SHORT REPORT Within-family intergenerational trends in age at menarche relative to political changes in Czechoslovakia after World War II Zuzana Sekajová 1,2 | Grażyna Liczbi  nska 3,1 | Miroslav Králík 1 | Martin Čuta 1 | Pavlína Ingrová 1 1 Laboratory of Morphology and Forensic Anthropology (LaMorFA), Department of Anthropology, Faculty of Science, Masaryk University, Brno, Czech Republic 2 Animal Ecology, Department of Ecology and Genetics, Uppsala University, Uppsala, Sweden 3 Institute of Human Biology and Evolution, Faculty of Biology, Adam Mickiewicz University, Pozna n, Poland Correspondence Miroslav Králík, Laboratory of Morphology and Forensic Anthropology (LaMorFA), Department of Anthropology, Faculty of Science, Masaryk University, Kotlářská 2, 61137, Brno, Czech Republic. Email: 18313@muni.cz Funding information Masaryk University, Grant/Award Number: Project MUNI/A/1379/2015; Polish National Agency for Academic Exchange, Grant/Award Number: PPN/ WYM/2018/1/00099 Abstract Objectives: The aim of the study was to examine a secular trend in age at menarche (AAM) in the former Czechoslovak (and descendant Slovak and Czech) population in relation to its large-scale political and social events tak- ing place after World War II. Methods: The study included 211 women aged 18–30 (born during 1984–1998), and their relatives: mothers, sisters, and grandmothers, yielding a total of 421 women. Changes in retrospectively recalled AAM between the three generations of women (oldest—grandmothers, middle—mothers, and youngest—daughters) were studied in pairwise comparisons. Relationships between AAM and the birth/conception date were analyzed relative to three events in the post-WWII Czechoslovakia (1948, 1968, and 1989). Results: AAM was the highest in the oldest generation, slightly lower in the middle generation and the lowest in the youngest generation. Mixed- Effect Model showed statistically significant interaction between the date of conception, historical events, and the period before and after the event. Conclusions: The recorded decline in AAM is congruent with secular trends reported in the literature. However, the decreasing trend was not linear and included an increase in AAM in women conceived within the five-year period after the invasion of Czechoslovakia by communist armies in 1968. 1 | INTRODUCTION Living conditions related to wars and social upheavals affect various environmentally sensitive human biologi- cal traits. Previous associations have been made between sociopolitical instability in Europe in the recent past with the timing of menarche (Kalichman et al., 2007; Liczbi  nska et al., 2017; Prebeg & Bralic, 2000; van Noord & Kaaks, 1991). Sensitivity to external factors is high especially during critical stages of human development: in utero, during early childhood, and dur- ing puberty (e.g., Liczbi  nska et al., 2017; Prebeg & Bralic, 2000; van Noord & Kaaks, 1991). The aim of this study was twofold: (a) to observe the occurrence and character of a widely recognized long- term secular trend (Harris et al., 2008) in age at menar- che in the former Czechoslovak population and (b) to link changes in age at menarche with significant large- scale political events after World War II in the Czech and Slovak republics (former Czechoslovakia). Received: 28 March 2020 Revised: 22 January 2021 Accepted: 12 February 2021 DOI: 10.1002/ajhb.23588 Am J Hum Biol. 2021;e23588. wileyonlinelibrary.com/journal/ajhb © 2021 Wiley Periodicals LLC. 1 of 5 https://doi.org/10.1002/ajhb.23588