  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 (\textit{p}-value $< 5 \times 10^{-5}$) 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.
