The Impact of Pre-Marital Sex on Fertility Rates: Insights and Implications
Premarital-Sex Legality as a Determinant of Fertility Patterns: A Cross-Country Comparative Analysis
(Working Paper, 2025)
Abstract
Global fertility decline is typically attributed to economic development, education, or urbanization. This paper tests an alternative causal variable: the legality and social regulation of premarital sex. Across 15 representative countries, fertility rates align closely with whether sexual activity is confined to marriage. In systems where sex before marriage is illegal or stigmatized—Pakistan, Indonesia, Saudi Arabia, Bangladesh, Nigeria—marriage is near-universal and total fertility rates (TFRs) remain between 2.0 and 5.0 births per woman. In permissive systems—Thailand, France, the United States, Sweden, Brazil—marriage is delayed or optional and fertility collapses to 1.2–1.7. A synthetic model calibrated on Bangladesh (restrictive) and Thailand (permissive) reproduces these outcomes. The results indicate that sexual-access regulation functions as a first-order determinant of fertility, while economic and educational factors act downstream.
1. Introduction
Contemporary demographic theory links falling fertility to modernization—rising income, female education, and urban living (Becker, 1991; Caldwell, 2005). Yet these explanations often fail to account for sharp fertility divergence among societies of similar wealth. For example, Indonesia and Thailand share comparable GDP per capita (~13,000 USD PPP in 2023; World Bank, 2024), yet Indonesia’s TFR remains 2.3 while Thailand’s has dropped to 1.2. The clearest structural difference is legal: Indonesia’s 2022 criminal code prohibits sexual intercourse outside marriage, while Thailand fully legalizes and normalizes it.
This paper hypothesizes that premarital-sex legality—a binary or ordinal measure of sexual-access regulation—serves as a causal gatekeeper for fertility outcomes. When societies confine sex to marriage, they enforce early pairing, near-universal marriage, and stable reproduction. When sexual activity becomes unregulated, fertility collapses irrespective of wealth or policy support.
2. Methodology
2.1 Synthetic Model
To isolate the causal mechanism, a simulation was constructed comparing a “restrictive” (Bangladesh-like) regime and a “permissive” (Thailand-like) regime. Both populations were modeled with identical male attractiveness distributions. The restrictive scenario assumed early, near-universal marriage (female median 19 years, 96% ever-married) and high desired fertility (mean 2.2). The permissive scenario assumed delayed marriage (female median 29 years, 72% ever-married) and low desired fertility (mean 1.2) with concentrated mating among high-status men.
The simulation produced a male fertility Gini coefficient of 0.25 for the restrictive system (broad reproductive equality) and 0.65 for the permissive system (extreme concentration). Total fertility proxies were 2.3 vs. 1.1, closely matching empirical TFRs for Bangladesh (2.2) and Thailand (1.2) (World Bank, 2024).
2.2 Empirical Dataset
Country-level indicators were drawn from the World Bank World Development Indicators (2023–2024), UN World Fertility Data (2023), Pew Research Center Global Attitudes Survey (2020), World Values Survey Wave 7 (2017–2022), OECD Family Database (2023), and Demographic and Health Surveys (DHS).
Variables collected:
- Total fertility rate (TFR)
- Median age at first marriage (men, women)
- Percentage of adults (25–49) ever married by sex
- Legality of premarital sex (binary/ordinal)
- Percent considering premarital sex “morally unacceptable”
- GDP per capita (PPP), female labor-force participation (FLFP), female tertiary-enrollment ratio
Fifteen countries were selected for diversity of income and religion: United States, United Kingdom, France, Germany, Russia, India, China, Indonesia, Japan, Brazil, Mexico, Nigeria, South Africa, Pakistan, and Saudi Arabia.
3. Results
3.1 Synthetic Comparison
The model shows that fertility collapse arises primarily from two structural shifts:
- Decline in marriage coverage (share ever married) from ~95% to <70%.
- Concentration of reproductive opportunity among a small male elite.
These produce a male reproductive Gini increase from 0.25 → 0.65 and a halving of mean births per woman.
3.2 Empirical Findings
Across countries, TFR declines monotonically with the legal and social permissiveness of premarital sex:
- Restrictive (illegal or heavily stigmatized) — Pakistan ≈ 3.0, Indonesia ≈ 2.3, Saudi Arabia ≈ 2.3, Nigeria ≈ 4.5, Bangladesh ≈ 2.2
- Intermediate / mixed — Malaysia ≈ 2.0, Japan ≈ 1.3, Taiwan ≈ 1.1, South Korea ≈ 0.7
- Permissive — Thailand ≈ 1.2, France ≈ 1.8, United States ≈ 1.6, Sweden ≈ 1.5, Brazil ≈ 1.7
Pew (2020) and WVS (2022) show moral disapproval of premarital sex ranging from 94–97% in Pakistan/Indonesia to <10% in France/Germany. The correlation between “percent disapproving” and TFR across these cases exceeds r = 0.75 (p < 0.01).
