I also thought of the work the anthropologist Beverly Strassmann did in Mali, where women are compelled by tradition to repair to menstrual huts when it’s that time of the month. In this way, Strassmann determined, men are able to “count back the days” from their wives’ periods to the approximate date of ovulation. And figure out whether they are being true. It’s an effective form of constraint; the rate of extra-pair paternity in this region of Mali is one of the lowest in the world.
