Falling fertility on the left as key driver of US birth decline

Abstract Political orientation has been shown to correlate with fertility, raising the possibility that demographic processes contribute to long-term ideological change. Using data from the US General Social Survey, we analyze completed fertility across 17 birth cohorts (1898–1982) to examine how political orientation has contributed to fertility decline in the United States and whether emerging selective forces can be detected. Earlier cohorts show little difference in fertility by political orientation. From the 1943–1947 birth cohort onward, however, a pronounced divergence emerges: individuals with right-wing political orientations maintain fertility at or above replacement level, whereas fertility among left-wing individuals declines sharply to well below replacement. Applying Lande–Arnold selection gradient analyses, we find increasing directional selection that may favor right-wing political orientation over time, while education shows consistent negative associations with fertility and religiosity positive but weaker effects. Separate analysis of Black and White Americans reveals, however, that the increasingly stronger association between political orientation and fertility in more recent cohorts holds only true for whites but not for blacks. Nonetheless, these findings suggest that recent fertility decline in the United States is driven disproportionately by left-leaning individuals and point to contemporary demographic processes that may gradually shift the ideological composition of populations. Similar content being viewed by others Acknowledgements This research uses data from the General Social Survey (GSS), conducted by NORC at the University of Chicago. The GSS is funded primarily by the National Science Foundation, with additional support from other organizations and agencies. The findings and conclusions presented here are solely those of the authors and do not necessarily reflect the views of NORC or the National Science Foundation. Funding We had no funding for this work. Author information Authors and Affiliations Corresponding author Ethics declarations Competing interests The authors declare no competing interests. Additional information Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Supplementary Information Below is the link to the electronic supplementary material. Rights and permissions Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/. About this article Cite this article Fieder, M., Huber, S. Falling fertility on the left as key driver of US birth decline. Sci Rep (2026). https://doi.org/10.1038/s41598-026-57582-3 Received: Accepted: Published: DOI: https://doi.org/10.1038/s41598-026-57582-3