Determinants of Sex Proportions in Man, with Consideration of the Evidence Concerning a Contribution from X-linked Mutations to Intrauterine Death

Literature and data from experiments on sex proportions and factors which may influence sex proportions are reviewed. Social and demographic factors relationships between stillbirth rates and sex ratios in utero mortality by sex and shifts in stillbirth ratios with falling stillbirth rates are discussed. Data from animal studies are presented on mutation rates gene frequencies and selective disadvantages related to x-linked mutations which reduce chances of survival in utero. A large number of assumptions are necessary to make any estimate of the supposed effects of x-linked mutations to late fetal mortality. The author doubts that it is possible to measure any component of male mortality in utero attributable to such mutations.