In nature, 105 boys are born for every 100 girls. This ratio is biologically ironclad. Between 104 and 106 is the normal range, and that's as far as the natural window goes. Any other number is the result of unnatural events.
Yet today in India there are 112 boys born for every 100 girls. In China, the number is 121—though plenty of Chinese towns are over the 150 mark. China's and India's populations are mammoth enough that their outlying sex ratios have skewed the global average to a biologically impossible 107. But the imbalance is not only in Asia. Azerbaijan stands at 115, Georgia at 118 and Armenia at 120.
What is causing the skewed ratio: abortion. If the male number in the sex ratio is above 106, it means that couples are having abortions when they find out the mother is carrying a girl. By Ms. Hvistendahl's counting, there have been so many sex-selective abortions in the past three decades that 163 million girls, who by biological averages should have been born, are missing from the world. Moral horror aside, this is likely to be of very large consequence.
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Ms. Hvistendahl argues that such imbalances are portents of Very Bad Things to come. "Historically, societies in which men substantially outnumber women are not nice places to live," she writes. "Often they are unstable. Sometimes they are violent." As examples she notes that high sex ratios were at play as far back as the fourth century B.C. in Athens—a particularly bloody time in Greek history—and during China's Taiping Rebellion in the mid-19th century. (Both eras featured widespread female infanticide.)
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This is where choice leads. This is where choice has already led. Ms. Hvistendahl may wish the matter otherwise, but there are only two alternatives: Restrict abortion or accept the slaughter of millions of baby girls and the calamities that are likely to come with it.