Department of Economics, University of Ottawa, Ottawa, ON, K1N 6N5, Canada.
Demography. 2013 Apr;50(2):421-44. doi: 10.1007/s13524-012-0161-5.
Infant mortality is higher in boys than girls in most parts of the world. This has been explained by sex differences in genetic and biological makeup, with boys being biologically weaker and more susceptible to diseases and premature death. At the same time, recent studies have found that numerous preconception or prenatal environmental factors affect the probability of a baby being conceived male or female. I propose that these environmental factors also explain sex differences in mortality. I contribute a new methodology of distinguishing between child biology and preconception environment by comparing male-female differences in mortality across opposite-sex twins, same-sex twins, and all twins. Using a large sample of twins from sub-Saharan Africa, I find that both preconception environment and child biology increase the mortality of male infants, but the effect of biology is substantially smaller than the literature suggests. I also estimate the interacting effects of biology with some intrauterine and external environmental factors, including birth order within a twin pair, social status, and climate. I find that a twin is more likely to be male if he is the firstborn, born to an educated mother, or born in certain climatic conditions. Male firstborns are more likely to survive than female firstborns, but only during the neonatal period. Finally, mortality is not affected by the interactions between biology and climate or between biology and social status.
在世界上大多数地区，男婴的死亡率高于女婴。这种性别差异可以用遗传和生物构成上的差异来解释，男孩在生物学上更脆弱，更容易患病和早逝。与此同时，最近的研究发现，许多受孕前或产前的环境因素会影响婴儿是男性还是女性的概率。我提出这些环境因素也可以解释死亡率上的性别差异。我通过比较异卵双胞胎、同卵双胞胎和所有双胞胎的性别差异，提出了一种区分儿童生物学和受孕前环境的新方法。利用来自撒哈拉以南非洲的大量双胞胎样本，我发现受孕前环境和儿童生物学都会增加男婴的死亡率，但生物学的影响比文献表明的要小得多。我还估计了生物学与一些宫内和外部环境因素的相互作用，包括双胞胎中出生顺序、社会地位和气候。我发现，如果双胞胎是第一胎、母亲受过教育或出生在某些气候条件下，那么他更有可能是男性。男胎比女胎更有可能在新生儿期存活，但只有在新生儿期。最后，生物学与气候或生物学与社会地位之间的相互作用并不影响死亡率。
