Until the early decades of the 20th century, women spent more than 60% of their prime-age years either pregnant or nursing. Since then, the introduction of infant formula reduced women's comparative advantage in infant care, by providing an effective breast milk substitute. In addition, improved...

Until the early decades of the 20th century, women spent more than 60% of their prime- age years either pregnant or nursing. Since then, improved medical knowledge and obstetric practices reduced the time cost associated with women's reproductive role. The introduction of infant formula also...