© April 2015 Paul Cooijmans
This article provides a first rough sketch of a possible explanation for an apparent influence of the sun on human behaviour. The hypothesis may be further refined and documented later.
The German psychologist S. E. Ertel has extensively studied the possible relation between solar activity and human behaviour. His starting point was the work of the Russian historian A. L. Chizhevsky, who had suggested that high sunspot activity promoted revolutions, mass migrations, wars, and other negative or destructive behaviours. Ertel extended this hypothesis to culturally positive behaviour such as achievement in science and art, which were supposedly stimulated by low sunspot activity.
Data used by Ertel included recorded sunspot activity (and, further back, analysis of C14 in trees), historical events such as wars and revolutions, and achievements of scientists and artists. The historical and achievement data were gathered or judged by others, and in ignorance of the theory being investigated. It turned out there was good evidence in favour of the theory; negative behaviours such as wars peaked within plus or minus one year from a solar maximum, while positive, creative achievements occurred most during low sunspot activity and were at their mininum within plus or minus one year from a solar maximum. The (positive) effect was also found in long-term solar minima like the Maunder minimum, and occurred simultaneously in places as remote as Europe and China, which is what one would expect given an extraterrestrial trigger. And, the effect regarding positive behaviours appeared to be an increase of the productivity of eminent scientists and artists, not of ordinary ones.
These outcomes are discussed by Hans Eysenck in his book Genius — The natural history of creativity, with reference to a number of publications by Ertel. Neither Chizhevsky nor Ertel had an explanation as to the causal mechanism behind this apparent extraterrestrial influence on human behaviour. A hypothesis regarding that mechanism is briefly formulated below.
A first step toward understanding the sun's role in modulating cultural and social affairs on Earth is to consider how sunspot activity may relate causally to the global climate. There exist multiple theories of solar influence on climate and weather; particularly interesting and plausible is the one associated with Henrik Svensmark, which concerns the role of galactic cosmic rays in cloud formation. In short, cosmic rays entering the atmosphere supposedly promote the formation of aerosols large enough to serve as condensation nuclei for clouds. Therefore, when much cosmic radiation reaches the Earth, there is more cloud formation, which has a cooling effect as sunlight is blocked. When little cosmic radiation reaches the Earth, the opposite is the case, and more sunlight will be let through.
The sunspot cycle enters into this because high sunspot activity goes with a strong magnetic field (of the sun). This deflects cosmic radiation away from the Earth, supposedly resulting in less cloud formation as just explained. With low sunspot activity, the opposite. Thus, around a solar maximum, there will be less clouds blocking the sunlight. During a minimum, the opposite. It may be relevant here that changes in the sun's magnetic field do not coincide perfectly with sunspot activity; the "magnetic maximum" may occur a year after the actual maximum in sunspot count. There is some controversy about Svensmark's theory, which is understandable given the current dominance of the greenhouse theory of global warming with which it is to some extent in contradiction.
Sunlight affects the levels of neurotransmitters in the brain, while these levels, in turn, affect behaviour. Important neurotransmitters in this respect (without claiming they are the only ones at play) are dopamine, serotonin, and melatonin. The levels of the first two rise when one is exposed to light, the last drops. This constitutes an activating impulse on the whole. One feels better, confident and inclined to undertake things, optimistic, courageous, risk-taking, perhaps reckless. One wants to be out and about, active, and meet people, rather than to stay indoors and work hard. While appearing pleasant and beneficial, this is also the state of mind that, in some classes of persons, leads to aggression, violence, and other negative behaviours. Thus it is thinkable that, in a period when sunlight is less hindered by clouds, one would see a lower productivity in creative persons, and more negative behaviour in general.
On the other hand, dark, cloudy weather would result in relatively lower levels of dopamine and serotonin, and a higher level of melatonin; therefore in a less outgoing, less daring mind state. In the absence of the sun-induced impulse to "go out and play", the creative and conscientious focus their energy on work, thus increasing their output. These effects of bright sunny weather versus dark cloudy weather on behaviour are probably recognizable for many, and, presuming the relation between solar activity and global climate is real, they may explain the statistical relation observed by Ertel and Chizhevski. This explanation does not depend on the exact correctness of the current supposed mechanisms for the sun-climate relation (cosmic rays) and climate-behaviour relation (neurotransmitters), but holds true even if the actual mechanisms turn out to be different. Also notice it concerns not a black-and-white, on/off effect; creativity does not seize completely under a sunspot maximum, nor do aggression and uproar under a solar minimum. Rather, it is a subtle quantitative modulation of behaviour by the variation in exposure to sunlight.