The underlying mechanisms of the recent declines in sex ratios at birth may be related to decreased fertilization of XY embryos by reduced motility of Y spermatozoa from a male factor approach and increased cortisol secretion prior to conception, low level of glucose at implantation and/or increased maternal adrenal androgens during pregnancy from a female factor approach. The present data suggest that the recent temperature fluctuation in Japan appears to be linked to a lower male to female ratio of newborn infants partially via increased male fetal deaths. Like sea turtles human male...