The bright side of the Moon: and its effects on life on Earth
Picture a night like last night. You gaze up to see the brilliant full moon overhead and look around at your surroundings, illuminated, almost as if it’s daytime. The Moon, Earth’s celestial sister, has profound effects on our planet, such as driving the oceanic tides. Without the Moon, life as we know it would not exist on Earth. The Moon stabilizes Earth in its rotation about its axis, causing a more stable, livable climate. But does the Moon influence the behavior of life on Earth? Humans have a longstanding relationship with the Moon. Ancient peoples had a variety of beliefs about the Moon including the belief by some ancient Greeks that the Moon was the home of the dead, and that of early Hindus that the souls of the dead returned to the Moon to await rebirth. The Tartars of Central Asia called the Moon the Queen of Life and Death (1).
And what about the full moon? Since ancient times, full moons have been associated with strange and insane behavior, such as sleepwalking, suicide, fits of violence and even transforming into werewolves. The words “lunacy” and “lunatic” come from Luna, the Roman goddess of the Moon. For thousands of years, doctors and mental health professionals believed in a strong correlation between mania and the Moon. Hippocrates wrote in the fifth century B.C. that “one who is seized with terror, fright and madness during the night is being visited by the goddess of the Moon.” In fact, in 18th-century England, people on trial for murder could plead for for a lighter sentence on grounds of lunacy if the crime occurred under a full moon (2). But is there any truth to this? Can the Moon actually affect our behavior?
Before we delve into behavior during the full moon, let’s first look at changes that coincide generally with the phases of the Moon. This is called circalunar behavior, behavior that cycles with a period of about a month. Unlike circadian rhythms (fluctuations in behavior and internal molecular functions, which occur over a 24-hour day), the mechanisms of circalunar rhythms are less well-studied or understood. In one study (3), a group led by Dr. Tessmar-Raible looked at the mechanism of the circalunar clock and how it interacts with the circadian clock in the marine worm (Platynereis dumerilii). Marine worms have a well-established monthly cycle in their reproductive behavior, with the number of sexually mature worms peaking during the new Moon and being lowest during the full moon. First, the team of researchers showed that artificial “nocturnal light” stimuli to simulate phases of the moon in a lab setting are sufficient to synchronize circalunar reproductive behavior cycles in the worms, indicating that, like the circadian clock, the circalunar clock gets entrained (meaning synchronized with the external environment) through light cues. Next, they looked at the worms’ circadian (daily) gene expression levels and behavioral rhythms and saw that the specific timing of those fluctuated with the monthly clock, indicating that the circalunar clock affects the circadian clock. While this study was done in worms, it does indicate the possibility of two distinct clocks in other animals. Though these two clocks have distinct oscillatory mechanisms, they converge on the regulation of gene expression levels and behavior.
Does the full moon actually affect behavior?
One of the most classic examples of animal behavior that is believed to be influenced by the full moon is in the case of wolves, which supposedly howl at the full moon. This likely drove the spooky folklore about werewolves, who are said to be humans that transition into half human, half wolf monsters on the night of full moon (4). Neither of these beliefs, however, are true. Wolves do not actually howl at the full moon, though their behavior is altered by the full moon in a way that you might not expect. It has been well documented that nocturnal prey animals reduce their activity during the full moon due to the risk of increased light exposure, and, therefore, increased likelihood of being seen and killed by predators. A predator’s response to this change could be one of two options: decrease activity as well in order to save energy with the knowledge that there are fewer prey to be caught, or increase activity to cover more ground in an effort to maintain normal levels of food consumption. To answer this, at least in the case of wild maned wolves, a team in Brazil used GPS tracking collars to test whether the distance traveled during the night, a measure of search effort, varied with the phase of the Moon (full or new). They found that indeed these maned wolves traveled significantly less during nights of a full moon than a new Moon(5), meaning these wolves chose the first option of conserving energy with less prey available. Similarly to wolves, it has been documented that the prey of lions are less abundant during the full moon which has driven lions to hunt more during the daytime following the full moon. Furthermore, lions greatly increase their frequency of attack on humans following the full moon, as measured by evaluating the over 1,000 attacks by lions on humans in Tanzania between 1988 and 2009. While it is not entirely known why, it is likely due to the fact that humans are often easy prey for lions as well as the fact that humans tend to be more active in the dusk and night following a full moon. It is theorized that this phenomenon and others like it during ancient times of humans coexisting with large mammalian predators helped to drive human superstition surrounding the full moon. With increased risk of being attacked and devoured, the full moon was surely a bad omen of things to come (6).
