Does the moon influence people?

If it exerts a major effect, the data haven’t proven what it might be. Oh, and forget werewolves


If the moon can exert potent effects on wildlife, from birds to fish and African buffalo, what can it do to people? Right now, the data are mixed and not all that convincing.

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We all know the full moon doesn’t turn people into hairy, scary werewolves (at least not without some Hollywood magic). But if other animals respond to the moon, why not people?

Scientists have investigated possible links between the moon and a broad range of human experiences. Some scientists have looked at rates of births, visits to emergency rooms or heart-disease events. Others have considered episodes of mental illness, aggression or crime. Some have even questioned whether the moon can impact ups and downs in the stock market. Much of the evidence is inconclusive or contradicts other data. For every study that finds, for instance, that people lose sleep during a full moon, there’s another study that says — hold on — there’s no link. One thing that does seem clear: It’s just a coincidence that the average length of a woman’s menstrual cycle (28 days) nearly matches the 29.5-day lunar cycle.

“It’s really hard to find definitive answers,” says Davide Dominoni. Why? Because most studies looking for a link between human behavior and the moon “are correlational,” points out this ecologist at the University of Glasgow in Scotland. It’s important to realize that correlations do not prove causation. Indeed, any effect that’s seen could be real. It also may be simply due to some unrelated factor.

In fact, much research has relied on data from studies that had not been looking for moon effects. What’s needed, researchers argue, are experiments with clear hypotheses seeking to probe how the moon might sway our behavior or how the body functions. Until then, they note, it’s hard to say if the moon’s hold over people is fact or fiction.

Erin Wayman is the magazine managing editor at Science News. She has a master’s degree in biological anthropology from the University of California, Davis and a master’s degree in science writing from Johns Hopkins University.

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