The mechanisms of sex selection
This chart sums up the main determinants of sex ratio variations from conception to adulthood, highlighting two types of factors. On the left side are endogenous factors that are mostly biological or linked to the general social and economic environment.
On the right side are factors that are directly related to social decisions and ultimately to gender preferences, including active and passive discrimination against girls (Chahnazarian 1988; Waldron 1998).
Missing girls and skewed sex ratios:
The sex ratio for the entire world population is 101 males to 100 females. In recent decades (Last 25 years) , sex-ratio imbalances have grown in favor of boy children in a number of South Asian, East Asian and Central Asian countries. Prenatal sex selection leads today to distorted levels of sex ratio at birth (SRB), reaching between 110 and 120 male births per 100 female births in several countries indicating an intensity of gender discrimination and son preference.
The trend has shifted geographically over time:
1980’s starting in a number of Asian countries (China, India, and the Republic of Korea)
1990’s followed by some countries in the Caucasus (Azerbaijan, Armenia and Georgia)
Recently been followed by Montenegro, Albania, and Vietnam.