The Human Female Paradox: Biological Disadvantage Preimplantation, Biological Advantage, Thereafter

The vital statistics show that human females outlive males at every biological stage. Once the embryo arrives in uterus, more die stage, least until eighth decade when majority of survivors are female. Unexpectedly, same also boys born than girls, which is difficult to explain, because sperm determine sex fetus, not skewed toward males. Recently, new data reveal reason for increased number male births; they imply significant loss before fetus womb. Thereafter, there an excessive – only utero but throughout their lives. One likely differences fetal survival way humans compensate difference X chromosomes.