For decades, economists have debated why men earn more than women. Discrimination, occupational choices, and differences in working hours have all been proposed as explanations. Yet a growing body of evidence suggests that motherhood remains the most important factor.
The debate about the causes of the gender pay gap has often focused on discrimination, occupational segregation, and differences in working hours. However, the Economist reports that much of the existing research indicates that once the constraints associated with bearing and raising children are taken into account, little of the gap remains unexplained.
The magazine illustrates the issue with a thought experiment drawn from Ursula K. Le Guin’s science-fiction novel The Left Hand of Darkness. In the novel, inhabitants of a distant planet are “ambisexual”, developing male or female characteristics only temporarily during a monthly reproductive phase. Because anyone might become pregnant, traditional gender hierarchies do not develop. As the article notes such a world would remove the social distinctions linked to reproduction that shape labour-market outcomes on Earth.
In the real world, the gender wage gap appears to emerge most clearly after the birth of children. The work of Harvard economist Claudia Goldin, who won the Nobel Prize in Economic Sciences in 2023, demonstrates that motherhood accounts for most of the persistent difference in earnings between men and women.
New studies using detailed administrative data have recently revisited this conclusion. According to the article several papers have matched health records with income data in Scandinavian countries, allowing economists to examine women undergoing in vitro fertilisation (IVF). By comparing women who successfully conceived with those who did not, researchers could observe how motherhood affects long-term earnings.
The findings show that women who became mothers initially experienced lower earnings than those who did not conceive. Over time, however, this gap narrowed. Around ten to fifteen years after childbirth, the mothers even appeared to earn a small premium relative to women who did not have children.
A further study discussed by the Economist, conducted by Camille Landais of the London School of Economics and colleagues, uses another natural experiment. The researchers focus on women with Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome, a rare condition in which girls are born without a uterus but otherwise develop normally.
Because these women know early in life that they will not bear children, their career decisions are unlikely to be shaped by expectations of future motherhood. According to the findings women with MRKH earn roughly the same as other women and men in early adulthood. However, during the period when the gender wage gap typically widens, their earnings trajectory closely mirrors that of male peers. The evidence therefore hints that when both motherhood and the anticipation of it are removed, the gender wage gap largely disappears.