Fewer boys were born nine months after the three worst earthquakes in Japan’s recent history, a study has revealed. The finding hints that stress makes it harder to conceive sons.

Misao Fukuda at M&K Health Institute in Japan and his colleagues studied the birth records of Japanese prefectures struck by the Kobe earthquake of 1995, the Tohoku earthquake responsible for the tsunami that hit the Fukushima Daichii nuclear plant in 2011, and the Kumamoto earthquake of 2016.

They found that the proportion of male babies born in …