In recent years, statisticians have ferreted out the truth behind many such beliefs. But the can-do and no-way of lunar misbehavior first requires a brief lesson in how to spot false alarms.
Take, for example, the Moon’s alleged link with human birth. Almost everyone who works in the hospital’s maternity wing voices the same opinion: “Definitely.” It’s fascinating – because it’s wrong. An exhaustive review of 50 years of Moon/birth studies, published in the journal Psychological Reports (Vol. 65, 923-934), showed that there is no connection at all between human birth and lunar phase.
The strong perceived relationship between births and the Moon is something else. We often hear of alleged Moon connections to hyperactivity in children, automobile accidents, moodiness. But it is wise to remember that whenever we look for associations we will usually see them.
In almost every field of activity (e.g. traffic accidents), sufficient studies have been made to expose any link with lunar phase if it existed. Ample data reveal no correlation with most of the “powers” that people traditionally ascribe to the Moon. Statistical studies show no lunar linkage to homicides, alcoholism, fire alarms, domestic violence, suicide, major disasters, prison violence, emergency room admissions, assaults, traffic accidents, crisis calls to police stations, epilepsy and sleepwalking, among other civil and personal disturbances.
Many popular books and magazine articles about the Moon’s supposed effects are unabashedly biased or riddled with bogus statistics. A typical failing is to cite a study “proving” that crime is linked with the Moon without bothering to mention 25 other studies that show no connection at all. Some make statements about lunar gravity pulling on body fluids that reveal utter ignorance about how tidal effects work, or attribute behavior to the Moon’s “magnetism.” (The Moon has no magnetic field.)
But several biological patterns are indeed tied with the Moon. Animals active during daylight hours generally come into “heat” in seasonal rather than lunar patterns. But a few nocturnal animals do have biological rhythms with a lunar linkage. This is particularly true of some ocean organisms. The greatest lunar influence is in the intertidal zones: the muddy marshes and endless beaches whose environment so radically changes with the twice-daily ebb and flow of the sea. Here, life depends on burrowing into the wet sand at clockwork intervals or finding other ways to survive periods of exposure. Algae, oysters, barnacles, snails, worms, mollusks, crabs and many others, and the life upon which they feed, and their own predators such as gulls, probably represent the biological realm most attuned to the position and phases of our nearest neighbor in space. Fiddler crabs, even when removed from an ocean environment, continue to be more active 50 minutes later each day, matching the lunar cycle of tides.
Fertility and menstrual cycles are popularly accepted human lunar links that may have truth behind them. Over 4,000 years ago the Babylonians believed women to be fertile according to the Moon, although we now know that just 22 percent of all women have menstrual cycles that match either the Moon’s 27 1/3-day sidereal period of revolution or the moon’s 29.5-day cycle of phases. If a woman does have her period on the day of Full Moon (or another phase), it is rare for that to repeat habitually and reliably. Nonetheless, a Scandinavian study of 826 women found that a higher number (28 percent) menstruated around the time of New Moon than would be expected by chance. However, the vast majority of women do not have phase-linked menstrual cycles.
Even if the Moon does not causally match the female reproductive cycle at the present time, it may still have relevance to it. For countless millennia, humans were undoubtedly more apt to venture out on bright than on dark nights. It is conceivable (no pun intended) that our reproductive rhythms grew attuned to the recurrent times of bright nights, when it would make more biological sense to be fertile. If so, the average menstrual cycle closely matching the moon’s 29 ½-day synodic period of phases is no coincidence, but rather a legacy of the many millennia when moonlight had real relevance to everyday life.
Arguing the other way, only the opossum has a similar menstrual cycle. We’d then have to assume that only humans and opossums were chosen by Nature to be linked to the Moon in this manner, with the rest of the animal kingdom exempt. For example, the estrus cycle is 21 days for cows, 25 days for macaque monkeys and 37 days for chimpanzees.
A further powerful argument against the connection is that if menstruation is linked with the Moon, then so too would be fertility. Since human gestation amazingly averages exactly nine synodic months – meaning that the Moon’s phase at conception is the same as it is at birth—the birth rate would show a resonance with lunar phase, which it does not.
Taken all together, the data neither prove nor disprove that the close match-up between lunar synodic period and menstrual cycles is coincidence rather than correspondence. Your choice.
What about moonlight and emotions? The time of Full Moon has a slight correlation with increased rainfall and cloudy weather. Much more importantly, moonlight undoubtedly evokes an ineffable “feeling.” Moreover, people probably have collective memories or instinctive familiarities that have been summoned for countless centuries – not to mention that anyone living in a rural, naturally dark area will attest that it simply feels different to be out for a stroll on a moonlit night compared with a moonless one. Like love and other imponderables, this unnamed impression is undeniable, even if it cannot be scientifically demonstrated.
Finally, the Moon’s mythical link with romance and courtship so pervades poetry and literature that most societies and individuals have a strong collective mindset in this direction. The mind is immensely powerful, and the Moon may have an actual influence on mood and emotion from sheer expectation and belief. In this way, some of the Moon’s more curious alleged “powers” may be valid without even needing to be true.