China is facing a potential crisis of .

On a smoggy morning in Lanzhou, a gritty industrial city in China’s Gansu province, crowds of young men gather outside a half-built construction site. Dressed in torn jeans and dirty shirts and carrying thermoses of tea, they push toward the exterior fence, jostling for the attention of a site manager who hands out short-term jobs. Most of the men are unmarried and have no families. Finding no work, they drift away from the site and, by midday, congregate at a riverside park, where they trade tea for large bottles of beer, which they gulp down. Many of them soon stumble in circles.

Lanzhou exemplifies a more insidious, possibly more dangerous threat to China’s development than financial imbalances, environmental disasters or unemployment: The People’s Republic has too many men. Today, roughly 120 boys are born in China for every 100 girls, perhaps the worst gender imbalance in modern human history. Within 15 years, the country may have 30 million men who cannot find wives. That could mean serious trouble.

For centuries, patrilineal Chinese households have preferred male children because men are viewed as better able to support rural families, and boys inherited the land. Some Chinese gender experts, such as Liu Bohong of the All-China Women’s Federation, also argue that there is deep-seated male chauvinism in Chinese culture that leads to a preference for boys.

Infanticide often resulted, which sometimes created gender imbalances. But after taking power in 1949, the Communist Party largely stamped out infanticide, and by the early 1980s, China had a relatively normal ratio of male and female babies.