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Moonshine by Isaac Asimov


WHEN I WAS VERY YOUNG I read a number of stories and saw several motion pictures which featured some unfortunate individual who tended to turn into a wolf at the time of the full Moon.

The logic behind this troubled me, however. Why the full Moon? I had frequently seen the full Moon and been exposed to its light and I had felt no effect of any kind as a result. Was moonshine substantially different from sunshine or from artificial light?

For that matter, was the light of a full Moon different from the light of a Moon one day past the full, or one day before it? I could hardly tell the difference in the Moon's shape on those three days. How could a werewolf tell, therefore, and on an all-or-nothing basis, too? Shouldn't such a werewolf turn 95 percent wolf on the day before or after the full Moon? In fact, should he not turn half wolf on the night of the half Moon?

I could work out no satisfactory answers to such questions and the easiest way out was to decide that werewolves could not be affected by the Moon in the manner described. (As I grew older, I began to realize there were much more serious questions raised by this matter of human beings turning into wolves, and concluded that there could be no such things as werewolves.)

This business of attributing strange powers to moonshine continues, however. Every once in a while, for instance, I hear of reports concerning statistical studies that seem to show that drugs have pronouncedly different effects on the human body according to the phases of the Moon, that crimes of violence, homicide, and suicide are particularly numerous when the Moon is full, and so on and so on. This makes it seem that there may be something tat old folk-beliefs concerning the importance of the Moon, such as the one that different plants ought to be sowed at particular phases of the Moon.

As a science fiction writer, I'm automatically attracted to such suggestions because of the plot suggestions to which they give rise, if nothing else; but, as a scientist, I must stop and consider–all the more so since I can't trust myself, in my s.f.writer aspect, to be objective.

First, I know very well that human beings have been aware of the changing shape of the Moon from prehistoric times. The first calendars were based on the Lunar cycle, and various religious, mathematical, and scientific concepts arose out of that cycle. The Moon was so incredibly important to the early thinking of humanity that it is only natural to suppose that all sorts of powers would have been attributed to the Moon that it may very likely fail to have in actual fact. (Thus, the connection between Moon and insanity is considered to be nonsense, but it is, nevertheless, enshrined in our word "lunacy.")

It is possible, therefore, that people are so predisposed to believe in Moon effects that in gathering statistics on the matter, they are unconsciously swayed in their data selection in such a way as to demonstrate what they already tend to believe; i.e., that human behavior varies with the phases of the Moon.

And yet suppose that, as more and more statistics were gathered, the results were to become irrefutable, and that it had to be admitted that the phases of the Moon had important effects on human behavior. How could that be explained?

One might conclude that moonshine has some powerful effect on human beings for some as yet unknown reason. That, however, although an attractive way out to those with a tendency to mysticism, is bad science. One does not fall back on the unknown umtil all possible known effects have been investigated and found wanting.

For instance, one obvious factor that changes with the phases of the Moon is the quantity of light that falls upon the landscape at night. In the preindustrial era, people who had to travel by night would prefer, if they could, to travel during the week of the full Moon so that there would be as much light as possible (assuming the absence of clouds). For similar reasons, when Astronomy Island (a group of amateur astronomers) carries through its annual summer expedition to Bermuda to observe the stars, they invariably choose the week of the new Moon so that the light of the stars won't be washed out in moonshine.

It is not that kind of behavior (voluntary and logical) we're interested in, however. What about the effect of the Moon on reaction to drugs or on psychopathology? Is there anything about the Moon's light that is different from that of the Sun? After all, moonshine is only reflected sunshine. To be sure, the light from the Moon is partly polarized, but so is scattered light from the daytime sky partly polarized.

One thing the Moon does affect is the tides. The pull of the Moon, exerted with greater intensity on the side of the Earth facing it than on the side opposite, produces two humps of water, and any given spot on Earth turns through these humps at half-day intervals. What's more, the humps of water grow higher or lower as the Moon's phases change. The phases change as the position of the Moon with respect to the Sun changes, and when the Sun is pulling in a direction parallel to that of the Moon (at full Moon or new Moon), the humps are highest. When the Sun is pulling in a direction at right angles to that of the Moon (at either half Moon), the humps are lowest.