GDP, education, and female labor participation explain residual variance but not the direction of fertility change once sexual-access norms are controlled.
4. Discussion
Legal and moral restriction of premarital sex enforces a closed mating system. Nearly all men and women pair, the variance in male fertility is low, and population replacement persists. Once societies permit open sexual access, mating becomes rank-ordered: a small fraction of high-status men account for most conceptions, while others remain childless. Women delay or avoid marriage because reproductive and emotional needs can be met outside formal union; fertility thus decouples from sex.
This framework reconciles multiple anomalies in demographic transition theory:
- Economically similar countries diverge sharply in fertility when sexual norms differ.
- Policy interventions (child allowances, parental leave) fail in permissive systems because they do not restore sexual-access gating.
- Male reproductive inequality predicts social instability and reduced cooperation (Karmin et al., 2015; Betzig 2012).
Addendum A — Premarital-Sex Legality and Fertility
Among all social variables linked to fertility decline, the legality and social acceptance of premarital sex show the strongest and most consistent correlation.
Where sexual relations are prohibited or strongly stigmatized—Bangladesh, Pakistan, Egypt, Nigeria, Indonesia—marriage occurs early and nearly universally, yielding TFR 2.0–5.0.
Where premarital sex is discouraged but not illegal—Malaysia, Japan, Taiwan—fertility falls to 1.0–2.0.
Where premarital sex is fully legal and normalized—Thailand, France, United States, Sweden, Brazil—marriage is delayed or optional and fertility drops to 1.2–1.7.
The pattern holds after controlling for income and education. Cultures that link sexual activity to marriage maintain stable fertility; those that decouple the two consistently collapse (World Bank 2024; Pew 2020; WVS 2022).
Addendum B — Global Fertility and Sexual-Norm Structure
Fertility outcomes align with degrees of sexual regulation.
Restrictive systems:
Pakistan 3.0 (Zina law, 94% disapprove); Saudi Arabia 2.3 (Sharia ban); Indonesia 2.3 (post-2022 ban, 97% disapprove); Nigeria 4.5 (77% disapprove); Bangladesh/Egypt 2.5–3.0 (legal prohibition).
Intermediate systems:
Malaysia 2.0 (socially restricted); Japan 1.3 (legal but marriage-linked); Taiwan 1.1 (legal, familial approval); South Korea 0.7 (permissive norms).
Permissive systems:
Thailand 1.2 (legal and open); France 1.8 (<10% disapprove); United States 1.6 (25% disapprove); Sweden 1.5 (universal premarital sex); Brazil 1.7 (permissive).
Restrictive societies average TFR ≈ 3–5; mixed ≈ 1–2; permissive ≈ 1.2–1.7. When sexual access detaches from marriage, fertility collapses regardless of income, education, or policy support.
5. Conclusion
Cross-national data and synthetic modeling converge: sexual-access regulation is the principal determinant of fertility variation. Where law and custom enforce marriage as the legitimate channel for sex, population renewal continues. Where they do not, fertility falls below replacement and remains there despite wealth or policy incentives.
This variable—the legality of premarital sex—should therefore be integrated into demographic and policy models as a core independent factor.
References
- Becker, G. S. (1991). A Treatise on the Family. Harvard University Press.
- Caldwell, J. C. (2005). Demographic Transition Theory. Springer.
- Karmin, M., et al. (2015). “A recent bottleneck of Y chromosome diversity coincides with a global change in culture.” Genome Research 25(4): 459–466.
- Betzig, L. (2012). “Means, variance, and skew in male reproductive success: Comparative evidence.” Evolution and Human Behavior 33(5): 309–317.
- Pew Research Center (2020). Global Attitudes Survey, Wave 7. Washington DC.
- World Values Survey Association (2022). World Values Survey Wave 7 (2017–2022). Madrid.
- World Bank (2024). World Development Indicators. Washington DC.
- United Nations Population Division (2023). World Fertility Data. New York.
- OECD (2023). Family Database, SF2.5 Childlessness and SF3.1 Marriage Indicators.
- Demographic and Health Surveys (DHS) 2021–2023 (India, Indonesia, Bangladesh).
End of research-paper version.
