The hypothesized hormonal control of mammalian sex ratio at birth--a second update.

Further evidence is adduced to support the hypothesis that the sexes of mammalian (including human) offspring are partially controlled by parental hormone levels at the time of conception. The evidence relates to variation of sex ratios at birth with (1) time of insemination within the cycle of several species, (2) excision of accessory sex glands in rodents, (3) occupation of parents, (4) dominance rating of human mothers and (5) the ordinal rank of wives in polygynous marriages. Much medical research will stem from the hypothesis if it proves to be true. (a) If it were, there would be implications for the testing of causes of many diseases: and it is noted here that the sex ratios of offspring of victims of two types of cancer (prostatic cancer and non-Hodgkin's lymphoma) are consistent with the suspected causes of these diseases. (b) There are a large number of rheumatic diseases associated with the HLA markers B 27 and B 8. These markers are apparently associated respectively with high testosterone levels in men and low testosterone levels in women. If these finding should be confirmed, a causal role for this hormone seems likely in some of these diseases. It will be interesting to examine sex ratios of relatives of probands with these diseases.