The idea that the phases of the moon are linked to the human psyche is one of the oldest and most pervasive examples of folk lore and mythology. It is woven into the fabric of our classic literature, poetry and music. Even today, a surprising number of people believe that our deepest emotions and mental states are influenced by the lunar cycle, and there are plenty of police officers, doctors, nurses and prison guards who would swear blind they’ve seen evidence of it in their everyday lives. But is the lunar effect real? How and why does it work? Humans have spent thousands of years discussing the lunar effect in stories and legends, and the last 40 years documenting it in the academic literature. So what’s the verdict? How does the moon affect us?
In it’s simplest form, the Werewolf exemplifies our most primitive understanding of a link between human behaviour and emotion and the moon. It captures our idea that during the full moon, man becomes wild, violent and instinctive, a reversion to a more basal, less civilised version of ourselves. This is probably the most pervasive aspect of the myth, that the moon controls human aggression, impulsivity, violence and mood. But the lunar effect has also been proposed for a range of scenarios so broad it will make your mind boggle. A quick google search will tell you that the moon controls our fertility and reproduction, influences violent crime, suicide and even traffic accidents, affects seizures, blood loss, sleep quality and even our political leanings. All of this begs the question, how and why might such a mechanism exist?
The field of research into personality and behavioural syndromes in animals has blossomed over the past few decades. With ample evidence for it’s existence, biologists have begun to consider its evolution; what is the adaptive benefit of personality? How are multiple personality types maintained in a population? Why do personalities exist when they sometimes result in maladaptive responses?
All these questions, and any evolutionary questions we might care to ask, make the assumption that personality is heritable. Without heritability, personality cannot be passed from generation to generation, and cannot be subject to natural selection. There is now plenty of evidence for high heritability of many personality traits in animals, although there is also an important influence of the environment too. Heritabilities estimates vary, from 0.22 – 0.61 in wild great tits, 0.32 in social spiders, 0.54 – 0.66 in humans and 0.2 – 0.8 in dumpling squid. These genetic influences may in part be reflected in brain morphology; one study in humans found differences in brain structure relating to neuroticism, conscientiousness, and extraversion. More neurotic people have a smaller total brain volume and a smaller frontotemporal surface area, whilst extraverts have a thinner inferior frontal gyrus.
To even the most casual observer, it is clear that people are not homogenous in their behaviour, and that this goes beyond possible nurture influences such as cultural upbringing. Individuals vary in their behaviour in a consistent manner; some people are generally more aggressive, friendly and adventurous in every aspect of their lives. So obvious is this observation that we even have a word for it – personality. Likewise, anyone who has spent any significant amount of time in the company of animals will almost certainly acknowledge that they are not all the same. The extent to which this is apparent varies from species to species, of course, but the observation is not a revolutionary one. And yet, until relatively recently the concept of ‘personality’ in non-human animals was revolutionary. And it has had to work hard to shake off the criticism of anthropomorphism and pseudoscience.
It was long assumed that animals were infinitely plastic in their behaviour, being able to respond adaptively to all environments. When people actually started to look, however, it became apparent that this wasn’t the case. Individuals showed substantial variation in their responses to certain events and environments, and these responses were not always adaptive. There was a strong correlation however, in the responses of a single individual over time. Personality, you say?
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