Journal Article

Masculinization of populations reverses sex differences in fertility

Schubert, H., Spoorenberg, T., Dudel, C., Skirbekk, V. F.

Proceedings of the National Academy of Sciences of the United States of America, 123:17, e2533317123 (2026)

DOI:10.1073/pnas.2533317123

Open Access

Reproducible

Abstract

Reproductive-age populations show a growing male surplus around the globe as aconsequence of declining mortality, narrowing sex differences in mortality, and sex-selective abortions in some countries. Population structures are important determinantsof marriage markets and childbearing. In this study, we estimate the past, current, andfuture difference between the male and the female total fertility rates around the worldusing an established indirect demographic approach drawing on data from the UNWorld Population Prospects. Our results indicate a crossover from historically highermale fertility to increasingly higher female fertility, which occurs globally in 2024.This shift is not toward parity, but rather reflects a growing disparity driven by theincreasing male surplus at reproductive ages, which exerts downward pressure on malefertility rates relative to those of women. The difference is expected to grow to up to20% in countries like China and India, where sex-selective abortion has reinforced seximbalances in population structures. Overall, we highlight the growing sex inequalitiesin reproduction and call for more research on sex differences in fertility.