Reproductive organs grow and shrink as they prepare for mass orgies at full moon (Image: Toby Melville/Reuters)
Read more: 鈥�The night: The nocturnal journey of body and mind鈥�
ANY doctor will tell you: when the moon is full, all hell breaks loose. 鈥淲hen you are in medical training, people are constantly bemoaning that everything happens on a full moon,鈥� says at the University of Virginia in Charlottesville. Other purported links include hikes in crime and suicide rates.
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The idea goes back centuries. The full moon was often implicated in spooky transformations of human behaviour. And as the word 鈥渓unatic鈥� attests, a full moon was credited with causing temporary insanity. Not to mention the close ties with witches and werewolves. It all sounds a bit kooky, but we are discovering more and more . Could humans be affected too?
Almost all animals have a circadian clock 鈥� an internal timer regulated by light that helps synchronise their lives to a 24-hour cycle. Some also possess clocks set to the moon, although how they work is still unclear. Intertidal species have activity rhythms based on the 24.8-hour lunar day. So, for example, breeds and feeds at high tide 鈥� generated by the moon鈥檚 gravitational pull. 鈥淭hey have not only a circadian clock, but a clock that helps them synchronise to the tides,鈥� says at Plymouth State University in New Hampshire.
Other animals link their activities to the 29.5-day lunar month. Many molluscs and fish, for example, change size: their reproductive organs grow and shrink as they prepare for mass orgies at the full moon. One of the most visually arresting displays takes place annually on Australia鈥檚 Great Barrier Reef when, on a full moon in November, billions of corals produce bundles of eggs and clouds of sperm that float to the surface to fertilise. Corals are extremely sensitive to blue light matching that produced by the moon, which may be how they synchronise their activities.
鈥淩eproductive organs grow and shrink as they prepare for mass orgies at full moon鈥�
Moonlight draws many creatures out from the shadows. Take the owl monkey, the only nocturnal New World primate. The fuller and brighter the moon, the more active it is, says at the University of Pennsylvania in Philadelphia. He has observed them before and during a lunar eclipse. 鈥淭hey were moving around like crazy and giving loud hoot calls,鈥� he says. 鈥淭hen when you turn off the moon, they stop right there.鈥�
Owl monkeys use moonlight to socialise. Barau鈥檚 petrel, the so-called 鈥渨erewolf bird鈥�, uses the lunar cycle to time when to mate. Other animals take advantage of the bright full moon to hunt 鈥� some birds forage for insects more on well-lit nights. Of course, a full moon exposes predators too, which is why some shun the light. 鈥淟unar-phobic鈥� predators include many species of bat, which stay in their roosts on bright nights.
Such considerations are mostly beyond modern humans, but what about our behaviour? When it comes to crime, the UK鈥檚 Sussex Police force took the link so seriously that in 2007 it experimented with . However, although its own investigations had found a correlation with violent incidents, a 2009 study suggests otherwise. It looked at over 20,000 reports of aggravated assault in Germany and . Some members of the same team also .
But the fabled link between the moon and mental illness may not have such lunatic origins. 鈥淚 think there鈥檚 something to it,鈥� says Quigg. that appears to be linked to the full moon because it is triggered by the hormonal changes of the menstrual cycle, which, like the lunar cycle, hovers around 29 days. And a study of hospital admissions over a four-year period found . This could be down to light levels rather than the lunar cycle itself, though, since another study found .
The brightness might have more general effects. Fernandez-Duque suggests that, especially where artificial lighting is limited, people use moonlight to get together, as owl monkeys do. 鈥淚n places like Argentina, it鈥檚 too hot in the day,鈥� he says.
Light levels could also explain recent reports that a full moon affects our ability to get a good night鈥檚 sleep. A study this year found that volunteers took around 5 minutes longer to get to sleep on nights around the full moon, and spent around 30 per cent less time in deep, restful sleep.
There may even be a rational explanation for one of the most fanciful full-moon stories. In 1964, Lee Illis of Guy鈥檚 Hospital in London pointed out that people suffering from a group of diseases called porphyria can be extremely sensitive to light, with exposure causing skin lesions and ulcers and sometimes disfigurement. Other symptoms include insomnia, mania, convulsions, skin pigmentation, and red teeth.
This article appeared in print under the headline 鈥淚ll met by moonlight鈥�
