# Natural selection on reproductive timing varies by education in twentieth-century Estonia

## TL;DR

The study shows that in Estonia, natural selection on reproductive timing varied by education level, with lower-educated individuals facing stronger selection pressures.

## Contribution

The novel contribution is demonstrating sexually antagonistic and stabilizing selection on reproductive timing traits across different education levels in Estonia.

## Key findings

- Women with primary education had the highest reproductive success across the study period.
- Men with tertiary education had higher reproductive success despite reproducing later.
- Stabilizing selection for intermediate interbirth intervals was strongest among minimally educated parents.

## Abstract

This register-based study investigates how natural selection acts on educational attainment and reproductive timing among Estonians born between 1925 and 1977. Women with primary education consistently achieved the highest reproductive success throughout the study period, whereas a positive educational gradient in reproduction emerged among men born since the 1950s, resulting in sexually antagonistic selection on educational attainment. Men with tertiary education had higher reproductive success than other men, despite initiating reproduction later. The lowest-educated women exhibited the strongest selection for early reproduction and the earliest start of reproduction throughout the study period. These women and the least-educated men also experienced the strongest selection for delayed reproductive cessation. Nonetheless, parents with primary education (particularly men) were typically the first to stop reproducing. Stabilizing selection for intermediate interbirth intervals also showed the strongest quadratic selection gradients among minimally educated parents of both sexes. At that, men with primary education had the fastest reproductive pace, whereas women in the same group had the slowest. Our study shows that selection on reproductive timing traits was consistently stronger among parents with lower educational attainment, and that variation in reproductive timing across educational strata does not consistently reflect the selective pressures acting on recent generations.