The stunning reversal of humanity’s oldest bias

The Economist estimated that the decline in sex preference at birth in the past 25 years has saved the equivalent of 7 million girls. | Antoine Lassalle/Getty Images

Perhaps the oldest, most pernicious form of human bias is that of men toward women. It often started at the moment of birth. In ancient Athens, at a public ceremony called the amphidromia, fathers would inspect a newborn and decide whether it would be part of the family, or be cast away. One often socially acceptable reason for abandoning the baby: It was a girl.