Son preference exists in many degrees around the globe. From subtle favoritism in the Western world to the outright extreme cases documented in many Asian nations (China, India, South Korea), many families are under pressure from various fronts, whether it be religious, cultural, or social, to believe that a son (or sons) in the family bring true happiness that daughters cannot. Every nation around the world has remnants of the patriarchal culture that, even in "enlightened" nations like the United States, gave rise to this belief that "boys can do no wrong" and "boys are more valuble than girls".
Intense discrimination of the girl-child exists in a number of Asian countries. India, China and South Korea stand out particularly in matters of neglect and mistreatment of girls. In parts of India (mainly in the north) for example, daughters are seen as a liability rather than an asset, and many are aborted at birth or perish in early childhood. This is partly due to economic reasons. In Bombay, a large number of ultrasound clinics used the advertising slogan "spend 500 rupees now, save 500,000 rupees later". This of course, is in reference to the "dowry" system, an old tradition which, when a bride marries, her parents are expected to pay all wedding expenses. Parents are willing to abort a fetus if the ultrasound detects it is a female, to save marriage by not having a daughter.
Cultural reasons for son preference are deeply rooted in Hindu and Confucian beliefs. In these heavily patriarchal Asian societies, the birth of a son is a cause for celebration, while the birth of a daughter is met with silence and shame. Sons have many benefits: carrying on of the family name, provide the income, provide efficient labor, honor one's ancestors after death, light the funeral pyre, and look after their parents in old age. Little wonder that this has been responsible for a skewed human sex ratio, with an average of 950 females to 1,000 males (the average worldwide is 106m/100f).