Ursula K. “The Left Hand of Darkness,” a classic science-fiction novel by Le Guin, imagines a distant planet called Winter where all humans are “bisexual.” Every month adults go through “camer”, within a few days they develop randomly assigned sexual characteristics: either male or female. Anyone, in other words, can get pregnant. After Kemer, all sexual characteristics fade. Duality – protected and protected; Dominance and submissiveness—which “pervade human thought,” writes Le Guin—are almost entirely absent in winter.
Illustration: Raven XiangSuch a planet will help answer a perennial question: Why do men earn more than women? Perhaps male “dominants” succeed where female “submissives” do not. Yet the weight of research suggests that, after accounting for the constraints women face in bearing and raising children, there is little left to explain. The most effective economist in this field, Claudia Goldin of Harvard University, who won the Nobel Prize in 2023, seems to have settled the debate. Motherhood, her work suggested, explains essentially all of the wage gap.
Some papers published in the last two years have renewed the debate. They were based on robust and novel datasets, matching health records with income data from the Scandinavian countries. This new evidence allows economists to exploit the powerful natural experiment provided by changes in female fertility. The researchers took women undergoing in vitro fertilization (IVF) — those who clearly wanted children — and examined long-term wage differences between those who became pregnant and those who did not. Initially, mothers earn much less, but this gap narrows over time. About 10-15 years after the birth of children, mothers even earned a small premium.
Now this method of exploiting natural variation in fertility has been used in a new study by Camille Landais of the London School of Economics and others. It looks at women with Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome, a rare condition in which a girl is born without a uterus but otherwise develops normally. These women know early in life that they will not have children, and are therefore different from those who discover this after failing to conceive naturally or through IVF. This may affect their future wages, since women who plan to conceive may make different investments in their human capital. They may, for example, spend less on education, knowing that they may withdraw from their careers after giving birth.
Such basic knowledge seems to make a big difference. Studies of women with MRKH have shown that they earn as much as other women and men in early adulthood. Then, in their 30s and 40s, as the wage gap between men and women opens, women with MRKH follow a different path. Their wage trajectory is almost identical to that of their male counterparts. In other words, remove both motherhood and any decision women can make while expecting, and the wage gap seems to disappear. It is difficult to imagine a better way to separate the effects of childbearing from other female characteristics and study their effects on earnings. At least on this planet.