A new book explores western involvement in what has become a scourge of the developing world: sex selection of babies

In 1979 China signed a $50m four-year deal with a UN body designed to help it control its spiralling population through family planning. It was the largest foreign aid package Beijing had accepted in almost 20 years.

But the funds became entwined in China's one-child policy that was just taking hold, and instead of sponsoring an education drive for small families, the money was used to pay for posters in Chinese villages proclaiming "You can abort it! But you cannot give birth to it."

The story of the complicity of the UNFPA, the UN's main population agency, in the tyranny of China's forced abortion policy is just one of the examples given in a book that explores western involvement in what has become a modern scourge: sex selection.

Unnatural Selection by Mara Hvistendahl charts how the trend towards choosing boys over girls, largely through sex-selective abortions, is rapidly spreading across the developing world.

While the natural sex ratio at birth is 105 boys born for every 100 girls, in India the figure has risen to 112 boys and in China 121. The Chinese city of Lianyungang recorded an astonishing 163 boys per 100 girls in 2007.

The bias towards boys has been estimated to have caused the "disappearance" of 160 million women and girls in Asia alone over the past few decades. The pattern has now spilled over to Azerbaijan, Georgia and Armenia, the Balkans and Albania, where the sex ratio is 115/100.

The unnatural skewing towards male populations has become so pronounced in recent decades that Hvistendahl, a writer for Science magazine, says it has given rise to a new "Generation XY". She raises the possibility that with so many surplus men – up to a fifth of men will be single in northwestern India by 2020 – large parts of the world could become like America's wild west, with excess testosterone leading to raised levels of crime and violence.

"Historically, societies in which men substantially outnumber women are not nice places to live," Hvistendahl writes. Already, the relative shortage of women in countries like China and Taiwan has helped create new markets in women.

They include arranged wedding agencies that set up marriages between South Korean men and foreigners, often women from poorer nearby countries like Vietnam, that now account for 11% of all marriages in South Korea.

There is also a booming trade in trafficking of women for prostitution out of Vietnam and a growing practice of child marriage in China, where wealthier families secure wives for their sons early by effectively buying young girls for their sons.

Much of the literature on sex selection has suggested that cultural patterns explain the phenomenon. But Hvisten dahl lays the blame squarely on western governments and businesses that have exported technology and pro-abortion practices without considering the consequences. Amniocentesis and ultrasound scans have had largely positive applications in the west, where they have been used to detect foetal abnormalities. But exported to Asia and eastern Europe they have been intricately linked to an explosion of sex selection and a mushrooming of female abortions.

Hvistendahl claims western governments actively promoted abortion and sex selection in the developing world, encouraging the liberalisation of abortion laws and subsidising sales of ultrasounds as a form of population control [see footnote].

"It took millions of dollars in funding from US organisations for sex determination and abortion to catch on in the developing world," she writes.

Even now, when the pattern of sex selection has been well documented and the prospect exists of the developing world accommodating tens of millions more men than women, the UNFPA is refusing to face up to its mistakes and confront the problem, she says.

"The effects of the major UN agency tasked with population advocacy distancing itself from the issue of sex selective abortion are immense," she writes, noting that the agency's foot-dragging has discouraged other global funds from engaging with the crisis.

• This footnote was appended on 22 July 2011. Mara Hvistendahl's Response column, I did not claim the UN was complicit in forced abortions in China, was published on 21 July 2011.