In the mid-19th Century , two devastating floods of the Yellow River , and the famine that followed , ravaged northeastern China . Outlaw bands , known as nien , attracted young men in unprecedented numbers , aggregating into militias that wrought chaos on the troops and infrastructure of the ruling Qing . Although this Nien Rebellion and the larger Taiping rebellion in the South were eventually crushed , they devastated the Chinese economy and contributed to the ending of the Qing dynasty . According to political scientists Valerie Hudson and Andrea den Boer , widespread female infanticide during the famine meant that as many as one quarter of young men in the region were `` bare branches '' -- as the Chinese expression goes -- unlikely ever to bear fruit . The Nien rebellion , they argued , was propelled by these surplus young men who had so few other prospects . This story of the Nien Rebellion foreshadows one of the biggest issues that China will face in coming decades : the dramatic excess of young men . A long history of son preference , particularly among the Han majority , has led to female infanticide and the neglect of daughters in some parts of China . But in recent decades , the spread of cheap ultrasound ( enabling sex-determination in early-mid pregnancy ) and easy access to abortion courtesy of the government 's one-child policy , has led to the widespread abortion of female fetuses . As a result , approximately 30 million more men than women will reach adulthood and enter China 's mating market by 2020 . The scale of this current sex-ratio bias dwarves that in the Nien rebellion , and the consequences could turn out to be more catastrophic . Young men with poor prospects of ever starting a family spell danger to themselves and to their societies . Over millions of years of evolution , large numbers of women and even larger numbers of men left no offspring at all . Yet everyone alive today descends from ancestors who managed to avoid that fate . Our male ancestors were the ones who strove most frantically for status and the respect of their peers , and who won the chance to mate . As a result , young men are hair-trigger sensitive to their circumstances , and when the number of men who will never find a mate rises , so does the intensity of the striving . Young men discount their futures and take ridiculous risks in order to improve their prospects . They also become more violent , rising more readily to perceived slights and insults , and starting more fights -- often over trivial issues . These are the triggers for most man-on-man assaults and homicides . Many factors contribute to the number of men who will never find a mate . Economic inequality , for one , leaves a great many poor young men unable to attract a wife . When a society allows powerful men to take several wives , too few women remain for many poor men to take even a single wife . But most dramatically of all , male-biased sex ratios consign the excess men to never having a family of their own . Under each of these scenarios , large numbers of young men competing for dominance elevate local rates of violence , homicide and lawlessness . Martin Daly and Margo Wilson 's studies show that local income inequality can explain variation in homicide rates on a number of scales : from Chicago neighborhoods to American States and Canadian provinces . Throughout history , a surplus of young men often heralded violence . The American frontier earned its `` Wild West '' reputation for lawlessness because its towns overflowed with men , yet marriageable women were vanishingly rare . In The Chivalrous Society , historian Georges Duby argued that European expansionism , from the Crusades to colonialism , was fueled by a surplus of ambitious and aggressive young men with otherwise poor reproductive prospects . China is already feeling the effects of so many bare branches . The economist Lena Edlund estimates that every one percent increase in the sex ratio results in a six percent increase in the rates of violent and property crime . In addition , the parts of China with the most male-biased sex ratios are experiencing a variety of other maladies , all tied to the presence of too many young men . Gambling , alcohol and drug abuse , kidnapping and trafficking of women are rising steeply in China . The bare branch problem will be compounded as income inequality rises . China 's Gini coefficient of income inequality has risen from less than 0.3 , 25 years ago , to almost 0.5 today . On the Gini scale , 0 represents perfect equality while a score of 1 represents complete inequality . It would be difficult to overstate the urgent need for China to emulate South Korea in eliminating sex-biased abortion and neglect . But just as urgently , China needs creative large-scale solutions to the problems that unprecedented cohorts of bare branches will cause as they come of age over the next two decades . Those millions of disaffected young men will not only present a danger to themselves , but those living alongside them . And , as Hudson and den Boer have been arguing for some time , the bare branches will also make perfect fodder for political agitation , fundamentalism and possibly terrorism . Join us on Facebook/CNNOpinion .
`` Dramatic excess of young men , '' key challenge for China , writer argues . The Chinese government has been trying to curb the excesses that have led to a surge in youth suicides and suicides, but it is unclear whether they are succeeding. Access to cheap ultrasound and abortions has increased abortion of female fetuses . In China , around 30 million more men than women are expected to reach adulthood by 2020 .