Is Excess (Fe)Male Mortality Caused by the Prenatal Environment, Child Biology, or Parental Discrimination? New Evidence from Male-Female Twins

Male-female differences in early age mortality continue to be an important source of child inequality in the world, and are a likely cause of gender disparities in human capital accumulation. Recent literature highlights the important role of the prenatal environment in inducing these differences, in addition to biological influences and gender discrimination in the allocation of resources. However, the distinct roles of these three sets of factors have not been quantified in a unified framework. We propose a new methodology for decomposing male-female differences in mortality into the distinct effects of the prenatal environment, child biology, and parental preferences. We implement this methodology by comparing the mortality sex gap among male-female twins versus all twins in India, a country where daughters are discriminated against, and sub-Saharan Africa, a region where sons and daughters have been found to be valued by their parents about equally. We uncover three main findings: (1) both the prenatal environment and biology increase the mortality risk of boys in these regions; (2) the relative importance of the prenatal environment increases with age, while the effect of biology decreases and even reverses in later childhood; and (3) parental discrimination against girls in India significantly raises their mortality; however, failure to control for the effect of the prenatal environment, biological influences, and the endogeneity of sex determination (due to parental factors and sex-selective abortion) leads traditional methodological approaches to underestimate the effect of discrimination on excess female mortality by 173 percent in the period from birth to 1 year, and by 23 percent between the ages of 1 and 5. Taken together, the findings provide novel quantitative evidence on the relative importance of nature versus nurture in the mortality gap between males and females, and show that the impact of discrimination against girls in certain societies has been underrated.