Lunar effect

The lunar effect is a purported correlation between specific stages of the roughly 29.5-day lunar cycle and behavior and physiological changes in living beings on Earth, including humans. A considerable number of studies have examined the effect on humans. By the late 1980s, there were at least 40 published studies on the purported lunar-lunacy connection,[1] and at least 20 published studies on the purported lunar-birthrate connection.[2] Literature reviews and metanalyses have found no correlation between the lunar cycle and human biology or behavior.[1][2][3][4] In cases such as the approximately monthly cycle of menstruation in humans (but not other mammals), the coincidence in timing reflects no known lunar influence. The widespread and persistent beliefs about the influence of the Moon may depend on illusory correlation – the perception of an association that does not in fact exist.[5]

In a number of marine animals, there is stronger evidence for the effects of lunar cycles. Observed effects relating to reproductive synchrony may depend on external cues relating to the presence or amount of moonlight. Corals contain light-sensitive cryptochromes, proteins that are sensitive to different levels of light. Coral species such as Dipsastraea speciosa tend to synchronize spawning in the evening or night, around the last quarter moon of the lunar cycle. In Dipsastraea speciosa, a period of darkness between sunset and moonrise appears to be a trigger for synchronized spawning. Another marine animal, the bristle worm Platynereis dumerilii, spawns a few days after a full moon. It contains a protein with light-absorbing flavin structures that differentially detect moonlight and sunlight. It is used as a model for studying the biological mechanisms of marine lunar cycles.[6][7][8]