It follows then that every half day there is a hightide/low-tide cycle, and every two weeks a high-hightide/low-high-tide cycle.

Can these tide cycles affect human beings? At first thought, one doesn't see how, but it is certain that they affect creatures who spend their lives at or near the seashore. The ebb and flow of the tide must be intimately involved with the rhythm of their lives. Thus, the time of highest tide may be the appropriate occasion to lay eggs, for instance. The behavior of such creatures therefore seems to be related to the phases of the Moon. That is not mysterious if you consider the Moon/tide/behavior connection. Ifs however, you leave out the intermediate stop and consider only a Moon/behavior connection, you change a rational view into a semimystical one.

But what connection can there be between worms and fish living at the edge of the sea, and human beings?

Surely there is an evolutionary connection. We may consider ourselves far removed from tidal creatures now but we are descended from organisms that, 400 million years ago, were probably living at the sea-land interface and were intimately affected by tidal rhythms.

Yes, but that was 400 million years ago. Can we argue that the tidal rhythms of those days would affect us now? It doesn't seem likely, but it is a conceivable possibility.

After all, we might argue it out thus–

We still have a few bones at the bottom end of our spine that represent all that is left of a tail that our ancestors haven't had for at least 20 million years. We have an appendix that is the remnant of an organ that hasn't been used by our ancestors for even longer. In the same way, whales and pythons have small bones that represent the hind legs their ancestors once had many millions of years ago; the young hoatzin bird has two claws on each wing that date back to the eons before birds developed full-fledged wings; the horse has thin bones that represent all that is left of two side hooves each leg once had but has no longer. In our own case, we (and other mammals), as embryos, even develop the beginnings of gills that quickly disappear, but that hark back to when our ancestors were sea creatures.

Such vestigial organs are well known and occur in almost all organisms (and represent extremely strong evidence in favor of biological evolution). Why should there not also be vestigial remnants of ancestral biochemical or psychological properties? In particular, why should we not retain some aspects of the old tidal rhythms?

Our complex minds might still sway rhythmically in the half-day and fourteen-day tidal cycles that affected our ancestors so many millions of years ago. This would be unusual and surprising but, nevertheless, rational and believable. To omit the tidal component of the chain of cause and effect, however, and to suppose that our behavior sways with the phases of the Moon is likely to send us on a mystical chase after nothing.

How can we demonstrate this tidal rhythm more effectively? Is there anything better than simply continuing to collect data and to correlate behavior with the Moon's phases?

It seems to me that if these rhythms affect such things as our response to drugs or our tendency to violence or depression, then the rhythms must affect our internal workings. There must be a fourteen-day rise and fall in hormone production, or hormone balance, or such a rise and fall in the activity of our immune system, or our cerebral drug receptors, or various aspects of our neurochemistry.

Such variations in our biochemistry would be much more persuasive, it seems to me, than the study of effects that are once or twice removed. We would then have more solid reasoning and less moonshine.

AFTERWORD: After this essay appeared, I received some angry letters from women berating me for not mentioning the menstrual cycle. They seemed to think this showed a deep antifeminist prejudice in me. In every case, I answered by saying that I had never dreamed anyone would think there was a connection. As nearly as I can make out from my knowledge of women, the menstrual cycle is often irregular, sometimes extremely so. Even the average period is not exactly equal to the Lunar cycle, and it's certainly not the case that the onset of menstruation invariably comes at the full Moon or at any other phase. Rather, on any given week, regardless of the phase of the Moon, roughly one quarter of the women of the appropriate age are menstruating. Why, then, is the menstrual period nearly equal to the Lunar cycle? Might there not be such a thing as coincidence? (The menstrual periods of other primates are widely removed from the Lunar cycle, by the way.)

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Copyright "Moonshine" by Isaac Asimov, copyright © 2003, with permission of the author.

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