In India each year, it is estimated that as many as a million baby girls are aborted by parents determined not to raise a daughter. Those unborn girls are the victims of a fierce cultural preference for boys — and of modern imaging technology that makes it easy to learn the sex of a baby in the womb. Ultrasound scans started becoming widely available in India in the 1980s; since then, an estimated 10 million female babies have been destroyed during pregnancy.

Sex-selection tests are illegal in India. So are sex-selective abortions. But the laws are rarely enforced and easily circumvented. Rather than openly disclose the sex of a fetus after an ultrasound exam, for example, some Indian doctors signal the results by giving the parents pink or blue candies or candles. Others dispense with subtlety altogether, advertising their services with such brazen slogans as “Spend 500 rupees now and save 50,000 rupees later” — an allusion to the potentially crippling dowry that an Indian bride’s parents are expected to pay when their daughter gets married. Many couples have taken that deal. The result is an alarming shortage of young Indian women — and a growing population of young Indian men with little prospect of finding a wife.

It isn’t only in India that unborn girls are being killed on such a mass scale.

Last week, in a chilling cover story titled “The worldwide war on baby girls,” The Economist noted that in many parts of China, the ratio of boys to girls is now 124-to-100. “These rates are biologically impossible without human intervention,” the magazine observed, and their consequences will be dire. The Chinese Academy of Social Sciences recently warned that within 10 years, 24 million Chinese men will find themselves condemned to permanent bachelorhood. Among Chinese 19 and younger, the prospects are even worse: By 2020, there will be 30 million to 40 million more males in this age group than females. That is a staggering number of what the Chinese call guanggun, or “bare branches” — young males with little prospect of marriage and a stable family life.

“In any country,” says The Economist, “rootless young males spell trouble; in Asian societies, where marriage and children are the recognized routes into society, single men are almost like outlaws. Crime rates, bride trafficking, sexual violence, even female suicide rates are all rising and will rise further as the lopsided generations reach their maturity.”

The war against baby girls has spread to South Korea, Singapore, and Taiwan, to the former Soviet republics of Armenia, Azerbaijan, and Georgia, and even to Asian-American communities in the United States. And if you think that the antidote to this “gendercide” is modernization, better living standards, and more education, think again.

“It is not the country’s poorest but its richest who are eliminating baby girls at the highest rate, regardless of religion or caste,” the Times of London reported in 2007. “Delhi’s leafiest suburbs have among the lowest ratio of girls to boys in India, while the two states with the absolute lowest ratio are those with the highest per-capita income: Punjab and Haryana.” Similarly in China, the higher a province’s literacy rate or income per head, the more skewed its sexual disparities.

It is not material poverty that leads these cultures to blithely accept the killing of their very youngest girls. It is a poverty of values, an ancient prejudice that views daughters as a financial burden to be avoided, rather than a blessing to be cherished.

The Chinese writer Xinran Xue writes in a new book, “Message from an Unkown Chinese Mother,” about visiting a peasant family in Shandong while the mother is giving birth. The baby turns out to be a girl, and Xinran hears a man’s voice mutter: “Useless thing!” To her horror, the “useless thing” is thrown into a pail of slops to be drowned.

“That’s a living child,” I said in a shaking voice, pointing at the slops pail.

“It’s not a child,” she corrected me. “It’s a girl baby, and we can’t keep it. Around these parts, you can’t get by without a son. Girl babies don’t count.”

On its cover, The Economist asks: “What happened to 100 million baby girls?” The answer is simple — and sickening: They didn’t count.