Son preference has been common for centuries in several countries in East and South Asia, the Middle East, and North Africa. In the mid-1980s, ultrasound technology became available for diagnostic purposes allowing for prenatal sex determination. Subsequently, the technology was exploited for sex determination and selective abortion, resulting in a large excess of male births in a number of countries. In some rural areas of China, up to 140 male births occur for every 100 females. This has led to increasing numbers of unmarried men, and a large surplus of young men are now reaching reproductive age in China.
The consequences of male surplus on these individuals and society are unclear. Failure of men to marry and have children affects their social status and acceptance in some societies. It has been hypothesized that such unmarried young men may have low self-esteem and suffer from a range of psychological difficulties. There is concern that they may exhibit antisocial behavior and have a propensity to aggression and violence and turn to crime, which pose a threat to societal stability and security.
Recent studies suggest that most of these assumptions are unfounded. Although these men have low self-esteem and some psychological problems, they show little sign of being aggressive or violent. Rather, most feel marginalized, lonely, withdrawn, and depressed. Governments are aware of the potentially disastrous consequences of male sex preference, and some are making efforts to reduce sex selection. Such efforts should include enforcement of existing laws forbidding fetal sex determination and sex-selective abortion, as well as making the public aware of the dangers of late abortion and gender imbalance. The results of these measures have been encouraging. A survey in China conducted in 2007 showed a significant decline in son preference.