In China in 2005, the ratio was 120 boys born for every 100 girls, according to the United Nations Population Fund. Vietnam reported a ratio of 110 boys to 100 girls last year. And although India recorded about 108 boys for every 100 girls in 2001, when the last census was taken, experts say the gap is sure to have widened by now.

The Population Fund warned in an October report that the rampant tinkering with nature’s probabilities in Asia could eventually lead to increased sexual violence and trafficking of women as a generation of boys finds marriage prospects severely limited.

In South Korea, the gap in the ratio of boys to girls born began to widen in the 1970s, but experts say it became especially pronounced in the mid-1980s as ultrasound technology became more widespread and increasing wages allowed more families to pay for the tests. The imbalance was widest from 1990 through 1995, when it remained above 112 to 100.

The imbalance has been closing steadily only since 2002. Last year’s ratio of 107.4 boys for every 100 girls was closer to the ratio of 105 to 100 that demographers consider normal and, according to The World Factbook, published by the Central Intelligence Agency, just above the global average of 107 boys born for every 100 girls.

The preference for boys here is centuries old and was rooted in part in an agrarian society that relied on sons to do the hard work on family farms. But in Asia’s Confucian societies, men were also accorded special status because they were considered the carriers of the family’s all-important bloodline.

That elevated status came with certain perquisites  men received their families’ inheritance  but also responsibilities. Once the eldest son married, he and his wife went to live with his family; he was expected to support his parents financially while his wife was expected to care for them in their old age.