Today, however, the most significant deviation of SRB from its biological value is due to a combination of socioeconomic factors in a number of countries of South and East Asia, including India and the People's Republic of China ( 3– 6).

SRB may vary with the number of children per birth, paternal age ( 1), and even season ( 2). In most human populations, sex ratio at birth (SRB) (the ratio of newborn boys per newborn girls) is close to 1.05. We then show how economic conditions can affect the dynamics of cultural change in an entire society, and may lead to a decrease in the country's sex ratio at birth. We start with an explicit mechanism by which economic incentives can change cultural beliefs of a given individual, and go on to include a mechanism of cultural inheritance from generation to generation. To bring greater clarity and understanding to this issue, we present a quantitative framework that describes the interaction between economics and cultural transmission. This culture is intricately linked with the economic reality of each couple's life, so that there are financial and psychological repercussions to parents who have no sons. The root of the problem lies in a 2,500-year-old culture of son preference. This trend has a number of alarming societal consequences, and has attracted the attention of scholars and politicians. In rural China, the ratio of newborn boys to newborn girls has been rising for several decades, to values significantly above its biological norm.

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