The statistics behind the warnings are grimly compelling.
Nature provides an unbending biological standard for the sex ratio at birth of 104-106 males to every 100 females. Any significant divergence from that narrow range can only be explained by abnormal factors.
In India and Vietnam the figure is around 112 boys for every 100 girls. In China it is almost 120 to 100 – and in some places higher than 130.
And the trend is spreading: to regions like the South Caucasus, where Azerbaijan, Georgia and Armenia all post birth ratios of more than 115 to 100, and further west to Serbia and Bosnia.
Global awareness of the problem was raised back in 1990 with an article by the Nobel Prize-winning Indian economist Amartya Sen that carried the now famous title: “More Than 100 Million Women Are Missing.”
Demographers say that figure is now more than 160 million – women selected out of existence by the convergence of traditional preferences for sons, declining fertility and, most crucially, the prevalence of cheap prenatal sex-determination technology.
As many as half a million female foetuses are estimated to be aborted each year in India, according to a study by British medical journal The Lancet.
“Earlier villagers had to go to the city to get a sonogram (ultrasound),” said Poonam Muttreja, executive director of the non-profit Population Foundation of India. “Today sonographers are going into the villages to cater to people who want sons.”
Even if the sex ratio at birth returned to normal in India and China within 10 years, Guilmoto says men in both countries would still face a “marriage squeeze” for decades to come.
“Not only would these men have to marry significantly older, but this growing marriage imbalance would also lead to a rapid rise in male bachelorhood … an important change in countries where almost everyone used to get married,” he said.