India’s 2011 census showed 914 females to one thousand males, the most skewed ratio since India’s independence in 1947. In some regions, such as the Northern state of Haryana, there are only 830 females to 1000 males. More than twenty years ago, Nobel prize winner economist Amartya Sen warned of more than 100 million “missing” girls from India as a result of this preference for male children.

The imbalance has squeezed poor and uneducated men out of the marriage market in particular, so there is a surplus of young men who are unable to find partners and assume standard adult roles in their societies. According to the Economist, China has nearly as many unmarried young men, known as ‘bare branches,’ as the entire population of American men. Ironically, the men themselves are harmed by the gender preference shown to them: unbalanced sex ratios may also increase the odds of ill health and early death in men. Something similar has been observed in a number of animal species: it is stressful to compete for mates and this stress can shorten lives.