators avoided children, slaves, freedmen and provincials kept having them. The elite was eventually replaced: Tenney Frank’s analysis of 14,000 burial inscriptions found that by the Imperial period, a large fraction of Rome’s population descended from freedmen. These individuals learned Latin, adopted Roman law and worshipped Roman gods. Elite replacement with cultural continuity.
The same will not happen today. Contraception is no longer a luxury good. The lifestyles that once required senatorial wealth — delayed marriage, serial relationships, voluntary childlessness — are now available to anyone with a smartphone. The fertility collapse isn’t confined to an elite that can be replaced from below. It’s universal among everyone who participates in the modern mating market.
Where did monogamy come from?
If monogamy runs against the interests of the powerful, and even draconian laws from a god-emperor do not change behavior, how did the West end up with near-universal monogamy? The answer is a thousand-year social engineering project by the Christian Church.
Joseph Henrich’s The WEIRDest People in the World documents this transformation in detail. The Church’s “Marriage and Family Programme” systematically dismantled the kin-based structures that supported polygyny. The Programme banned cousin marriage out to sixth cousins, breaking up the tight clan networks that had organized society. It prohibited not only polygyny itself, but also concubinage and divorce. It required consent from both bride and groom, undermining arranged marriages that served family interests.
The Programme was strictly enforced. Kings were excommunicated for taking second wives. Nobles were denied church burial for keeping concubines. Communities were mobilized to report violations. No one was exempt.
The effects were profound. As clans dissolved, people had to form relationships beyond their kin. This created what Henrich calls “WEIRD” psychology: individualistic, guilt- rather than shame-based, high in impersonal trust and oriented toward abstract principles. The historian David Herlihy has described the Programme as “a great social achievement of the early Middle Ages”, since it enforced the same rules of sexual conduct for rich and poor alike.
Monogamy proved advantageous in competition with other societies. Monogamous societies had lower male violence, broader trust networks, and more investment in children. They out-competed polygamous ones. By the 20th century, formal monogamy had spread globally — not because it comes naturally to humans, but because the societies that practiced it dominated.
This makes sense from a game theoretic perspective: monogamy benefits society but runs against the interests of those with power to defect. High-status men benefit from polygyny. Women may even prefer to share a high-status man over exclusive access to a low-status one. The incentives favour defection. Maintaining monogamy requires external enforcement."