There are a lot of commonly held beliefs that few question, they are received wisdom which millions accept without question. One such belief is that the moon can effect human behaviour. Many doctors, nurses, health professionals and police, believe that the moon, and in particular the full moon, can influence a person's behaviour, mental health, likely hood to commit crime and many other factors.
Known as the "lunar lunacy effect" or the "Transylvania effect", belief that the moon can cause negative behaviours in some, especially those with mental illness, is certainly not new. Probably the first thing that we think of when considering the effect of the full moon is the werewolf, a man transformed by some mystical force possessed by the lunar cycle. As the name "lunacy" suggests the French were so convinced of the connection between mental health issues and the moon, they named erratic behaviour in honour of the moon "la lune" itself.
The effect of the full moon is now no longer solely a factor in the supernatural and folklore, there are pseudo scientific explanations for its effects. Which are of course, as in error as earlier more primitive myths, but these explanations are very convincing to some, Sussex police went as far as to put out extra patrols on full-moon nights in 2007.
In 1996 Ivan Kelly, James Rotton and Roger Culver assessed over 100 clinical studies regarding the lunar cycle and a wide catalogue of behaviours and afflictions* and found no reliable or statistically significant correlation between the two factors.
So why does the myth persist? Here are a couple of factors that may aid its propagation:
1. Representation in the media: The idea that the full moon can influence behaviour is a common theme in both fiction and actual news reports, in the latter the connection is based purely on anecdote, and it is surely worth noting that it would be more of a news story if no crime, etc... occurred at a full moon.
2. Communal reinforcement: The idea is repeated in police stations, infirmaries and emergency rooms around the world. The people whom's anecdotes support this story are often well-educated professionals, surely their anecdotes carry more weight than most people? Actually no. This is almost an argument from authority. The educated still make cognitive errors like the rest of us. Such as...
3. Confirmation bias and illusory correlation: Essentially remembering the hits and forgetting the misses. Let's say an ER nurse has a particularly hectic night, multiple car accidents, a domestic abuse victim and a patient with a stab wound. "Must be a full-moon!" she mutters to a colleague as another victim of a violent crime is brought in. Later her colleague goes outside for a quick smoke, looks up... and sure enough it is! Both are quick to remember this when ever the effect of the moon to our behaviour is mentioned. They forget, however, the multiple times "Must be a full-moon!" has been said only for them to go outside and not notice the moon is not full. They remember and hits, and often don't even register the misses. This selective memory helps to confirm our preconceptions and we are all vulnerable to it.
4. Plausibility: The idea that the moon can have an effect on our bodies sounds probable to most people who are aware that the common belief is that Earth's surface is about 80% water, as are our bodies (actually this is only in infants, the percentage in adults is normally around 65%). Its an intuitive idea, if the moon's gravity effects the tides surely it effects the water in our bodies. Right?
Its analysis of this proposed mechanism for how the moon effects behaviour (i.e. Via its gravitational effects upon the water in our bodies) that shows there is nothing to this myth, unless another mechanism can be proposed.
There are several reasons why gravity isn't a likely cause of alterations in the water in a human body.
Firstly gravity is an incredibly weak force. This may seem silly to you, as the effects of gravity can clearly be seen all around us, but if you drop a book to the floor and then pick it up, you have just overcome the gravitational force of an entire planet! Consider another thought experiment, if you placed a glass of water on a table during an entire lunar cycle, would you expect the water to shift in position or any other quality, based on the phase of the moon? No, you probably wouldn't, and that is 100% water, not 65% like the human body. Its also unbound water, like the water in the oceans, not bound water as is found in the human body.
Essentially bound water in the body is divided into very thin layers on surfaces and bound to macromolecules. Unlikely to feel anything but a negligible effect from gravity. This water is also subject electro magnetic forces which at this scale are much stronger than gravity.
But aside from all this, the killer to this hypothesis, the moon isn't actually closer to the Earth during the full moon! Therefore, as gravity is inversely proportional to distance of separation between two objects, the gravitational force on anything on Earth isn't greater during a full moon than at any other particular phase during its cycle!
As the moon's orbit is elliptical rather than circular, meaning there are periods when it is closer to the Earth and periods when it is further away, the perigee and apogee respectively. This cycle isn't synchronised meaning we can have full moons at both apogee and perigee. If gravity could effect the water within our body, it would be at these times, when the gravitational force is stronger.
If you'd like to read more about this CSI have just published this really in depth article: http://www.csicop.org/si/show/the_moon_was_full_and_nothing_happened
*Effects examined by Kelly, et al (1996) and found to have no significant correlation with the lunar cycle: the homicide rate, traffic accidents, crisis calls to police or fire stations, domestic violence, births of babies, suicide, major disasters,casino payout rates, assassinations, kidnappings, violence in prisons, psychiatric admissions, agitated behaviour by nursing home residents, assaults, gunshot wounds, stabbings, emergency room admissions, alcoholism, sleep walking and epilepsy.
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