The lunar cycle's influence on sex determination at conception in humans

Abstract. The lunar cycle has long been suspected to influence biological phenomena. Folklore alludes to such a relationship, but previous scientific analyses have failed to find significant associations. It has been shown that lunar cycles indeed have effects on animals; significant associations between human circadian rhythms and lunar cycles have also been reported. We set out to determine whether a significant statistical correlation exists between the lunar phase and sex determination during conception. We found that significant associations (p-value < 5 × 10−5) exist between the average sex ratio (male:female) and the lunar month. The likelihood of conception of a male is at its highest point five days after the full moon, whereas the highest likelihood of female conception occurs nineteen days after the full moon. Furthermore, we found that the strength of this influence is correlated with the amount of solar radiation (which is proportional to moonlight). Our results suggest that sex determination may be influenced by the moon cycle, which suggests the possibility of lunar influence on other biological phenomena. We suggest for future research the exploration of similar effects in other phenomena involving humans and other species.