Insight into human sex ratio imbalance: the more boys born, the more infertile men

This study investigated, through large-scale statistical analysis of the global population, whether the human sex ratio is skewing worldwide, and if so, why and how it shifts, and the impact of any shift on human reproduction. A significant imbalance of the sex ratio was observed in the whole human population, resulting in a vicious circle where the more boys born, the more infertile men occur as a consequence of the adjustment of the human sex ratio. It is proposed that both accelerated degeneration of the Y chromosome and dynamically differential fertilization of the egg by the X- and Y-bearing spermatozoa may contribute to the changing structure of the human population, suggesting a potential selection pressure favouring an alternative sex-determining/differentiation system for the human species: the DMRT1 gene on the autosome may tend to replace the SRY gene on the Y chromosome as a master sex-determining gene during evolution. These viewpoints may open a debate on the future of the human race, and assist in guiding diagnostic, prognostic and preventive treatments of human infertility and in defining population policy.