AEON MAGAZINE: The end of night

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- The end of night

On land, artificial lighting causes a cascade of negative physiological changes in diurnal creatures, many brought about by delayed release of the hormone melatonin. Davide Dominoni and his colleagues at the Max Planck Institute in Germany found it was suppressed in European blackbirds exposed to just 0.3 lux at night. These birds developed their reproductive systems a month earlier, and moulted earlier, than birds kept in the dark. A different study, by Travis Longcore of the Urban Wildlands Group in Los Angeles, found that blue tits under the influence of streetlamps laid their eggs earlier than those experiencing dark nights. And in mammals, from mice to men, the effects of melatonin suppression might be far worse.

A growing body of evidence shows that light pollution exacerbates, and might directly cause, cancer, obesity, and depression, the troublesome triumvirate of industrialised society. One of the first people to notice this correlation, at least as it applies to cancer, is Richard Stevens, a professor at the University of Connecticut, respected cancer epidemiologist, and mild insomniac. In the early 1980s, Stevens and other researchers were beginning to realise there was little or no connection between diet and rising rates of breast cancer, contrary to what had been suspected. As Stevens puts it, it was like a light bulb going on when he realised that, in fact, a light bulb going on might be a culprit. - Rebecca Boyle