Moonlight becomes you: how lunar phases affect our sleeping and waking lives. From the study:

Our results show that sleep timing is synchronized with the moon cycle under a range of living environments. Toba/Qom participants slept less and stayed up later on the days previous to full moon nights, when moonlight is available during the early night. This pattern could represent a response to the availability of moonlight during the first half of the night for communities with limited or no access to electric light. The amplitude of the lunar phase effect on sleep parameters appears to be stronger the more limited the access to electric light is. However, we were able to corroborate this modulation both in a Toba/Qom community living with full access to electricity and in a sample of college students living in a modern city. Together, these results strongly suggest that human sleep is synchronized with lunar phases regardless of ethnic and sociocultural background, and of the level of urbanization….

What could be the potential adaptive value of increased activity during moonlit nights? Our interviews with Toba/Qom individuals indicate that moonlit nights are particularly rich in social activities. Toba/Qom elders report that, at times when food was obtained from the forest, moonlit nights had particularly high hunting and fishing activity. Furthermore, mythological stories associate the moon with the female reproductive cycle and sexual relations…. Although the true adaptive value of human activity during moonlit nights remains to be determined, our data seem to show that humans—in a variety of environments—are more active and sleep less when moonlight is available during the early hours of the night. This finding, in turn, suggests that the effect of electric light on modern humans may have tapped into an ancestral regulatory role of moonlight on sleep.