In Science News, J. Raloff writes that boys’ birth rates are falling and scientists aren’t sure why. During fetal development, "the male sex is clearly the more fragile one," says Bruce B. Allan, an obstetrician-gynecologist in Alberta, Canada. While some 125 males are conceived for every 100 females, only about 106 boys are actually born for every 100 girls. Stillbirths and miscarriages disproportionately affect boys.
Devra Lee Davis of the World Resources Institute (WRI) in Washington, D.C., and her colleagues have analyzed recent surveys by Allan and others who have looked at trends in sex ratios in several countries. They find a broad pattern of decling male births and increasing reproductive defects.