What is it about?
For most of recorded demographic history, men on average fathered more children than women bore. That era has ended. We show that 2024 marks the year when global male fertility fell definitively below female fertility, and projects that the gap will widen substantially in the decades ahead. The study tracks the total fertility rate (TFR) — the average number of children a person would have over a lifetime at current age-specific rates — for both sexes across all countries and territories from 1950 to 2100, using data from the United Nations World Population Prospects 2024. In 1950, men had a higher TFR than women in 96% of countries. By 2025, the split was roughly equal. By 2100, only around 10% of countries are projected to still show higher male than female fertility. The underlying mechanism is the progressive masculinization of populations: as overall mortality declines and the gap in survival between men and women narrows, the natural male surplus at birth (roughly 105 boys per 100 girls) is sustained further into adulthood. More men competing for a given number of reproductive partnerships means that, on average, each man fathers fewer children. In countries such as China, India, and South Korea — where sex-selective abortion has pushed sex ratios further from balance — the effect is amplified, and the difference between male and female TFRs is projected to reach 20% or more by mid-century.
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Why is it important?
A new study finds that male fertility has fallen below female fertility worldwide for the first time, driven by the growing surplus of men in reproductive-age populations across most of the globe. The study highlights that the reversal carries downstream consequences for marriage markets, childlessness, and social stability. We call for systematic measurement of male fertility alongside female fertility, expanded social support for childless men, and policies to prevent sex-selective abortion.
Perspectives
Lower fertility among men is indicative of structural constraints to partnering and childbearing for men. This will likely lead to increased singlehood and childlessness among men, particularly in East Asian countries. Some men will therefore rely on institutional care at old age, as family networks will be smaller. Moreover, it is important as partnership and children are strongly protective for men's health, career and civic role.
Henrik-Alexander Schubert
Max-Planck-Gesellschaft zur Forderung der Wissenschaften
Read the Original
This page is a summary of: Masculinization of populations reverses sex differences in fertility, Proceedings of the National Academy of Sciences, April 2026, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2533317123.
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