Answers are grounded in this paper and cite their sources.
It is shown that the seasonality of sex ratio in US Black births in synchronous with that of US White births. This seasonality is comparable with that of dizygotic twin births and of the births of boys with undescended testes. These comparisons are consistent with the hypothesis that the sex of an infant is partially controlled by the maternal gonadotrophin levels at the time of its conception.
No takes yet. Share an insight, caveat, or question.
W. H. James (1984) studied this question.
Synapse has enriched 10 related papers. Consider them for comparative context: