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women and girls in Asia was at least 100 million lower than expected, and suggested that this vast number of “miss-ing ” women “tell[s] us, quietly, a terrible story of inequality and neglect leading to the excess mortality of women.”1 Although Sen’s interpretation of a gender bias was initially challenged—for example, by the suggestion that hepatitis B was altering the natural sex ratio at birth in parts of Asia2— there is now widespread acceptance that the deficit in the number of women is the result of the combination of sex-selective abortion (aided by easy access to ultrasonogra-phy), infanticide and childhood neglect.3 Both infanticide and childhood neglect act after birth to alter sex ratios. Only sex-selective abortion, however, can affect the sex ratio at birth. Biologically, the sex ratio at birth is about 105 boys for every 100 girls, an imbalance believed to be an evolutionary response to the elevated probability of death in childhood among boys.4,5 The sex ratio at birth is remarkably consistent across countries, with very few exceptions.6 Five of the exceptions—China