The hypothesized hormonal control of human sex ratio at birth--an update.

I have reviewed the literature on the human sex ratio at birth (W.H. James, 1987 a. Hum. Biol. 59, 721), and proposed a hypothesis to account for its variation (W.H. James, 1987 b. Hum. Biol. 59, 873). Since submitting those papers, some sets of data have been published which bear on the hypothesis and on how it may be tested. In this note some comments are made on these new data sets. The hypothesis proposes that hormone levels of both parents at the time of conception affect the sex of the resulting zygotes. This suggestion is unlikely to gain wide credence unless and until it has been demonstrated that sex ratios can thus be manipulated in experimental animals. This paper is offered in the hope that it may prompt workers to try testing the hypothesis in whatever way is open to them.