Another predatory animal that alters its behavior during the full moon is called the antlion. And before you get nightmarish thoughts of a giant half-ant, half-lion monster roaming about, rest assured you have nothing to fear. Antlions, or rather antlion larvae, are very small beetle-like insects which capture their prey by digging cone-shaped holes in the sand and waiting, mouth opened wide, at the bottom for their prey to fall into. Interestingly, the size of holes these antlions dig nightly fluctuates and it has been well documented that antlions dig their largest holes during the full moon. Unlike the prey of lions and wolves, antlion prey tend to be more active during the full moon as they use the moonlight to help them forage for their own food. Because of this, it is presumed that antlions are willing to put in more work to dig bigger pits during the full moon because of their increased likelihood of a high yield of food. One interesting thing that has been discovered about this circalunar antlion behavior, due to the fact that they can be studied in a controlled laboratory environment unlike large predatory mammals, is that their fluctuating circalunar pit digging behavior still persists even in total darkness. So even when they don’t have light cues from the Moon itself, their pit size still fluctuates with the phase of the Moon, suggesting an internal monthly timekeeping mechanism, kind of like the aforementioned marine worms (7,8).
Now we’ve seen some examples of animal behaviors affected by the lunar cycle, but what about humans? Do we go crazy during the full moon? The answer to that is no; there is no evidence to suggest that humans get any more irrational during the full moon. However, we do seem to be influenced by the lunar cycle, though it should be noted that humans are far less susceptible to the effects of moonlight with the use of shelters and artificial lighting. There are two main ways the lunar phase may influence humans and both have been largely controversial. The first is the impact on our sleep. To study this, Leandro Casiraghi and colleagues (9) worked with three Western Toba/Qom communities of the Argentinian province of Formosa; one in an urban setting with full access to electricity, and two rural communities, one with access to limited electric light and another with no access to electric light. These studies were done using wrist actimetry (measurement of activity using a wrist monitor), and surprisingly, all three populations showed sleep patterns that fluctuate with the lunar phase. They found consistent clustering of the troughs of sleep duration and the peaks of sleep onset on the days before the full moon. Changes in each participant’s sleep duration across the lunar cycle ranged from 20 to more than 90 minutes and did not differ considerably between groups. In other words, even with access to artificial light, humans tend to sleep less, and take longer to fall asleep, right before a full moon.
Another aspect of human biology that has been argued to correlate with the lunar cycle is the human menstrual cycle. Some even refer to the time of uterine shedding (menses) as one’s “Moon time”. It is not an unreasonable hypothesis, as reproduction is synchronized with a particular Moon phase in many animal species and the period (time for one complete cycle) of the human menstrual cycle (average of about 28-29 days) is about the same as the period of the lunar cycle (29.5 days) (10). In a short-term study, over 300 menstruating people were studied. Those with a cycle of 29.5 days (about 28% of the total group) were tracked, and within those, a significant pattern of menses onset at the time of the full moon emerged (11-13). There was still, however, much skepticism by the scientific community on whether the lunar phase influences the human reproductive cycle. To study this, a group led by Dr. Wehr looked at the menstruation data of 22 people who had kept a long-term (average 15 years and up to 32 years) record of their menses onset. These findings were not highly conclusive due to the very small sample size and the fact that menstrual cycles tend to shorten with age; however, there were significant intermittent synchronizations with the full moon that emerged (14). These largely inconclusive data do suggest the possibility that menstrual cycles in early humans were synchronized with the lunar cycle, but due to modern lifestyle practices, like hormonal birth control usage, exposure to artificial light at night, and other factors, this synchronization is largely lost.
While the Moon does not drive people to madness or into transforming into half-wolf monsters, nor does it cause wolves to howl more frequently, it does have some pretty profound effects on life on Earth. Since the Moon has been around since before life existed on this planet, and has very consistently cycled through drastic changes in appearance and brightness, it is perhaps unsurprising that life has adapted to using the Moon as a means of keeping track of time. This is not that different from life using the rising and setting sun to synchronize its daily oscillatory rhythms. And because the Moon has its most drastic visual effect on the Earth during the full moon, it makes sense that this monthly phenomenon would serve as a strong stimulus for behavioral and molecular changes to occur in biology. So note how much sleep you’ve gotten over the past couple of days; perhaps our Moon has more of an effect on you than you may have thought.
