So...there's a full moon coming up. What should you do? Is it time to A) Show extra caution in your drive home tonight so you don't run over any werewolves, B) Go grab your party clothes and run out to join the fun, or C) Grab the kids from their beds, lock the doors, and huddle in the reinforced cellar until it passes, lest some crazy out there driven by full moon rage decide to rape and pillage your family?
The idea that a full moon alters behavior and incites crime or violence has been around for a while. One recent survey found that 45% of college students believe that moon-stricken humans are prone to unusual behaviors. More interesting yet, other surveys have suggested mental health professionals are even more prone to believe such a thing than the general public. Pop-culture asserts that the moons gravitational pull impacts humans (who are mostly comprised of water) in the same way it exerts a tug on the ocean, thus causing the brain (also mostly water) to behave in altered ways. In fact, such beliefs are so strong that in 2007 several police departments in the UK added extra officers on full moon nights; an effort to cope with what they perceived to be increased crime rates. Even the word "lunatic" originates from the Roman goddess of the moon, Luna. So, is someone really more likely to go crazy against you or your family when the moon is full and bright?
The answer to this question can be derived from examining a few basic facts:
1) The gravitational pull of the moon effects only open bodies of water, such as oceans or lakes. It has no effect on contained sources of water, such as that lump of gray matter inside your skull that some of us occasionally use to think with. (Some people very occasionally.)
2) The gravitational effect of the moon is just as potent during new moons (when you can't see it) as it is during full moons when it hangs bright and prominent in the sky. The stages of the moon are created by reflections of light from its angle to the sun, not because it's any closer to the earth.
3) A mosquito sitting on your arm exerts a more powerful gravitational pull on us than does the moon. So if this is driving us crazy, we have become delicate creatures indeed.
Cold, hard physics aside, this myth is prevalent enough that it's warranted study throughout several scientific papers. A meta-analysis of 37 such studies revealed that there is no effect whatsoever of the moon on crime or human behavior. No research claiming a moon-lunacy link has ever survived scientific scrutiny and held its credibility.
But if this is the case, why do so many people, including entire police departments, still believe it? One factor at work is cognitive consistency: we remember crazy events more when they happen on full moon nights because it fits within our stereotypes and makes such a correlation memorable, whereas crazy things that don't happen on full moon nights don't prompt this association and aren't elevated to the same status in our minds. Therefore our recollection of all those 'crazy things' that happened when the full moon was out are biased in our memory.
There is one aspect of such a myth, however, that does hold some water: people who believe that full moons drive people crazy may be subconsciously driven to behave in crazier ways themselves. Decades of psychological research has shown us that expectations inadvertently alter behavior. The belief influences our actions even without us realizing it, causing us to act in a way befitting of our expectations. To what extent this principle drives full moon madness is debatable, but the research would suggest its effect is limited to general silliness, and doesn't induce a mad-rush towards criminal behavior.
So it's probably safe to let your kids out of the cellar. Assuming, of course, that's the reason you locked them there in the first place.
1. Scott 0. Lilienfeld & Hal Arkowitz, "Lunacy and the full moon," Scientific American. Mind, Vol. 20(1): 64-65, Feb. 2009
2. James Rotton & Ivan W. Kelly, "Much ado about the full moon: A meta-analysis of lunar-lunacy research." Psychological Bulletin, Vol. 97(2): 286-306, March 1985