HONG KONG - Researchers have expressed alarm about cultures that favor male babies, saying sex-ratio imbalances could destabilize society because more men will remain unmarried, raising the risks of anti-social and violent behavior.

In a paper published in the Proceedings of the National Academy of Sciences, they said parts of China and India would have 12 percent to 15 percent more men over the next 20 years -- many of them rural peasants with limited education.

"The growing number of young men with a lack of family prospects will have little outlet for sexual energy," wrote Zhu Weixing of China's Zhejian Normal University and Therese Hesketh of the Institute of Child Health at University College London.

"This trend would lead to increased levels of anti-social behavior and violence, as gender is a well-established correlate of crime, and especially violent crime," they said, adding the trend would threaten stability and security in many societies.

Sex ratios were already distorted in large parts of Asia and North Africa, and sex-selective abortion and discrimination in healthcare for girls have led to higher female mortality.

"There are now an estimated 80 million missing females in India and China alone," they wrote.

China introduced a one-child policy in 1979 to control population growth, but it has led to a rise in the male-to-female ratio from 1.11 in 1980-1989 to 1.23 in 1996-2001, according to a study published this month in the British Medical Journal.

In 2004, 48.6 percent and 48.7 percent of the population in China and India, respectively, were female.

In contrast, females comprised 49.1 percent of the total population in East Asia, and 52.1 percent in all of Europe and Central Asia, according to figures from the World Bank.

The authors called in the paper for measures to reduce sex selection and an urgent change in cultural attitudes, or dire consequences could follow.

"When single young men congregate, the potential for more organised aggression is likely to increase substantially and this has worrying implications for organized crime and terrorism," they said.

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