A Japanese zodiac superstition has helped researchers crack one of East Asia’s most debated demographic questions, with a new study finding that women’s education is not a meaningful driver of Japan’s declining marriage and fertility rates.
The study, published in the journal Demography on April 1, 2026, was led by Associate Professor Rong Fu of Waseda University (WU) in Tokyo and a visiting scholar at the Columbia Population Research Center, Columbia University, in the United States. Her collaborators included Assistant Professor Senhu Wang of the National University of Singapore (NUS), Assistant Professor Yichen Shen of Kanagawa University of Human Services, and Professor Haruko Noguchi of Waseda University.
The researchers used the Japanese zodiac concept of the “Year of the Firehorse” as a natural experiment. Women born in this zodiac year are considered inauspicious marriage partners under the superstition, with folklore suggesting they carry fierce temperaments that invite marital discord. When the Firehorse year fell in 1966, widespread birth avoidance produced a sharply smaller cohort of women, an anomaly the research team exploited to isolate the true effect of education on family formation.
Women born between January and March 1967, just after the Firehorse year, entered a less crowded educational environment due to that reduced birth cohort. This gave them greater access to schooling without being subject to the superstition’s social stigma, creating a rare, clean comparison group for the study.
The findings were striking in what they disproved. More educated women in this cohort delayed marriage by roughly two weeks and delayed first childbirth by around 40 days. Crucially, by their mid-40s, these women were just as likely to be married and to have children as their less educated peers. Education shifted the timing of family milestones, but it did not eliminate them.
“Is women’s education really to blame for declining marriage and fertility?” Dr. Fu posed in explaining the study’s purpose. The answer her team found was largely no.
The research points instead to structural barriers as the real obstacles: workplaces that penalise mothers, an unequal division of childcare and housework that still falls disproportionately on women, and a lack of flexible career pathways after childbirth. Japan’s total fertility rate hit a record low of 1.20 in 2024, even as the government repeatedly expanded childcare subsidies and parental leave provisions.
The researchers argue that pronatalist policies targeting education levels are therefore misaligned with the evidence. Meaningful progress, they conclude, requires genuine enforcement of paternity leave, flexible work arrangements without career penalties, and affordable high-quality childcare.
The timing of the publication carries its own irony. The Firehorse year returns in 2026 for the first time in six decades, and the researchers note that any renewed birth avoidance behaviour this year could generate a new natural experiment, allowing policymakers and scholars to examine whether the same dynamics hold under today’s very different social and economic conditions.