- Encyclopedia.com. (2022, December 8). .” myths and legends of the world. . encyclopedia.com. 29 Nov. 2022 . Encyclopedia.com. Retrieved December 8, 2022, from https://www.encyclopedia.com/philosophy-and-religion/other-religious-beliefs-and-general-terms/religion-general/moon#:~:text=Some%20ancient%20Greek%20sects%20thought,Queen%20of%20Life%20and%20Death.
- History.com Staff. (2013, August 27). 7 unusual myths and theories about the Moon. History.com. Retrieved December 8, 2022, from https://www.history.com/news/7-unusual-myths-and-theories-about-the-moon
- Zantke, J., Ishikawa-Fujiwara, T., Arboleda, E., Lohs, C., Schipany, K., Hallay, N., Straw, A. D., Todo, T., & Tessmar-Raible, K. (2013). Circadian and circalunar clock interactions in a marine annelid. Cell Reports, 5(1), 99–113. https://doi.org/10.1016/j.celrep.2013.08.031
- Wikimedia Foundation. (2022, November 30). Werewolf. Wikipedia. Retrieved December 7, 2022, from https://en.wikipedia.org/wiki/Werewolf
- Sábato, M. A., Melo, L. F., Magni, E. M., Young, R. J., & Coelho, C. M. (2006). A note on the effect of the full moon on the activity of Wild Maned Wolves, Chrysocyon Brachyurus. Behavioural Processes, 73(2), 228–230. https://doi.org/10.1016/j.beproc.2006.05.012
- Packer, C., Swanson, A., Ikanda, D., & Kushnir, H. (2011). Fear of darkness, the full moon and the nocturnal ecology of African Lions. PLoS ONE, 6(7). https://doi.org/10.1371/journal.pone.0022285
- Goodenough, Judith E., B. McGuire, and R. A. Wallace. 1993. Perspectives on Animal Behavior. New York: John Wiley & Sons.
- Poppick, L. (2013, July 2). 6 wild ways the Moon Affects Animals. LiveScience. Retrieved December 7, 2022, from https://www.livescience.com/37928-ways-the-moon-affects-animals.html
- Casiraghi, L., Spiousas, I., Dunster, G. P., McGlothlen, K., Fernández-Duque, E., Valeggia, C., & de la Iglesia, H. O. (2021). Moonstruck sleep: Synchronization of human sleep with the Moon cycle under field conditions. Science Advances, 7(5). https://doi.org/10.1126/sciadv.abe0465
- Salimgaraev, R. (n.d.). Menstrual cycle and the Moon: How are they related? Flo.health – #1 mobile product for women’s health. Retrieved December 7, 2022, from https://flo.health/menstrual-cycle/health/period/menstrual-cycle-and-moon#:~:text=How%20long%20are%20lunar%20and,around%2028%E2%80%9329%20days%20long
- Cutler, W. B. (1980). Lunar and menstrual phase locking. American Journal of Obstetrics and Gynecology, 137(7), 834–839. https://doi.org/10.1016/0002-9378(80)90895-9
- CUTLER, W. B., SCHLEIDT, W. M., FRIEDMANN, E., PRETI, G., & STINE, R. (1987). Lunar Influences on the Reproductive Cycle in Women. Human Biology, 59(6), 959–972. http://www.jstor.org/stable/41463960
- Friedmann, E. (1981). Menstrual and lunar cycles. American Journal of Obstetrics and Gynecology, 140(3), 350. https://doi.org/10.1016/0002-9378(81)90294-5
- Helfrich-Förster, C., Monecke, S., Spiousas, I., Hovestadt, T., Mitesser, O., & Wehr, T. A. (2021). Women temporarily synchronize their menstrual cycles with the luminance and gravimetric cycles of the Moon. Science Advances, 7(5). https://doi.org/10.1126/sciadv.abe1358
- Phases of the full Moon: NASA. (n.d.). Phases of the Moon. NASA. Retrieved December 7, 2022, from https://solarsystem.nasa.gov/resources/676/phases-of-the-moon/
- Maned wolf: Potozniak, B. (2018, May 7). The maned wolf at the Buffalo Zoo. Just a Blonde in Buffalo. Retrieved December 7, 2022, from https://www.justablondeinbuffalo.com/blog-1/2018/5/3/the-maned-wolf
- Antlion larvae and pit: The hunt of the antlion at the Full Moon. Full moon blog. (n.d.). Retrieved December 7, 2022, from https://www.fullmoon.info/en/blog/antlion-full-moon.html
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